inabox/inabox.wpf/DigitalForms/Designer/DynamicFormDesignGrid.cs

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Diagnostics.CodeAnalysis;
using System.Drawing;
using System.Drawing.Design;
using System.Globalization;
using System.IO;
using System.Linq;
using System.Reflection;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Controls.Primitives;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Markup.Localizer;
using System.Windows.Media;
using System.Windows.Media.Effects;
using System.Windows.Media.Imaging;
using InABox.Clients;
using InABox.Core;
using InABox.WPF;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using Brush = System.Windows.Media.Brush;
using Color = System.Drawing.Color;
using Image = System.Windows.Controls.Image;
using Point = System.Windows.Point;
using Rectangle = System.Windows.Shapes.Rectangle;

namespace InABox.DynamicGrid
{
    public class DynamicFormCreateElementArgs : EventArgs
    {
        public DynamicFormCreateElementArgs(DFLayoutElement element, string name)
        {
            Element = element;
            Name = name;
        }

        public DFLayoutElement Element { get; }

        public string Name { get; }
    }

    public delegate FrameworkElement DynamicFormCreateElementDelegate(object sender, DynamicFormCreateElementArgs e);

    public delegate void DynamicFormAfterDesignDelegate(object sender);

    public delegate void DynamicFormAfterRenderDelegate(DynamicFormDesignGrid sender);

    public delegate void DynamicFormOnChangedDelegate(DynamicFormDesignGrid sender, string fieldName);

    public enum FormMode
    {
        /// <summary>
        /// The form is read-only.
        /// </summary>
        ReadOnly,
        /// <summary>
        /// Standard option for when the form is being filled in by the associated employee.
        /// </summary>
        Filling,
        /// <summary>
        /// Standard option for when the form is being previewed - that is, it is acting with placeholder values that will not get saved.
        /// It is still editable.
        /// </summary>
        Preview,
        /// <summary>
        /// Once the form has been completed, or the person editing is not the employee the form applies to, then they are put in Editing Mode.<br/>
        /// This is only possible if <see cref="CanEditCompletedForms"/> is enabled.
        /// </summary>
        Editing,
        /// <summary>
        /// The form layout is being designed
        /// </summary>
        Designing
    }

    public class DynamicFormDesignGrid : Grid, IDFRenderer
    {


        //private bool _designing;

        public bool GridInitialized { get; private set; } = false;

        //private bool _readonly;


        private readonly SolidColorBrush BackgroundBrush = new(Colors.WhiteSmoke);
        private readonly SolidColorBrush BorderBrush = new(Colors.Silver);

        private readonly Dictionary<Type, IDynamicGrid> elementgrids = new();

        private readonly Dictionary<DFLayoutControl, FrameworkElement> elementmap = new();
        private readonly Dictionary<DFLayoutControl, Border> borderMap = new();
        private readonly SolidColorBrush FieldBrush = new(Colors.LightYellow);


        private readonly SolidColorBrush RequiredFieldBrush = new(Colors.Orange);

        public DynamicFormDesignGrid()
        {
            PreviewMouseLeftButtonDown += Grid_PreviewMouseLeftButtonDown;
            PreviewMouseMove += Grid_PreviewMouseMove;
            PreviewMouseLeftButtonUp += Grid_PreviewMouseLeftButtonUp;
        }

        #region Backing Properties

        private readonly List<DynamicFormElement> _elements = new();
        private readonly List<DynamicFormElementAction> _elementActions = new();
        private bool _showBorders = true;
        private IDigitalFormDataModel? _datamodel;
        private DFLayout form = new();
        private FormMode _mode;
        private IList<DigitalFormVariable> _variables = new List<DigitalFormVariable>();
        private bool _isChanged;
        private bool _changing = false;

        #endregion

        #region Public Properties

        public bool ShowBorders
        {
            get => _showBorders || _mode == FormMode.Designing;
            set
            {
                _showBorders = value;
                CheckRefresh();
            }
        }

        public IDigitalFormDataModel? DataModel
        {
            get => _datamodel;
            set
            {
                _datamodel = value;
                if(_datamodel != null)
                {
                    var task = Task.Run(() =>
                    {
                        var waiting = true;
                        _datamodel.Load(m => { waiting = false; });
                        while (waiting) ;
                    });
                    task.Wait();
                }

                CheckRefresh();
            }
        }

        public DFLayout Form
        {
            get => form;
            set
            {
                form = value;
                form.Renderer = this;

                CheckRefresh();
            }
        }

        public FormMode Mode
        {
            get => _mode;
            set
            {
                if (_mode != value)
                {
                    var oldMode = _mode;
                    if (_mode == FormMode.Designing)
                    {
                        OnAfterDesign?.Invoke(this);
                    }

                    _mode = value;

                    CheckRefresh(oldMode != FormMode.Designing);
                }
            }
        }

        public bool IsDesigning { get => _mode == FormMode.Designing; }
        public bool IsReadOnly { get => _mode == FormMode.ReadOnly; }
        public bool IsEditing { get => _mode == FormMode.Editing || _mode == FormMode.Filling; }
        public bool IsChanged => _isChanged;

        public delegate DigitalFormVariable? CreateVariableHandler(Type fieldType);
        public delegate bool EditVariableHandler(DigitalFormVariable variable);

        public event CreateVariableHandler? OnCreateVariable;
        public event EditVariableHandler? OnEditVariable;

        public delegate void CustomiseElementContextMenuHandler(ContextMenu menu, DFLayoutElement element);
        public event CustomiseElementContextMenuHandler? CustomiseElementContextMenu;

        public IList<DigitalFormVariable> Variables
        {
            get => _variables;
            set
            {
                _variables = value;
                CheckRefresh();
            }
        }

        #endregion

        #region Events

        public event DynamicFormAfterDesignDelegate? OnAfterDesign;

        public event DynamicFormCreateElementDelegate? OnCreateElement;

        public event DynamicFormAfterRenderDelegate? OnAfterRender;

        public event DynamicFormOnChangedDelegate? OnChanged;

        #endregion

        #region Rows

        class RowData
        {
            public string RowHeight { get; set; }

            public RowData(string rowHeight)
            {
                RowHeight = rowHeight;
            }
        }

        internal void CollapseRows(FormHeader header, bool collapsed)
        {
            var startRow = this.GetRow(header) + this.GetRowSpan(header);

            var nextRow = elementmap
                .Where(x => x.Value is DFHeaderControl headerControl && headerControl.Header != header)
                .Select(x => this.GetRow(x.Value))
                .Where(x => x >= startRow).DefaultIfEmpty(-1).Min();

            if (nextRow == -1)
            {
                nextRow = RowDefinitions.Count;
            }

            for (int row = startRow; row < nextRow; ++row)
            {
                var rowDefinition = RowDefinitions[row];
                if(rowDefinition.Tag is not RowData rowData)
                {
                    throw new Exception("Row definition tag is not RowData");
                }

                if (collapsed)
                {
                    rowDefinition.Height = new GridLength(0);
                }
                else
                {
                    rowDefinition.Height = StringToGridLength(rowData.RowHeight);
                }
            }
        }

        #endregion

        #region Elements

        class DynamicFormElement
        {
            public string Caption { get; set; }
            public Type ElementType { get; set; }
            public string Category { get; set; }
            public bool AllowDuplicate { get; set; }
            public object? Tag { get; set; }
            public Func<object?, DFLayoutElement>? CreateElement { get; set; }

            public bool Visible { get; set; }

            public DynamicFormElement(string caption, Type elementType, string category, bool allowDuplicate, bool visible, object? tag, Func<object?, DFLayoutElement>? createElement)
            {
                Caption = caption;
                ElementType = elementType;
                Category = category;
                AllowDuplicate = allowDuplicate;
                Tag = tag;
                CreateElement = createElement;
                Visible = visible;
            }
        }

        class DynamicFormElementAction
        {
            public string Caption { get; set; }

            public Bitmap? Image { get; set; }

            public string Category { get; set; }

            public object? Tag { get; set; }

            public Func<object?, DFLayoutElement?> OnClick { get; set; }

            public DynamicFormElementAction(string caption, Bitmap? image, string category, object? tag, Func<object?, DFLayoutElement> onClick)
            {
                Caption = caption;
                Image = image;
                Category = category;
                Tag = tag;
                OnClick = onClick;
            }
        }

        public void ClearElementTypesAndActions()
        {
            _elements.Clear();
            _elementActions.Clear();
        }

        public void AddElementType<TElement>(string caption, string category, bool allowduplicate = false, bool visible = true)
            where TElement : DFLayoutElement
        {
            AddElementType(typeof(TElement), caption, category, allowduplicate, visible: visible);
        }
        public void AddElementType<TElement, TTag>(string caption, string category, TTag tag, Func<TTag, TElement> createElement, bool allowduplicate = false, bool visible = true)
            where TElement : DFLayoutElement
        {
            AddElementType(typeof(TElement), caption, category, tag, createElement, allowduplicate, visible: visible);
        }

        public void AddElementType(Type TElement, string caption, string category, bool allowduplicate = false, bool visible = true)
        {
            _elements.Add(new DynamicFormElement(caption, TElement, category, allowduplicate, visible, null, null));
        }

        public void AddElementType<TTag>(Type TElement, string caption, string category, TTag tag, Func<TTag, DFLayoutElement> createElement, bool allowduplicate = false, bool visible = true)
        {
            _elements.Add(new DynamicFormElement(caption, TElement, category, allowduplicate, visible, tag, x => createElement((TTag)x)));
        }

        public void AddElementAction<TTag>(string caption, Bitmap? image, string category, TTag tag, Func<TTag, DFLayoutElement?> onClick)
        {
            _elementActions.Add(new(caption, image, category, tag, x => onClick((TTag)x)));
        }

        internal FrameworkElement? CreateElement(DFLayoutElement element)
        {
            var elementType = element.GetType();
            if(_elements.FirstOrDefault(x => x.ElementType == elementType) is DynamicFormElement el)
            {
                return OnCreateElement?.Invoke(this, new DynamicFormCreateElementArgs(element, el.Caption));
            }
            return null;
        }

        #endregion

        #region Utilities

        private static VerticalAlignment GetVerticalAlignment(DFLayoutAlignment alignment)
        {
            return alignment == DFLayoutAlignment.Start
                ? VerticalAlignment.Top
                : alignment == DFLayoutAlignment.End
                    ? VerticalAlignment.Bottom
                    : alignment == DFLayoutAlignment.Middle
                        ? VerticalAlignment.Center
                        : VerticalAlignment.Stretch;
        }

        private static HorizontalAlignment GetHorizontalAlignment(DFLayoutAlignment alignment)
        {
            return alignment == DFLayoutAlignment.Start
                ? HorizontalAlignment.Left
                : alignment == DFLayoutAlignment.End
                    ? HorizontalAlignment.Right
                    : alignment == DFLayoutAlignment.Middle
                        ? HorizontalAlignment.Center
                        : HorizontalAlignment.Stretch;
        }

        private static GridLength StringToGridLength(string length)
        {
            if (string.IsNullOrWhiteSpace(length) || string.Equals(length.ToUpper(), "AUTO"))
                return new GridLength(1, GridUnitType.Auto);

            if (!double.TryParse(length.Replace("*", ""), out var value))
                value = 1.0F;
            var type = length.Contains('*') ? GridUnitType.Star : GridUnitType.Pixel;
            return new GridLength(value, type);
        }

        private static string GridLengthToString(GridLength length)
        {
            if (length.IsStar)
                return length.Value == 1.0F ? "*" : string.Format("{0}*", length.Value);
            if (length.IsAuto)
                return "Auto";
            return length.Value.ToString();
        }

        private static string FormatGridLength(GridLength length, IEnumerable<GridLength> others)
        {
            if (length.IsStar)
            {
                double total = 0.0F;
                foreach (var other in others.Where(x => x.IsStar))
                    total += other.Value;
                return string.Format("{0:F0}%", total != 0 ? length.Value * 100.0F / total : 0);
            }

            if (length.IsAuto)
                return "Auto";
            return string.Format("{0}px", length.Value);
        }

        private static void AddClick<TTag>(ButtonBase button, TTag tag, Action<TTag> click)
        {
            button.Tag = tag;
            button.Click += (o, e) => click((TTag)(o as FrameworkElement)!.Tag);
        }

        #endregion

        #region Design Mode

        #region Selection

        private class CellSelection : Border
        {
            private static readonly System.Windows.Media.Color MainSelectionBorder = Colors.LightBlue;

            private int startRow;
            private int endRow;
            private int startColumn;
            private int endColumn;

            public int StartRow
            {
                get => startRow;
                set
                {
                    startRow = value;
                    UpdatePosition();
                }
            }

            public int StartColumn
            {
                get => startColumn;
                set
                {
                    startColumn = value;
                    UpdatePosition();
                }
            }

            public int EndRow
            {
                get => endRow;
                set
                {
                    endRow = value;
                    UpdatePosition();
                }
            }

            public int EndColumn
            {
                get => endColumn;
                set
                {
                    endColumn = value;
                    UpdatePosition();
                }
            }

            public bool Selecting = true;

            public enum SelectionTypes
            {
                Main,
                Secondary,
                Resizable,
                ResizeBackground
            }

            public SelectionTypes SelectionType;

            public enum Direction
            {
                None,
                Left,
                Right,
                Top,
                Bottom,
                All
            }
            public Direction DragDirection;
            public bool IsDragging => DragDirection != Direction.None;

            public bool IsRowSelection => StartColumn == 0;
            public bool IsColumnSelection => StartRow == 0;

            public CellSelection(int startRow, int startColumn, int endRow, int endColumn, SelectionTypes selectionType)
            {
                SelectionType = selectionType;
                switch (selectionType)
                {
                    case SelectionTypes.Main:
                        InitialiseMain();
                        break;
                    case SelectionTypes.Secondary:
                        InitialiseSecondary();
                        break;
                    case SelectionTypes.Resizable:
                        InitializeResizable();
                        break;
                    case SelectionTypes.ResizeBackground:
                        InitializeResizeBackground();
                        break;
                }

                this.startRow = startRow;
                this.startColumn = startColumn;
                this.endRow = endRow;
                this.endColumn = endColumn;
                UpdatePosition();
            }

            private void InitialiseMain()
            {
                var colour = MainSelectionBorder;
                BorderBrush = new SolidColorBrush(colour);
                Background = new SolidColorBrush(new System.Windows.Media.Color
                {
                    A = (byte)(colour.A / 2),
                    R = colour.R,
                    G = colour.G,
                    B = colour.B
                });
                SetZIndex(this, 2);
                BorderThickness = new Thickness(1);
            }

            private void InitialiseSecondary()
            {
                var rectangle = new Rectangle
                {
                    StrokeDashArray = new DoubleCollection { 4, 4 },
                    Stroke = new SolidColorBrush(Colors.Gray),
                    StrokeThickness = 1.5
                };
                rectangle.SetBinding(Rectangle.WidthProperty, new Binding("ActualWidth") { Source = this });
                rectangle.SetBinding(Rectangle.HeightProperty, new Binding("ActualHeight") { Source = this });
                var brush = new VisualBrush { Visual = rectangle };

                BorderBrush = brush;
                BorderThickness = new Thickness(1.5);
                Margin = new Thickness(3);
            }

            private void InitializeResizable()
            {
                var rectangle = new Rectangle
                {
                    StrokeDashArray = new DoubleCollection { 4, 4 },
                    Stroke = new SolidColorBrush(Colors.Gray),
                    StrokeThickness = 3
                };
                rectangle.SetBinding(Rectangle.WidthProperty, new Binding("ActualWidth") { Source = this });
                rectangle.SetBinding(Rectangle.HeightProperty, new Binding("ActualHeight") { Source = this });
                var brush = new VisualBrush { Visual = rectangle };

                BorderBrush = brush;

                Background = new SolidColorBrush(Colors.Transparent);
                SetZIndex(this, 2);
                BorderThickness = new Thickness(10);

                MouseMove += Resizable_MouseMove;
            }

            private void InitializeResizeBackground()
            {
                var colour = Colors.WhiteSmoke;
                Background = new SolidColorBrush(new System.Windows.Media.Color
                {
                    A = (byte)(colour.A / 2),
                    R = colour.R,
                    G = colour.G,
                    B = colour.B
                });
                SetZIndex(this, 1);
                BorderThickness = new Thickness(0);
            }

            public bool StartDragging(Point position)
            {
                if (!IsMouseDirectlyOver) return false;

                var dX = Math.Min(position.X, ActualWidth - position.X);
                var dY = Math.Min(position.Y, ActualHeight - position.Y);
                if(Math.Min(dX, dY) < 10)
                {
                    if (dX < dY)
                    {
                        DragDirection = position.X < ActualWidth / 2 ? Direction.Left : Direction.Right;
                    }
                    else
                    {
                        DragDirection = position.Y < ActualHeight / 2 ? Direction.Top : Direction.Bottom;
                    }
                }
                else
                {
                    DragDirection = Direction.All;
                    return false;
                }
                return true;
            }

            private void Resizable_MouseMove(object sender, MouseEventArgs e)
            {
                if (!IsMouseDirectlyOver || IsDragging) return;

                var position = e.GetPosition(this);

                var dX = Math.Min(position.X, ActualWidth - position.X);
                var dY = Math.Min(position.Y, ActualHeight - position.Y);
                if (Math.Min(dX, dY) < 10)
                {
                    if (dX < dY)
                    {
                        Cursor = Cursors.SizeWE;
                    }
                    else
                    {
                        Cursor = Cursors.SizeNS;
                    }
                }
                else
                {
                    Cursor = Cursors.Arrow;
                }
            }

            public void SetEnd(int endRow, int endColumn)
            {
                this.endRow = endRow;
                this.endColumn = endColumn;
                UpdatePosition();
            }

            public void SetSize(int startRow, int startColumn, int endRow, int endColumn)
            {
                this.startRow = startRow;
                this.startColumn = startColumn;
                this.endRow = endRow;
                this.endColumn = endColumn;
                UpdatePosition();
            }

            private void UpdatePosition()
            {
                Grid.SetRow(this, Math.Min(startRow, endRow));
                Grid.SetRowSpan(this, Math.Abs(endRow - startRow) + 1);

                Grid.SetColumn(this, Math.Min(startColumn, endColumn));
                Grid.SetColumnSpan(this, Math.Abs(endColumn - startColumn) + 1);
            }

            public CellRange ToRange() => new CellRange(StartRow, StartColumn, EndRow, EndColumn);
        }

        private CellSelection? Selection;
        private Dictionary<DFLayoutControl, CellSelection> SelectedItemsSelections = new();

        private class Range
        {
            public int Start { get; set; }

            public int End { get; set; }

            public int Min => Math.Min(Start, End);
            public int Max => Math.Max(Start, End);

            public Range(int start, int end)
            {
                Start = start;
                End = end;
            }

            public override string ToString() => $"{Start} -> {End}";
        }
        
        private class CellRange
        {
            public int StartRow { get; set; }
            public int StartColumn { get; set; }
            public int EndRow { get; set; }
            public int EndColumn { get; set; }

            public int MinRow => Math.Min(StartRow, EndRow);
            public int MinColumn => Math.Min(StartColumn, EndColumn);
            
            public int MaxRow => Math.Max(StartRow, EndRow);
            public int MaxColumn => Math.Max(StartColumn, EndColumn);

            public int RowSpan => Math.Abs(EndRow - StartRow) + 1;
            public int ColumnSpan => Math.Abs(EndColumn - StartColumn) + 1;

            public CellRange(int row, int column)
            {
                StartRow = row;
                EndRow = row;
                StartColumn = column;
                EndColumn = column;
            }

            public CellRange(int startRow, int startColumn, int endRow, int endColumn)
            {
                StartRow = startRow;
                EndRow = endRow;
                StartColumn = startColumn;
                EndColumn = endColumn;
            }

            public override string ToString() => $"({StartColumn}, {StartRow}) -> ({EndColumn}, {EndRow})";
        }

        private void ClearSelection()
        {
            if (Selection is null) return;

            Children.Remove(Selection);
            Selection = null;

            UpdateSecondarySelection();
        }

        private void StartSelection(int row, int column)
        {
            if (Selection is not null) ClearSelection();

            Selection = new CellSelection(row, column, row, column, CellSelection.SelectionTypes.Main);
            Selection.MouseRightButtonDown += Selection_MouseRightButtonDown;
            Children.Add(Selection);

            UpdateSecondarySelection();
        }
        private void StartRowSelection(int row)
        {
            if (Selection is not null) ClearSelection();

            Selection = new CellSelection(row, 0, row, ColumnDefinitions.Count - 1, CellSelection.SelectionTypes.Main);
            Selection.MouseRightButtonDown += Selection_MouseRightButtonDown;
            Children.Add(Selection);

            UpdateSecondarySelection();
        }
        private void StartColumnSelection(int column)
        {
            if (Selection is not null) ClearSelection();

            Selection = new CellSelection(0, column, RowDefinitions.Count - 1, column, CellSelection.SelectionTypes.Main);
            Selection.MouseRightButtonDown += Selection_MouseRightButtonDown;
            Children.Add(Selection);

            UpdateSecondarySelection();
        }

        private Tuple<int, int> GetRowColIndex(Point point)
        {
            int rowIdx = -1;
            int colIdx = -1;
            for(var c = 0; c < ColumnDefinitions.Count; ++c)
            {
                var column = ColumnDefinitions[c];
                if(point.X >= column.Offset && point.X < column.Offset + column.ActualWidth)
                {
                    colIdx = c;
                    break;
                }
            }
            for(var r = 0; r < RowDefinitions.Count; ++r)
            {
                var row = RowDefinitions[r];
                if(point.Y >= row.Offset && point.Y < row.Offset + row.ActualHeight)
                {
                    rowIdx = r;
                    break;
                }
            }
            return new Tuple<int, int>(rowIdx, colIdx);
        }

        private void UpdateSecondarySelection()
        {
            List<DFLayoutControl> items;
            if (Selection is null || Selection.IsRowSelection || Selection.IsColumnSelection)
            {
                items = new List<DFLayoutControl>();
            }
            else
            {
                items = GetSelectedItems().ToList();
            }

            var removes = new List<DFLayoutControl>();
            foreach(var (control, selection) in SelectedItemsSelections)
            {
                if (!items.Contains(control))
                {
                    removes.Add(control);
                    Children.Remove(selection);
                }
            }
            foreach(var remove in removes)
            {
                SelectedItemsSelections.Remove(remove);
            }

            foreach(var item in items)
            {
                if (!SelectedItemsSelections.ContainsKey(item))
                {
                    var selection = new CellSelection(
                        item.Row, item.Column,
                        item.Row + item.RowSpan - 1, item.Column + item.ColumnSpan - 1,
                        CellSelection.SelectionTypes.Secondary);
                    SelectedItemsSelections.Add(item, selection);
                    Children.Add(selection);
                }
            }
        }

        private void ContinueSelection(int row, int column)
        {
            if (Selection is null) return;

            row = Math.Max(row, 1);
            column = Math.Max(column, 1);

            Selection.Selecting = true;

            if (Selection.IsRowSelection)
            {
                Selection.EndRow = row;
            }
            else if (Selection.IsColumnSelection)
            {
                Selection.EndColumn = column;
            }
            else
            {
                Selection.SetEnd(row, column);
            }

            UpdateSecondarySelection();
        }

        private void Grid_PreviewMouseLeftButtonDown(object sender, System.Windows.Input.MouseButtonEventArgs e)
        {
            if (!IsDesigning) return;
            if(Resizer is not null)
            {
                if (Resizer.StartDragging(e.GetPosition(Resizer)))
                {
                    Cursor = Resizer.DragDirection switch
                    {
                        CellSelection.Direction.All => Cursors.SizeAll,
                        CellSelection.Direction.Left or CellSelection.Direction.Right => Cursors.SizeWE,
                        _ => Cursors.SizeNS
                    };
                    if(Resizer.DragDirection == CellSelection.Direction.All)
                    {
                        StartDragPosition = GetRowColIndex(e.GetPosition(this));
                    }
                }
                return;
            }

            var (row, column) = GetRowColIndex(e.GetPosition(this));

            if(Selection is not null && (Keyboard.IsKeyDown(Key.LeftShift) || Keyboard.IsKeyDown(Key.RightShift)))
            {
                ContinueSelection(row, column);
            }
            else if(Selection is not null && Selection.Selecting)
            {
                Selection.Selecting = false;
            }
            else
            {
                if (column == 0)
                {
                    if (row == 0) return;
                    StartRowSelection(row);
                }
                else if (row == 0)
                {
                    if (column == 0) return;
                    StartColumnSelection(column);
                }
                else
                {
                    StartSelection(row, column);
                }
            }
        }

        private void Grid_PreviewMouseMove(object sender, System.Windows.Input.MouseEventArgs e)
        {
            if (!IsDesigning) return;

            var (row, column) = GetRowColIndex(e.GetPosition(this));
            if (Resizer is not null)
            {
                ResizeMouseMove(sender, e);
                return;
            }

            if (Selection is null || !Selection.Selecting) return;
            
            ContinueSelection(row, column);
        }

        private void Grid_PreviewMouseLeftButtonUp(object sender, System.Windows.Input.MouseButtonEventArgs e)
        {
            if(Resizer is not null)
            {
                Resizer.DragDirection = CellSelection.Direction.None;
                Cursor = Cursors.Arrow;
            }
            else if (Selection is not null)
            {
                Selection.Selecting = false;
            }
        }

        private IEnumerable<Tuple<DFLayoutControl, FrameworkElement>> GetSelectedMaps(CellRange? range = null)
        {
            range ??= Selection?.ToRange();
            if (range is null) yield break;

            var minRow = Math.Min(range.StartRow, range.EndRow);
            var maxRow = Math.Max(range.StartRow, range.EndRow);
            var minCol = Math.Min(range.StartColumn, range.EndColumn);
            var maxCol = Math.Max(range.StartColumn, range.EndColumn);

            foreach(var (control, element) in elementmap)
            {
                if(control.Row <= maxRow && control.Row + control.RowSpan - 1 >= minRow
                    && control.Column <= maxCol && control.Column + control.ColumnSpan - 1 >= minCol)
                {
                    yield return new(control, element);
                }
            }
        }

        private IEnumerable<DFLayoutControl> GetSelectedItems(CellRange? range = null) => GetSelectedMaps(range).Select(x => x.Item1);

        private void PopulateSelectionMenu(ContextMenu menu)
        {
            if (Selection is null) return;

            if (Selection.IsRowSelection)
            {
                var nRows = Math.Abs(Selection.EndRow - Selection.StartRow) + 1;
                if (nRows == 1)
                {
                    PopulateRowMenu(menu, Selection.StartRow - 1);
                }
                else
                {
                    menu.AddItem(nRows == 1 ? "Delete Row" : "Delete Rows", null, new Range(Selection.StartRow - 1, Selection.EndRow - 1), DeleteRows);
                }
            }
            else if (Selection.IsColumnSelection)
            {
                var nColumns = Math.Abs(Selection.EndColumn - Selection.StartColumn) + 1;
                if (nColumns == 1)
                {
                    PopulateColumnMenu(menu, Selection.StartColumn - 1);
                }
                else
                {
                    menu.AddItem(nColumns == 1 ? "Delete Column" : "Delete Columns", null, new Range(Selection.StartColumn - 1, Selection.EndColumn - 1), DeleteColumns);
                }
            }
            else
            {
                var selectedItems = GetSelectedItems().ToList();
                if (selectedItems.Count == 0)
                {
                    PopulateEmptyCellMenu(menu, Selection.ToRange());
                }
                if (selectedItems.Count == 1)
                {
                    var item = selectedItems.First();

                    PopulateElementContextMenu(menu, item);
                }
                else if (selectedItems.Count > 1)
                {
                    menu.AddItem("Delete Items", null, selectedItems, DeleteElements);
                }
            }
        }

        private void Selection_MouseRightButtonDown(object sender, System.Windows.Input.MouseButtonEventArgs e)
        {
            if (!IsDesigning || Selection is null) return;

            var menu = new ContextMenu();

            PopulateSelectionMenu(menu);

            if(menu.Items.Count == 0)
            {
                menu.AddItem("No actions available", null, null, false);
            }
            menu.IsOpen = true;
        }

        #endregion

        #region Resizing

        private CellSelection? Resizer;
        private Tuple<int, int> StartDragPosition;

        private CellSelection? TopResizeBackground;
        private CellSelection? LeftResizeBackground;
        private CellSelection? RightResizeBackground;
        private CellSelection? BottomResizeBackground;

        private DFLayoutControl? ResizingControl;

        private CellSelection GetResizeBackground(ref CellSelection? background)
        {
            if(background is null)
            {
                background = new CellSelection(0, 0, 0, 0, CellSelection.SelectionTypes.ResizeBackground);
                background.PreviewMouseDown += ResizerBackground_PreviewMouseDown;
                Children.Add(background);
            }
            return background;
        }
        private void ClearResizeBackground(ref CellSelection? background)
        {
            if(background is not null)
            {
                Children.Remove(background);
                background = null;
            }
        }

        private void ResizerBackground_PreviewMouseDown(object sender, MouseButtonEventArgs e)
        {
            FinishResize();
        }

        private void SetResizerBackgroundSize(CellSelection background, int startRow, int startColumn, int endRow, int endColumn)
        {
            background.SetSize(startRow, startColumn, endRow, endColumn);
            background.Visibility = endColumn >= startColumn && endRow >= startRow ? Visibility.Visible : Visibility.Collapsed;
        }

        private void UpdateResizer(CellRange newSize)
        {
            if (Resizer is null) return;

            Resizer.StartRow = newSize.StartRow;
            Resizer.StartColumn = newSize.StartColumn;
            Resizer.EndRow = newSize.EndRow;
            Resizer.EndColumn = newSize.EndColumn;

            SetResizerBackgroundSize(GetResizeBackground(ref LeftResizeBackground), 0, 0, RowDefinitions.Count - 1, newSize.MinColumn - 1);
            SetResizerBackgroundSize(GetResizeBackground(ref RightResizeBackground), 0, newSize.MaxColumn + 1, RowDefinitions.Count - 1, ColumnDefinitions.Count - 1);
            SetResizerBackgroundSize(GetResizeBackground(ref TopResizeBackground), 0, newSize.MinColumn, newSize.MinRow - 1, newSize.MaxColumn);
            SetResizerBackgroundSize(GetResizeBackground(ref BottomResizeBackground), newSize.MaxRow + 1, newSize.MinColumn, RowDefinitions.Count - 1, newSize.MaxColumn);
        }

        private void ResizeMouseMove(object sender, System.Windows.Input.MouseEventArgs e)
        {
            if (Resizer is null) return;
            if (!Resizer.IsDragging) return;

            var (row, column) = GetRowColIndex(e.GetPosition(this));

            var newSize = Resizer.ToRange();

            switch (Resizer.DragDirection)
            {
                case CellSelection.Direction.Right:
                    var startColumn = newSize.MinColumn;
                    for (int c = column; c >= startColumn; --c)
                    {
                        newSize.StartColumn = startColumn;
                        newSize.EndColumn = Math.Max(c, startColumn);
                        if (ResizeAllowed(newSize))
                        {
                            break;
                        }
                    }
                    break;
                case CellSelection.Direction.Left:
                    var endColumn = newSize.MaxColumn;
                    for (int c = column; c <= endColumn; ++c)
                    {
                        newSize.StartColumn = Math.Min(c, endColumn);
                        newSize.EndColumn = endColumn;
                        if (ResizeAllowed(newSize))
                        {
                            break;
                        }
                    }
                    break;
                case CellSelection.Direction.Bottom:
                    var startRow = newSize.MinRow;
                    for (int r = row; r >= startRow; --r)
                    {
                        newSize.StartRow = startRow;
                        newSize.EndRow = Math.Max(r, startRow);
                        if (ResizeAllowed(newSize))
                        {
                            break;
                        }
                    }
                    break;
                case CellSelection.Direction.Top:
                    var endRow = newSize.MaxRow;
                    for (int r = row; r <= endRow; ++r)
                    {
                        newSize.StartRow = Math.Min(r, endRow);
                        newSize.EndRow = endRow;
                        if (ResizeAllowed(newSize))
                        {
                            break;
                        }
                    }
                    break;
                case CellSelection.Direction.None:
                    return;
            }
            UpdateResizer(newSize);
        }

        private bool ResizeAllowed(CellRange range)
        {
            var items = GetSelectedItems(range).ToList();
            if (items.Count > 1) return false;
            return items.Count == 0 ||
                (items.Count == 1 && items.First() == ResizingControl);
        }

        private void ClearResize()
        {
            if (Resizer is null) return;

            Children.Remove(Resizer);
            Resizer = null;
            ResizingControl = null;

            ClearResizeBackground(ref LeftResizeBackground);
            ClearResizeBackground(ref RightResizeBackground);
            ClearResizeBackground(ref TopResizeBackground);
            ClearResizeBackground(ref BottomResizeBackground);
        }

        private void FinishResize()
        {
            if (Resizer is null) return;

            var range = Resizer.ToRange();

            if(ResizingControl is not null)
            {
                ResizingControl.Row = range.MinRow;
                ResizingControl.Column = range.MinColumn;
                ResizingControl.RowSpan = range.RowSpan;
                ResizingControl.ColumnSpan = range.ColumnSpan;
            }

            ClearResize();
            Render();
        }

        private void ResizeItem(DFLayoutControl control)
        {
            ClearSelection();
            ClearResize();

            Resizer = new CellSelection(
                control.Row, control.Column,
                control.Row + control.RowSpan - 1, control.Column + control.ColumnSpan - 1,
                CellSelection.SelectionTypes.Resizable);
            ResizingControl = control;
            Children.Add(Resizer);

            UpdateResizer(Resizer.ToRange());
        }

        public void HandleKeyDown(KeyEventArgs e)
        {
            if (Resizer is null) return;
            if(e.Key == Key.Enter)
            {
                FinishResize();
            }
            else if(e.Key == Key.Escape)
            {
                ClearResize();
            }
        }

        #endregion

        #region Rows

        private void ShiftDown(int row)
        {
            foreach (var element in form.Elements)
                if (element.Row > row)
                    element.Row++;
                else if (element.Row + element.RowSpan - 1 > row)
                    element.RowSpan++;
        }

        private void AddRowBeforeClick(int row)
        {
            var length = new GridLength(1.0F, GridUnitType.Auto);
            var result = GridLengthToString(length);
            if (form.RowHeights.Count == 0)
                form.RowHeights.Add(result);
            else
                form.RowHeights.Insert(row, result);
            ShiftDown(row);
            Render();
        }

        private void AddRowAfterClick(int row)
        {
            var length = new GridLength(1.0F, GridUnitType.Auto);
            var result = GridLengthToString(length);
            if (row == form.RowHeights.Count - 1)
                form.RowHeights.Add(result);
            else
                form.RowHeights.Insert(row + 1, result);
            ShiftDown(row + 1);
            Render();
        }

        private void SplitRow(int row)
        {
            foreach (var element in form.Elements)
                if (element.Row > row)
                    element.Row++;
                else if (element.Row == row)
                    element.RowSpan++;
                else if (element.Row + element.RowSpan - 1 >= row)
                    element.RowSpan++;
        }

        private void SplitRowClick(int row)
        {
            var height = StringToGridLength(form.RowHeights[row]);
            var newHeight = height.GridUnitType == GridUnitType.Auto
                ? height
                : new GridLength(height.Value / 2, height.GridUnitType);
            var result = GridLengthToString(newHeight);
            form.RowHeights[row] = result;
            
            if (row == form.RowHeights.Count - 1)
                form.RowHeights.Add(result);
            else
                form.RowHeights.Insert(row + 1, result);
            SplitRow(row + 1);
            Render();
        }

        private void RowPropertiesClick(int row)
        {
            var length = StringToGridLength(form.RowHeights[row]);

            var editor = new DynamicFormDesignLength(length);
            if (editor.ShowDialog() == true)
            {
                form.RowHeights[row] = GridLengthToString(editor.GridLength);
                Render();
            }
        }

        private void ShiftUp(int row)
        {
            var deletes = new List<DFLayoutControl>();
            foreach (var element in form.Elements)
                if (element.Row > row)
                    element.Row--;
                else if (element.Row == row && element.RowSpan <= 1)
                    deletes.Add(element);
                else if (element.Row + element.RowSpan - 1 >= row)
                    element.RowSpan--;
            foreach (var delete in deletes)
                form.Elements.Remove(delete);
        }

        private void DeleteRows(Range rows)
        {
            for(var row = rows.Max; row >= rows.Min; --row)
            {
                form.RowHeights.RemoveAt(row);
                ShiftUp(row + 1);
            }
            if(form.RowHeights.Count == 0)
            {
                form.RowHeights.Add("Auto");
            }
            Render();
        }

        private void PopulateRowMenu(ContextMenu menu, int row)
        {
            menu.AddItem("Add Row Before", null, row, AddRowBeforeClick);
            menu.AddItem("Add Row After", null, row, AddRowAfterClick);
            menu.AddSeparator();
            menu.AddItem("Split Row", null, row, SplitRowClick);

            var propertiesSeparator = menu.AddSeparator();
            var propertiesMenu = menu.AddItem("Row Properties", null, row, RowPropertiesClick);

            menu.AddSeparator();
            menu.AddItem("Delete Row", null, new Range(row, row), DeleteRows);
            menu.Opened += (o, e) =>
            {
                propertiesSeparator.Visibility = form.RowHeights.Count > 1 ? Visibility.Visible : Visibility.Collapsed;
                propertiesMenu.Visibility = form.RowHeights.Count > 1 ? Visibility.Visible : Visibility.Collapsed;
            };
        }

        private ContextMenu CreateRowMenu(Button button, int row)
        {
            var result = new ContextMenu();
            PopulateRowMenu(result, row);
            button.SetValue(ContextMenuProperty, result);
            return result;
        }

        #endregion

        #region Columns

        private void ShiftRight(int column)
        {
            foreach (var element in form.Elements)
                if (element.Column > column)
                    element.Column++;
                else if (element.Column + element.ColumnSpan - 1 > column)
                    element.ColumnSpan++;
        }

        private void AddColumnBeforeClick(int column)
        {
            var length = new GridLength(1.0F, form.ColumnWidths.Count == 0 ? GridUnitType.Star : GridUnitType.Auto);
            var result = GridLengthToString(length);
            if (form.ColumnWidths.Count == 0)
                form.ColumnWidths.Add(result);
            else
                form.ColumnWidths.Insert(column, result);
            ShiftRight(column);
            Render();
        }

        private void AddColumnAfterClick(int column)
        {
            var length = new GridLength(1.0F, form.ColumnWidths.Count == 0 ? GridUnitType.Star : GridUnitType.Auto);

            var result = GridLengthToString(length);
            if (column == form.ColumnWidths.Count - 1)
                form.ColumnWidths.Add(result);
            else
                form.ColumnWidths.Insert(column + 1, result);
            ShiftRight(column + 1);
            Render();
        }

        private void SplitColumn(int column)
        {
            foreach (var element in form.Elements)
                if (element.Column > column)
                    element.Column++;
                else if (element.Column == column)
                    element.ColumnSpan++;
                else if (element.Column + element.ColumnSpan - 1 >= column)
                    element.ColumnSpan++;
        }

        private void SplitColumnClick(int column)
        {
            var length = StringToGridLength(form.ColumnWidths[column]);
            var newLength = length.GridUnitType == GridUnitType.Auto
                ? length
                : new GridLength(length.Value / 2, length.GridUnitType);
            var result = GridLengthToString(newLength);
            form.ColumnWidths[column] = result;

            if (column == form.ColumnWidths.Count - 1)
                form.ColumnWidths.Add(result);
            else
                form.ColumnWidths.Insert(column + 1, result);
            SplitColumn(column + 1);
            Render();
        }

        private void ColumnPropertiesClick(int column)
        {
            var length = StringToGridLength(form.ColumnWidths[column]);

            var editor = new DynamicFormDesignLength(length);
            if (editor.ShowDialog() == true)
            {
                form.ColumnWidths[column] = GridLengthToString(editor.GridLength);
                Render();
            }
        }

        private void ShiftLeft(int column)
        {
            var deletes = new List<DFLayoutControl>();
            foreach (var element in form.Elements)
                if (element.Column > column)
                    element.Column--;
                else if (element.Column == column && element.ColumnSpan <= 1)
                    deletes.Add(element);
                else if (element.Column + element.ColumnSpan - 1 >= column)
                    element.ColumnSpan--;
            foreach (var delete in deletes)
                form.Elements.Remove(delete);
        }

        private void DeleteColumns(Range columns)
        {
            for(var column = columns.Max; column >= columns.Min; --column)
            {
                form.ColumnWidths.RemoveAt(column);
                ShiftLeft(column + 1);
            }
            if(form.ColumnWidths.Count == 0)
            {
                form.ColumnWidths.Add("*");
            }
            Render();
        }

        private void PopulateColumnMenu(ContextMenu menu, int column)
        {
            menu.AddItem("Add Column Before", null, column, AddColumnBeforeClick);
            menu.AddItem("Add Column After", null, column, AddColumnAfterClick);
            menu.AddSeparator();
            menu.AddItem("Split Column", null, column, SplitColumnClick);
            var propertiesSeparator = menu.AddSeparator();
            var propertiesMenu = menu.AddItem("Column Properties", null, column, ColumnPropertiesClick);
            menu.AddSeparator();
            menu.AddItem("Delete Column", null, new Range(column, column), DeleteColumns);
            menu.Opened += (o, e) =>
            {
                propertiesSeparator.Visibility = form.ColumnWidths.Count > 1 ? Visibility.Visible : Visibility.Collapsed;
                propertiesMenu.Visibility = form.ColumnWidths.Count > 1 ? Visibility.Visible : Visibility.Collapsed;
            };
        }

        private ContextMenu CreateColumnMenu(Button button, int column)
        {
            var result = new ContextMenu();
            PopulateColumnMenu(result, column);
            button.SetValue(ContextMenuProperty, result);
            return result;
        }

        #endregion

        #region Add Element

        private void AddNewElement<TElement>(DynamicFormElement elementDef, CellRange range)
            where TElement : DFLayoutElement, new()
        {
            TElement? element;
            if (elementDef.CreateElement is not null)
            {
                element = elementDef.CreateElement(elementDef.Tag) as TElement;
            }
            else
            {
                element = new();
            }
            if(element is null)
            {
                return;
            }
            SetControlRange(element, range);

            var result = new FormControlGrid<TElement>().EditItems(new[] { element });
            if (result)
            {
                form.Elements.Add(element);
                Render();
            }
        }

        private void AddElementClick(Tuple<DynamicFormElement, CellRange> tuple)
        {
            var method = typeof(DynamicFormDesignGrid)
                .GetMethod(nameof(AddNewElement), BindingFlags.NonPublic | BindingFlags.Instance)!
                .MakeGenericMethod(tuple.Item1.ElementType);
            method.Invoke(this, new object[] { tuple.Item1, tuple.Item2 });
        }

        private void ElementActionClick(Tuple<DynamicFormElementAction, CellRange> tuple)
        {
            var element = tuple.Item1.OnClick(tuple.Item1.Tag);
            if(element is not null)
            {
                SetControlRange(element, tuple.Item2);
                form.Elements.Add(element);
                Render();
            }
        }

        private void SetControlRange(DFLayoutControl control, CellRange range)
        {
            var minRow = Math.Min(range.StartRow, range.EndRow);
            var maxRow = Math.Max(range.StartRow, range.EndRow);
            var minColumn = Math.Min(range.StartColumn, range.EndColumn);
            var maxColumn = Math.Max(range.StartColumn, range.EndColumn);

            control.Row = minRow;
            control.RowSpan = (maxRow - minRow) + 1;
            control.Column = minColumn;
            control.ColumnSpan = (maxColumn - minColumn) + 1;
        }

        private void CreateLabelClick(CellRange range)
        {
            var label = new DFLayoutLabel();
            SetControlRange(label, range);
            var result = new FormControlGrid<DFLayoutLabel>().EditItems(new[] { label });
            if (result)
            {
                form.Elements.Add(label);
                Render();
            }
        }

        private void CreateHeaderClick(CellRange range)
        {
            var header = new DFLayoutHeader();
            SetControlRange(header, range);
            var result = new FormControlGrid<DFLayoutHeader>().EditItems(new[] { header });
            if (result)
            {
                form.Elements.Add(header);
                Render();
            }
        }

        private void CreateImageClick(CellRange range)
        {
            var image = new DFLayoutImage();
            SetControlRange(image, range);
            var result = new FormControlGrid<DFLayoutImage>().EditItems(new[] { image });
            if (result)
            {
                form.Elements.Add(image);
                Render();
            }
        }

        private void AddVariable(Tuple<DigitalFormVariable, CellRange> tuple)
        {
            if(Activator.CreateInstance(tuple.Item1.FieldType()) is not DFLayoutField field)
            {
                MessageBox.Show(string.Format("{0}: Unknown Type {1}", tuple.Item1.Code, tuple.Item1.VariableType.ToString()));
                return;
            }

            field.Name = tuple.Item1.Code;
            SetControlRange(field, tuple.Item2);
            form.Elements.Add(field);
            form.LoadVariable(tuple.Item1, field);
            Render();
        }

        private void PopulateEmptyCellMenu(ContextMenu menu, CellRange cellRange)
        {
            menu.Items.Clear();
            menu.AddItem("Add Label", null, cellRange, CreateLabelClick);
            menu.AddItem("Add Header", null, cellRange, CreateHeaderClick);
            menu.AddItem("Add Image", null, cellRange, CreateImageClick);

            var fields = menu.AddItem("Add Field", null, null);

            if (OnCreateVariable is not null)
            {
                var variables = fields.AddItem("Create new variable", null, null);

                foreach (var fieldType in DFUtils.GetFieldTypes())
                {
                    var caption = fieldType.GetCaption();
                    if (string.IsNullOrWhiteSpace(caption))
                    {
                        caption = CoreUtils.Neatify(fieldType.Name);
                    }
                    variables.AddItem(caption, null, new Tuple<Type, CellRange>(fieldType, cellRange), (tuple) =>
                    {
                        var variable = OnCreateVariable?.Invoke(tuple.Item1);
                        if (variable is not null)
                        {
                            _variables.Add(variable);
                            AddVariable(new(variable, tuple.Item2));
                        }
                    });
                }
            }

            var filtered = _variables.Where(x => !x.Hidden && !form.Elements.Any(v => string.Equals((v as DFLayoutField)?.Name, x.Code)));
            fields.AddSeparatorIfNeeded();
            foreach (var variable in filtered)
                fields.AddItem(variable.Code, null, new Tuple<DigitalFormVariable, CellRange>(variable, cellRange), AddVariable);
            fields.RemoveUnnecessarySeparators();
            if(fields.Items.Count == 0)
            {
                menu.Items.Remove(fields);
            }

            var elements = menu.AddItem("Add Object", null, cellRange, null);

            var available = _elements.Where(x => x.Visible && (x.AllowDuplicate || !form.Elements.Any(v => (v as DFLayoutElement)?.GetType() == x.ElementType)))
                .ToArray();

            var cats = available.Select(x => x.Category).Concat(_elementActions.Select(x => x.Category)).Distinct().OrderBy(x => x);
            foreach (var cat in cats)
            {
                var parentMenu = elements;
                if (!string.IsNullOrWhiteSpace(cat))
                {
                    parentMenu = elements.AddItem(cat, null, null);
                }

                foreach(var action in _elementActions.Where(x => x.Category == cat))
                {
                    parentMenu.AddItem(action.Caption, action.Image, new Tuple<DynamicFormElementAction, CellRange>(action, cellRange), ElementActionClick);
                }

                parentMenu.AddSeparatorIfNeeded();

                foreach (var element in available.Where(x => string.Equals(x.Category, cat)))
                    parentMenu.AddItem(element.Caption, null, new Tuple<DynamicFormElement, CellRange>(element, cellRange), AddElementClick);
                parentMenu.RemoveUnnecessarySeparators();
            }

            if (elements.Items.Count == 0)
                menu.Items.Remove(elements);
        }

        private ContextMenu CreateEmptyCellMenu(Border border, int row, int column)
        {
            var result = new ContextMenu();
            result.Opened += (o, e) =>
            {
                PopulateEmptyCellMenu(result, new CellRange(row, column));
            };

            border.SetValue(ContextMenuProperty, result);
            return result;
        }

        #endregion

        #region Element Context Menu

        private void DeleteElements(IEnumerable<DFLayoutControl> controls)
        {
            foreach(var control in controls)
            {
                if (form.Elements.Contains(control))
                {
                    form.Elements.Remove(control);
                }
            }
            Render();
        }

        private void DeleteElementClick(DFLayoutControl control)
        {
            if (form.Elements.Contains(control))
            {
                form.Elements.Remove(control);
                Render();
            }
        }

        private void ElementPropertiesClick(DFLayoutControl control)
        {
            if(!elementgrids.TryGetValue(control.GetType(), out var grid))
            {
                var type = typeof(FormControlGrid<>).MakeGenericType(control.GetType());
                grid = (Activator.CreateInstance(type) as IDynamicGrid)!;
                elementgrids[control.GetType()] = grid;
            }

            control.CommitChanges();
            if (grid.EditItems(new[] { control }))
            {
                Render();
            }
        }

        private void EditVariableClick(DFLayoutField field)
        {
            var variable = _variables.FirstOrDefault(x => x.Code == field.Name);
            if (variable is null) return;

            if(OnEditVariable?.Invoke(variable) == true)
            {
                field.LoadFromString(variable.Parameters);
            }
        }

        private void ConvertToHeaderClick(DFLayoutLabel label)
        {
            var header = new DFLayoutHeader
            {
                Row = label.Row,
                RowSpan = label.RowSpan,
                Column = label.Column,
                ColumnSpan = label.ColumnSpan,
                Collapsed = false,
                Header = label.Caption
            };
            header.Style.Synchronise(label.Style);
            header.Style.IsBold = true;
            form.Elements.Remove(label);
            form.Elements.Add(header);
            Render();
        }

        private void ConvertToLabelClick(DFLayoutHeader header)
        {
            var label = new DFLayoutLabel
            {
                Row = header.Row,
                RowSpan = header.RowSpan,
                Column = header.Column,
                ColumnSpan = header.ColumnSpan,
                Caption = header.Header
            };
            label.Style.Synchronise(header);
            label.Style.IsBold = false;

            form.Elements.Remove(header);
            form.Elements.Add(label);
            Render();
        }

        private void PopulateElementContextMenu(ContextMenu menu, DFLayoutControl control)
        {
            var selectedItems = GetSelectedItems().ToList();
            if (selectedItems.Count > 1 && selectedItems.Contains(control))
            {
                PopulateSelectionMenu(menu);
                if(menu.Items.Count > 0) return;
            }

            menu.AddItem("Edit Properties", null, control, ElementPropertiesClick);
            if (OnEditVariable is not null && control is DFLayoutField field)
            {
                menu.AddItem("Edit Variable", null, field, EditVariableClick);
            }
            else if (control is DFLayoutLabel label)
            {
                menu.AddItem("Convert to Header", null, label, ConvertToHeaderClick);
            }
            else if (control is DFLayoutHeader header)
            {
                menu.AddItem("Convert to Label", null, header, ConvertToLabelClick);
            }
            else if(control is DFLayoutElement element)
            {
                CustomiseElementContextMenu?.Invoke(menu, element);
            }
            menu.AddSeparatorIfNeeded();
            menu.AddItem("Resize Item", null, control, ResizeItem);
            menu.AddItem("Delete Item", null, control, DeleteElementClick);
        }

        private ContextMenu CreateElementContextMenu(FrameworkElement element, DFLayoutControl control)
        {
            var result = new ContextMenu();
            result.Opened += (s, e) =>
            {
                result.Items.Clear();
                PopulateElementContextMenu(result, control);
            };
            element.SetValue(ContextMenuProperty, result);
            return result;
        }

        #endregion

        #endregion

        #region Render

        private static void SetDimensions(FrameworkElement element, int row, int column, int rowspan, int colspan, int offset)
        {
            if (column <= 0) return;
            if (row <= 0) return;

            element.MinHeight = 50.0F;
            element.MinWidth = 50.0F;
            element.SetGridPosition(row - offset, column - offset, rowspan, colspan);
        }

        private Border CreateBorder(int row, int column, int rowspan, int colspan, int offset, bool horzstar, bool vertstar)
        {
            var border = new Border();
            if (ShowBorders)
            {
                border.BorderThickness = new Thickness(
                    0.0F,//!IsDesigning && column == 1 - offset ? 0.00F /*0.75F*/ : 0.0F,
                    0.0F,//!IsDesigning && row == 1 - offset ? 0.00F /*0.75F*/ : 0.0F,
                    column - offset == ColumnDefinitions.Count - 1 ? horzstar ? 0.00F : 0.75F : 0.75F,
                    row - offset == RowDefinitions.Count - 1 ? vertstar ? 0.00F : 0.75F : 0.75F
                );

                border.BorderBrush = BorderBrush;
            }

            border.Background = BackgroundBrush;

            SetDimensions(border, row, column, rowspan, colspan, offset);

            return border;
        }

        private static BitmapImage HeaderClosed =Wpf.Resources.rightarrow.AsBitmapImage(32, 32);
        private static BitmapImage HeaderOpen =Wpf.Resources.downarrow.AsBitmapImage(32, 32);

        private FrameworkElement CreateHeader(DFLayoutHeader header)
        {
            var formHeader = new FormHeader
            {
                Collapsed = header.Collapsed,
                HeaderText = header.Header
            };
            formHeader.CollapsedChanged += (o, c) =>
            {
                CollapseRows(formHeader, c);
            };
            if (IsDesigning)
            {
                formHeader.IsEnabled = false;
            }
            return formHeader;
        }

        // DFLayoutField -> IDynamicFormFieldControl
        private static Dictionary<Type, Type>? _fieldControls;
        private DynamicFormControl? CreateFieldControl(DFLayoutField field)
        {
            if (_fieldControls == null)
            {
                _fieldControls = new();
                foreach (var controlType in CoreUtils.Entities.Where(x => x.IsClass && !x.IsGenericType && x.HasInterface<IDynamicFormFieldControl>()))
                {
                    var superDefinition = controlType.GetSuperclassDefinition(typeof(DynamicFormFieldControl<,,,>));
                    if (superDefinition != null)
                    {
                        _fieldControls[superDefinition.GenericTypeArguments[0]] = controlType;
                    }
                }
            }

            var fieldControlType = _fieldControls.GetValueOrDefault(field.GetType());
            if (fieldControlType is not null)
            {
                var element = (Activator.CreateInstance(fieldControlType) as DynamicFormControl)!;

                if(element is IDynamicFormFieldControl fieldControl)
                {
                    fieldControl.FieldChangedEvent += () =>
                    {
                        ChangeField(field.Name);
                    };
                }

                return element;
            }
            return null;
        }

        private DynamicFormControl? CreateFieldPlaceholder(DFLayoutField field)
        {
            var controlType = typeof(DFFieldPlaceholderControl<>).MakeGenericType(field.GetType());
            return Activator.CreateInstance(controlType) as DynamicFormControl;
        }

        private DynamicFormControl? CreateControl(DFLayoutControl item)
        {
            if (item is DFLayoutField field)
            {
                if (IsDesigning)
                {
                    return CreateFieldPlaceholder(field);
                }

                return CreateFieldControl(field);
            }
            else if (item is DFLayoutElement)
            {
                return IsDesigning
                    ? new DFElementPlaceholderControl()
                    : new DFElementControl();
            }
            else if (item is DFLayoutLabel)
            {
                return new DFLabelControl();
            }
            else if (item is DFLayoutHeader)
            {
                return new DFHeaderControl();
            }
            else if (item is DFLayoutImage)
            {
                return new DFImageControl();
            }

            return null;
        }

        private FrameworkElement? CreateElement(DFLayoutControl item)
        {
            var control = CreateControl(item);
            if(control != null)
            {
                control.FormDesignGrid = this;
                control.SetControl(item);
            }
            return control;
        }

        private Brush GetItemBackgroundBrush(DFLayoutControl item, Color? colour = null)
        {
            if(colour != null)
            {
                var colourValue = colour.Value;
                return new SolidColorBrush(new System.Windows.Media.Color { R = colourValue.R, G = colourValue.G, B = colourValue.B, A = colourValue.A });
            }

            if (item is DFLayoutField field)
                return field.GetPropertyValue<bool>("Required") ? RequiredFieldBrush : FieldBrush;
            else
                return IsDesigning ? FieldBrush : BackgroundBrush;
        }

        private void RenderElement(DFLayoutControl item, int offset, bool horzstar, bool vertstar)
        {
            var border = CreateBorder(item.Row, item.Column, item.RowSpan, item.ColumnSpan, offset, horzstar, vertstar);

            border.Background = GetItemBackgroundBrush(item);

            if (!ShowBorders)
                border.Padding = new Thickness(
                    item.Column == 1 ? 4 : 2,
                    item.Row == 1 ? 4 : 2,
                    item.Column + item.ColumnSpan - 1 == ColumnDefinitions.Count ? 4 : 2,
                    item.Row + item.RowSpan - 1 == RowDefinitions.Count ? 4 : 2
                );
            else
                border.Padding = new Thickness(5);

            var element = CreateElement(item);
            border.Child = element;
            Children.Add(border);
            if (IsDesigning)
            {
                CreateElementContextMenu(border, item);
            }
            borderMap[item] = border;

            if (element != null)
            {
                if(item is DFLayoutField)
                {
                    element.IsEnabled = element.IsEnabled && !IsReadOnly;
                }
                elementmap[item] = element;

                element.HorizontalAlignment = GetHorizontalAlignment(item.HorizontalAlignment);
                element.VerticalAlignment = GetVerticalAlignment(item.VerticalAlignment);
                if (IsDesigning)
                {
                    CreateElementContextMenu(element, item);
                }
            }

        }

        private void AfterRender()
        {
            if (!IsDesigning)
            {
                foreach (var header in elementmap.Where(x => x.Value is DFHeaderControl head).Select(x => x.Value).Cast<DFHeaderControl>())
                {
                    if (header.Header.Collapsed)
                    {
                        CollapseRows(header.Header, true);
                    }
                }
            }

            OnAfterRender?.Invoke(this);
        }

        private void Render()
        {
            ClearSelection();
            ClearResize();

            foreach (var item in elementmap.Keys)
            {
                var e = elementmap[item];
                if (VisualTreeHelper.GetParent(e) is Border parent)
                    parent.Child = null;
            }

            elementmap.Clear();

            Children.Clear();

            ColumnDefinitions.Clear();

            RowDefinitions.Clear();

            if (form == null)
                return;

            foreach (var column in form.ColumnWidths)
                ColumnDefinitions.Add(new ColumnDefinition { Width = StringToGridLength(column) });

            foreach (var row in form.RowHeights)
                RowDefinitions.Add(new RowDefinition { Height = StringToGridLength(row), Tag = new RowData(row) });

            var horzstar = ColumnDefinitions.Any(x => x.Width.IsStar);
            var vertstar = RowDefinitions.Any(x => x.Height.IsStar);

            var offset = 1;
            if (IsDesigning)
            {
                ColumnDefinitions.Insert(0, new ColumnDefinition { Width = new GridLength(1, GridUnitType.Auto) });
                RowDefinitions.Insert(0, new RowDefinition { Height = new GridLength(1, GridUnitType.Auto) });

                var topleft = new Button();
                topleft.SetValue(RowProperty, 0);
                topleft.SetValue(ColumnProperty, 0);
                topleft.Content =
                    ""; // new Image() { Source = _designing ? Wpf.Resources.view.AsBitmapImage() : Wpf.Resources.design.AsBitmapImage() };
                topleft.BorderBrush = BorderBrush;
                topleft.BorderThickness = new Thickness(
                    0.00F,
                    0.00F,
                    0.75F,
                    0.75F
                );
                topleft.Background = BackgroundBrush;
                //topleft.Click += (o, e) =>
                //{
                //    Designing = !Designing;
                //};
                Children.Add(topleft);

                for (var i = 1; i < ColumnDefinitions.Count; i++)
                {
                    var Button = new Button();
                    Button.SetValue(RowProperty, 0);
                    Button.SetValue(ColumnProperty, i);
                    Button.Content = FormatGridLength(ColumnDefinitions[i].Width, ColumnDefinitions.Select(x => x.Width));
                    Button.BorderBrush = BorderBrush;
                    Button.BorderThickness = new Thickness(
                        0.00F, //(i == 1) ? 0.75F : 0.0F,
                        0.00F, //0.75F,
                        i == ColumnDefinitions.Count - 1 ? horzstar ? 0.00F : 0.75F : 0.75F,
                        0.75F
                    );
                    Button.Background = BackgroundBrush;
                    Button.Padding = new Thickness(10);
                    Button.MinHeight = 35;
                    CreateColumnMenu(Button, i - 1);
                    AddClick(Button, i - 1, ColumnPropertiesClick);
                    Children.Add(Button);
                }

                for (var i = 1; i < RowDefinitions.Count; i++)
                {
                    var Button = new Button();
                    Button.SetValue(RowProperty, i);
                    Button.SetValue(ColumnProperty, 0);
                    Button.Content = FormatGridLength(RowDefinitions[i].Height, RowDefinitions.Select(x => x.Height));
                    Button.BorderBrush = BorderBrush;
                    Button.BorderThickness = new Thickness(
                        0.00F, //0.75F,
                        0.00F, //(i == 1) ? 0.75F : 0.0F,
                        0.75F,
                        i == RowDefinitions.Count - 1 ? vertstar ? 0.00F : 0.75F : 0.75F
                    );
                    Button.Background = BackgroundBrush;
                    Button.Padding = new Thickness(10);
                    CreateRowMenu(Button, i - 1);
                    AddClick(Button, i - 1, RowPropertiesClick);
                    Children.Add(Button);
                }

                offset = 0;
            }

            var filledcells = new List<Point>();
            foreach (var item in form.GetElements(IsDesigning))
            {
                try
                {
                    if(item.Row > 0 && item.Column > 0)
                    {
                        RenderElement(item, offset, horzstar, vertstar);
                        for (var c = item.Column; c < item.Column + item.ColumnSpan; c++)
                            for (var r = item.Row; r < item.Row + item.RowSpan; r++)
                                filledcells.Add(new Point(c, r));
                    }
                }
                catch (Exception e)
                {
                    Logger.Send(LogType.Error, "", string.Format("*** Unknown Error: {0}\n{1}", e.Message, e.StackTrace));
                }
            }

            for (var c = 1; c <= form.ColumnWidths.Count; c++)
                for (var r = 1; r <= form.RowHeights.Count; r++)
                    if (!filledcells.Any(x => x.X.Equals(c) && x.Y.Equals(r)))
                    {
                        var border = CreateBorder(r, c, 1, 1, offset, horzstar, vertstar);
                        if (IsDesigning)
                        {
                            CreateEmptyCellMenu(border, r, c);
                        }
                        Children.Add(border);
                    }

            AfterRender();
        }

        #endregion

        /// <summary>
        /// Renders the form; after this is called, any changes to properties triggers a refresh.
        /// </summary>
        /// <remarks>
        /// This should be called before <see cref="LoadValues(Dictionary{string, object})"/> or <see cref="SaveValues"/>
        /// </remarks>
        public void Initialize()
        {
            GridInitialized = true;
            CheckRefresh(false);
        }

        public void Refresh()
        {
            CheckRefresh(false);
        }

        private void CheckRefresh(bool keepValues = true)
        {
            if (!GridInitialized) return;

            if (_mode == FormMode.Designing)
            {
                Render();
            }
            else if(keepValues)
            {
                var values = SaveValues();
                Render();
                LoadValues(values.ToLoadStorage());
            }
            else
            {
                Render();
                Form.EvaluateExpressions();
            }
        }

        #region Fields

        private void ChangeField(string fieldName)
        {
            if (!_changing)
            {
                form.ChangeField(fieldName);
                _isChanged = true;
                OnChanged?.Invoke(this, fieldName);
            }
        }

        private IDynamicFormFieldControl? GetFieldControl(DFLayoutField field)
        {
            return elementmap.GetValueOrDefault(field) as IDynamicFormFieldControl;
        }

        private void LoadFieldValue(string fieldName, DFLoadStorageEntry entry)
        {
            var field = form.Elements.FirstOrDefault(x => string.Equals(fieldName, (x as DFLayoutField)?.Name)) as DFLayoutField;
            if (field != null)
            {
                var fieldControl = GetFieldControl(field);
                if (fieldControl != null)
                {
                    string? property = (DataModel != null) ? field.GetPropertyValue<string>("Property") : null;
                    if (!property.IsNullOrWhiteSpace())
                        fieldControl.SetValue(DataModel!.GetEntityValue(property));
                    else
                        fieldControl.Deserialize(entry);
                }
            }
        }

        public void SetFieldValue(string fieldName, object? value)
        {
            var field = form.Elements.FirstOrDefault(x => string.Equals(fieldName, (x as DFLayoutField)?.Name)) as DFLayoutField;
            if (field != null)
            {
                var fieldControl = GetFieldControl(field);
                if (fieldControl != null)
                {
                    string? property = (DataModel != null) ? field.GetPropertyValue<string>("Property") : null;
                    if (!property.IsNullOrWhiteSpace())
                        fieldControl.SetValue(DataModel!.GetEntityValue(property));
                    else
                        fieldControl.SetValue(value);
                }
            }
        }

        private void GetFieldValue(DFLayoutField field, DFSaveStorageEntry storage, out object? entityValue)
        {
            var fieldControl = GetFieldControl(field);
            if(fieldControl != null)
            {
                entityValue = fieldControl.GetEntityValue();
                fieldControl.Serialize(storage);
            }
            else
            {
                entityValue = null;
            }
        }

        public object? GetFieldValue(string fieldName)
        {
            var field = form.Elements.Where(x => (x as DFLayoutField)?.Name == fieldName).FirstOrDefault() as DFLayoutField;
            if (field is null)
            {
                return null;
            }
            var fieldControl = GetFieldControl(field);
            return fieldControl?.GetValue();
        }

        public object? GetFieldData(string fieldName, string dataField)
        {
            var field = form.Elements.Where(x => (x as DFLayoutField)?.Name == fieldName).FirstOrDefault() as DFLayoutField;
            if (field is null)
            {
                return null;
            }
            var fieldControl = GetFieldControl(field);
            return fieldControl?.GetData(dataField);
        }

        public void SetFieldColour(string fieldName, Color? colour)
        {
            var field = form.Elements.Where(x => (x as DFLayoutField)?.Name == fieldName).FirstOrDefault() as DFLayoutField;
            if (field is null || !borderMap.TryGetValue(field, out var border))
            {
                return;
            }
            border.Background = GetItemBackgroundBrush(field, colour);
        }

        /// <summary>
        /// Load values into editor; Must be called after <see cref="Initialize"/>.
        /// </summary>
        /// <remarks>
        /// Resets <see cref="IsChanged"/>.
        /// </remarks>
        /// <param name="values">A storage object.</param>
        public void LoadValues(DFLoadStorage values)
        {
            _changing = true;
            InitializeEntityValues();
            foreach (var (key, value) in values.Items())
            {
                if (!key.Contains('.'))
                {
                    LoadFieldValue(key, values.GetEntry(key));
                }
            }
            Form.EvaluateExpressions();
            _changing = false;
            _isChanged = false;
        }

        public void InitializeEntityValues()
        {
            _changing = true;
            foreach (var field in form.Elements.OfType<DFLayoutField>())
            {
                var property = DataModel != null ? field.GetPropertyValue<string>("Property") : null;
                if (!property.IsNullOrWhiteSpace())
                {
                    var fieldControl = GetFieldControl(field);
                    if(fieldControl != null)
                    {
                        fieldControl.SetValue(DataModel!.GetEntityValue(property));
                    }
                }
            }
            Form.EvaluateExpressions();
            _changing = false;
            _isChanged = false;
        }

        /// <summary>
        /// Takes values from editors and saves them to a dictionary; must be called after <see cref="Initialize"/>.
        /// </summary>
        /// <returns>A dictionary of <see cref="DigitalFormVariable.Code"/> -> value.</returns>
        public DFSaveStorage SaveValues()
        {
            var result = new DFSaveStorage();
            foreach (var formElement in form.Elements)
                if (formElement is DFLayoutField field)
                {
                    GetFieldValue(field, result.GetEntry(field.Name), out var entityValue);

                    if(DataModel != null)
                    {
                        var property = field.GetPropertyValue<string>("Property");
                        if (!string.IsNullOrWhiteSpace(property))
                            DataModel.SetEntityValue(property, entityValue);
                    }
                }

            return result;
        }

        public bool Validate(out List<string> messages)
        {
            messages = new List<string>();
            var valid = true;
            foreach(var formElement in form.Elements)
            {
                if(formElement is DFLayoutField field)
                {
                    var fieldControl = GetFieldControl(field);
                    if(fieldControl != null && !fieldControl.Validate(out var message))
                    {
                        messages.Add(message);
                        valid = false;
                    }
                }
            }
            return valid;
        }

        #endregion

    }
}