namespace System.Windows.Forms
{
    public class Splitter : Control
    {
        private Control indicator;
        private System.Drawing.Point mouseDownPoint;

        public override DockStyle Dock 
        { 
            get => base.Dock;
            set
            {
                base.Dock = value;
                Cursor = value == DockStyle.Left || value == DockStyle.Right ? Cursors.VSplit : Cursors.HSplit;
                if (value == DockStyle.Left || value == DockStyle.Right)
                    Width = 3;
                else
                    Height = 3;
            }
        }

        public int MinSize { get; set; } // TODO: check

        public int MinExtra { get; set; } // TODO?

        public event SplitterEventHandler SplitterMoved;

        private Control GetResizableControl()
        {
            for (int i = Parent.Controls.Count - 1; i >= 0; i--)
            {
                var c = Parent.Controls[i];
                if (c != this && c.Dock == this.Dock)
                    return c;
            }
            return null;
        }

        protected virtual void OnSplitterMoved(SplitterEventArgs e) => SplitterMoved?.Invoke(this, e);

        protected override void OnMouseDown(MouseEventArgs e)
        {
            base.OnMouseDown(e);

            if (GetResizableControl() == null)
                return;

            mouseDownPoint = e.Location;

            indicator = new Control();
            indicator.BackColor = System.Drawing.Color.Black;
            indicator.Parent = this.Parent;
            indicator.Location = this.Location;
            indicator.Size = this.Size;
            indicator.BringToFront();
        }

        protected override void OnMouseMove(MouseEventArgs e)
        {
            base.OnMouseMove(e);

            if (e.Button == MouseButtons.Left)
            {
                if (indicator == null)
                    return;

                if (Dock == DockStyle.Left || Dock == DockStyle.Right)
                {
                    int x = Left + e.X - mouseDownPoint.X;
                    if (x >= 0 && x < Parent.Width - Width && x >= MinSize)
                        indicator.Left = x;
                }
                else
                {
                    int y = Top + e.Y - mouseDownPoint.Y;
                    if (y >= 0 && y < Parent.Height - Height && y >= MinSize)
                        indicator.Top = y;
                }
            }
        }

        protected override void OnMouseUp(MouseEventArgs e)
        {
            base.OnMouseUp(e);

            if (indicator == null)
                return;

            Control resizableControl = GetResizableControl();
            if (resizableControl == null)
                return;

            if (Dock == DockStyle.Left)
                resizableControl.Width -= Left - indicator.Left;
            else if (Dock == DockStyle.Right)
                resizableControl.Width += Left - indicator.Left;
            else if (Dock == DockStyle.Top)
                resizableControl.Height -= Top - indicator.Top;
            else if (Dock == DockStyle.Bottom)
                resizableControl.Height += Top - indicator.Top;

            indicator.Dispose();

            // TODO: check arguments
            OnSplitterMoved(new SplitterEventArgs(0, 0, resizableControl.Width, resizableControl.Height));
        }

        public Splitter()
        {
            Dock = DockStyle.Left;
        }
    }
}