using Comal.Classes;
using InABox.Configuration;
using InABox.Core;
using InABox.Database;
using InABox.Database.Stores;
using InABox.Scripting;
using org.omg.CosNaming.NamingContextPackage;
using sun.util.resources.cldr.haw;
using Syncfusion.UI.Xaml.Grid.Converters;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace PRSStores.AssignmentCosting
{
    public class TimeSheetBlock
    {
        public TimeSpan Start { get; set; }
        public TimeSpan Finish { get; set; }

        public TimeSpan Duration => Finish - Start;

        public required bool IsPaid { get; set; }
    }

    public class DayTimeSheet
    {
        public IList<TimeSheetBlock> Blocks { get; private init; }

        public IEnumerable<TimeSheetBlock> PaidBlocks => Blocks.Where(x => x.IsPaid);

        public TimeSpan PaidDuration => PaidBlocks.Aggregate(TimeSpan.Zero, (a, b) => a + b.Duration);

        private DayTimeSheet(IList<TimeSheetBlock> blocks)
        {
            Blocks = blocks;
        }

        /// <summary>
        /// Create a new <see cref="DayTimeSheet"/> from a given list of <see cref="TimeSheet"/>s. The <paramref name="overtime"/> is
        /// used to create blocks for unpaid time on the timesheet.
        /// </summary>
        /// <exception cref="Exception">If there are no elements in <paramref name="sheets"/></exception>
        public static DayTimeSheet FromTimeSheets(IEnumerable<TimeSheet> sheets, IList<OvertimeInterval> overtime)
        {
            var sheetArray = sheets.Select(x =>
            {
                return (
                    start: x.Approved != DateTime.MinValue ? x.ApprovedStart : x.Start,
                    finish: x.Approved != DateTime.MinValue ? x.ApprovedFinish : x.Finish,
                    sheet: x);
            }).ToArray();
            sheetArray.SortBy(x => x.start);
            if(sheetArray.Length == 0)
            {
                throw new Exception("No timesheets provided.");
            }

            // Merge all timesheets into a single list of time blocks; overlapping timesheets will be merged into one.
            var blocks = new List<TimeSheetBlock>();
            TimeSheetBlock? current = null;
            foreach(var (start, finish, sheet) in sheetArray)
            {
                if(current is null || start > current.Finish)
                {
                    current = new TimeSheetBlock
                    {
                        Start = start,
                        Finish = finish,
                        // Doesn't matter what we put here, since this block will not appear in the final list.
                        IsPaid = true
                    };
                    blocks.Add(current);
                }
                else
                {
                    current.Finish = finish;
                }
            }

            // Now, apply overtime to take out chunks of time that are unpaid.
            var newBlocks = new List<TimeSheetBlock>();
            current = null;
            TimeSheetBlock? currentUnpaidBlock = null;

            // We will definitely have at least one block, based on the above algorithm, and since we ensured that sheetArray is non-empty.
            var currentTime = TimeSpan.Zero;
            var met = new HashSet<TimeSheetBlock>();
            OvertimeUtils.EvaluateOvertime(blocks, overtime, x => x.Duration, (block, interval, duration) =>
            {
                if (interval is null) return;

                if (met.Add(block))
                {
                    currentTime = block.Start;
                }

                if (interval.IsPaid)
                {
                    if(current is null || currentTime > current.Finish)
                    {
                        current = new TimeSheetBlock
                        {
                            Start = currentTime,
                            Finish = currentTime + duration,
                            IsPaid = true
                        };
                        newBlocks.Add(current);
                        currentUnpaidBlock = null;
                    }
                    else
                    {
                        current.Finish = currentTime + duration;
                    }
                }
                else
                {
                    if(currentUnpaidBlock is null || currentTime > currentUnpaidBlock.Finish)
                    {
                        currentUnpaidBlock = new TimeSheetBlock
                        {
                            Start = currentTime,
                            Finish = currentTime + duration,
                            IsPaid = false
                        };
                        newBlocks.Add(currentUnpaidBlock);
                        current = null;
                    }
                    else
                    {
                        currentUnpaidBlock.Finish = currentTime + duration;
                    }
                }

                currentTime += duration;
            });

            return new(newBlocks);
        }
    }

    public class Block
    {
        public Assignment? Assignment { get; set; } // Set to null for lost time blocks that won't be costed anywhere.

        public TimeSpan Start { get; set; }

        public TimeSpan Finish { get; set; }

        public TimeSpan Duration
        {
            get => Finish - Start;
            set => Finish = Start + value;
        }

        public Block Copy()
        {
            return new Block
            {
                Assignment = Assignment,
                Start = Start,
                Finish = Finish,
            };
        }

        public static Block FromAssignment(Assignment assignment)
        {
            return new Block
            {
                Assignment = assignment,
                Start = assignment.EffectiveStartTime(),
                Finish = assignment.EffectiveFinishTime()
            };
        }

        public static Block Transient(TimeSpan start, TimeSpan finish)
        {
            return new Block
            {
                Assignment = null,
                Start = start,
                Finish = finish
            };
        }
    }

    public class BeforeProcessArgs(Assignment[] assignments, TimeSheet[] timesheets)
    {
        public Assignment[] Assignments { get; } = assignments;
        public TimeSheet[] TimeSheets { get; } = timesheets;
    }

    public class AdjustTimeBlocksArgs(DayTimeSheet timeSheet, List<Block> blocks)
    {
        public DayTimeSheet TimeSheet { get; } = timeSheet;

        public List<Block> Blocks { get; set; } = blocks;
    }

    public class ProcessTimeBlocksArgs(DayTimeSheet timeSheet, List<Block> blocks)
    {
        public DayTimeSheet TimeSheet { get; } = timeSheet;

        public List<Block> Blocks { get; set; } = blocks;
    }

    public class AfterOvertimeArgs(DayTimeSheet timeSheet, List<Block> blocks, OvertimeInterval[] overtime, Assignment[] assignments)
    {
        public DayTimeSheet TimeSheet { get; } = timeSheet;

        public List<Block> Blocks { get; } = blocks;

        public OvertimeInterval[] Overtime { get; } = overtime;

        public Assignment[] Assignments { get; } = assignments;
    }

    public interface IAssignmentCostingScript
    {
        void BeforeProcess(BeforeProcessArgs args);

        void AdjustTimeBlocks(AdjustTimeBlocksArgs args);

        void ProcessTimeBlocks(ProcessTimeBlocksArgs args);

        void AfterOvertime(AfterOvertimeArgs args);
    }

    public class AssignmentCostingUtils : ISettingsStoreEventHandler<AssignmentCostSettings>
    {
        static AssignmentCostSettings? _costSettings;

        public static AssignmentCostSettings GetSettings(IStore store)
        {
            _costSettings ??= new GlobalConfiguration<AssignmentCostSettings>("", new DbConfigurationProvider<GlobalSettings>(store.UserID))
                .Load(false);
            return _costSettings;
        }

        #region ISettingsStoreEventHandler

        public IStore Parent { get; set; } = null!; // Set by GlobalSettingsStore

        public void AfterDelete(AssignmentCostSettings entity)
        {
            _costSettings = null;
            ClearScript();
        }

        public void AfterSave(AssignmentCostSettings entity)
        {
            _costSettings = entity;
            ClearScript();
        }

        public void BeforeDelete(AssignmentCostSettings entity)
        {
        }

        public void BeforeSave(AssignmentCostSettings entity)
        {
        }

        #endregion

        #region Script

        public static string DefaultScript()
        {
            return
@"using PRSStores.AssignmentCosting;
using InABox.Core;
using System.Collections.Generic;

// 'Module' *must* implement " + nameof(IAssignmentCostingScript) + @"
public class Module: " + nameof(IAssignmentCostingScript) + @"
{
    public void " + nameof(IAssignmentCostingScript.BeforeProcess) + @"(" + nameof(BeforeProcessArgs) + @" args)
    {
        // Perform pre-processing
    }

    public void " + nameof(IAssignmentCostingScript.AdjustTimeBlocks) + @"(" + nameof(AdjustTimeBlocksArgs) + @" args)
    {
        // At this stage, adjust the list of blocks (given by args." + nameof(AdjustTimeBlocksArgs.Blocks) + @") before any algorithm has
        // been applied to them. The blocks are ordered by start time, and are represented by one per each assignment being processed. At this stage,
        // they may overlap.

        // args." + nameof(AdjustTimeBlocksArgs.Blocks) + @" will then be passed through algorithm given in the settings, which will fill
        // up all the time on the day's timesheet by extending blocks as needed to fill all unfilled time.
    }

    public void " + nameof(IAssignmentCostingScript.ProcessTimeBlocks) + @"(" + nameof(ProcessTimeBlocksArgs) + @" args)
    {
        // Called after the time filling algorithm has been applied, but before the overtime rules. args." + nameof(ProcessTimeBlocksArgs.Blocks) + @" will
        // now contain a list of blocks, filling continuous time from the start of the timesheet to its end. Process as desired.
    }

    public void " + nameof(IAssignmentCostingScript.AfterOvertime) + @"(" + nameof(AfterOvertimeArgs) + @" args)
    {
        // Once the overtime rules have been applied and the assignment cost calculated, post-process the assignments before saving to the database.
    }
}";
        }

        private static Type? _scriptObjectType;
        private static bool _hasCheckedScript;

        private static void ClearScript()
        {
            _scriptObjectType = null;
            _hasCheckedScript = false;
        }

        private static Type? GetScriptObjectType(IStore store)
        {
            if (_hasCheckedScript)
            {
                return _scriptObjectType;
            }

            var settings = GetSettings(store);
            if (!string.IsNullOrWhiteSpace(settings.Script))
            {
                var document = new ScriptDocument(settings.Script);
                if (!document.Compile())
                {
                    Logger.Send(LogType.Error, store.UserID, "Script failed to compile!");
                    _scriptObjectType = null;
                }
                else
                {
                    _scriptObjectType = document.GetClassType();
                }
            }
            else
            {
                _scriptObjectType = null;
            }

            _hasCheckedScript = true;
            return _scriptObjectType;
        }

        private static IAssignmentCostingScript? GetScriptObject(IStore store)
        {
            var type = GetScriptObjectType(store);
            if(type is not null)
            {
                var obj = Activator.CreateInstance(type) as IAssignmentCostingScript;
                if(obj is null)
                {
                    Logger.Send(LogType.Error, store.UserID, $"Assignment costing script module does not implement {typeof(IAssignmentCostingScript).Name}");
                }
                return obj;
            }
            else
            {
                return null;
            }
        }

        private static void ScriptBeforeProcess(IAssignmentCostingScript? script, Assignment[] assignments, TimeSheet[] timesheets)
        {
            script?.BeforeProcess(new(assignments, timesheets));
        }

        private static List<Block> ScriptAdjustTimeBlocks(IAssignmentCostingScript? script, DayTimeSheet timeSheet, List<Block> blocks)
        {
            if(script is not null)
            {
                var args = new AdjustTimeBlocksArgs(timeSheet, blocks);
                script.AdjustTimeBlocks(args);
                return args.Blocks;
            }
            else
            {
                return blocks;
            }
        }

        private static List<Block> ScriptProcessTimeBlocks(IAssignmentCostingScript? script, DayTimeSheet timeSheet, List<Block> blocks)
        {
            if(script is not null)
            {
                var args = new ProcessTimeBlocksArgs(timeSheet, blocks);
                script.ProcessTimeBlocks(args);
                return args.Blocks;
            }
            else
            {
                return blocks;
            }
        }

        private static void ScriptAfterOvertime(IAssignmentCostingScript? script, DayTimeSheet timeSheet, List<Block> blocks, OvertimeInterval[] overtime, Assignment[] assignments)
        {
            script?.AfterOvertime(new(timeSheet, blocks, overtime, assignments));
        }

        #endregion

        private static List<Block> AdjustTimeBlocksBasic(List<Block> blocks)
        {
            // No change for basic mode.
            return blocks;
        }

        private static List<Block> AdjustTimeBlocksScale(DayTimeSheet timeSheet, List<Block> blocks)
        {
            // We scale the blocks until their total is equal to 'PaidDuration'
            var totalBlockDuration = blocks.Aggregate(TimeSpan.Zero, (a, b) => a + b.Duration);
            var adjustFactor = timeSheet.PaidDuration.TotalHours / totalBlockDuration.TotalHours;

            // Adjust block size
            foreach(var block in blocks)
            {
                block.Duration *= adjustFactor;
            }

            // Now we need to adjust the block positioning.
            var paidBlocks = timeSheet.PaidBlocks.ToList();

            var curPaidBlockIdx = 0;
            TimeSheetBlock? GetPaidBlock() => curPaidBlockIdx < paidBlocks.Count ? paidBlocks[curPaidBlockIdx] : null;
            var timeSheetStart = GetPaidBlock()?.Start ?? TimeSpan.Zero;
            var curTime = timeSheetStart;
            var curPaidBlockDuration = GetPaidBlock()?.Duration ?? TimeSpan.Zero;
            void AdvancePaidBlock()
            {
                ++curPaidBlockIdx;
                var paidBlock = GetPaidBlock();
                curPaidBlockDuration = paidBlock?.Duration ?? TimeSpan.Zero;
                if(paidBlock is not null)
                {
                    curTime = paidBlock.Start;
                }
            }

            var newBlocks = new List<Block>();

            foreach (var block in blocks)
            {
                var duration = block.Duration;
                if(duration == TimeSpan.Zero)
                {
                    block.Start = curTime;
                    block.Finish = curTime + duration;
                    newBlocks.Add(block);
                    continue;
                }

                while (duration > TimeSpan.Zero)
                {
                    var paidBlock = GetPaidBlock();
                    if (paidBlock != null)
                    {
                        if (duration > curPaidBlockDuration)
                        {
                            // In this case, the block is more than the rest of
                            // the current timesheet, so we use up all the remaining timesheet
                            // time, and then move to the next timesheet.
                            var newBlock = block.Copy();
                            newBlock.Start = curTime;
                            newBlock.Finish = curTime + curPaidBlockDuration;
                            newBlocks.Add(newBlock);

                            duration -= curPaidBlockDuration;
                            AdvancePaidBlock();
                        }
                        else
                        {
                            // Otherwise, we use up the entire block, and decrease the interval by the duration remaining.
                            block.Start = curTime;
                            block.Finish = curTime + duration;
                            newBlocks.Add(block);

                            curPaidBlockDuration -= duration;
                            curTime += duration;
                            duration = TimeSpan.Zero;

                            if(curPaidBlockDuration == TimeSpan.Zero)
                            {
                                AdvancePaidBlock();
                            }
                        }
                    }
                    else
                    {
                        // Do nothing; we've finished the timesheets, so now we just set all the remaining blocks to zero.
                        block.Start = curTime;
                        block.Duration = TimeSpan.Zero;
                        newBlocks.Add(block);
                        break;
                    }
                }
            }

            return newBlocks;
        }

        /// <summary>
        /// Taking a list of <see cref="Block"/>, chop and extend them to match the bounds of the <paramref name="timeSheet"/>.
        /// </summary>
        /// <remarks>
        /// <paramref name="blocks"/> <b>must</b> be in continuous time, however they need not correspond at all to <paramref name="timeSheet"/> yet;
        /// that is what this function does.
        /// </remarks>
        private static List<Block> MaskBlocksToTimeSheet(DayTimeSheet timeSheet, List<Block> blocks)
        {
            var paidBlocks = timeSheet.PaidBlocks.ToList();
            if(paidBlocks.Count == 0)
            {
                // No time to be paid, so all assignments have effective duration of zero.
                foreach(var block in blocks)
                {
                    block.Duration = TimeSpan.Zero;
                }
                return blocks;
            }

            // Fill in gaps in the time sheet with unpaid blocks, so we get a continuous time sheet.
            var timeSheetBlocks = new List<TimeSheetBlock>();
            foreach(var block in timeSheet.Blocks)
            {
                if(timeSheetBlocks.Count > 0)
                {
                    var last = timeSheetBlocks[^1];
                    if(last.Finish < block.Start)
                    {
                        timeSheetBlocks.Add(new TimeSheetBlock
                        {
                            IsPaid = false,
                            Start = last.Finish,
                            Finish = block.Start
                        });
                    }
                }
                timeSheetBlocks.Add(block);
            }

            // Now that the blocks have continuous time, we chop to match the timesheet paid blocks.

            // First, shove all the blocks at the start of the day up to match with the time sheet start.
            var timeSheetStart = timeSheetBlocks[0].Start;
            var anyAtStart = false;
            foreach(var block in blocks)
            {
                if(block.Start < timeSheetStart)
                {
                    anyAtStart = true;
                    block.Start = timeSheetStart;
                    if(block.Finish < timeSheetStart)
                    {
                        block.Finish = timeSheetStart;
                    }
                }
                else
                {
                    // Once we've found the first block that doesn't begin before the timesheet begins, we can set its time to start
                    // at the time sheet, unless we already have one at the start.
                    if (!anyAtStart)
                    {
                        block.Start = timeSheetStart;
                        anyAtStart = true;
                    }
                    break;
                }
            }

            var curBlockIdx = 0;
            TimeSheetBlock? GetTimeSheetBlock() => curBlockIdx < timeSheetBlocks.Count ? timeSheetBlocks[curBlockIdx] : null;
            var curBlockDuration = GetTimeSheetBlock()?.Duration ?? TimeSpan.Zero;
            var curTime = timeSheetStart;
            void AdvanceBlock()
            {
                ++curBlockIdx;
                var block = GetTimeSheetBlock();
                curBlockDuration = block?.Duration ?? TimeSpan.Zero;
                if(block is not null)
                {
                    curTime = block.Start;
                }
            }

            var newBlocks = new List<Block>();
            foreach (var block in blocks)
            {
                var duration = block.Duration;
                if(duration == TimeSpan.Zero)
                {
                    newBlocks.Add(block);
                    continue;
                }

                while (duration > TimeSpan.Zero)
                {
                    var paidBlock = GetTimeSheetBlock();
                    if (paidBlock != null)
                    {
                        if (duration > curBlockDuration)
                        {
                            // In this case, the block is more than the rest of
                            // the current timesheet, so we use up all the remaining timesheet
                            // time, and then move to the next timesheet.
                            var newBlock = block.Copy();
                            newBlock.Start = curTime;
                            newBlock.Finish = curTime + curBlockDuration;
                            if (paidBlock.IsPaid)
                            {
                                newBlocks.Add(newBlock);
                            }

                            duration -= curBlockDuration;
                            AdvanceBlock();
                        }
                        else
                        {
                            // Otherwise, we use up the entire block, and decrease the interval by the duration remaining.
                            block.Start = curTime;
                            block.Finish = curTime + duration;
                            if (paidBlock.IsPaid)
                            {
                                newBlocks.Add(block);
                            }

                            curTime = block.Finish;
                            curBlockDuration -= duration;
                            duration = TimeSpan.Zero;

                            if(curBlockDuration == TimeSpan.Zero)
                            {
                                AdvanceBlock();
                            }
                        }
                    }
                    else
                    {
                        // Do nothing; we've finished the timesheets, so now we just set all the remaining blocks to zero.
                        block.Duration = TimeSpan.Zero;
                        break;
                    }
                }
            }

            // Extend the last block to the end of the current timesheet block, if we haven't reached the end already.
            var lastBlock = newBlocks[^1];
            if(GetTimeSheetBlock() is TimeSheetBlock nextTimeSheetBlock)
            {
                lastBlock.Finish = nextTimeSheetBlock.Finish;
                AdvanceBlock();
            }

            // Next, if there are still more timesheet blocks, fill them with 'lastBlock' as well.
            while(GetTimeSheetBlock() is TimeSheetBlock block)
            {
                var newBlock = lastBlock.Copy();
                newBlock.Start = block.Start;
                newBlock.Finish = block.Finish;
                AdvanceBlock();
            }

            return newBlocks;
        }

        private static List<Block> AdjustTimeBlocksExtend(DayTimeSheet timeSheet, List<Block> blocks)
        {
            if(blocks.Count == 0)
            {
                return blocks;
            }

            // First, chop and extend blocks to fill continuous time, from the beginning of the first block to the end of the last block.

            // Block chopping
            var lastEnd = TimeSpan.Zero;
            foreach(var block in blocks)
            {
                // We know this check is enough to check overlap, since the blocks are in increasing order of their start time.
                if (lastEnd <= block.Start)
                {
                    // This block does not overlap any previous blocks. Do not update duration.
                    lastEnd = block.Finish;
                }
                else if(block.Finish >= lastEnd)
                {
                    // This block ends after the block that we are overlapping. Update start.
                    block.Start = lastEnd;
                    lastEnd = block.Finish;
                }
                else
                {
                    // This assignment is entirely contained within the assignment being overlapped.
                    block.Start = lastEnd;
                    block.Finish = lastEnd;
                }
            }

            // Block extending
            for(int i = 0; i < blocks.Count - 1; ++i)
            {
                var block = blocks[i];
                var nextBlock = blocks[i + 1];
                if(block.Finish < nextBlock.Start)
                {
                    block.Finish = nextBlock.Start;
                }
            }

            // Now that the blocks have continuous time, we chop to match the timesheet paid blocks.
            return MaskBlocksToTimeSheet(timeSheet, blocks);
        }

        private static List<Block> AdjustTimeBlocksFillTimeSheet(DayTimeSheet timeSheet, List<Block> blocks)
        {
            if(blocks.Count == 0)
            {
                return blocks;
            }

            // First, chop blocks to ensure they don't overlap
            var lastEnd = TimeSpan.Zero;
            foreach(var block in blocks)
            {
                // We know this check is enough to check overlap, since the blocks are in increasing order of their start time.
                if (lastEnd <= block.Start)
                {
                    // This block does not overlap any previous blocks. Do not update duration.
                    lastEnd = block.Finish;
                }
                else if(block.Finish >= lastEnd)
                {
                    // This block ends after the block that we are overlapping. Update start.
                    block.Start = lastEnd;
                    lastEnd = block.Finish;
                }
                else
                {
                    // This assignment is entirely contained within the assignment being overlapped.
                    block.Start = lastEnd;
                    block.Finish = lastEnd;
                }
            }

            // Fill up remaining gaps in time with transient, "lost time" blocks. For simplicity, so that we don't have to query
            // the timesheet yet, we just go from the start to the end of the day. 'MaskBlocksToTimeSheet' will take care of the rest.
            var start = TimeSpan.Zero;
            var finish = TimeSpan.FromDays(1).Subtract(TimeSpan.FromTicks(1));

            // Fill to start of day.
            if (blocks[0].Start > start)
            {
                blocks.Insert(0, Block.Transient(start, blocks[0].Start));
            }

            // Fill in gaps between blocks
            var i = 0;
            while(i < blocks.Count - 1)
            {
                var block = blocks[i];
                var nextBlock = blocks[i + 1];
                if(nextBlock.Start > block.Finish)
                {
                    blocks.Insert(i + 1, Block.Transient(block.Finish, nextBlock.Start));
                    i += 2;
                }
                else
                {
                    i += 1;
                }
            }

            // Fill to end of day.
            if (blocks[^1].Finish < finish)
            {
                blocks.Add(Block.Transient(blocks[^1].Finish, finish));
            }
            
            return MaskBlocksToTimeSheet(timeSheet, blocks);
        }

        public static List<Block> AdjustTimeBlocks(AssignmentCostSettings settings, DayTimeSheet timeSheet, List<Block> blocks)
        {
            return settings.Algorithm switch
            {
                AssignmentCostFillAlgorithm.Basic => AdjustTimeBlocksBasic(blocks),
                AssignmentCostFillAlgorithm.Scale => AdjustTimeBlocksScale(timeSheet, blocks),
                AssignmentCostFillAlgorithm.Extend => AdjustTimeBlocksExtend(timeSheet, blocks),
                AssignmentCostFillAlgorithm.FillTimeSheet => AdjustTimeBlocksFillTimeSheet(timeSheet, blocks),
                _ => blocks,
            };
        }
        
        public static void CheckAssignmentCosts(IStore store, DateTime date, Guid employeeID)
        {
            var settings = GetSettings(store);

            if (employeeID == Guid.Empty) return;

            var assignmentTask = Task.Run(() =>
                store.Provider.Query(
                    Filter<Assignment>.Where(x => x.Date).IsEqualTo(date)
                        .And(x => x.EmployeeLink.ID).IsEqualTo(employeeID),
                    Columns.Required<Assignment>()
                        .Add(x => x.ID)
                        .Add(x => x.Cost)
                        .Add(x => x.Actual.Start)
                        .Add(x => x.Actual.Finish)
                        .Add(x => x.Actual.Duration)
                        .Add(x => x.Booked.Start)
                        .Add(x => x.Booked.Finish)
                        .Add(x => x.Booked.Duration))
                    .ToArray<Assignment>());
            var timesheetTask = Task.Run(() =>
                store.Provider.Query(
                    Filter<TimeSheet>.Where(x => x.Date).IsEqualTo(date)
                        .And(x => x.EmployeeLink.ID).IsEqualTo(employeeID),
                    Columns.None<TimeSheet>()
                        .Add(x => x.Approved)
                        .Add(x => x.Start)
                        .Add(x => x.Finish)
                        .Add(x => x.ApprovedStart)
                        .Add(x => x.ApprovedFinish))
                    .ToArray<TimeSheet>());

            var employeeTask = Task.Run(() =>
                store.Provider.Query(
                    Filter<Employee>.Where(x => x.ID).IsEqualTo(employeeID),
                    Columns.None<Employee>()
                        .Add(x => x.RosterStart)
                        .Add(x => x.HourlyRate))
                    .ToObjects<Employee>().FirstOrDefault());

            var rosterItemsTask = Task.Run(() =>
                store.Provider.Query(
                    Filter<EmployeeRosterItem>.Where(x => x.Employee.ID).IsEqualTo(employeeID),
                    Columns.None<EmployeeRosterItem>()
                        .Add(x => x.Overtime.ID),
                    new SortOrder<EmployeeRosterItem>(x => x.Day))
                    .ToArray<EmployeeRosterItem>());

            var timesheets = timesheetTask.Result;
            var employee = employeeTask.Result;

            if (timesheets.Length == 0 || employee is null) return;

            var assignments = assignmentTask.Result;
            var rosterItems = rosterItemsTask.Result;

            var overtimeID = RosterUtils.GetRoster(rosterItems, employee.RosterStart, date)?.Overtime.ID ?? Guid.Empty;
            if(overtimeID == Guid.Empty) return;

            var overtime = store.Provider.Query(
                Filter<OvertimeInterval>.Where(x => x.Overtime.ID).IsEqualTo(overtimeID),
                Columns.None<OvertimeInterval>()
                    .Add(x => x.Interval)
                    .Add(x => x.IntervalType)
                    .Add(x => x.Multiplier)
                    .Add(x => x.IsPaid),
                new SortOrder<OvertimeInterval>(x => x.Sequence))
                .ToArray<OvertimeInterval>();

            var script = GetScriptObject(store);

            ScriptBeforeProcess(script, assignments, timesheets);

            // We need to sort the assignments, because both the chopping algorithm and the overtime algorithm requires it.
            assignments.SortBy(x => x.EffectiveStartTime());

            var blocks = new List<Block>();
            foreach(var assignment in assignments)
            {
                blocks.Add(Block.FromAssignment(assignment));
            }

            var timeSheet = DayTimeSheet.FromTimeSheets(timesheets, overtime);

            blocks = ScriptAdjustTimeBlocks(script, timeSheet, blocks);

            blocks = AdjustTimeBlocks(settings, timeSheet, blocks);

            blocks = ScriptProcessTimeBlocks(script, timeSheet, blocks);

            var totalAccountingHours = new Dictionary<Assignment, double>();
            var totalHours = new Dictionary<Assignment, double>();
            OvertimeUtils.EvaluateOvertime(
                blocks,
                // We've already taken into account the IsPaid flags, so here we remove the unpaid ones from the intervals.
                overtime.Where(x => x.IsPaid).ToArray(),
                x => x.Duration,
                (block, interval, duration) =>
                {
                    if(block.Assignment is not null)
                    {
                        totalAccountingHours[block.Assignment] =
                            totalAccountingHours.GetValueOrAdd(block.Assignment)
                            + duration.TotalHours;
                        totalHours[block.Assignment] =
                            totalHours.GetValueOrAdd(block.Assignment)
                            + duration.TotalHours * (interval?.Multiplier ?? 1);
                    }
                });

            foreach(var assignment in assignments)
            {
                assignment.Cost = totalHours.GetValueOrDefault(assignment) * employee.HourlyRate;
                assignment.CostedHours = totalAccountingHours.GetValueOrDefault(assignment);
            }
            ScriptAfterOvertime(script, timeSheet, blocks, overtime, assignments);

            store.Provider.Save(assignments.Where(x => x.IsChanged()));
        }
    }
}