using Common;
using Common.Helpers;
using CommunityToolkit.Mvvm.ComponentModel;
using CommunityToolkit.Mvvm.Input;
using MultiTerm.Core.Types;
using MultiTerm.Protocols.Model;
using System.Collections.ObjectModel;
using System.Diagnostics;
using System.Text;

namespace MultiTerm.Core.ViewModel;

public partial class MultiFormatDataViewModel : ObservableObject
{
    private readonly IContext uiContext;
    private int dataCharacterCount = 0;
    private List<byte>? listOfPreviousCharacters = null;

    #region Observable Properties
    [ObservableProperty]
    private ObservableCollection<ByteDataViewModel> data = new();
    
    [ObservableProperty]
    private string dataAsString = string.Empty;

    [ObservableProperty]
    private ObservableCollection<ByteDataViewModel>? selected = new();

    [ObservableProperty]
    NewlineSeparatorType newlineSeparator = NewlineSeparatorType.None;

    [ObservableProperty]
    private string selectedDataFirstAbsoluteTime = string.Empty;

    [ObservableProperty]
    private string selectedDataTimediff = string.Empty;
    #endregion

    /// <summary>
    /// Newline Sequence string inserted on every newline in the <see cref="DataAsString"/>.
    /// </summary>
    public static readonly string NewlineSequence = Environment.NewLine;

    public MultiFormatDataViewModel(IContext context)
    {
        this.uiContext = context;
    }

    public void HandleNewData(IEnumerable<ExtendedByte> newRawData)
    {
        // update collection and string, invoke ui thread if necessary
        ContextHelpers.InvokeIfNecessary(this.uiContext, (Action)delegate
        {
            this.DataAsString = InsertNewNewCharactersIntoCollection(this.Data, this.DataAsString,
                ref this.dataCharacterCount, ref this.listOfPreviousCharacters,
                this.NewlineSeparator, newRawData);
        });
    }

    /// <summary>
    /// After changing the newline separator, the data needs to be reordered.
    /// </summary>
    partial void OnNewlineSeparatorChanged(NewlineSeparatorType value)
    {
        // update collection, invoke ui thread if necessary
        ContextHelpers.InvokeIfNecessary(this.uiContext, (Action)delegate
        {
            var reorderedCollection = ReorderCollection(this.Data, value);
            this.Data = reorderedCollection.Item1;
            this.DataAsString = reorderedCollection.Item2;
        });
    }

    [RelayCommand]
    public void Clear()
    {
        // update collection and string, invoke ui thread if necessary
        ContextHelpers.InvokeIfNecessary(this.uiContext, (Action)delegate
        {
            this.DataAsString = string.Empty;
            this.Data.Clear();
        });
    }

    partial void OnSelectedChanging(ObservableCollection<ByteDataViewModel>? value)
    {
        // remove event handler when there was previously a collection of selected
        if(this.Selected != null)
        {
            this.Selected.CollectionChanged -= this.Selected_CollectionChanged;
        }
    }

    partial void OnSelectedChanged(ObservableCollection<ByteDataViewModel>? value)
    {
        // add event handler
        if (this.Selected != null)
        {
            this.Selected.CollectionChanged += Selected_CollectionChanged;
        }

        // manually update 
        this.UpdateTimeProperties();
    }

    private void Selected_CollectionChanged(object? sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
    {
        this.UpdateTimeProperties();
    }

    private void UpdateTimeProperties()
    {
        if (this.Selected == null || this.Selected.Count == 0)
        {
            this.SelectedDataFirstAbsoluteTime = string.Empty;
            this.SelectedDataTimediff = string.Empty;
            return;
        }

        if (this.Selected.Count == 1)
        {
            this.SelectedDataFirstAbsoluteTime = $"Time: {this.Selected.First().Time:HH:mm:ss.ff}";
            this.SelectedDataTimediff = string.Empty;
        }

        if (this.Selected.Count > 1)
        {
            TimeSpan timediff;
            TimeOnly lastSelected = this.Selected.Last().Time, firstSelected = this.Selected.First().Time;

            Debug.WriteLine($"First time selected: {firstSelected:HH.mm:ss.ff} Ticks: {firstSelected.Ticks}");
            Debug.WriteLine($"Last time selected: {lastSelected:HH.mm:ss.ff} Ticks: {lastSelected.Ticks}");

            // calculate timedifference according to selection direction
            // (preventive. selection should arrive sorted correctly)
            if (lastSelected > firstSelected)
            {
                timediff = lastSelected - firstSelected;
            }
            else
            {
                timediff = firstSelected - lastSelected;
            }

            Debug.WriteLine($"Calculated timediff Ticks: {timediff.Ticks}");

            this.SelectedDataFirstAbsoluteTime = $"Time (first selected): {firstSelected:HH:mm:ss.ff}";
            this.SelectedDataTimediff = $"Difference (first to last): {timediff.TotalMilliseconds:n} ms";
        }
    }

    #region Collection Manipulation
    /// <summary>
    /// Function that reorders a given collection with item type <see cref="ByteDataViewModel"/> using the given <paramref name="newlineSeparatorType"/>.
    /// Reordered collection is returned, but LineIdentifier is also overwritten in the <paramref name="currentCollection"/> parameter.
    /// </summary>
    /// <param name="currentCollection">items in this collection will be reordered</param>
    /// <param name="newlineSeparatorType">separator between lines</param>
    /// <returns>reordered collection and string</returns>
    private static Tuple<ObservableCollection<ByteDataViewModel>, string> ReorderCollection(ObservableCollection<ByteDataViewModel> currentCollection, NewlineSeparatorType newlineSeparatorType)
    {
        ObservableCollection<ByteDataViewModel> newCollection = new();
        StringBuilder stringBuilder = new();
        
        // local vars
        int lineCounter = 0;
        List<byte>? previousBytes = null;

        // iterate through items
        foreach (ByteDataViewModel item in currentCollection)
        {
            item.LineIdentifier = lineCounter;
            newCollection.Add(item);
            stringBuilder.Append(item.DisplayStringChar);

            switch (ShouldIntroduceNewlineAfterThisByte(item.Byte, previousBytes, newlineSeparatorType))
            {
                case ShouldIntroduceNewlineAfterThisByteResult.NoNewline:
                    // a decision could be made, previousBytes can be cleared
                    if (previousBytes != null) { previousBytes = null; }
                    // nothing to do
                    break;

                case ShouldIntroduceNewlineAfterThisByteResult.IntroduceNewline:
                    // a decision could be made, previousBytes can be cleared
                    if (previousBytes != null) { previousBytes = null; }
                    // increase line count
                    lineCounter++;
                    // append line in string
                    stringBuilder.Append(NewlineSequence);
                    break;

                case ShouldIntroduceNewlineAfterThisByteResult.RequiresMoreCharacters:
                    // first time that more bytes are required => create new list
                    previousBytes ??= new List<byte>();
                    // add current byte to list
                    previousBytes.Add(item.Byte);
                    break;

                default:
                    throw new Exception($"'{nameof(ReorderCollection)}()' failed because of error when checking if a newline should be introduced.");
            }
        }

        return Tuple.Create(newCollection, stringBuilder.ToString());
    }

    /// <summary>
    /// Function that handles a collection of new bytes that should end up in the collection <paramref name="dataCollection"/>.
    /// In case a new line is required, according to the given <paramref name="newlineSeparatorType"/>, it is automatically introduced.
    /// Following parameters need to be referenced and stored outside: <paramref name="collectionLineCounter"/> and <paramref name="previousBytes"/>.
    /// </summary>
    /// <param name="dataCollection">collection to add the bytes to</param>
    /// <param name="dataCollectionAsString">collection as string</param>
    /// <param name="collectionLineCounter">current line count</param>
    /// <param name="previousBytes">list of previous bytes, newest at the last position of the list, null if nothing is stored</param>
    /// <param name="newlineSeparatorType">separator between seperate lines</param>
    /// <param name="newBytes">bytes to add to the <paramref name="dataCollection"/></param>
    /// <returns>string representation of data</returns>
    /// <exception cref="Exception">in case of any error</exception>
    private static string InsertNewNewCharactersIntoCollection(
        ObservableCollection<ByteDataViewModel> dataCollection,
        string dataCollectionAsString,
        ref int collectionLineCounter,
        ref List<byte>? previousBytes,
        NewlineSeparatorType newlineSeparatorType,
        IEnumerable<ExtendedByte> newBytes)
    {
        StringBuilder stringBuilder = new();
        stringBuilder.Append(dataCollectionAsString);

        // go through every byte
        foreach (ExtendedByte newByte in newBytes)
        {
            // add to collection and string with the current counter, invoking UI context if necssary
            var currentLineCounter = collectionLineCounter;
            dataCollection.Add(new ByteDataViewModel(newByte, currentLineCounter));
            stringBuilder.Append(newByte.ToCharacterString());

            switch (ShouldIntroduceNewlineAfterThisByte(newByte.Byte, previousBytes, newlineSeparatorType))
            {
                case ShouldIntroduceNewlineAfterThisByteResult.NoNewline:
                    // a decision could be made, previousBytes can be cleared
                    if (previousBytes != null) { previousBytes = null; }
                    // nothing to do
                    break;

                case ShouldIntroduceNewlineAfterThisByteResult.IntroduceNewline:
                    // a decision could be made, previousBytes can be cleared
                    if (previousBytes != null) { previousBytes = null; }
                    // increase line count
                    collectionLineCounter++;
                    // append line in string
                    stringBuilder.Append(NewlineSequence); 
                    break;

                case ShouldIntroduceNewlineAfterThisByteResult.RequiresMoreCharacters:
                    // first time that more bytes are required => create new list
                    previousBytes ??= new List<byte>();
                    // add current byte to list
                    previousBytes.Add(newByte.Byte);
                    break;

                default:
                    throw new Exception($"'{nameof(InsertNewNewCharactersIntoCollection)}()' failed because of error when checking if a newline should be introduced.");
            }
        }

        return stringBuilder.ToString();
    }

    /// <summary>
    /// Result type for <see cref="ShouldIntroduceNewlineAfterThisByte"/>
    /// </summary>
    public enum ShouldIntroduceNewlineAfterThisByteResult
    {
        /// <summary>
        /// No newline is required.
        /// </summary>
        NoNewline,

        /// <summary>
        /// A newline shall be introduced after this byte.
        /// </summary>
        IntroduceNewline,

        /// <summary>
        /// Following characters are required to finalize result wether a newline shall be introduced or not.
        /// </summary>
        RequiresMoreCharacters
    }

    /// <summary>
    /// Function to check wether a newline shall be introduced after the given <paramref name="dataByte"/>.
    /// Since some newline sequences will require multiple bytes in correct order, a more complex handling is required, which is possible using this function.
    /// </summary>
    /// <param name="dataByte">the current dataByte in the collection (or a single byte)</param>
    /// <param name="previousBytes">list of previous bytes, newest at the last position of the list, null if not required</param>
    /// <param name="newlineSeparatorType">separator type</param>
    /// <returns>enum result of type <see cref="ShouldIntroduceNewlineAfterThisByteResult"/></returns>
    /// <exception cref="NotImplementedException">if the handling for the <paramref name="newlineSeparatorType"/> is not implemented</exception>
    private static ShouldIntroduceNewlineAfterThisByteResult ShouldIntroduceNewlineAfterThisByte(byte dataByte, List<byte>? previousBytes, NewlineSeparatorType newlineSeparatorType)
    {
        var result = ShouldIntroduceNewlineAfterThisByteResult.NoNewline;

        switch (newlineSeparatorType)
        {
            case NewlineSeparatorType.None:
                break;

            case NewlineSeparatorType.CR:
                if (dataByte == (byte)'\r')
                {
                    result = ShouldIntroduceNewlineAfterThisByteResult.IntroduceNewline;
                }
                break;

            case NewlineSeparatorType.LF:
                if (dataByte == (byte)'\n')
                {
                    result = ShouldIntroduceNewlineAfterThisByteResult.IntroduceNewline;
                }
                break;

            case NewlineSeparatorType.CR_LF:
                if (dataByte == (byte)'\r')
                {
                    result = ShouldIntroduceNewlineAfterThisByteResult.RequiresMoreCharacters;
                }
                if (dataByte == (byte)'\n')
                {
                    if (previousBytes != null && previousBytes.Last() == (byte)'\r')
                    {
                        result = ShouldIntroduceNewlineAfterThisByteResult.IntroduceNewline;
                    }
                }
                break;

            default:
                throw new NotImplementedException($"'{nameof(ShouldIntroduceNewlineAfterThisByte)}()' does not implement handling for {nameof(NewlineSeparatorType)} {newlineSeparatorType}");
        }

        return result;
    }



    #endregion
}