using System;
using System.Collections;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Windows;
using ScreenToGif.ImageUtil.Gif.Encoder.Quantization;
using ScreenToGif.Util;
using Color = System.Windows.Media.Color;

namespace ScreenToGif.ImageUtil.Gif.Encoder
{
    /// <summary>
    /// New gif encoder. Made by Nicke Manarin.
    /// </summary>
    public class GifFile : IDisposable
    {
        #region Properties

        /// <summary>
        /// Repeat Count for the gif.
        /// </summary>
        public int RepeatCount { get; set; } = 0;

        /// <summary>
        /// When enabled, the entire (star and end) gif will contain a transparent background.
        /// Not related to the option to "paint unchanged pixels".
        /// </summary>
        public bool UseFullTransparency { get; set; }

        /// <summary>
        /// The color marked as transparent. Null if not in use.
        /// </summary>
        public Color? TransparentColor { get; set; }

        /// <summary>
        /// The maximum number of colors of each frame of the gif.
        /// </summary>
        public int MaximumNumberColor { get; set; } = 256;

        /// <summary>
        /// The maximum number of colors of each frame of the gif.
        /// </summary>
        public ColorQuantizationType QuantizationType { get; set; } = ColorQuantizationType.Octree;

        /// <summary>
        /// True if the gif should use a global color table instead of a local one.
        /// </summary>
        public bool UseGlobalColorTable { get; set; } = false;

        /// <summary>
        /// The sampling factor of the neural network quantizer.
        /// </summary>
        public int SamplingFactor { get; set; }


        /// <summary>
        /// The stream which the gif is writen on.
        /// </summary>
        private Stream InternalStream { get; set; }

        /// <summary>
        /// True if it's the first frame of the gif.
        /// </summary>
        private bool IsFirstFrame { get; set; } = true;

        /// <summary>
        /// The list of indexed pixels, based on a color table (palette).
        /// </summary>
        private byte[] IndexedPixels { get; set; }

        /// <summary>
        /// The current color table. Global or local.
        /// </summary>
        private List<Color> ColorTable { get; set; }

        /// <summary>
        /// True if the color table contains the color that will be treated as transparent.
        /// </summary>
        private bool ColorTableHasTransparency { get; set; }

        /// <summary>
        /// The size of the current color table.
        /// </summary>
        private int ColorTableSize { get; set; }

        /// <summary>
        /// Cumulative non adjusted time.
        /// </summary>
        private int OrganicTime { get; set; }
        
        /// <summary>
        /// Adjusted and rounded off time.
        /// </summary>
        private int AdjustedTime { get; set; }

        /// <summary>
        /// If a quantizer needs to be contructed only once (for example, to use with PaletteQuantizers), this property will be used.
        /// </summary>
        private Quantizer GlobalQuantizer { get; set; }

        #endregion


        public GifFile(Stream stream)
        {
            InternalStream = stream;
        }


        #region Public methods

        public void AddFrame(byte[] pixels, Int32Rect rect, int delay = 66, bool isLastFrame = false)
        {
            ReadPixels(pixels);

            //For global color table, only generate a new palette if it's the first frame.
            if (!UseGlobalColorTable || IsFirstFrame)
                CalculateColorTableSize();

            if (IsFirstFrame)
            {
                WriteLogicalScreenDescriptor(rect);

                //Global color table.
                if (UseGlobalColorTable)
                    WritePalette();

                if (RepeatCount > -1)
                    WriteApplicationExtension();
            }

            WriteGraphicControlExtension(delay, isLastFrame);
            WriteImageDescriptor(rect);

            IsFirstFrame = false;

            //Local color table.
            if (!UseGlobalColorTable)
                WritePalette();

            WriteImage();
        }

        #endregion

        #region Main methods

        private void WriteLogicalScreenDescriptor(Int32Rect rect)
        {
            //File Header, 6 bytes
            WriteString("GIF89a");

            //Initial Logical Size (Width, Height), 4 bytes
            WriteShort(rect.Width);
            WriteShort(rect.Height);

            //Packed fields, 1 byte
            var bitArray = new BitArray(8);
            bitArray.Set(0, UseGlobalColorTable);

            //Color resolution: 111 = (8 bits - 1)
            //Color depth - 1
            //Global colors count = 2^color depth
            var pixelBits = ToBitValues(ColorTableSize);

            bitArray.Set(1, pixelBits[0]);
            bitArray.Set(2, pixelBits[1]);
            bitArray.Set(3, pixelBits[2]);

            //Sort flag (for the global color table): 0
            bitArray.Set(4, true);

            //Size of the Global Color Table (Zero, if not used.): 
            var sizeInBits = ToBitValues(UseGlobalColorTable ? ColorTableSize : 0);

            bitArray.Set(5, sizeInBits[0]);
            bitArray.Set(6, sizeInBits[1]);
            bitArray.Set(7, sizeInBits[2]);

            WriteByte(ConvertToByte(bitArray));
            WriteByte(UseFullTransparency ? FindTransparentColorIndex() : 0); //Background color index, 1 byte
            WriteByte(0); //Pixel aspect ratio - Assume 1:1, 1 byte
        }

        private void WritePalette()
        {
            foreach (var color in ColorTable)
            {
                WriteByte(color.R);
                WriteByte(color.G);
                WriteByte(color.B);
            }

            //Do I need to fill up the rest of the color table? 
            //Or just seek the stream to the next place?

            //(MaximumColorsCount -  ColorCount) * 3 channels [rgb]
            var emptySpace = (GetMaximumColorCount() - ColorTable.Count) * 3;

            for (var index = 0; index < emptySpace; index++)
                WriteByte(0);
        }

        private void WriteApplicationExtension()
        {
            WriteByte(0x21); //Extension Introducer.
            WriteByte(0xff); //Extension Label.

            WriteByte(0x0b); //Application Block Size. It says "11 bytes".
            WriteString("NETSCAPE2.0"); //Extension type, 11 bytes
            WriteByte(0x03); // Application block length
            WriteByte(0x01); //Loop sub-block ID. 1 byte
            WriteShort(RepeatCount); // Repeat count. 2 bytes.
            WriteByte(0x00); //Terminator
        }

        private void WriteGraphicControlExtension(int delay, bool isLastFrame)
        {
            WriteByte(0x21); //Extension Introducer.
            WriteByte(0xf9); //Extension Label.
            WriteByte(0x04); //Block size.

            //Packed fields
            var bitArray = new BitArray(8);

            //Reserved for future use. Hahahaha. Yeah...
            bitArray.Set(0, false);
            bitArray.Set(1, false);
            bitArray.Set(2, false);

            #region Disposal Method

            //Use Inplace if you want to Leave the last frame pixel.
            //GCE_DISPOSAL_NONE = Undefined = 0
            //GCE_DISPOSAL_INPLACE = Leave = 1
            //GCE_DISPOSAL_BACKGROUND = Restore Background = 2
            //GCE_DISPOSAL_RESTORE = Restore Previous = 3

            if (UseFullTransparency)
            {
                //If full "Transparency" is set:
                //All starting frames as "Restore Background".
                //The last frame as "Leave".

                if (isLastFrame)
                {
                    //Leave.
                    bitArray.Set(3, false);
                    bitArray.Set(4, false);
                    bitArray.Set(5, true);
                }
                else
                {
                    //Restore background.
                    bitArray.Set(3, false);
                    bitArray.Set(4, true);
                    bitArray.Set(5, false);
                }
            }
            else
            {
                //If "Detect Unchanged Pixels" is set:
                //First frame as "Leave" with no Transparency. IsFirstFrame
                //Following frames as "Undefined" with Transparency.

                //Was TransparentColor.HasValue && 
                if (IsFirstFrame)
                {
                    //Leave.
                    bitArray.Set(3, false);
                    bitArray.Set(4, false);
                    bitArray.Set(5, true);
                }
                else
                {
                    //Undefined.
                    bitArray.Set(3, false);
                    bitArray.Set(4, false);
                    bitArray.Set(5, false);
                }
            }

            #endregion

            //User Input Flag.
            bitArray.Set(6, false);

            //Transparent Color Flag, uses tranparency?
            bitArray.Set(7, (!IsFirstFrame || UseFullTransparency) && ColorTableHasTransparency);

            //Write the packed fields.
            WriteByte(ConvertToByte(bitArray));

            //Calculates the delay, taking into consideration overall rounding. Bug!
            //OrganicTime += delay;
            //delay = (int)Math.Round((OrganicTime > delay ? OrganicTime - AdjustedTime * 10 : delay) / 10.0f, MidpointRounding.AwayFromZero);
            //AdjustedTime += delay;
            //WriteShort(delay);

            WriteShort((int)Math.Round(delay / 10.0f, MidpointRounding.AwayFromZero));
            WriteByte(FindTransparentColorIndex()); //Transparency Index.
            WriteByte(0); //Terminator.
        }

        private void WriteImageDescriptor(Int32Rect rect)
        {
            WriteByte(0x2c); //Image Separator.
            WriteShort(rect.X); //Position X. 2 bytes.
            WriteShort(rect.Y); //Position Y. 2 bytes.
            WriteShort(rect.Width); //Width. 2 bytes.
            WriteShort(rect.Height); //Height. 2 bytes.

            if (UseGlobalColorTable)
            {
                //No Local Color Table. Every packed field values are zero.
                WriteByte(0);
                return;
            }

            //Packed fields.
            var bitArray = new BitArray(8);

            //Uses local color table?
            bitArray.Set(0, true);

            //Interlace Flag.
            bitArray.Set(1, false);

            //Sort Flag.
            bitArray.Set(2, true);

            //Reserved for future use. Hahahah again.
            bitArray.Set(3, false);
            bitArray.Set(4, false);

            //Size of Local Color Table.
            var sizeInBits = ToBitValues(ColorTableSize);

            bitArray.Set(5, sizeInBits[0]);
            bitArray.Set(6, sizeInBits[1]);
            bitArray.Set(7, sizeInBits[2]);

            //Write the packed fields.
            WriteByte(ConvertToByte(bitArray));
        }

        private void WriteImage()
        {
            //TODO: Fix the new LZW encoder when ColorTableSize == 7. It's getting corrupted. 

            //if (ColorTableSize < 6)
            //{
            //    //New LZW encoder, ColorTableSize from 1 to 8.
            //    var encoder = new LzwEncoder(IndexedPixels, ColorTableSize + 1);
            //    encoder.Encode(InternalStream);
            //}
            //else
            //{
            //Old LZW encoder, only works with ColorTableSize 8.
            var encoder = new Gif.LegacyEncoder.LzwEncoder(0, 0, IndexedPixels, 8);
            encoder.Encode(InternalStream);
            //}
        }

        #endregion

        #region Helper methods

        private void ReadPixels(byte[] pixels)
        {
            if (QuantizationType == ColorQuantizationType.Neural)
            {
                #region Neural

                if (GlobalQuantizer == null || !UseGlobalColorTable)
                {
                    GlobalQuantizer = new NeuralQuantizer(SamplingFactor, MaximumNumberColor)
                    {
                        MaxColors = MaximumNumberColor,
                        TransparentColor = !IsFirstFrame || UseGlobalColorTable || UseFullTransparency ? TransparentColor : null
                    };

                    GlobalQuantizer.FirstPass(pixels);
                    ColorTable = GlobalQuantizer.GetPalette();
                }

                //Indexes the pixels to the color table.
                IndexedPixels = GlobalQuantizer.SecondPass(pixels);
                
                #endregion
            }
            else if (QuantizationType == ColorQuantizationType.Octree)
            {
                #region Octree

                var quantizer = new OctreeQuantizer
                {
                    MaxColors = MaximumNumberColor,
                    TransparentColor = !IsFirstFrame || UseGlobalColorTable || UseFullTransparency ? TransparentColor : null
                };

                IndexedPixels = quantizer.Quantize(pixels);
                ColorTable = quantizer.ColorTable;

                #endregion
            }
            else if (QuantizationType == ColorQuantizationType.MedianCut)
            {
                #region Median cut

                if (GlobalQuantizer == null || !UseGlobalColorTable)
                {
                    GlobalQuantizer = new MedianCutQuantizer
                    {
                        MaxColors = MaximumNumberColor,
                        TransparentColor = !IsFirstFrame || UseGlobalColorTable || UseFullTransparency ? TransparentColor : null
                    };

                    GlobalQuantizer.FirstPass(pixels);
                    ColorTable = GlobalQuantizer.GetPalette();
                }

                //Indexes the pixels to the color table.
                IndexedPixels = GlobalQuantizer.SecondPass(pixels);

                #endregion
            }
            else if (QuantizationType == ColorQuantizationType.Grayscale)
            {
                #region Grayscale

                //This quantizer uses a fixed palette (generated during object instantiation), so most calculations are called one time.
                if (GlobalQuantizer == null)
                {
                    //Since the color table does not change among frames, it can be stored globally.
                    UseGlobalColorTable = true;

                    var transparent = !IsFirstFrame || UseGlobalColorTable || UseFullTransparency ? TransparentColor : null;

                    GlobalQuantizer = new GrayscaleQuantizer(transparent, MaximumNumberColor)
                    {
                        MaxColors = MaximumNumberColor,
                        TransparentColor = transparent
                    };

                    ColorTable = GlobalQuantizer.GetPalette();
                }
                
                //Each frame still needs to be quantized.
                IndexedPixels = GlobalQuantizer.SecondPass(pixels);

                #endregion
            }
            else if (QuantizationType == ColorQuantizationType.MostUsed)
            {
                #region Most used colors

                if (GlobalQuantizer == null || !UseGlobalColorTable)
                {
                    GlobalQuantizer = new MostUsedQuantizer
                    {
                        MaxColors = MaximumNumberColor,
                        TransparentColor = !IsFirstFrame || UseGlobalColorTable || UseFullTransparency ? TransparentColor : null
                    };

                    GlobalQuantizer.FirstPass(pixels);
                    ColorTable = GlobalQuantizer.GetPalette();
                }

                //Indexes the pixels to the color table.
                IndexedPixels = GlobalQuantizer.SecondPass(pixels);

                #endregion
            }
            else
            {
                #region Palette

                //This quantizer uses a fixed palette (generated during object instantiation), so it will be only called once.
                if (GlobalQuantizer == null)
                {
                    //Since the color table does not change among frames, it can be stored globally.
                    UseGlobalColorTable = true;

                    var transparent = !IsFirstFrame || UseGlobalColorTable || UseFullTransparency ? TransparentColor : null;

                    //TODO: Pass the palette.
                    //Default palettes: Windows, etc.
                    //User submitted > Presets > Generate palette based on first frame.

                    GlobalQuantizer = new PaletteQuantizer(new ArrayList()) 
                    {
                        MaxColors = MaximumNumberColor,
                        TransparentColor = transparent
                    };

                    ColorTable = GlobalQuantizer.GetPalette();
                }

                //Each frame still needs to be quantized.
                IndexedPixels = GlobalQuantizer.SecondPass(pixels);

                #endregion
            }

            //I need to signal the other method that I'll need transparency.
            ColorTableHasTransparency = TransparentColor.HasValue && ColorTable.Contains(TransparentColor.Value);
        }

        private void WriteByte(int value)
        {
            InternalStream.WriteByte(Convert.ToByte(value));
        }

        /// <summary>
        /// Writes a int value as 2 bytes, but inverted. 
        /// 100 = 64 00 instead of 00 64.
        /// </summary>
        /// <param name="value"></param>
        private void WriteShort(int value)
        {
            //Writes the second part first.
            //The "& 0xff" makes sure that the int will stay on range 0-255, it will cut any number above 255.
            InternalStream.WriteByte(Convert.ToByte(value & 0xff));
            InternalStream.WriteByte(Convert.ToByte((value >> 8) & 0xff));
        }

        private void WriteString(string value)
        {
            InternalStream.Write(value.ToArray().Select(c => (byte)c).ToArray(), 0, value.Length);
        }

        /// <summary>
        /// Writes the comment for the animation.
        /// </summary>
        /// <param name="comment">The comment to write to the gif.</param>
        private void WriteComment(string comment)
        {
            InternalStream.WriteByte(0x21);
            InternalStream.WriteByte(0xfe);

            //byte[] length = StringToByteArray(comment.Length.ToString("X"));

            //foreach (byte b in length)
            //    fs.WriteByte(b);

            var bytes = System.Text.Encoding.ASCII.GetBytes(comment);

            InternalStream.WriteByte((byte) bytes.Length);
            InternalStream.Write(bytes, 0, bytes.Length);
            InternalStream.WriteByte(0);
        }

        private byte ConvertToByte(BitArray bits)
        {
            if (bits.Count != 8)
                throw new ArgumentException("bits");

            var bytes = new byte[1];
            var reversed = new BitArray(bits.Cast<bool>().Reverse().ToArray());
            reversed.CopyTo(bytes, 0);
            return bytes[0];
        }

        private void CalculateColorTableSize()
        {
            //Logical Screen Description, Number of Colors, Byte length.
            //0 = 2 = 6
            //1 = 4 = 12
            //2 = 8 = 24
            //3 = 16 = 48
            //4 = 32 = 96
            //5 = 64 = 192
            //6 = 128 = 384
            //7 = 256 = 768
            //The inverse calculation is: 2^(N + 1) 
            //and x3 for the byte length.

            //If the colorsCount == 1, 
            //return zero instead of calculating it, because of the Log(0) call.
            //The "-1" assures that the count stays in range.
            ColorTableSize = ColorTable.Count > 1 ? (int)Math.Log(ColorTable.Count - 1, 2) : 0;
        }

        /// <summary>
        /// Calculates the maximum number of colors for the 
        /// specified Logical Screen Description value.
        /// </summary>
        /// <returns>The maximum number of colors in the Color Table.</returns>
        private int GetMaximumColorCount()
        {
            //2^(N+1)
            return (int)Math.Pow(2, ColorTableSize + 1);
        }

        private int FindTransparentColorIndex()
        {
            if (IsFirstFrame && !UseFullTransparency || !ColorTableHasTransparency) 
                return 0;

            //ReSharper disable once PossibleInvalidOperationException
            var index = ColorTable.IndexOf(TransparentColor.Value);

            return index > -1 ? index : 0;
        }

        /// <summary>
        /// Transforms a number to a bool array of 3 positions.
        /// </summary>
        /// <param name="number">The number to convert.</param>
        /// <returns>A 3-sized byte array.</returns>
        private bool[] ToBitValues(int number)
        {
            return new BitArray(new[] { number }).Cast<bool>().Take(3).Reverse().ToArray();
        }

        #endregion

        public void Dispose()
        {
            //Add a comment section.
            WriteComment("Made with ScreenToGif");

            //Complete the file.
            WriteByte(0x3b);
            //Push data.
            InternalStream.Flush();
            //Resets the stream position to save afterwards.
            InternalStream.Position = 0;
        }
    }
}