using System;
using System.Collections.Generic;
using System.Drawing;
using System.Drawing.Imaging;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Media.Imaging;
using Tango.RemoteDesktop.Frames;

namespace Tango.RemoteDesktop.Comparers
{
    /// <summary>
    /// Represents a vector <see cref="IBitmapComparer{TFrame}"/> comparer which will compare and return a <see cref="VectorFrame"/> difference.
    /// </summary>
    /// <seealso cref="Tango.RemoteDesktop.IBitmapComparer{Tango.RemoteDesktop.Frames.VectorFrame}" />
    public class VectorBitmapComparer : IBitmapComparer<VectorFrame>
    {
        /// <summary>
        /// When max number of differences reached, the comparer will immediately return the current difference frame.
        /// This should enforce the screen capture engine to report 'No Difference Available'.
        /// </summary>
        public long? MaxDifferencesThrow { get; set; }

        /// <summary>
        /// Creates the difference as <see cref="VectorFrame"/>.
        /// </summary>
        /// <param name="previousBitmap">The previous bitmap.</param>
        /// <param name="currentBitmap">The current bitmap.</param>
        /// <returns></returns>
        /// <exception cref="InvalidOperationException">
        /// Cannot compare image. They are the same instance
        /// or
        /// Cannot compare image of different size.
        /// </exception>
        public unsafe BitmapComparerResult<VectorFrame> CreateDifference(Bitmap previousBitmap, Bitmap currentBitmap)
        {
            VectorFrame vector = new VectorFrame(previousBitmap.Width, previousBitmap.Height);

            uint count = 0;

            if (previousBitmap == null | currentBitmap == null)
                throw new InvalidOperationException("Cannot compare image. They are the same instance");

            if (previousBitmap.Height != currentBitmap.Height || previousBitmap.Width != currentBitmap.Width)
                throw new InvalidOperationException("Cannot compare image of different size.");

            int height = previousBitmap.Height;
            int width = previousBitmap.Width;

            BitmapData data1 = previousBitmap.LockBits(new Rectangle(0, 0, width, height),
                                               ImageLockMode.ReadOnly, PixelFormat.Format32bppArgb);
            BitmapData data2 = currentBitmap.LockBits(new Rectangle(0, 0, width, height),
                                               ImageLockMode.ReadOnly, PixelFormat.Format32bppArgb);
            byte* data1Ptr = (byte*)data1.Scan0;
            byte* data2Ptr = (byte*)data2.Scan0;

            int rowPadding = data1.Stride - (previousBitmap.Width * 4);

            // iterate over height (rows)
            for (int i = 0; i < height; i++)
            {
                // iterate over width (columns)
                for (int j = 0; j < width; j++)
                {
                    int same = 0;

                    byte[] tmp = new byte[4];

                    // compare pixels and copy new values into temporary array
                    for (int x = 0; x < 4; x++)
                    {
                        tmp[x] = data2Ptr[0];
                        if (data1Ptr[0] == data2Ptr[0])
                        {
                            same++;
                        }
                        data1Ptr++; // advance image1 ptr
                        data2Ptr++; // advance image2 ptr
                    }

                    if (same != 4)
                    {
                        int colorIndex = vector.Colors.Count;

                        VectorFrameColor color = new VectorFrameColor()
                        {
                            B = tmp[0],
                            G = tmp[1],
                            R = tmp[2],
                            Index = colorIndex
                        };

                        VectorFrameColor existingColor;

                        if (vector.Colors.TryGetValue(color.ToInt32(), out existingColor))
                        {
                            colorIndex = existingColor.Index;
                        }
                        else
                        {
                            vector.Colors.Add(color.ToInt32(), color);
                        }

                        vector.Pixels.Add(new VectorFramePixel()
                        {
                            X = j,
                            Y = i,
                            ColorIndex = colorIndex,
                            Color = color
                        });

                        count++;

                        if (MaxDifferencesThrow != null && count > MaxDifferencesThrow.Value)
                        {
                            previousBitmap.UnlockBits(data1);
                            currentBitmap.UnlockBits(data2);
                            throw new MaxDifferencesReachedException();
                        }
                    }
                }

                // at the end of each column, skip extra padding
                if (rowPadding > 0)
                {
                    data1Ptr += rowPadding;
                    data2Ptr += rowPadding;
                }
            }

            previousBitmap.UnlockBits(data1);
            currentBitmap.UnlockBits(data2);

            return new BitmapComparerResult<VectorFrame>()
            {
                Frame = vector,
                DifferenceCount = count
            };
        }
    }
}