using System;
using System.IO;
using SkiaSharp;

namespace Gif.Components
{
    public class AnimatedGifEncoder
    {
        protected int width; // image size
        protected int height;
        protected SKColor transparent = SKColor.Empty; // transparent color if given
        protected int transIndex; // transparent index in color table
        protected int repeat = -1; // no repeat
        protected int delay = 0; // frame delay (hundredths)
        protected bool started = false; // ready to output frames
                                        //	protected BinaryWriter bw;
        protected MemoryStream ms;
        //		protected FileStream fs;

        protected SKBitmap image; // current frame
        protected byte[] pixels; // BGR byte array from frame
        protected byte[] indexedPixels; // converted frame indexed to palette
        protected int colorDepth; // number of bit planes
        protected byte[] colorTab; // RGB palette
        protected bool[] usedEntry = new bool[256]; // active palette entries
        protected int palSize = 7; // color table size (bits-1)
        protected int dispose = -1; // disposal code (-1 = use default)
        protected bool closeStream = false; // close stream when finished
        protected bool firstFrame = true;
        protected bool sizeSet = false; // if false, get size from first frame
        protected int sample = 10; // default sample interval for quantizer

        /**
		 * Sets the delay time between each frame, or changes it
		 * for subsequent frames (applies to last frame added).
		 *
		 * @param ms int delay time in milliseconds
		 */
        public void SetDelay(int ms)
        {
            delay = (int)Math.Round(ms / 10.0f);
        }

        /**
		 * Sets the GIF frame disposal code for the last added frame
		 * and any subsequent frames.  Default is 0 if no transparent
		 * color has been set, otherwise 2.
		 * @param code int disposal code.
		 */
        public void SetDispose(int code)
        {
            if (code >= 0)
            {
                dispose = code;
            }
        }

        /**
		 * Sets the number of times the set of GIF frames
		 * should be played.  Default is 1; 0 means play
		 * indefinitely.  Must be invoked before the first
		 * image is added.
		 *
		 * @param iter int number of iterations.
		 * @return
		 */
        public void SetRepeat(int iter)
        {
            if (iter >= 0)
            {
                repeat = iter;
            }
        }

        /**
		 * Sets the transparent color for the last added frame
		 * and any subsequent frames.
		 * Since all colors are subject to modification
		 * in the quantization process, the color in the final
		 * palette for each frame closest to the given color
		 * becomes the transparent color for that frame.
		 * May be set to null to indicate no transparent color.
		 *
		 * @param c Color to be treated as transparent on display.
		 */
        public void SetTransparent(SKColor c)
        {
            transparent = c;
        }

        /**
		 * Adds next GIF frame.  The frame is not written immediately, but is
		 * actually deferred until the next frame is received so that timing
		 * data can be inserted.  Invoking <code>finish()</code> flushes all
		 * frames.  If <code>setSize</code> was not invoked, the size of the
		 * first image is used for all subsequent frames.
		 *
		 * @param im BufferedImage containing frame to write.
		 * @return true if successful.
		 */
        public bool AddFrame(SKBitmap im)
        {
            if ((im == null) || !started)
            {
                return false;
            }
            bool ok = true;
            try
            {
                if (!sizeSet)
                {
                    // use first frame's size
                    SetSize(im.Width, im.Height);
                }
                image = im;
                GetImagePixels(); // convert to correct format if necessary
                AnalyzePixels(); // build color table & map pixels
                if (firstFrame)
                {
                    WriteLSD(); // logical screen descriptior
                    WritePalette(); // global color table
                    if (repeat >= 0)
                    {
                        // use NS app extension to indicate reps
                        WriteNetscapeExt();
                    }
                }
                WriteGraphicCtrlExt(); // write graphic control extension
                WriteImageDesc(); // image descriptor
                if (!firstFrame)
                {
                    WritePalette(); // local color table
                }
                WritePixels(); // encode and write pixel data
                firstFrame = false;
            }
            catch (IOException)
            {
                ok = false;
            }

            return ok;
        }

        /**
		 * Flushes any pending data and closes output file.
		 * If writing to an OutputStream, the stream is not
		 * closed.
		 */
        public bool Finish()
        {
            if (!started) return false;
            bool ok = true;
            started = false;
            try
            {
                ms.WriteByte(0x3b); // gif trailer
                ms.Flush();
                if (closeStream)
                {
                    //					ms.Close();
                }
            }
            catch (IOException)
            {
                ok = false;
            }

            // reset for subsequent use
            transIndex = 0;
            //			fs = null;
            image = null;
            pixels = null;
            indexedPixels = null;
            colorTab = null;
            closeStream = false;
            firstFrame = true;

            return ok;
        }

        /**
		 * Sets frame rate in frames per second.  Equivalent to
		 * <code>setDelay(1000/fps)</code>.
		 *
		 * @param fps float frame rate (frames per second)
		 */
        public void SetFrameRate(float fps)
        {
            if (fps != 0f)
            {
                delay = (int)Math.Round(100f / fps);
            }
        }

        /**
		 * Sets quality of color quantization (conversion of images
		 * to the maximum 256 colors allowed by the GIF specification).
		 * Lower values (minimum = 1) produce better colors, but slow
		 * processing significantly.  10 is the default, and produces
		 * good color mapping at reasonable speeds.  Values greater
		 * than 20 do not yield significant improvements in speed.
		 *
		 * @param quality int greater than 0.
		 * @return
		 */
        public void SetQuality(int quality)
        {
            if (quality < 1) quality = 1;
            sample = quality;
        }

        /**
		 * Sets the GIF frame size.  The default size is the
		 * size of the first frame added if this method is
		 * not invoked.
		 *
		 * @param w int frame width.
		 * @param h int frame width.
		 */
        public void SetSize(int w, int h)
        {
            if (started && !firstFrame) return;
            width = w;
            height = h;
            if (width < 1) width = 320;
            if (height < 1) height = 240;
            sizeSet = true;
        }

        /**
		 * Initiates GIF file creation on the given stream.  The stream
		 * is not closed automatically.
		 *
		 * @param os OutputStream on which GIF images are written.
		 * @return false if initial write failed.
		 */

        public bool Start(MemoryStream os)
        {
            if (os == null) return false;
            bool ok = true;
            closeStream = false;
            ms = os;
            try
            {
                WriteString("GIF89a"); // header
            }
            catch (IOException)
            {
                ok = false;
            }
            return started = ok;
        }

        /**
		 * Initiates writing of a GIF file to a memory stream.
		 *
		 * @return false if open or initial write failed.
		 */
        public bool Start()
        {
            bool ok;
            try
            {
                ok = Start(new MemoryStream(10 * 1024));
                closeStream = true;
            }
            catch (IOException)
            {
                ok = false;
            }
            return started = ok;
        }

        /**
		 * Initiates writing of a GIF file with the specified name.
		 *
		 * @return false if open or initial write failed.
		 */
        public bool Output(string file)
        {
            try
            {
                FileStream fs = new FileStream(file, FileMode.OpenOrCreate, FileAccess.Write, FileShare.None);
                fs.Write(ms.ToArray(), 0, (int)ms.Length);
                fs.Close();
            }
            catch (IOException)
            {
                return false;
            }
            return true;
        }

        public MemoryStream Output()
        {
            return ms;
        }

        /**
		 * Analyzes image colors and creates color map.
		 */
        protected void AnalyzePixels()
        {
            int len = pixels.Length;
            int nPix = len / 3;
            indexedPixels = new byte[nPix];
            NeuQuant nq = new NeuQuant(pixels, len, sample);
            // initialize quantizer
            colorTab = nq.Process(); // create reduced palette
                                     // convert map from BGR to RGB
                                     //			for (int i = 0; i < colorTab.Length; i += 3) 
                                     //			{
                                     //				byte temp = colorTab[i];
                                     //				colorTab[i] = colorTab[i + 2];
                                     //				colorTab[i + 2] = temp;
                                     //				usedEntry[i / 3] = false;
                                     //			}
                                     // map image pixels to new palette
            int k = 0;
            for (int i = 0; i < nPix; i++)
            {
                int index =
                    nq.Map(pixels[k++] & 0xff,
                    pixels[k++] & 0xff,
                    pixels[k++] & 0xff);
                usedEntry[index] = true;
                indexedPixels[i] = (byte)index;
            }
            pixels = null;
            colorDepth = 8;
            palSize = 7;
            // get closest match to transparent color if specified
            if (transparent != SKColor.Empty)
            {
                //transIndex = FindClosest(transparent);
                transIndex = nq.Map(transparent.Blue, transparent.Green, transparent.Red);
            }
        }

        /**
		 * Returns index of palette color closest to c
		 *
		 */
        protected int FindClosest(SKColor c)
        {
            if (colorTab == null) return -1;
            int r = c.Red;
            int g = c.Green;
            int b = c.Blue;
            int minpos = 0;
            int dmin = 256 * 256 * 256;
            int len = colorTab.Length;
            for (int i = 0; i < len;)
            {
                int dr = r - (colorTab[i++] & 0xff);
                int dg = g - (colorTab[i++] & 0xff);
                int db = b - (colorTab[i] & 0xff);
                int d = dr * dr + dg * dg + db * db;
                int index = i / 3;
                if (usedEntry[index] && (d < dmin))
                {
                    dmin = d;
                    minpos = index;
                }
                i++;
            }
            return minpos;
        }

        /**
		 * Extracts image pixels into byte array "pixels"
		 */
        protected void GetImagePixels()
        {
            int w = image.Width;
            int h = image.Height;
            //		int type = image.GetType().;
            if ((w != width)
                || (h != height)
                )
            {
                // create new image with right size/format
                //Image temp =
                //    new Bitmap(width, height);
                //Graphics g = Graphics.FromImage(temp);
                //g.DrawImage(image, 0, 0);
                //image = temp;
                //g.Dispose();
                var temp = new SKBitmap(width, height);
                var canvas = new SKCanvas(temp);
                canvas.DrawBitmap(image, 0, 0);
                image = temp;
                canvas.Dispose();
            }
            /*
				ToDo:
				improve performance: use unsafe code 
			*/
            pixels = new byte[3 * image.Width * image.Height];
            int count = 0;
            for (int th = 0; th < image.Height; th++)
            {
                for (int tw = 0; tw < image.Width; tw++)
                {
                    var color = image.GetPixel(tw, th);
                    pixels[count] = color.Red;
                    count++;
                    pixels[count] = color.Green;
                    count++;
                    pixels[count] = color.Blue;
                    count++;
                }
            }

            //		pixels = ((DataBufferByte) image.getRaster().getDataBuffer()).getData();
        }

        /**
		 * Writes Graphic Control Extension
		 */
        protected void WriteGraphicCtrlExt()
        {
            ms.WriteByte(0x21); // extension introducer
            ms.WriteByte(0xf9); // GCE label
            ms.WriteByte(4); // data block size
            int transp, disp;
            if (transparent == SKColor.Empty)
            {
                transp = 0;
                disp = 0; // dispose = no action
            }
            else
            {
                transp = 1;
                disp = 2; // force clear if using transparent color
            }
            if (dispose >= 0)
            {
                disp = dispose & 7; // user override
            }
            disp <<= 2;

            // packed fields
            ms.WriteByte(Convert.ToByte(0 | // 1:3 reserved
                disp | // 4:6 disposal
                0 | // 7   user input - 0 = none
                transp)); // 8   transparency flag

            WriteShort(delay); // delay x 1/100 sec
            ms.WriteByte(Convert.ToByte(transIndex)); // transparent color index
            ms.WriteByte(0); // block terminator
        }

        /**
		 * Writes Image Descriptor
		 */
        protected void WriteImageDesc()
        {
            ms.WriteByte(0x2c); // image separator
            WriteShort(0); // image position x,y = 0,0
            WriteShort(0);
            WriteShort(width); // image size
            WriteShort(height);
            // packed fields
            if (firstFrame)
            {
                // no LCT  - GCT is used for first (or only) frame
                ms.WriteByte(0);
            }
            else
            {
                // specify normal LCT
                ms.WriteByte(Convert.ToByte(0x80 | // 1 local color table  1=yes
                    0 | // 2 interlace - 0=no
                    0 | // 3 sorted - 0=no
                    0 | // 4-5 reserved
                    palSize)); // 6-8 size of color table
            }
        }

        /**
		 * Writes Logical Screen Descriptor
		 */
        protected void WriteLSD()
        {
            // logical screen size
            WriteShort(width);
            WriteShort(height);
            // packed fields
            ms.WriteByte(Convert.ToByte(0x80 | // 1   : global color table flag = 1 (gct used)
                0x70 | // 2-4 : color resolution = 7
                0x00 | // 5   : gct sort flag = 0
                palSize)); // 6-8 : gct size

            ms.WriteByte(0); // background color index
            ms.WriteByte(0); // pixel aspect ratio - assume 1:1
        }

        /**
		 * Writes Netscape application extension to define
		 * repeat count.
		 */
        protected void WriteNetscapeExt()
        {
            ms.WriteByte(0x21); // extension introducer
            ms.WriteByte(0xff); // app extension label
            ms.WriteByte(11); // block size
            WriteString("NETSCAPE" + "2.0"); // app id + auth code
            ms.WriteByte(3); // sub-block size
            ms.WriteByte(1); // loop sub-block id
            WriteShort(repeat); // loop count (extra iterations, 0=repeat forever)
            ms.WriteByte(0); // block terminator
        }

        /**
		 * Writes color table
		 */
        protected void WritePalette()
        {
            ms.Write(colorTab, 0, colorTab.Length);
            int n = (3 * 256) - colorTab.Length;
            for (int i = 0; i < n; i++)
            {
                ms.WriteByte(0);
            }
        }

        /**
		 * Encodes and writes pixel data
		 */
        protected void WritePixels()
        {
            LZWEncoder encoder =
                new LZWEncoder(width, height, indexedPixels, colorDepth);
            encoder.Encode(ms);
        }

        /**
		 *    Write 16-bit value to output stream, LSB first
		 */
        protected void WriteShort(int value)
        {
            ms.WriteByte(Convert.ToByte(value & 0xff));
            ms.WriteByte(Convert.ToByte((value >> 8) & 0xff));
        }

        /**
		 * Writes string to output stream
		 */
        protected void WriteString(string s)
        {
            char[] chars = s.ToCharArray();
            for (int i = 0; i < chars.Length; i++)
            {
                ms.WriteByte((byte)chars[i]);
            }
        }
    }

}