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/*
    This file is part of the iText (R) project.
    Copyright (c) 1998-2023 Apryse Group NV
    Authors: Apryse Software.

    This program is offered under a commercial and under the AGPL license.
    For commercial licensing, contact us at https://itextpdf.com/sales.  For AGPL licensing, see below.

    AGPL licensing:
    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU Affero General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU Affero General Public License for more details.

    You should have received a copy of the GNU Affero General Public License
    along with this program.  If not, see .
 */
package com.itextpdf.io.image;

import com.itextpdf.io.exceptions.IOException;
import com.itextpdf.io.exceptions.IoExceptionMessageConstant;
import com.itextpdf.io.font.PdfEncodings;
import com.itextpdf.io.util.StreamUtil;

import java.io.ByteArrayInputStream;
import java.io.InputStream;
import java.net.URL;
import java.util.HashMap;
import java.util.Map;

public final class GifImageHelper {

    // max decoder pixel stack size
    static final int MAX_STACK_SIZE = 4096;

    private static class GifParameters {

        public GifParameters(GifImageData image) {
            this.image = image;
        }

        InputStream input;
        // global color table used
        boolean gctFlag;

        // background color index
        int bgIndex;
        // background color
        int bgColor;
        // pixel aspect ratio
        int pixelAspect;

        // local color table flag
        boolean lctFlag;
        // interlace flag
        boolean interlace;
        // local color table size
        int lctSize;

        // current image rectangle
        int ix, iy, iw, ih;

        // current data block
        byte[] block = new byte[256];
        // block size
        int blockSize = 0;

        // last graphic control extension info
        // 0=no action; 1=leave in place; 2=restore to bg; 3=restore to prev
        int dispose = 0;
        // use transparent color
        boolean transparency = false;
        // delay in milliseconds
        int delay = 0;
        // transparent color index
        int transIndex;

        // LZW decoder working arrays
        short[] prefix;
        byte[] suffix;
        byte[] pixelStack;
        byte[] pixels;

        byte[] m_out;
        int m_bpc;
        int m_gbpc;
        byte[] m_global_table;
        byte[] m_local_table;
        byte[] m_curr_table;
        int m_line_stride;
        byte[] fromData;
        URL fromUrl;
        int currentFrame;

        GifImageData image;
    }

    /**
     * Reads image source and fills GifImage object with parameters (frames, width, height)
     * @param image GifImage
     */
    public static void processImage(GifImageData image) {
        processImage(image, -1);
    }

    /**
     * Reads image source and fills GifImage object with parameters (frames, width, height)
     * @param image GifImage
     * @param lastFrameNumber the last frame of the gif image should be read
     */
    public static void processImage(GifImageData image, int lastFrameNumber) {
        GifParameters gif = new GifParameters(image);
        InputStream gifStream;
        try {
            if (image.getData() == null) {
                image.loadData();
            }
            gifStream = new ByteArrayInputStream(image.getData());
            process(gifStream, gif, lastFrameNumber);
        } catch (java.io.IOException e) {
            throw new IOException(IoExceptionMessageConstant.GIF_IMAGE_EXCEPTION, e);
        }
    }

    private static void process(InputStream stream, GifParameters gif, int lastFrameNumber) throws java.io.IOException {
        gif.input = stream;
        readHeader(gif);
        readContents(gif, lastFrameNumber);
        if (gif.currentFrame <= lastFrameNumber) {
            throw new IOException(IoExceptionMessageConstant.CANNOT_FIND_FRAME).setMessageParams(lastFrameNumber);
        }
    }

    /**
     * Reads GIF file header information.
     */
    private static void readHeader(GifParameters gif) throws java.io.IOException {
        StringBuilder id = new StringBuilder("");
        for (int i = 0; i < 6; i++)
            id.append((char)gif.input.read());
        if (!id.toString().startsWith("GIF8")) {
            throw new IOException(IoExceptionMessageConstant.GIF_SIGNATURE_NOT_FOUND);
        }

        readLSD(gif);
        if (gif.gctFlag) {
            gif.m_global_table = readColorTable(gif.m_gbpc, gif);
        }
    }

    /**
     * Reads Logical Screen Descriptor
     */
    private static void readLSD(GifParameters gif) throws java.io.IOException {

        // logical screen size
        gif.image.setLogicalWidth(readShort(gif));
        gif.image.setLogicalHeight(readShort(gif));

        // packed fields
        int packed = gif.input.read();
        // 1   : global color table flag
        gif.gctFlag = (packed & 0x80) != 0;
        gif.m_gbpc = (packed & 7) + 1;
        // background color index
        gif.bgIndex = gif.input.read();
        // pixel aspect ratio
        gif.pixelAspect = gif.input.read();
    }

    /**
     * Reads next 16-bit value, LSB first
     */
    private static int readShort(GifParameters gif) throws java.io.IOException {
        // read 16-bit value, LSB first
        return gif.input.read() | gif.input.read() << 8;
    }

    /**
     * Reads next variable length block from input.
     *
     * @return number of bytes stored in "buffer"
     */
    private static int readBlock(GifParameters gif) throws java.io.IOException {
        gif.blockSize = gif.input.read();
        if (gif.blockSize <= 0)
            return gif.blockSize = 0;

        gif.blockSize = gif.input.read(gif.block, 0, gif.blockSize);

        return gif.blockSize;
    }

    private static byte[] readColorTable(int bpc, GifParameters gif) throws java.io.IOException {
        int ncolors = 1 << bpc;
        int nbytes = 3*ncolors;
        bpc = newBpc(bpc);
        byte[] table = new byte[(1 << bpc) * 3];
        StreamUtil.readFully(gif.input, table, 0, nbytes);
        return table;
    }


    private static int newBpc(int bpc) {
        switch (bpc) {
            case 1:
            case 2:
            case 4:
                break;
            case 3:
                return 4;
            default:
                return 8;
        }
        return bpc;
    }

    private static void readContents(GifParameters gif, int lastFrameNumber) throws java.io.IOException {
        // read GIF file content blocks
        boolean done = false;
        gif.currentFrame = 0;
        while (!done) {
            int code = gif.input.read();
            switch (code) {
                case 0x2C:
                    // image separator
                    readFrame(gif);
                    if (gif.currentFrame == lastFrameNumber) {
                        done = true;
                    }
                    gif.currentFrame++;
                    break;
                case 0x21:
                    // extension
                    code = gif.input.read();
                    switch (code) {
                        case 0xf9:
                            // graphics control extension
                            readGraphicControlExt(gif);
                            break;
                        case 0xff:
                            // application extension
                            readBlock(gif);
                            // don't care
                            skip(gif);
                            break;
                        default:
                            // uninteresting extension
                            skip(gif);
                    }
                    break;
                default:
                    done = true;
                    break;
            }
        }
    }

    /**
     * Reads next frame image
     */
    private static void readFrame(GifParameters gif) throws java.io.IOException {
        // (sub)image position & size
        gif.ix = readShort(gif);
        gif.iy = readShort(gif);
        gif.iw = readShort(gif);
        gif.ih = readShort(gif);

        int packed = gif.input.read();
        // 1 - local color table flag
        gif.lctFlag = (packed & 0x80) != 0;
        // 2 - interlace flag
        gif.interlace = (packed & 0x40) != 0;
        // 3 - sort flag
        // 4-5 - reserved
        // 6-8 - local color table size
        gif.lctSize = 2 << (packed & 7);
        gif.m_bpc = newBpc(gif.m_gbpc);
        if (gif.lctFlag) {
            // read table
            gif.m_curr_table = readColorTable((packed & 7) + 1, gif);
            gif.m_bpc = newBpc((packed & 7) + 1);
        }
        else {
            gif.m_curr_table = gif.m_global_table;
        }
        if (gif.transparency && gif.transIndex >= gif.m_curr_table.length / 3)
            gif.transparency = false;
        // Acrobat 5.05 doesn't like this combination
        if (gif.transparency && gif.m_bpc == 1) {
            byte[] tp = new byte[12];
            System.arraycopy(gif.m_curr_table, 0, tp, 0, 6);
            gif.m_curr_table = tp;
            gif.m_bpc = 2;
        }
        // decode pixel data
        boolean skipZero = decodeImageData(gif);
        if (!skipZero)
            skip(gif);

        try {
            Object[] colorspace = new Object[4];
            colorspace[0] = "/Indexed";
            colorspace[1] = "/DeviceRGB";
            int len = gif.m_curr_table.length;
            colorspace[2] = len / 3 - 1;
            colorspace[3] = PdfEncodings.convertToString(gif.m_curr_table, null);
            Map ad = new HashMap<>();
            ad.put("ColorSpace", colorspace);
            RawImageData img = new RawImageData(gif.m_out, ImageType.GIF);
            RawImageHelper.updateRawImageParameters(img, gif.iw, gif.ih, 1, gif.m_bpc, gif.m_out);
            RawImageHelper.updateImageAttributes(img, ad);
            gif.image.addFrame(img);
            if (gif.transparency) {
                img.setTransparency(new int[]{gif.transIndex, gif.transIndex});
            }
        } catch (Exception e) {
            throw new IOException(IoExceptionMessageConstant.GIF_IMAGE_EXCEPTION, e);
        }
    }

    private static boolean decodeImageData(GifParameters gif) throws java.io.IOException {
        int NullCode = -1;
        int npix = gif.iw * gif.ih;
        int available, clear, code_mask, code_size, end_of_information, in_code, old_code,
                bits, code, count, i, datum, data_size, first, top, bi;
        boolean skipZero = false;

        if (gif.prefix == null)
            gif.prefix = new short[MAX_STACK_SIZE];
        if (gif.suffix == null)
            gif.suffix = new byte[MAX_STACK_SIZE];
        if (gif.pixelStack == null)
            gif.pixelStack = new byte[MAX_STACK_SIZE +1];

        gif.m_line_stride = (gif.iw * gif.m_bpc + 7) / 8;
        gif.m_out = new byte[gif.m_line_stride * gif.ih];
        int pass = 1;
        int inc = gif.interlace ? 8 : 1;
        int line = 0;
        int xpos = 0;

        //  Initialize GIF data stream decoder.

        data_size = gif.input.read();
        clear = 1 << data_size;
        end_of_information = clear + 1;
        available = clear + 2;
        old_code = NullCode;
        code_size = data_size + 1;
        code_mask = (1 << code_size) - 1;
        for (code = 0; code < clear; code++) {
            gif.prefix[code] = 0;
            gif.suffix[code] = (byte) code;
        }

        //  Decode GIF pixel stream.

        datum = bits = count = first = top = bi = 0;

        for (i = 0; i < npix; ) {
            if (top == 0) {
                if (bits < code_size) {
                    //  Load bytes until there are enough bits for a code.
                    if (count == 0) {
                        // Read a new data block.
                        count = readBlock(gif);
                        if (count <= 0) {
                            skipZero = true;
                            break;
                        }
                        bi = 0;
                    }
                    datum += (gif.block[bi] & 0xff) << bits;
                    bits += 8;
                    bi++;
                    count--;
                    continue;
                }

                //  Get the next code.

                code = datum & code_mask;
                datum >>= code_size;
                bits -= code_size;

                //  Interpret the code

                if (code > available || code == end_of_information)
                    break;
                if (code == clear) {
                    //  Reset decoder.
                    code_size = data_size + 1;
                    code_mask = (1 << code_size) - 1;
                    available = clear + 2;
                    old_code = NullCode;
                    continue;
                }
                if (old_code == NullCode) {
                    gif.pixelStack[top++] = gif.suffix[code];
                    old_code = code;
                    first = code;
                    continue;
                }
                in_code = code;
                if (code == available) {
                    gif.pixelStack[top++] = (byte) first;
                    code = old_code;
                }
                while (code > clear) {
                    gif.pixelStack[top++] = gif.suffix[code];
                    code = gif.prefix[code];
                }
                first = gif.suffix[code] & 0xff;

                //  Add a new string to the string table,

                if (available >= MAX_STACK_SIZE)
                    break;
                gif.pixelStack[top++] = (byte) first;
                gif.prefix[available] = (short) old_code;
                gif.suffix[available] = (byte) first;
                available++;
                if ((available & code_mask) == 0 && available < MAX_STACK_SIZE) {
                    code_size++;
                    code_mask += available;
                }
                old_code = in_code;
            }

            //  Pop a pixel off the pixel stack.

            top--;
            i++;

            setPixel(xpos, line, gif.pixelStack[top], gif);
            ++xpos;
            if (xpos >= gif.iw) {
                xpos = 0;
                line += inc;
                if (line >= gif.ih) {
                    if (gif.interlace) {
                        do {
                            pass++;
                            switch (pass) {
                                case 2:
                                    line = 4;
                                    break;
                                case 3:
                                    line = 2;
                                    inc = 4;
                                    break;
                                case 4:
                                    line = 1;
                                    inc = 2;
                                    break;
                                default:
                                    // this shouldn't happen
                                    line = gif.ih - 1;
                                    inc = 0;
                            }
                        } while (line >= gif.ih);
                    }
                    else {
                        // this shouldn't happen
                        line = gif.ih - 1;
                        inc = 0;
                    }
                }
            }
        }
        return skipZero;
    }


    private static void setPixel(int x, int y, int v, GifParameters gif) {
        if (gif.m_bpc == 8) {
            int pos = x + gif.iw * y;
            gif.m_out[pos] = (byte)v;
        }
        else {
            int pos = gif.m_line_stride * y + x / (8 / gif.m_bpc);
            int vout = v << 8 - gif.m_bpc * (x % (8 / gif.m_bpc))- gif.m_bpc;
            gif.m_out[pos] |= (byte) vout;
        }
    }

    /**
     * Reads Graphics Control Extension values
     */
    private static void readGraphicControlExt(GifParameters gif) throws java.io.IOException {
        // block size
        gif.input.read();
        // packed fields
        int packed = gif.input.read();
        // disposal method
        gif.dispose = (packed & 0x1c) >> 2;
        if (gif.dispose == 0){
            // elect to keep old image if discretionary
            gif.dispose = 1;
        }
        gif.transparency = (packed & 1) != 0;
        // delay in milliseconds
        gif.delay = readShort(gif) * 10;
        // transparent color index
        gif.transIndex = gif.input.read();
        // block terminator
        gif.input.read();
    }

    /**
     * Skips variable length blocks up to and including
     * next zero length block.
     */
    private static void skip(GifParameters gif) throws java.io.IOException {
        do {
            readBlock(gif);
        } while (gif.blockSize > 0);
    }
}