/*
  * GIF demuxer
  * Copyright (c) 2012 Vitaliy E Sugrobov
  *
  * This file is part of FFmpeg.
  *
  * FFmpeg is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
  * License as published by the Free Software Foundation; either
  * version 2.1 of the License, or (at your option) any later version.
  *
  * FFmpeg 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
  * Lesser General Public License for more details.
  *
  * You should have received a copy of the GNU Lesser General Public
  * License along with FFmpeg; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
 /**
  * @file
  * GIF demuxer.
  */
 
 #include "avformat.h"
 #include "libavutil/intreadwrite.h"
 #include "libavutil/opt.h"
 #include "internal.h"
 #include "libavcodec/gif.h"
 
 typedef struct GIFDemuxContext {
     const AVClass *class;
     /**
      * Time span in hundredths of second before
      * the next frame should be drawn on screen.
      */
     int delay;
     /**
      * Minimum allowed delay between frames in hundredths of
      * second. Values below this threshold considered to be
      * invalid and set to value of default_delay.
      */
     int min_delay;
     int default_delay;
 } GIFDemuxContext;
 
 /**
  * Major web browsers display gifs at ~10-15fps when rate
  * is not explicitly set or have too low values. We assume default rate to be 10.
  * Default delay = 100hundredths of second / 10fps = 10hos per frame.
  */
 #define GIF_DEFAULT_DELAY   10
 /**
  * By default delay values less than this threshold considered to be invalid.
  */
 #define GIF_MIN_DELAY       2
 
 static int gif_probe(AVProbeData *p)
 {
     /* check magick */
     if (memcmp(p->buf, gif87a_sig, 6) && memcmp(p->buf, gif89a_sig, 6))
         return 0;
 
     /* width or height contains zero? */
     if (!AV_RL16(&p->buf[6]) || !AV_RL16(&p->buf[8]))
         return 0;
 
     return AVPROBE_SCORE_MAX;
 }
 
 static int gif_read_header(AVFormatContext *s)
 {
     GIFDemuxContext *gdc = s->priv_data;
     AVIOContext     *pb  = s->pb;
     AVStream        *st;

     int width, height, ret;

 
     /* skip 6-byte magick */
     if ((ret = avio_skip(pb, 6)) < 0)
         return ret;
 
     gdc->delay  = gdc->default_delay;

     width  = avio_rl16(pb);
     height = avio_rl16(pb);

     if (width == 0 || height == 0)

         return AVERROR_INVALIDDATA;
 
     st = avformat_new_stream(s, NULL);
     if (!st)
         return AVERROR(ENOMEM);
 
     /* GIF format operates with time in "hundredths of second",
      * therefore timebase is 1/100 */
     avpriv_set_pts_info(st, 64, 1, 100);
     st->codec->codec_type = AVMEDIA_TYPE_VIDEO;
     st->codec->codec_id   = AV_CODEC_ID_GIF;

     st->codec->width      = width;
     st->codec->height     = height;

 
     /* jump to start because gif decoder needs header data too */
     if (avio_seek(pb, 0, SEEK_SET) != 0)
         return AVERROR(EIO);
 
     return 0;
 }
 
 static int gif_skip_subblocks(AVIOContext *pb)
 {
     int sb_size, ret = 0;
 
     while (0x00 != (sb_size = avio_r8(pb))) {
         if ((ret = avio_skip(pb, sb_size)) < 0)
             return ret;
     }
 
     return ret;
 }
 
 static int gif_read_ext(AVFormatContext *s)
 {
     GIFDemuxContext *gdc = s->priv_data;
     AVIOContext *pb = s->pb;
     int sb_size, ext_label = avio_r8(pb);
     int ret;
 
     if (ext_label == GIF_GCE_EXT_LABEL) {
         if ((sb_size = avio_r8(pb)) < 4) {
             av_log(s, AV_LOG_FATAL, "Graphic Control Extension block's size less than 4.\n");
             return AVERROR_INVALIDDATA;
         }
 
         /* skip packed fields */
         if ((ret = avio_skip(pb, 1)) < 0)
             return ret;
 
         gdc->delay = avio_rl16(pb);
 
         if (gdc->delay < gdc->min_delay)
             gdc->delay = gdc->default_delay;
 
         /* skip the rest of the Graphic Control Extension block */
         if ((ret = avio_skip(pb, sb_size - 3)) < 0 )
             return ret;
     }
 
     if ((ret = gif_skip_subblocks(pb)) < 0)
         return ret;
 
     return 0;
 }
 
 static int gif_read_packet(AVFormatContext *s, AVPacket *pkt)
 {
     GIFDemuxContext *gdc = s->priv_data;
     AVIOContext *pb = s->pb;
     int packed_fields, block_label, ct_size,
         keyframe, frame_parsed = 0, ret;
     int64_t frame_start = avio_tell(pb), frame_end;
     unsigned char buf[6];
 
     if ((ret = avio_read(pb, buf, 6)) == 6) {
         keyframe = memcmp(buf, gif87a_sig, 6) == 0 ||
                    memcmp(buf, gif89a_sig, 6) == 0;
     } else if (ret < 0) {
         return ret;
     } else {
         keyframe = 0;
     }
 
     if (keyframe) {
         /* skip 2 bytes of width and 2 of height */
         if ((ret = avio_skip(pb, 4)) < 0)
             return ret;
 
         packed_fields = avio_r8(pb);
 
         /* skip 1 byte of Background Color Index and 1 byte of Pixel Aspect Ratio */
         if ((ret = avio_skip(pb, 2)) < 0)
             return ret;
 
         /* glogal color table presence */
         if (packed_fields & 0x80) {
             ct_size = 3 * (1 << ((packed_fields & 0x07) + 1));
 
             if ((ret = avio_skip(pb, ct_size)) < 0)
                 return ret;
         }
     } else {
         avio_seek(pb, -ret, SEEK_CUR);
         ret = AVERROR_EOF;
     }
 
     while (GIF_TRAILER != (block_label = avio_r8(pb)) && !url_feof(pb)) {
         if (block_label == GIF_EXTENSION_INTRODUCER) {
             if ((ret = gif_read_ext (s)) < 0 )
                 return ret;
         } else if (block_label == GIF_IMAGE_SEPARATOR) {
             /* skip to last byte of Image Descriptor header */
             if ((ret = avio_skip(pb, 8)) < 0)
                 return ret;
 
             packed_fields = avio_r8(pb);
 
             /* local color table presence */
             if (packed_fields & 0x80) {
                 ct_size = 3 * (1 << ((packed_fields & 0x07) + 1));
 
                 if ((ret = avio_skip(pb, ct_size)) < 0)
                     return ret;
             }
 
             /* read LZW Minimum Code Size */
             if (avio_r8(pb) < 1) {
                 av_log(s, AV_LOG_ERROR, "lzw minimum code size must be >= 1\n");
                 return AVERROR_INVALIDDATA;
             }
 
             if ((ret = gif_skip_subblocks(pb)) < 0)
                 return ret;
 
             frame_end = avio_tell(pb);
 
             if (avio_seek(pb, frame_start, SEEK_SET) != frame_start)
                 return AVERROR(EIO);
 
             ret = av_get_packet(pb, pkt, frame_end - frame_start);
             if (ret < 0)
                 return ret;
 
             if (keyframe)
                 pkt->flags |= AV_PKT_FLAG_KEY;
 
             pkt->stream_index = 0;
             pkt->duration = gdc->delay;
 
             /* Graphic Control Extension's scope is single frame.
              * Remove its influence. */
             gdc->delay = gdc->default_delay;
             frame_parsed = 1;
 
             break;
         } else {
             av_log(s, AV_LOG_ERROR, "invalid block label\n");
             return AVERROR_INVALIDDATA;
         }
     }
 
     if (ret >= 0 && !frame_parsed) {
         /* This might happen when there is no image block
          * between extension blocks and GIF_TRAILER or EOF */
         return  AVERROR_EOF;
     } else
         return ret;
 }
 
 static const AVOption options[] = {
     { "min_delay"    , "minimum valid delay between frames (in hundredths of second)", offsetof(GIFDemuxContext, min_delay)    , AV_OPT_TYPE_INT, {.i64 = GIF_MIN_DELAY}    , 0, 100 * 60, AV_OPT_FLAG_DECODING_PARAM },
     { "default_delay", "default delay between frames (in hundredths of second)"      , offsetof(GIFDemuxContext, default_delay), AV_OPT_TYPE_INT, {.i64 = GIF_DEFAULT_DELAY}, 0, 100 * 60, AV_OPT_FLAG_DECODING_PARAM },
     { NULL },
 };
 
 static const AVClass demuxer_class = {
     .class_name = "GIF demuxer",
     .item_name  = av_default_item_name,
     .option     = options,
     .version    = LIBAVUTIL_VERSION_INT,
     .category   = AV_CLASS_CATEGORY_DEMUXER,
 };
 
 AVInputFormat ff_gif_demuxer = {
     .name           = "gif",
     .long_name      = NULL_IF_CONFIG_SMALL("CompuServe Graphics Interchange Format (GIF)"),
     .priv_data_size = sizeof(GIFDemuxContext),
     .read_probe     = gif_probe,
     .read_header    = gif_read_header,
     .read_packet    = gif_read_packet,

     .flags          = AVFMT_GENERIC_INDEX,

     .priv_class     = &demuxer_class,
 };