/*

 * GIF parser

 * Copyright (c) 2018 Paul B Mahol

 *

 * 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 parser

 */

#include "gif.h"

#include "parser.h"

#include "parser_internal.h"

typedef enum GIFParseStates {

    GIF_HEADER = 1,

    GIF_EXTENSION,

    GIF_EXTENSION_BLOCK,

    GIF_IMAGE,

    GIF_IMAGE_BLOCK,

} gif_states;

typedef struct GIFParseContext {

    ParseContext pc;

    unsigned found_sig;

    int found_start;

    int found_end;

    int index;

    int state;

    int gct_flag;

    int gct_size;

    int block_size;

    int etype;

    int delay;

    int keyframe;

} GIFParseContext;

static int gif_find_frame_end(GIFParseContext *g, const uint8_t *buf,

                              int buf_size, void *logctx)

{

    ParseContext *pc = &g->pc;

    int index, next = END_NOT_FOUND;

    for (index = 0; index < buf_size; index++) {

        if (!g->state) {

            if (!memcmp(buf + index, gif87a_sig, 6) ||

                !memcmp(buf + index, gif89a_sig, 6)) {

                g->state = GIF_HEADER;

                g->found_sig++;

                g->keyframe = 1;

            } else if (buf[index] == GIF_EXTENSION_INTRODUCER) {

                g->state = GIF_EXTENSION;

                g->found_start = pc->frame_start_found = 1;

            } else if (buf[index] == GIF_IMAGE_SEPARATOR) {

                if (g->state != GIF_EXTENSION_BLOCK && g->found_start &&

                    g->found_end && g->found_sig) {

                    next = index;

                    g->found_start = pc->frame_start_found = 1;

                    g->found_end = 0;

                    g->index = 0;

                    g->gct_flag = 0;

                    g->gct_size = 0;

                    g->state = GIF_IMAGE;

                    break;

                }

                g->state = GIF_IMAGE;

            } else if (buf[index] == GIF_TRAILER) {

                g->state = 0;

                g->found_end = 1;

                g->found_sig = 0;

            } else {

                g->found_sig = 0;

            }

        }

        if (g->state == GIF_HEADER) {

            if (g->index == 10) {

                g->gct_flag = !!(buf[index] & 0x80);

                g->gct_size = 3 * (1 << ((buf[index] & 0x07) + 1));

            }

            if (g->index >= 12 + g->gct_flag * g->gct_size) {

                g->state = 0;

                g->index = 0;

                g->gct_flag = 0;

                g->gct_size = 0;

                continue;

            }

            g->index++;

        } else if (g->state == GIF_EXTENSION) {

            if (g->found_start && g->found_end && g->found_sig) {

                next = index;

                g->found_start = pc->frame_start_found = 0;

                g->found_end = 0;

                g->index = 0;

                g->gct_flag = 0;

                g->gct_size = 0;

                g->state = 0;

                break;

            }

            if (g->index == 1) {

                g->etype = buf[index];

            }

            if (g->index >= 2) {

                g->block_size = buf[index];

                g->index = 0;

                g->state = GIF_EXTENSION_BLOCK;

                continue;

            }

            g->index++;

        } else if (g->state == GIF_IMAGE_BLOCK) {

            if (!g->index)

                g->block_size = buf[index];

            if (g->index >= g->block_size) {

                g->index = 0;

                if (!g->block_size) {

                    g->state = 0;

                    g->found_end = 1;

                }

                continue;

            }

            g->index++;

        } else if (g->state == GIF_EXTENSION_BLOCK) {

            if (g->etype == GIF_GCE_EXT_LABEL) {

                if (g->index == 0)

                    g->delay = 0;

                if (g->index >= 1 && g->index <= 2) {

                    g->delay |= buf[index] << (8 * (g->index - 1));

                }

            }

            if (g->index >= g->block_size) {

                g->block_size = buf[index];

                g->index = 0;

                if (!g->block_size)

                    g->state = 0;

                continue;

            }

            g->index++;

        } else if (g->state == GIF_IMAGE) {

            if (g->index == 9) {

                g->gct_flag = !!(buf[index] & 0x80);

                g->gct_size = 3 * (1 << ((buf[index] & 0x07) + 1));

            }

            if (g->index >= 10 + g->gct_flag * g->gct_size) {

                g->state = GIF_IMAGE_BLOCK;

                g->index = 0;

                g->gct_flag = 0;

                g->gct_size = 0;

                continue;

            }

            g->index++;

        }

    }

    return next;

}

static int gif_parse(AVCodecParserContext *s, AVCodecContext *avctx,

                     const uint8_t **poutbuf, int *poutbuf_size,

                     const uint8_t *buf, int buf_size)

{

    GIFParseContext *g = s->priv_data;

    int next;

    *poutbuf_size = 0;

    *poutbuf = NULL;

    if (s->flags & PARSER_FLAG_COMPLETE_FRAMES) {

        next = buf_size;

    } else {

        next = gif_find_frame_end(g, buf, buf_size, avctx);

        if (ff_combine_frame(&g->pc, next, &buf, &buf_size) < 0) {

            *poutbuf      = NULL;

            *poutbuf_size = 0;

            return buf_size;

        }

    }

    s->duration  = g->delay ? g->delay : 10;

    s->key_frame = g->keyframe;

    s->pict_type = g->keyframe ? AV_PICTURE_TYPE_I : AV_PICTURE_TYPE_P;

    g->keyframe  = 0;

    *poutbuf      = buf;

    *poutbuf_size = buf_size;

    return next;

}

const FFCodecParser ff_gif_parser = {

    PARSER_CODEC_LIST(AV_CODEC_ID_GIF),

    .priv_data_size = sizeof(GIFParseContext),

    .parse          = gif_parse,

    .close          = ff_parse_close,

};