#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>

#include <libavformat/avformat.h>
#include <libavcodec/avcodec.h>
#include <libavutil/avutil.h>
#include <libswscale/swscale.h>

static void
pgm_save(unsigned char *buf, int wrap, int xsize, int ysize, char *filename)
{
    FILE *f;
    int i;

    f = fopen(filename, "w");
    fprintf(f, "P5\n%d %d\n%d\n", xsize, ysize, 255);
    for(i=0; i < ysize; i++)
        fwrite(buf + i * wrap, 1, xsize, f);
    fclose(f);
}

static void
ppm_save(unsigned char *buf, int wrap, int xsize, int ysize, char *filename)
{
    FILE *f;
    int i;

    f = fopen(filename, "w");
    fprintf(f,"P6\n%d %d\n%d\n", xsize, ysize, 255);
    for(i=0; i < ysize; i++)
        fwrite(buf + i * wrap, 3, xsize, f);
    fclose(f);
}

int
main(int argc, char *argv[])
{
	const char *filename = argv[1];
	AVFormatContext *fmt_ctx = NULL;
	int vid_stream = -1;
	AVCodecContext *codec_ctx = NULL;
	AVCodec *codec;
	AVFrame *frame;
	AVPacket packet;
	int bytes_decoded, got_picture;
	AVFrame *frame_rgb;
	int nbytes;
	uint8_t *buffer;
	struct SwsContext *sws_ctx;
	int timestamp = 0;

	av_register_all();
#if DEBUG
	av_log_set_level(AV_LOG_DEBUG);
	printf("file: %s\n", filename);
#endif
	
	if (argc < 2) {
		fprintf(stderr, "usage: %s filename [timestamp]\n", argv[0]);
		exit(1);
	}
	if (avformat_open_input(&fmt_ctx, filename, NULL, NULL) != 0)
		exit(2);

	if (avformat_find_stream_info(fmt_ctx, NULL) < 0)
		exit(3);

#if DEBUG
	av_dump_format(fmt_ctx, 0, filename, 0);
#endif

	vid_stream = av_find_best_stream(fmt_ctx, AVMEDIA_TYPE_VIDEO,
					 -1, -1, NULL, 0);
	if (vid_stream == -1)
		exit(4);
	codec_ctx = fmt_ctx->streams[vid_stream]->codec;

	timestamp = fmt_ctx->start_time==AV_NOPTS_VALUE ? 0:fmt_ctx->start_time;
#if 1
	if (argc == 3 && atoi(argv[2]) > 0)
		timestamp += atoi(argv[2]);
#endif
	avformat_seek_file(fmt_ctx, -1, INT64_MIN, timestamp, INT64_MAX, 0);

	codec = avcodec_find_decoder(codec_ctx->codec_id);
	if (codec == NULL) {
		fprintf(stderr, "Failed to find decoder!\n");
		exit(5);
	}

#if DEBUG
	printf("has cap truncated: %d\n",
	       codec->capabilities & CODEC_CAP_TRUNCATED);
#endif
#if 0
	if (codec->capabilities & CODEC_CAP_TRUNCATED)
		codec_ctx->flags |= CODEC_FLAG_TRUNCATED;
#endif

	if (avcodec_open2(codec_ctx, codec, NULL) < 0) {
		fprintf(stderr, "Failed to open codec!\n");
		exit(6);
	}

	packet.data = NULL;
	do {
		if (packet.data != NULL)
			av_free_packet(&packet);
		if (av_read_frame(fmt_ctx, &packet) < 0) {
			fprintf(stderr, "Found no video stream packet!\n");
			exit(30);
		}
	} while (packet.stream_index != vid_stream);

	frame = avcodec_alloc_frame();
	do {
#if DEBUG
		printf("packet.data: %p, packet.size: %d, packet.stream_index: %d\n",
		       packet.data, packet.size, packet.stream_index);
#endif

		bytes_decoded = avcodec_decode_video2(codec_ctx, frame,
						      &got_picture, &packet);
		if (bytes_decoded < 0) {
			fprintf(stderr, "Error while decoding frame!\n");
			exit(12);
		}
#if DEBUG
		printf("bytes_decoded: %d, got_picture: %d\n",
		       bytes_decoded, got_picture);
#endif
		
	} while (got_picture == 0 && packet.size > 0);
	av_free_packet(&packet);
	if (got_picture == 0)
		exit(9);

	pgm_save(frame->data[0], frame->linesize[0],
		 codec_ctx->width, codec_ctx->height, "foo.pgm");

#define CONVERT_TO_RGB 1
#if CONVERT_TO_RGB
	frame_rgb = avcodec_alloc_frame();
	if (!frame_rgb)
		exit(9);

	nbytes = avpicture_get_size(PIX_FMT_RGB24,
					codec_ctx->width, codec_ctx->height);
	buffer = calloc(nbytes, sizeof(uint8_t));
	if (!buffer)
		exit(10);
	avpicture_fill((AVPicture *) frame_rgb, buffer, PIX_FMT_RGB24,
		       codec_ctx->width, codec_ctx->height);

	sws_ctx = sws_getCachedContext(NULL,
				       codec_ctx->width, codec_ctx->height,
				       codec_ctx->pix_fmt,
				       codec_ctx->width, codec_ctx->height,
				       PIX_FMT_RGB24, SWS_BILINEAR,
				       NULL, NULL, NULL);

	sws_scale(sws_ctx,
		  (const uint8_t *const *) frame->data, frame->linesize, 0,
		  codec_ctx->height,  frame_rgb->data, frame_rgb->linesize);

	ppm_save(frame_rgb->data[0], frame_rgb->linesize[0],
		 codec_ctx->width, codec_ctx->height, "foo.ppm");
#endif

	free(buffer);
	av_free(frame_rgb);
	av_free(frame);
	avcodec_close(codec_ctx);
#if LIBAVFORMAT_VERSION_INT >= AV_VERSION_INT(53, 17, 0)
	avformat_close_input(&fmt_ctx);
#else
	av_close_input_file(fmt_ctx);
#endif

	return 0;
}