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

#include <libavutil/frame.h>
#include <libavutil/mem.h>

#include <libavcodec/avcodec.h>

#define AUDIO_INBUF_SIZE 20480
#define AUDIO_REFILL_THRESH 4096

static void decode(AVCodecContext *dec_ctx, AVPacket *pkt, AVFrame *frame,
		FILE *outfile)
{
  int i, ch;
  int ret, data_size;

  /* send the packet with the compressed data to the decoder */
  ret = avcodec_send_packet(dec_ctx, pkt);

  if(ret < 0) {
    fprintf(stderr, "Error submitting the packet to the decoder\n");
    exit(1);
  }

  /* read all the output frames (in general there may be any number of
   * them */
  while(ret >= 0) {
    ret = avcodec_receive_frame(dec_ctx, frame);
    if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
      return;
    else if (ret <0) {
      fprintf(stderr, "Error during decoding\n");
      exit(1);
    }
    data_size = av_get_bytes_per_sample(dec_ctx->sample_fmt);
    if(data_size < 0){
      /* This should not occur, checking just for parania */
      fprintf(stderr, "Failed to calculate data size\n");
      exit(1);
    }
    for(i = 0; i< frame->nb_samples; i++)
      for(ch =0; ch < dec_ctx->channels; ch++)
	fwrite(frame->data[ch] + data_size * i, 1, data_size, outfile);
  }
}

int main(int argc, char **argv)
{
  const char *outfilename, *filename;
  const AVCodec *codec;
  AVCodecContext *c = NULL;
  AVCodecParserContext *parser = NULL;
  int len, ret;
  FILE *f, *outfile;
  uint8_t inbuf[AUDIO_INBUF_SIZE + AV_INPUT_BUFFER_PADDING_SIZE];
  uint8_t *data;
  size_t data_size;
  AVPacket *pkt;
  AVFrame *decoded_frame = NULL;

  if (argc <= 2) {
    fprintf(stderr, "Usage: %s <input file> <output file>\n", argv[0]);
    exit(0);
  }
  filename = argv[1];
  outfilename = argv[2];


  /* register all the codecs */
  avcodec_register_all();

  pkt = av_packet_alloc();

  /* find the AMR audio decoder */
  codec = avcodec_find_decoder(AV_CODEC_ID_MP2);
  if(!codec) {
    fprintf(stderr, "Codec not found\n");
    exit(1);
  }

  parser = av_parser_init(codec->id);
  if(!parser){
    fprintf(stderr, "Parser not found\n");
    exit(1);
  }

  c = avcodec_alloc_context3(codec);
  if(!c) {
    fprintf(stderr, "Could not allocate audio codec context\n");
    exit(1);
  }


  /* open it */
  if (avcodec_open2(c, codec, NULL) < 0) {
    fprintf(stderr, "Could not open codec\n");
    exit(1);
  }

  f = fopen(filename, "rb");
  if (!f) {
    fprintf(stderr, "could not open %s\n", filename);
    exit(1);
  }
  outfile = fopen(outfilename, "wb");
  if(!outfile) {
    av_free(c);
    exit(1);
  }

  /* decode until eof */
  data = inbuf;
  data_size = fread(inbuf, 1, AUDIO_INBUF_SIZE, f);

  while(data_size > 0){
    if(!decoded_frame) {
      if(!(decoded_frame = av_frame_alloc())) {
	fprintf(stderr, "Could not allocate audio frame\n");
	exit(1);
      }
    }

    ret = av_parser_parse2(parser, c, &pkt->data, &pkt->size,
	data, data_size,
	AV_NOPTS_VALUE, AV_NOPTS_VALUE, 0);
    if (ret <0){
      fprintf(stderr, "Error while parsing\n");
      exit(1);
    }
    data += ret;
    data_size -= ret;


    if(pkt->size)
      decode(c, pkt, decoded_frame, outfile);

    if(data_size < AUDIO_REFILL_THRESH) {
      memmove(inbuf, data, data_size);
      data = inbuf;
      len = fread(data + data_size, 1, AUDIO_INBUF_SIZE - data_size, f);

      if(len>0)
	data_size += len;
    }
  }

  /* flush the decoder */
  pkt->data = NULL;
  pkt->size = 0;
  decode(c, pkt, decoded_frame, outfile);
  fclose(outfile);
  fclose(f);

  avcodec_free_context(&c);
  av_parser_close(parser);
  av_frame_free(&decoded_frame);
  av_packet_free(&pkt);

  return 0;
}