#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "img_png.h"

#define BUFSIZE 1024

const unsigned char img_png_signature[] = {0x89, 'P', 'N', 'G', '\r', '\n', 0x1a, '\n'};

uint32_t char_to_uint32 (unsigned char* input) {
  uint32_t val = (input[0] << 24) + (input[1] << 16) + (input[2] << 8) + input[3];

  return val;
}

int read_chunk(FILE *fp) {
  struct img_png_chunk cur_chunk;

  // Read chunk length
  unsigned char len[4];
  if(fread(len, sizeof(*len), 4, fp) < 4) {
    fprintf(stderr, "Couldn\'t read chunk length.\n");
    exit(EXIT_FAILURE);
  }

  cur_chunk.length = char_to_uint32(len);
  printf("Chunk length: %lu\n", (unsigned long) cur_chunk.length);
  
  // Read chunk type
  if(fread(cur_chunk.chunk_type, sizeof(*cur_chunk.chunk_type), 4, fp) < 4) {
    fprintf(stderr, "Couldn\'t read chunk type.\n");
    exit(EXIT_FAILURE);
  }
  printf("Chunk type: %.*s\n", 4, cur_chunk.chunk_type);

  // Read chunk data
  size_t chunk_size = cur_chunk.length / sizeof(unsigned char);
  printf("Chunk size: %zu\n", chunk_size);
  cur_chunk.chunk_data = malloc(chunk_size);

  if(!cur_chunk.chunk_data) {
    perror("Failed to allocate chunk data!");
    exit(EXIT_FAILURE);
  }

  if(fread(cur_chunk.chunk_data, 1, cur_chunk.length, fp) != cur_chunk.length) {
    if(feof(fp)) {
      fprintf(stderr, "File ended prematurely.\n");
      exit(EXIT_FAILURE);
    }
    fprintf(stderr, "Failed to read chunk data!\n");
    exit(EXIT_FAILURE);
  }

  return feof(fp);
}

uint8_t* img_png_decode(FILE *fp) {
  unsigned char magic[8];

  // Check PNG Magic
  if(fread(magic, sizeof(*magic), 8, fp) < 8) {
    fprintf(stderr, "Couldn\'t read PNG magic.");
    exit(EXIT_FAILURE);
  }

  if(memcmp(magic, img_png_signature, 8) != 0) {
    fprintf(stderr, "Invalid PNG magic\n");
    exit(EXIT_FAILURE);
  }
  
  printf("PNG Magic: %#04x%02x%02x%02x%02x%02x%02x%02x\n", magic[0], magic[1], magic[2],
         magic[3], magic[4], magic[5], magic[6], magic[7]);

  struct img_png_chunk cur_chunk;  

  // Read chunk   
  
  while (read_chunk(fp) == 0);
  
  if(!feof(fp)) {
    perror("fread() failed!");
    exit(EXIT_FAILURE);
  }
  

  return NULL;
}