#include <stdio.h>
#include <stdlib.h>
#include <string.h>  // for the memcmp function

#include "arr_dbl_t.h"
#include "read_l7a.h"

#define T2A_BASE_CAP 4

int read_l7a(const char *filename, arr_dbl_t *ad)
{
  // Zero out *ad in case of failure.
  ad->arr = NULL;
  ad->len = ad->cap = 0;

  FILE *fp = fopen(filename, "rb");
  char first4read[4], trailer_first4[4];
  unsigned int el_count, trailer_count;
  double *storage;
  size_t read_count;

  if (fp == NULL)
    return RL7A_OPEN_FAIL;

  read_count = fread((void *) first4read, 1, 4, fp);
  if (read_count != 4)
    return RL7A_TOO_SHORT;

  // memcmp returns 0 if two blocks of bytes of the same len
  // match exactly.
  if (memcmp((void *) first4read, (void *) L7A_FIRST_4, 4) != 0)
    return RL7A_BAD_HEADER;

  read_count = fread((void *) &el_count, sizeof(unsigned int), 1, fp);
  if (read_count != 1)
    return RL7A_TOO_SHORT;

  storage = malloc(el_count * sizeof(double));
  if (storage == NULL)
    return RL7A_MALLOC_FAIL;

  read_count = fread((void *) storage, sizeof(double), el_count, fp);
  if (read_count != el_count) {
    free(storage);
    return RL7A_TOO_SHORT;
  }

  read_count = fread((void *) trailer_first4, 1, 4, fp);
  if (read_count != 4) {
    free(storage);
    return RL7A_TOO_SHORT;
  }
  read_count = fread((void *) &trailer_count, sizeof(unsigned int), 1, fp);
  if (read_count != 1) {
    free(storage);
    return RL7A_TOO_SHORT;
  }
  if (memcmp((void *) trailer_first4, (void *) L7A_FIRST_4, 4) != 0
      || el_count != trailer_count) {
    free(storage);
    return RL7A_BAD_TRAILER;
  }

  if (fclose(fp) != 0) {
    free(storage);
    return RL7A_CLOSE_FAIL;
  }

  ad->arr = storage;
  ad->len = el_count;
  ad->cap = el_count;
  return RL7A_SUCCESS;
}