/* Calcite, src/user-libs/silver/pam.c
 * Copyright 2025 Benji Dial
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program 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 General Public License
 * for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program. If not, see <https://www.gnu.org/licenses/>.
 */

#include <calcite/file-streams.h>
#include <silver/pam.h>

static int starts_with(const char *big_string, const char *little_string) {
  while (*little_string) {
    if (*big_string != *little_string)
      return 0;
    ++big_string;
    ++little_string;
  }
  return 1;
}

static int strequ(const char *str1, const char *str2) {
  while (1) {
    if (!*str1 && !*str2)
      return 1;
    if (*str1 != *str2)
      return 0;
    ++str1;
    ++str2;
  }
}

static int parse_uint(const char *str) {
  int i = 0;
  while (*str)
    i = i * 10 + *(str++) - '0';
  return i;
}

enum pam_tupltype {
  PTT_RGB_ALPHA
};

#define MAX_LINE_LENGTH 1023

int load_pam(const char *path, struct image **image_out) {

  struct file_stream *stream;
  if (open_file_stream(path, &stream) != FAR_SUCCESS)
    return 0;

  if (read_file_stream_byte(stream) != 'P' ||
      read_file_stream_byte(stream) != '7' ||
      read_file_stream_byte(stream) != '\n') {
    close_file_stream(stream);
    return 0;
  }

  int width = -1, height = -1, depth = -1, maxval = -1, tupltype = -1;

  while (1) {

    char line[MAX_LINE_LENGTH + 1];
    int line_length = 0;
    while (1) {
      int c = read_file_stream_byte(stream);
      if (c == -1) {
        close_file_stream(stream);
        return 0;
      }
      if (c == '\n') {
        line[line_length] = 0;
        break;
      }
      if (line_length == MAX_LINE_LENGTH) {
        close_file_stream(stream);
        return 0;
      }
      line[line_length++] = c;
    }

    if (line[0] == '#')
      continue;

    if (starts_with(line, "WIDTH "))
      width = parse_uint(&line[6]);
    else if (starts_with(line, "HEIGHT "))
      height = parse_uint(&line[7]);
    else if (starts_with(line, "DEPTH "))
      depth = parse_uint(&line[6]);
    else if (starts_with(line, "MAXVAL "))
      maxval = parse_uint(&line[7]);
    else if (strequ(line, "TUPLTYPE RGB_ALPHA"))
      tupltype = PTT_RGB_ALPHA;
    else if (strequ(line, "ENDHDR"))
      break;

  }

  if (width == -1 || height == -1 || depth != 4 || maxval != 255 || tupltype != PTT_RGB_ALPHA) {
    close_file_stream(stream);
    return 0;
  }

  create_image(width, height, image_out);

  if (read_file_stream(
        stream,
        (*image_out)->pixels,
        width * height * 4) != FAR_SUCCESS) {
    close_file_stream(stream);
    destroy_image(*image_out);
    return 0;
  }

  close_file_stream(stream);
  return 1;

}