#include <stdint.h>
#include <stdbool.h>
#include <string.h>
#include <stdio.h>
#include <ctype.h>
#include <stdlib.h>
#include <errno.h>

#include <dirent.h>


#define LINE_MAX UINT16_MAX

// appended to the input directory to get the path to the feed's config
const char* fmjconfp = ".fmjconf";

const char* fmj_extension = ".fmj";

// .fmjconf and .fmj option names
const char* description = "description";
const char* title = "title";
const char* link = "link";
const char* default_author = "default_author";
const char* author = "author";
const char* category = "category";
const char* comments = "comments";
const char* pub_date = "pub_date";

// global for the default_author from the .fmjconf
char* default_author_name = NULL;

void print_usage(void) {
  puts("usage:\nfmj dir [output file]");
}

// caller must free returned ptr
char* join_path(const char* a, const char* b) {
  char* buf = malloc(strlen(a) + strlen(b) + 2);
  strcpy(buf, a);
  strncat(buf, "/", 2);
  strncat(buf, b, strlen(b) + 1);
  return buf;
}

// parses an option from `line` that is formatted like this:
// "title = contents"
//
// it will ignore the whitespace around the "=",
// and return a pointer to the beginning of "contents",
// or  return NULL if it didn't match.
const char* parse_option(const char* line, const char* option) {
  size_t optlen = strlen(option);
  // if it doesn't have an "=" and then at least one
  // char of content then its not valid
  if (strlen(line) < optlen + 2) {
    return NULL;
  }

  if (strncmp(line, option, optlen) != 0) {
    return NULL;
  }

  const char* cur = line + optlen;

  bool foundequals = false;

  while (true) {
    if (isblank(*cur)) {
      cur++;
      continue;
    }
    if (!foundequals && *cur == '=') {
      foundequals = true;
      cur++;
      continue;
    }
    // empty option is invalid
    if (foundequals && *cur != '\n') {
      break;
    }
    // at this point any valid cases have been exhausted
    return NULL;
  }

  return cur;
}

void write_without_newline(const char* content, FILE* output) {
  while (*content != '\0' && *content != '\n') {
    fputc(*content, output);
    content++;
  }
}
/* broken old version with out of bounds read because of `||` xd

  void write_without_newline(FILE* output, const char* content) {
  while (*content != '\0' || *content != '\n') {
    fputc(*content, output);
    content++;
  }
}*/


void write_feed_header(FILE* output, FILE* fmjconf) {
  fputs("<?xml version=\"1.0\" encoding=\"UTF-8\" ?><rss version=\"2.0\"><channel>", output);

  bool found_title = false;
  bool found_link = false;
  bool found_description = false;
  bool found_default_author = false;

  char buf[LINE_MAX];
  if (fmjconf != NULL) {
    while (fgets(buf, LINE_MAX, fmjconf) != NULL) {
      const char* opt;
      if ((opt = parse_option(buf, title)) != NULL && !found_title) {
        fputs("<title>", output);
        write_without_newline(opt, output);
        fputs("</title>", output);
        found_title = true;
        continue;
      }
      if ((opt = parse_option(buf, link)) != NULL && !found_link) {
        fputs("<link>", output);
        write_without_newline(opt, output);
        fputs("</link>", output);
        found_link = true;
        continue;
      }
      if ((opt = parse_option(buf, description)) != NULL && !found_description) {
        fputs("<description>", output);
        write_without_newline(opt, output);
        fputs("</description>", output);
        found_description = true;
        continue;
      }
      if ((opt = parse_option(buf, default_author)) != NULL && !found_default_author) {
        default_author_name = malloc(strlen(opt) + 1);
        strcpy(default_author_name, opt);
        found_default_author = true;
        continue;
      }
    }
  }

  if (!found_title) {
    fputs("<title>fmj generated feed</title>", output);
  }

  if (!found_link) {
    fputs("<link>http://example.com/</link>", output);
  }

  if (!found_description) {
    fputs("<description>an rss feed generated by fmj</description>", output);
  }

  fputs("<generator>fmj</generator>", output);
}

void write_feed_item(FILE* output, const char* dir, const char* entryname) {
  if (dir == NULL || entryname == NULL) {
    return;
  }

  // only consider .fmj files
  size_t namelen = strlen(entryname);
  size_t extlen = strlen(fmj_extension);
  if (namelen < extlen) {
    return;
  }
  if (strncmp(entryname + namelen - extlen, fmj_extension, extlen) != 0) {
    return;
  }

  char* path = join_path(dir, entryname);
  FILE* file = fopen(path, "r");
  if (file == NULL) {
    free(path);
    return;
  }

  char buf[LINE_MAX];

  // make sure it has either a title or description
  bool has_requirements = false;
  while (fgets(buf, LINE_MAX, file) != NULL) {
    if (parse_option(buf, title) || parse_option(buf, description)) {
      has_requirements = true;
      break;
    }
  }
  if (!has_requirements) {
    return;
  }
  rewind(file);

  bool found_title = false;
  bool found_description = false;
  bool found_link = false;
  bool found_pub_date = false;
  bool found_author = false;

  fputs("<item>", output);

  while (fgets(buf, LINE_MAX, file) != NULL) {
    const char* opt;
    if ((opt = parse_option(buf, title)) != NULL && !found_title) {
      fputs("<title>", output);
      write_without_newline(opt, output);
      fputs("</title>", output);
    }
    if ((opt = parse_option(buf, link)) != NULL && !found_link) {
      fputs("<link>", output);
      write_without_newline(opt, output);
      fputs("</link>", output);
    }
    if ((opt = parse_option(buf, description)) != NULL && !found_description) {
      fputs("<description>", output);
      write_without_newline(opt, output);
      fputs("</description>", output);
    }
    if ((opt = parse_option(buf, author)) != NULL && !found_author) {
      fputs("<author>", output);
      write_without_newline(opt, output);
      fputs("</author>", output);
    }
    if ((opt = parse_option(buf, pub_date)) != NULL && !found_pub_date) {
      fputs("<pubDate>", output);
      write_without_newline(opt, output);
      fputs("</pubDate>", output);
    }
    if ((opt = parse_option(buf, category)) != NULL) {
      fputs("<category>", output);
      write_without_newline(opt, output);
      fputs("</category>", output);
    }
  }

  if (!found_author && default_author_name != NULL) {
    fputs("<author>", output);
    write_without_newline(default_author_name, output);
    fputs("</author>", output);
  }

  fputs("</item>", output);

  free(path);
}

void write_feed_footer(FILE* output) {
  fputs("</channel></rss>", output);
}


int main(int argc, char** argv) {
  if (argc < 2) {
    print_usage();
    return 1;
  }


  DIR* dir = opendir(argv[1]);
  if (dir == NULL) {
    puts("failed to open the input directory!!!");
    return 1;
  }


  char* outfilepath = "rss.xml";

  if (argc >= 3) {
    outfilepath = argv[2];
  }

  FILE* output;

  if (*outfilepath == '-') {
    output = stdout;
  } else {
    output = fopen(outfilepath, "w");
    if (output == NULL) {
      puts("failed to open output file!!!!");
      return 1;
    }
  }


  char* fmjconfpath = join_path(argv[1], fmjconfp);

  FILE* fmjconf = fopen(fmjconfpath, "r");

  write_feed_header(output, fmjconf);

  if (fmjconf != NULL) {
    fclose(fmjconf);
  }

  free(fmjconfpath);


  struct dirent* entry;

  while (true) {
    errno = 0;
    entry = readdir(dir);
    if (entry != NULL) {
      write_feed_item(output, argv[1], entry->d_name);
    } else {
      if (errno == 0) {
        closedir(dir);
        break;
      }
      // i am going to assume getting here is bad and exit
      puts("assertion failed, readdir errored.");
      return 1;
    }
  }


  write_feed_footer(output);


  if (output != stdout) {
    fclose(output);
  }
}