/**
 * Utility functions for the parser module.
 */

/**
 * Generates a deterministic hash from URL and published date.
 * Uses djb2 algorithm for fast, consistent hashing.
 */
export function generateId(url: string, publishedAt: Date): string {
  const str = `${url}::${publishedAt.toISOString()}`;
  let hash = 5381;
  for (let i = 0; i < str.length; i++) {
    hash = ((hash << 5) + hash) + str.charCodeAt(i);
  }
  return (hash >>> 0).toString(16); // Convert to unsigned and hex
}

/**
 * Parses dates from RSS (RFC 822) and Atom (ISO 8601) formats.
 * Tries multiple formats for robustness.
 * Throws if date cannot be parsed.
 */
export function parseDate(dateStr: string): Date {
  if (!dateStr || typeof dateStr !== 'string') {
    throw new Error(`Invalid date string: ${dateStr}`);
  }

  const trimmed = dateStr.trim();

  // Try native Date parsing first (handles ISO 8601 and many common formats)
  let date = new Date(trimmed);
  if (!isNaN(date.getTime())) {
    return date;
  }

  // Try RFC 822 format: Mon, 06 Sep 2024 09:00:00 GMT
  const rfc822Match = trimmed.match(/^\w{3},?\s+(\d{1,2})\s+(\w{3})\s+(\d{4})\s+(\d{1,2}):(\d{2}):(\d{2})\s*(?:GMT|UTC|[+-]\d{4})?$/i);
  if (rfc822Match) {
    const months: { [key: string]: number } = {
      jan: 0, feb: 1, mar: 2, apr: 3, may: 4, jun: 5,
      jul: 6, aug: 7, sep: 8, oct: 9, nov: 10, dec: 11
    };
    const month = months[rfc822Match[2].toLowerCase()];
    if (month !== undefined) {
      date = new Date(
        parseInt(rfc822Match[3]),
        month,
        parseInt(rfc822Match[1]),
        parseInt(rfc822Match[4]),
        parseInt(rfc822Match[5]),
        parseInt(rfc822Match[6])
      );
      if (!isNaN(date.getTime())) {
        return date;
      }
    }
  }

  throw new Error(`Unable to parse date: ${dateStr}`);
}

/**
 * Validates if a string is valid XML.
 * Basic check for XML declaration or root element.
 */
export function isValidXml(xml: string): boolean {
  if (!xml || typeof xml !== 'string') {
    return false;
  }
  const trimmed = xml.trim();
  return trimmed.startsWith('<?xml') || 
         trimmed.startsWith('<rss') || 
         trimmed.startsWith('<feed') ||
         trimmed.startsWith('<channel');
}