/**
 * Timezone-aware date formatting utilities for Outlook MCP Server.
 *
 * All user-visible timestamps are formatted in the configured timezone
 * (MS_TIMEZONE env var, default America/New_York) so that dates
 * rendered inside the UTC container still match the user's local time.
 */
const config = require('../config');

/**
 * Format an ISO 8601 or Graph dateTime string for display.
 * @param {string} isoString - ISO 8601 / UTC timestamp from Graph API
 * @param {string} [timeZone] - IANA or Windows timezone name (defaults to config.DEFAULT_TIMEZONE)
 * @returns {string} Formatted date/time string with timezone abbreviation
 */
function formatDateTime(isoString, timeZone = config.DEFAULT_TIMEZONE) {
  if (!isoString) return 'Unknown';

  const d = new Date(isoString);
  if (isNaN(d.getTime())) return String(isoString);

  try {
    return d.toLocaleString('en-US', {
      timeZone,
      month: 'numeric',
      day: 'numeric',
      year: 'numeric',
      hour: 'numeric',
      minute: '2-digit',
      hour12: true,
      timeZoneName: 'short'
    });
  } catch (err) {
    // If the configured timezone identifier is invalid, fall back to ISO.
    console.error(`Invalid timezone "${timeZone}", falling back to ISO: ${err.message}`);
    return d.toISOString();
  }
}

module.exports = {
  formatDateTime
};