const { createEvent } = require('ics');

// Event.startDate/endDate are stored as true UTC instants (the admin event form's
// datetime-local input is parsed in the browser's local time before being sent as an
// ISO string), so serializing them as UTC here requires no timezone math and lets every
// viewer's calendar app localize correctly to *their own* timezone.
function toUtcArray(date) {
  const d = new Date(date);
  return [d.getUTCFullYear(), d.getUTCMonth() + 1, d.getUTCDate(), d.getUTCHours(), d.getUTCMinutes()];
}

/**
 * Build an RFC 5545 .ics file (as a string) for a single event.
 *
 * @param {object} event - Prisma Event row: title, description?, startDate, endDate, location?
 * @param {string} eventUrl - absolute URL to the event's public page
 * @returns {string}
 */
function buildEventIcs(event, eventUrl) {
  const { error, value } = createEvent({
    title: event.title,
    start: toUtcArray(event.startDate),
    end: toUtcArray(event.endDate),
    startInputType: 'utc',
    endInputType: 'utc',
    startOutputType: 'utc',
    endOutputType: 'utc',
    location: event.location || undefined,
    description: event.description || undefined,
    url: eventUrl,
  });
  if (error) throw error;
  return value;
}

module.exports = { buildEventIcs };