export const DOWNLOAD_PLATFORMS = ['windows', 'macos', 'linux'];

export function monthKeyFromDate(date = new Date()) {
  const y = date.getUTCFullYear();
  const m = String(date.getUTCMonth() + 1).padStart(2, '0');
  return `${y}-${m}`;
}

export function normalizeDownloadPlatform(platform) {
  const p = String(platform ?? '').trim().toLowerCase();
  if (DOWNLOAD_PLATFORMS.includes(p)) return p;
  return null;
}

export function ensureDownloadStats(data) {
  data.downloadStats ??= { byMonth: {} };
  data.downloadStats.byMonth ??= {};
  return data.downloadStats;
}

export function recordDownload(data, platform, date = new Date()) {
  const normalized = normalizeDownloadPlatform(platform);
  if (!normalized) return { ok: false, error: 'invalid_platform' };

  const stats = ensureDownloadStats(data);
  const month = monthKeyFromDate(date);
  stats.byMonth[month] ??= { windows: 0, macos: 0, linux: 0 };
  stats.byMonth[month][normalized] += 1;
  return { ok: true, month, platform: normalized, count: stats.byMonth[month][normalized] };
}

export function getDownloadStatsForMonth(data, month) {
  const stats = ensureDownloadStats(data);
  const row = stats.byMonth[month] ?? { windows: 0, macos: 0, linux: 0 };
  const total = row.windows + row.macos + row.linux;
  return { month, windows: row.windows, macos: row.macos, linux: row.linux, total };
}

export function listDownloadMonths(data) {
  const stats = ensureDownloadStats(data);
  return Object.keys(stats.byMonth).sort((a, b) => b.localeCompare(a));
}