function parseDateTimeValue(value) {
  if (!value || typeof value !== 'string') return null;

  const directDate = new Date(value);
  if (!Number.isNaN(directDate.getTime())) return directDate;

  const normalizedDate = new Date(value.replace(' ', 'T'));
  return Number.isNaN(normalizedDate.getTime()) ? null : normalizedDate;
}

function formatDateTimeForSqlite(date = new Date()) {
  const target = date instanceof Date ? date : new Date(date);
  const year = target.getFullYear();
  const month = String(target.getMonth() + 1).padStart(2, '0');
  const day = String(target.getDate()).padStart(2, '0');
  const hours = String(target.getHours()).padStart(2, '0');
  const minutes = String(target.getMinutes()).padStart(2, '0');
  const seconds = String(target.getSeconds()).padStart(2, '0');
  return `${year}-${month}-${day} ${hours}:${minutes}:${seconds}`;
}

function getDateKeyFromDate(date = new Date()) {
  const target = date instanceof Date ? date : new Date(date);
  if (Number.isNaN(target.getTime())) return null;
  const year = target.getFullYear();
  const month = String(target.getMonth() + 1).padStart(2, '0');
  const day = String(target.getDate()).padStart(2, '0');
  return `${year}-${month}-${day}`;
}

function getRecentDateKeys(days = 30, now = new Date()) {
  const safeDays = Math.max(1, Math.floor(Number(days) || 30));
  const keys = [];
  for (let i = safeDays - 1; i >= 0; i -= 1) {
    const date = new Date(now.getTime());
    date.setDate(date.getDate() - i);
    const key = getDateKeyFromDate(date);
    if (key) keys.push(key);
  }
  return keys;
}

function getNextDownloadResetTime(lastResetAt, resetCycle) {
  const baseDate = parseDateTimeValue(lastResetAt);
  if (!baseDate) return null;

  const next = new Date(baseDate.getTime());
  if (resetCycle === 'daily') next.setDate(next.getDate() + 1);
  else if (resetCycle === 'weekly') next.setDate(next.getDate() + 7);
  else if (resetCycle === 'monthly') next.setMonth(next.getMonth() + 1);
  else return null;
  return next;
}

function normalizeTimeHHmm(value) {
  if (typeof value !== 'string') return null;
  const match = value.trim().match(/^(\d{2}):(\d{2})$/);
  if (!match) return null;
  const hours = Number(match[1]);
  const minutes = Number(match[2]);
  if (hours < 0 || hours > 23 || minutes < 0 || minutes > 59) return null;
  return `${String(hours).padStart(2, '0')}:${String(minutes).padStart(2, '0')}`;
}

function toMinutesOfDay(hhmm) {
  const normalized = normalizeTimeHHmm(hhmm);
  if (!normalized) return null;
  const [hours, minutes] = normalized.split(':').map(Number);
  return hours * 60 + minutes;
}

function isCurrentTimeInWindow(startTime, endTime, now = new Date()) {
  const start = toMinutesOfDay(startTime);
  const end = toMinutesOfDay(endTime);
  if (start === null || end === null) return true;

  const nowMinutes = now.getHours() * 60 + now.getMinutes();
  if (start === end) return true;
  if (start < end) return nowMinutes >= start && nowMinutes < end;
  return nowMinutes >= start || nowMinutes < end;
}

module.exports = {
  parseDateTimeValue,
  formatDateTimeForSqlite,
  getDateKeyFromDate,
  getRecentDateKeys,
  getNextDownloadResetTime,
  normalizeTimeHHmm,
  toMinutesOfDay,
  isCurrentTimeInWindow
};