import cronParser from 'cron-parser';

export const cronToBackend = (expression: string) =>
  convertCronTz(expression, new Date().getTimezoneOffset()).replaceAll('L', '$');

export const cronFromBackend = (expression: string) =>
  convertCronTz(expression.replaceAll('$', 'L'), -new Date().getTimezoneOffset());

const convertCronTz = (cronExpression: string, timeZoneOffset: number): string => {
  const interval = cronParser.parseExpression(cronExpression);

  if (timeZoneOffset === 0) {
    return cronExpression;
  }

  const c = getDaysHoursMinutes(
    interval.fields.hour[0]!,
    interval.fields.minute[0]!,
    timeZoneOffset,
  );
  const cronExpressionFields = getFieldsCron(cronExpression);

  // Minute
  cronExpressionFields.minute = addMinutes(cronExpressionFields.minute, c.minutes);

  // Hour
  cronExpressionFields.hour = addHours(cronExpressionFields.hour, c.hours);

  // Month
  if (
    (cronExpressionFields.dayOfMonth.indexOf(1) >= 0 && c.days === -1) ||
    (cronExpressionFields.dayOfMonth.indexOf(31) >= 0 && c.days === 1)
  ) {
    cronExpressionFields.month = addMonth(cronExpressionFields.month, c.days);
  }

  // Day of month
  cronExpressionFields.dayOfMonth = addDayOfMonth(cronExpressionFields.dayOfMonth, c.days);

  // Day of week
  cronExpressionFields.dayOfWeek = addDayOfWeek(cronExpressionFields.dayOfWeek, c.days);
  try {
    return setFieldsCron(cronExpressionFields);
  } catch (err: any) {
    if (err.message.includes('Invalid explicit day of month definition')) {
      cronExpressionFields.dayOfMonth = [1];
      cronExpressionFields.month = addMonth(cronExpressionFields.month, 1);
      return setFieldsCron(cronExpressionFields);
    }
    return cronExpression;
  }
};

const getDaysHoursMinutes = (hour: number, minute: number, timeZoneOffset: number) => {
  const minutes = hour * 60 + minute;
  const newMinutes = minutes + timeZoneOffset;
  const diffHour = (Math.floor(newMinutes / 60) % 24) - hour;
  const diffMinutes = (newMinutes % 60) - minute;
  const diffDays = Math.floor(newMinutes / (60 * 24));

  return { hours: diffHour, minutes: diffMinutes, days: diffDays };
};

const getFieldsCron = (expression: string): any => {
  const interval = cronParser.parseExpression(expression);
  return JSON.parse(JSON.stringify(interval.fields));
};

const setFieldsCron = (fields: any): string => cronParser.fieldsToExpression(fields).stringify();

const addHours = (hours: number[], hour: number) =>
  hours.map((n) => {
    const h = n + hour;
    if (h > 23) {
      return h - 24;
    }
    if (h < 0) {
      return h + 24;
    }
    return h;
  });

const addMinutes = (minutes: number[], minute: number) =>
  minutes.map((n) => {
    const m = n + minute;
    if (m > 59) {
      return m - 60;
    }
    if (m < 0) {
      return m + 60;
    }
    return m;
  });

const addDayOfMonth = (dayOfMonth: any[], day: number) => {
  if (dayOfMonth.length > 30) {
    return dayOfMonth;
  }
  return dayOfMonth.map((n) => {
    const d = n + day;
    if (d > 31 || n === 'L') {
      return 1;
    }
    if (d < 1) {
      return 'L';
    }
    return d;
  });
};

const addDayOfWeek = (dayOfWeek: any[], day: number) => {
  if (dayOfWeek.length > 6) {
    return dayOfWeek;
  }
  return dayOfWeek.map((n) => {
    const d = n + day;
    if (d > 6) {
      return 0;
    }
    if (d < 0) {
      return 6;
    }
    return d;
  });
};

const addMonth = (month: any[], mon: number) => {
  if (month.length > 11) {
    return month;
  }
  return month.map((n) => {
    const m = n + mon;
    if (m > 12) {
      return 1;
    }
    if (m < 1) {
      return 12;
    }
    return m;
  });
};

/**
 * Extracts the template expense ID from a pg_cron job command.
 * The command format is: SELECT duplicate_expense_with_participants('UUID'::UUID);
 */
export const extractTemplateExpenseId = (command: string): string | null => {
  const match = /duplicate_expense_with_participants\('([0-9a-f-]{36})'::UUID\)/i.exec(command);
  return match?.[1] ?? null;
};