/*
 * Copyright 2020 Adobe. All rights reserved.
 * This file is licensed to you under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License. You may obtain a copy
 * of the License at http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under
 * the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR REPRESENTATIONS
 * OF ANY KIND, either express or implied. See the License for the specific language
 * governing permissions and limitations under the License.
 */

// Portions of the code in this file are based on code from ICU.
// Original licensing can be found in the NOTICE file in the root directory of this source tree.

import {AnyCalendarDate, Calendar, CalendarIdentifier} from '../types';
import {CalendarDate} from '../CalendarDate';
import {mod, Mutable} from '../utils';

const EPOCH = 1721426; // 001/01/03 Julian C.E.
export function gregorianToJulianDay(era: string, year: number, month: number, day: number): number {
  year = getExtendedYear(era, year);

  let y1 = year - 1;
  let monthOffset = -2;
  if (month <= 2) {
    monthOffset = 0;
  } else if (isLeapYear(year)) {
    monthOffset = -1;
  }

  return (
    EPOCH -
    1 +
    365 * y1 +
    Math.floor(y1 / 4) -
    Math.floor(y1 / 100) +
    Math.floor(y1 / 400) +
    Math.floor((367 * month - 362) / 12 + monthOffset + day)
  );
}

export function isLeapYear(year: number): boolean {
  return year % 4 === 0 && (year % 100 !== 0 || year % 400 === 0);
}

export function getExtendedYear(era: string, year: number): number {
  return era === 'BC' ? 1 - year : year;
}

export function fromExtendedYear(year: number): [string, number] {
  let era = 'AD';
  if (year <= 0) {
    era = 'BC';
    year = 1 - year;
  }

  return [era, year];
}

const daysInMonth = {
  standard: [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31],
  leapyear: [31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]
};

/**
 * The Gregorian calendar is the most commonly used calendar system in the world. It supports two eras: BC, and AD.
 * Years always contain 12 months, and 365 or 366 days depending on whether it is a leap year.
 */
export class GregorianCalendar implements Calendar {
  identifier: CalendarIdentifier = 'gregory';

  fromJulianDay(jd: number): CalendarDate {
    let jd0 = jd;
    let depoch = jd0 - EPOCH;
    let quadricent = Math.floor(depoch / 146097);
    let dqc = mod(depoch, 146097);
    let cent = Math.floor(dqc / 36524);
    let dcent = mod(dqc, 36524);
    let quad = Math.floor(dcent / 1461);
    let dquad = mod(dcent, 1461);
    let yindex = Math.floor(dquad / 365);

    let extendedYear = quadricent * 400 + cent * 100 + quad * 4 + yindex + (cent !== 4 && yindex !== 4 ? 1 : 0);
    let [era, year] = fromExtendedYear(extendedYear);
    let yearDay = jd0 - gregorianToJulianDay(era, year, 1, 1);
    let leapAdj = 2;
    if (jd0 < gregorianToJulianDay(era, year, 3, 1)) {
      leapAdj = 0;
    } else if (isLeapYear(year)) {
      leapAdj = 1;
    }
    let month = Math.floor(((yearDay + leapAdj) * 12 + 373) / 367);
    let day = jd0 - gregorianToJulianDay(era, year, month, 1) + 1;

    return new CalendarDate(era, year, month, day);
  }

  toJulianDay(date: AnyCalendarDate): number {
    return gregorianToJulianDay(date.era, date.year, date.month, date.day);
  }

  getDaysInMonth(date: AnyCalendarDate): number {
    return daysInMonth[isLeapYear(date.year) ? 'leapyear' : 'standard'][date.month - 1];
  }

  // eslint-disable-next-line @typescript-eslint/no-unused-vars
  getMonthsInYear(date: AnyCalendarDate): number {
    return 12;
  }

  getDaysInYear(date: AnyCalendarDate): number {
    return isLeapYear(date.year) ? 366 : 365;
  }

  // eslint-disable-next-line @typescript-eslint/no-unused-vars
  getYearsInEra(date: AnyCalendarDate): number {
    return 9999;
  }

  getEras(): string[] {
    return ['BC', 'AD'];
  }

  isInverseEra(date: AnyCalendarDate): boolean {
    return date.era === 'BC';
  }

  balanceDate(date: Mutable<AnyCalendarDate>): void {
    if (date.year <= 0) {
      date.era = date.era === 'BC' ? 'AD' : 'BC';
      date.year = 1 - date.year;
    }
  }
}