fairnesscoop / permacoop

import {

  format as fnsFormat,

  isWeekend as fnsIsWeekend,

  getDaysInMonth as fnsGetDaysInMonth,

  eachDayOfInterval,

  addDays

} from 'date-fns';

import { MonthDate } from 'src/Application/Common/MonthDate';

import { IDateUtils } from 'src/Application/IDateUtils';

@Injectable()

export class DateUtilsAdapter implements IDateUtils {

  private makeDate(year: number, month: number, day: number): Date {

    /**

     * This creates a date in UTC timezone.

     *

     * The intent is to remedy possible timezone issues.

     *

     * Indeed, you might be tempted to write code like this:

     *

     * ```js

     * const d = new Date(year, month, day);

     * ```

     *

     * Sadly, this is wrong.

     *

     * Indeed, if your computer's (or the server's) timezone is not UTC, then

     * the actual `day` stored in `d` might be different.

     *

     * For example, if your computer is on UTC+1 (Paris time), then..

     *

     * ```js

     * > new Date(2022, 11, 14).toISOString() // Dec 14th, 2022

     * 2022-12-13T23:00:00.000Z // Oops, it was stored as Dec 13th!

     * ```

     *

     * (Yes, timezones are a bit of a pain.)

     *

     * To remedy this, we create a date from an ISO date string (yyyy-mm-dd),

     * with leading zero padding and all that.

     *

     * JavaScript's `Date()` will properly interpret this as an UTC-timezoned date.

     */

    const fMonth = String(month).padStart(2, '0');

    const fDay = String(day).padStart(2, '0');

    return new Date(`${year}-${fMonth}-${fDay}`);

  }

  public format(date: Date, format: string): string {

    return fnsFormat(date, format);

  }

  public getDaysInMonth(date: Date): number {

    return fnsGetDaysInMonth(date);

  }

  public isWeekend(date: Date): boolean {

    return fnsIsWeekend(date);

  }

  public isAWorkingDay(date: Date): boolean {

    if (this.isWeekend(date)) {

      return false;

    }

    const workedFreeDays = this.getWorkedFreeDays(this.getYear(date));

    const formatedDate = this.format(date, 'yyyy-MM-dd');

    for (const day of workedFreeDays) {

      const formatedDay = this.format(day, 'yyyy-MM-dd');

      if (formatedDate === formatedDay) {

        return false;

      }

    }

    return true;

  }

  public getCurrentDate(): Date {

    return new Date();

  }

  public getYear(date: Date): number {

    return date.getUTCFullYear();

  }

  public getLastDayOfYear(date: Date): Date {

    return this.makeDate(this.getYear(date), 12, 31);

  }

  public getFirstDayOfYear(date: Date): Date {

    return this.makeDate(this.getYear(date), 1, 1);

  }

  public getCurrentDateToISOString(): string {

    return this.getCurrentDate().toISOString();

  }

  public addDaysToDate(date: Date, days: number): Date {

    return addDays(date, days);

  }

  public getWorkedDaysDuringAPeriod(start: Date, end: Date): Date[] {

    const dates: Date[] = [];

    const workedFreeDays: Date[] = [];

    for (let year = this.getYear(start); year <= this.getYear(end); year++) {

      workedFreeDays.push(...this.getWorkedFreeDays(year));

    }

    for (let day of eachDayOfInterval({ start, end })) {

      // date-fns returns local-timezone dates. Be sure to convert to

      // UTC-timezoned dates for ISO string comparison with work-free days.

      day = new Date(this.format(day, 'yyyy-MM-dd'));

      if (

        this.isWeekend(day) ||

        workedFreeDays.filter(d => d.toISOString() === day.toISOString())

          .length > 0

      ) {

        continue;

      }

      dates.push(day);

    }

    return dates;

  }

  public getWorkedFreeDays(year: number): Date[] {

    const fixedDays: Date[] = [

      this.makeDate(year, 1, 1), // New Year's Day

      this.makeDate(year, 5, 1), // Labour Day

      this.makeDate(year, 5, 8), // Victory in 1945

      this.makeDate(year, 7, 14), // National Day

      this.makeDate(year, 8, 15), // Assumption

      this.makeDate(year, 11, 1), // All Saints' Day

      this.makeDate(year, 11, 11), // The Armistice

      this.makeDate(year, 12, 25) // Christmas

    ];

    const easterDate = this.getEasterDate(year);

    const easterDays: Date[] = [

      addDays(easterDate, 1), // Easter Monday

      addDays(easterDate, 39) // Ascension

    ];

    return [...fixedDays, ...easterDays];

  }

  public getEasterDate(year: number): Date {

    const a = year % 19;

    const b = Math.floor(year / 100);

    const c = year % 100;

    const d = Math.floor(b / 4);

    const e = b % 4;

    const f = Math.floor((b + 8) / 25);

    const g = Math.floor((b - f + 1) / 3);

    const h = (19 * a + b - d - g + 15) % 30;

    const i = Math.floor(c / 4);

    const k = c % 4;

    const l = (32 + 2 * e + 2 * i - h - k) % 7;

    const m = Math.floor((a + 11 * h + 22 * l) / 451);

    const n0 = h + l + 7 * m + 114;

    const n = Math.floor(n0 / 31);

    const p = (n0 % 31) + 1;

    return this.makeDate(year, n, p);

  }

  public getLeaveDuration(

    startDate: string,

    isStartsAllDay: boolean,

    endDate: string,

    isEndsAllDay: boolean

  ): number {

    let duration = this.getWorkedDaysDuringAPeriod(

      new Date(startDate),

      new Date(endDate)

    ).length;

    if (false === isStartsAllDay) {

      duration -= 0.5;

    }

    if (false === isEndsAllDay && duration > 0.5) {

      duration -= 0.5;

    }

    return duration;

  }

}