DHBW-RaPla-Vorratsdatenspeicherung/Frontend/src/app/components/datepicker/datepicker.component.ts

import {Component, EventEmitter, OnInit, Output} from '@angular/core';

@Component({
    selector: 'app-datepicker',
    templateUrl: './datepicker.component.html',
    styleUrls: ['./datepicker.component.css']
})
export class DatepickerComponent implements OnInit {
    selectedYear: string = '';
    selectedMonth: string = '';
    selectedDay: string = '';

    years: string[] = [];
    months: string[] = [];
    days: string[] = [];

    itIsWednesday: boolean = false;

    @Output() selectedMonday = new EventEmitter<string>();

    constructor() {
    }

    ngOnInit(): void {
        this.fillDatePickers();
        this.handleDateChange();
    }

    /**
     * Fills all the date pickers and sets the itIsWednesday variable
     */
    fillDatePickers(): void {
        let currentDate = new Date();

        if (currentDate.getDay() === 3) {
            this.itIsWednesday = true;
        }

        this.fillYearPicker();
        this.fillMonthPicker();
        this.fillDayPicker();
    }

    /**
     * Fills the "year" picker with the appropriate values and pre-selects the current year
     */
    fillYearPicker(): void {
        this.years = [];
        let currentDate = new Date();
        let currentYear = currentDate.getFullYear().toString();

        this.years = [
            '2020',
            '2021',
            '2022'
        ];
        this.selectedYear = currentYear;
    }

    /**
     * Fills the "month" picker with the appropriate values and pre-selects the current month
     */
    fillMonthPicker(): void {
        this.months = [];
        let currentDate = new Date();
        let currentMonth = (currentDate.getMonth() + 1).toString().padStart(2, '0');

        for (let month = 1; month <= 12; month++) {
            let monthString = month.toString().padStart(2, '0');
            this.months.push(monthString);
        }
        this.selectedMonth = currentMonth;
    }

    /**
     * Fills the "day" picker with the appropriate values and pre-selects the current day if possible
     */
    fillDayPicker(): void {
        this.days = [];
        let currentDate = new Date();
        let currentDay = currentDate.getDate().toString().padStart(2, '0');

        let maxDays = 31;
        if (this.selectedMonth !== '') {
            maxDays = this.getDaysInGivenMonth(parseInt(this.selectedYear), parseInt(this.selectedMonth));
        } else {
            maxDays = 31;
        }

        for (let day = 1; day <= maxDays; day++) {
            let dayString = day.toString().padStart(2, '0');
            this.days.push(dayString);
        }
        this.selectedDay = parseInt(currentDay) < maxDays ? currentDay : maxDays.toString().padStart(2, '0');
    }

    /**
     * Handles the change of the "year" picker
     */
    handleYearChange(): void {
        this.fillDayPicker();
        this.handleDateChange();
    }

    /**
     * Handles the change of the "month" picker
     */
    handleMonthChange(): void {
        this.fillDayPicker();
        this.handleDateChange();
    }

    /**
     * Handles a change of the "day" picker
     */
    handleDayChange(): void {
        this.handleDateChange();
    }

    /**
     * Handles changed date selections and fills the selectedMonday variable
     */
    handleDateChange(): void {
        let mondayDate = this.findMondayInWeek(this.selectedYear, this.selectedMonth, this.selectedDay);
        this.selectedMonday.emit(mondayDate);
    }

    /**
     * Calculates the date of the monday in the week for any given date.
     * If you e.g. enter 2021, 09, 30 the result will be 2021-09-27
     * @param year The year
     * @param month The month
     * @param day The day
     */
    findMondayInWeek(year: string, month: string, day: string): string {
        let selectedDate = new Date(parseInt(year), parseInt(month) - 1, parseInt(day));
        let mondayInWeekDate = selectedDate;

        let selectedDayInWeek = selectedDate.getDay();

        // Sunday is 0 and Monday is 1, hence we want to substract until we land at 1.
        // Sunday is the exeption as we need to go to 1 in the "previous" week
        if (selectedDayInWeek === 0) {
            mondayInWeekDate.setDate(selectedDate.getDate() - 6);
        } else {
            let difference = selectedDayInWeek - 1;
            mondayInWeekDate.setDate(selectedDate.getDate() - difference);
        }

        let yearString = mondayInWeekDate.getFullYear();
        let monthString = (mondayInWeekDate.getMonth() + 1).toString().padStart(2, '0');
        let dayString = mondayInWeekDate.getDate().toString().padStart(2, '0');

        return yearString + '-' + monthString + '-' + dayString;
    }

    /**
     * Returns the number of days in the given month
     * @param year The year
     * @param month The month for which to return the number of days for
     */
    getDaysInGivenMonth(year: number, month: number) {
        return new Date(year, month, 0).getDate();
    }

}