///
/// Copyright 2015-2026 Micro Focus or one of its affiliates.
///
/// Licensed 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 CONDITIONS OF ANY KIND, either express or implied.
/// See the License for the specific language governing permissions and
/// limitations under the License.
///

import { WeekDay } from '@angular/common';
import { inject, Injectable, OnDestroy } from '@angular/core';
import { BehaviorSubject, combineLatest, Subscription } from 'rxjs';
import { DateTimePickerService, ModeDirection } from '../date-time-picker.service';
import { compareDays, dateRange, gridify } from '../date-time-picker.utils';

@Injectable()
export class DayViewService implements OnDestroy {
  private readonly _datepicker = inject(DateTimePickerService);

  grid$ = new BehaviorSubject<DayViewItem[][]>([[]]);
  focused$ = new BehaviorSubject<FocusedDayItem>(null);

  private readonly _subscription: Subscription;

  constructor() {
    this._subscription = combineLatest(
      this._datepicker.month$,
      this._datepicker.year$,
      this._datepicker.startOfWeek$
    ).subscribe(([month, year]) => this.createDayGrid(month, year));
  }

  ngOnDestroy(): void {
    this._subscription.unsubscribe();
  }

  setFocus(day: number, month: number, year: number): void {
    this.focused$.next({ day, month, year });

    // update the date picker to show the required month and year
    this._datepicker.setViewportMonth(month);
    this._datepicker.setViewportYear(year);
  }

  private createDayGrid(month: number, year: number): void {
    // update the header
    this._datepicker.setHeader(this._datepicker.months[month] + ' ' + year);

    // find the lower and upper boundaries
    const start = new Date(year, month, 1);
    const end = new Date(year, month + 1, 0);

    // ensure the startOfWeek value is between 0-6 to prevent any infinite loop
    const startOfWeek = Math.min(
      WeekDay.Saturday,
      Math.max(WeekDay.Sunday, this._datepicker.startOfWeek$.value)
    );

    // we always want to show from the specified start of week - this may include showing some dates from the previous month
    while (start.getDay() !== startOfWeek) {
      start.setDate(start.getDate() - 1);
    }

    // we also want to make sure that the range ends on a saturday
    end.setDate(end.getDate() + (6 - end.getDay()));

    // create an array of all the days to display
    const dates: DayViewItem[] = dateRange(start, end).map(date => ({
      day: date.getDate(),
      month: date.getMonth(),
      year: date.getFullYear(),
      date,
      isToday: this.isToday(date),
      isActive: this.isActive(date),
      isCurrentMonth: date.getMonth() === month,
    }));

    // turn the dates into a grid
    const items: DayViewItem[][] = gridify(dates, 7);

    this.grid$.next(items);

    // if no item has yet been focused then focus the first day of the month
    if (
      (this._datepicker.modeDirection === ModeDirection.None ||
        this._datepicker.modeDirection === ModeDirection.Descend) &&
      this.focused$.value === null
    ) {
      // check if the selected item is visible
      const selectedDay = dates.find(day => day.isCurrentMonth && day.isActive);

      if (selectedDay) {
        this.setFocus(selectedDay.day, selectedDay.month, selectedDay.year);
      } else {
        // find the first day of the month
        const first = dates.find(date => date.day === 1);

        // focus the date
        this.setFocus(first.day, first.month, first.year);
      }
    }
  }

  /**
   * Determine whether or not a specific date is today
   * @param date The date to check
   */
  private isToday(date: Date): boolean {
    return compareDays(new Date(), date);
  }

  /**
   * Determines whether or not a specific date is the selected one
   * @param date the date to check
   */
  private isActive(date: Date): boolean {
    return this._datepicker.selected$.value
      ? compareDays(this._datepicker.selected$.value, date)
      : false;
  }
}

export interface DayViewItem {
  day: number;
  month: number;
  year: number;
  date: Date;
  isToday: boolean;
  isActive: boolean;
  isCurrentMonth: boolean;
}

export interface FocusedDayItem {
  day: number;
  month: number;
  year: number;
}