Calendar/src/utils/DateService.ts

/**
 * DateService - Unified date/time service using date-fns
 * Handles all date operations, timezone conversions, and formatting
 */

import {
  format,
  parse,
  addMinutes,
  differenceInMinutes,
  startOfDay,
  endOfDay,
  setHours,
  setMinutes as setMins,
  getHours,
  getMinutes,
  parseISO,
  isValid,
  addDays,
  startOfWeek,
  endOfWeek,
  addWeeks,
  addMonths,
  isSameDay,
  getISOWeek
} from 'date-fns';
import {
  toZonedTime,
  fromZonedTime,
  formatInTimeZone
} from 'date-fns-tz';

export class DateService {
  private timezone: string;
  
  constructor(timezone: string = 'Europe/Copenhagen') {
    this.timezone = timezone;
  }
  
  // ============================================
  // CORE CONVERSIONS
  // ============================================
  
  /**
   * Convert local date to UTC ISO string
   * @param localDate - Date in local timezone
   * @returns ISO string in UTC (with 'Z' suffix)
   */
  public toUTC(localDate: Date): string {
    return fromZonedTime(localDate, this.timezone).toISOString();
  }
  
  /**
   * Convert UTC ISO string to local date
   * @param utcString - ISO string in UTC
   * @returns Date in local timezone
   */
  public fromUTC(utcString: string): Date {
    return toZonedTime(parseISO(utcString), this.timezone);
  }
  
  // ============================================
  // FORMATTING
  // ============================================
  
  /**
   * Format time as HH:mm or HH:mm:ss
   * @param date - Date to format
   * @param showSeconds - Include seconds in output
   * @returns Formatted time string
   */
  public formatTime(date: Date, showSeconds = false): string {
    const pattern = showSeconds ? 'HH:mm:ss' : 'HH:mm';
    return format(date, pattern);
  }
  
  /**
   * Format time range as "HH:mm - HH:mm"
   * @param start - Start date
   * @param end - End date
   * @returns Formatted time range
   */
  public formatTimeRange(start: Date, end: Date): string {
    return `${this.formatTime(start)} - ${this.formatTime(end)}`;
  }
  
  /**
   * Format date and time in technical format: yyyy-MM-dd HH:mm:ss
   * @param date - Date to format
   * @returns Technical datetime string
   */
  public formatTechnicalDateTime(date: Date): string {
    return format(date, 'yyyy-MM-dd HH:mm:ss');
  }
  
  /**
   * Format date as yyyy-MM-dd
   * @param date - Date to format
   * @returns ISO date string
   */
  public formatDate(date: Date): string {
    return format(date, 'yyyy-MM-dd');
  }
  
  /**
   * Format date as ISO string (same as formatDate for compatibility)
   * @param date - Date to format
   * @returns ISO date string
   */
  public formatISODate(date: Date): string {
    return this.formatDate(date);
  }
  
  /**
   * Format time in 12-hour format with AM/PM
   * @param date - Date to format
   * @returns Time string in 12-hour format (e.g., "2:30 PM")
   */
  public formatTime12(date: Date): string {
    const hours = getHours(date);
    const minutes = getMinutes(date);
    const period = hours >= 12 ? 'PM' : 'AM';
    const displayHours = hours % 12 || 12;
    
    return `${displayHours}:${String(minutes).padStart(2, '0')} ${period}`;
  }
  
  /**
   * Get day name for a date
   * @param date - Date to get day name for
   * @param format - 'short' (e.g., 'Mon') or 'long' (e.g., 'Monday')
   * @returns Day name
   */
  public getDayName(date: Date, format: 'short' | 'long' = 'short'): string {
    const formatter = new Intl.DateTimeFormat('en-US', {
      weekday: format
    });
    return formatter.format(date);
  }
  
  /**
   * Format a date range with customizable options
   * @param start - Start date
   * @param end - End date
   * @param options - Formatting options
   * @returns Formatted date range string
   */
  public formatDateRange(
    start: Date,
    end: Date,
    options: {
      locale?: string;
      month?: 'numeric' | '2-digit' | 'long' | 'short' | 'narrow';
      day?: 'numeric' | '2-digit';
      year?: 'numeric' | '2-digit';
    } = {}
  ): string {
    const { locale = 'en-US', month = 'short', day = 'numeric' } = options;
    
    const startYear = start.getFullYear();
    const endYear = end.getFullYear();
    
    const formatter = new Intl.DateTimeFormat(locale, {
      month,
      day,
      year: startYear !== endYear ? 'numeric' : undefined
    });

    // @ts-ignore - formatRange is available in modern browsers
    if (typeof formatter.formatRange === 'function') {
      // @ts-ignore
      return formatter.formatRange(start, end);
    }
    
    return `${formatter.format(start)} - ${formatter.format(end)}`;
  }
  
  // ============================================
  // TIME CALCULATIONS
  // ============================================
  
  /**
   * Convert time string (HH:mm or HH:mm:ss) to total minutes since midnight
   * @param timeString - Time in format HH:mm or HH:mm:ss
   * @returns Total minutes since midnight
   */
  public timeToMinutes(timeString: string): number {
    const parts = timeString.split(':').map(Number);
    const hours = parts[0] || 0;
    const minutes = parts[1] || 0;
    return hours * 60 + minutes;
  }
  
  /**
   * Convert total minutes since midnight to time string HH:mm
   * @param totalMinutes - Minutes since midnight
   * @returns Time string in format HH:mm
   */
  public minutesToTime(totalMinutes: number): string {
    const hours = Math.floor(totalMinutes / 60);
    const minutes = totalMinutes % 60;
    const date = setMins(setHours(new Date(), hours), minutes);
    return format(date, 'HH:mm');
  }
  
  /**
   * Format time from total minutes (alias for minutesToTime)
   * @param totalMinutes - Minutes since midnight
   * @returns Time string in format HH:mm
   */
  public formatTimeFromMinutes(totalMinutes: number): string {
    return this.minutesToTime(totalMinutes);
  }
  
  /**
   * Get minutes since midnight for a given date
   * @param date - Date to calculate from
   * @returns Minutes since midnight
   */
  public getMinutesSinceMidnight(date: Date): number {
    return getHours(date) * 60 + getMinutes(date);
  }
  
  /**
   * Calculate duration in minutes between two dates
   * @param start - Start date or ISO string
   * @param end - End date or ISO string
   * @returns Duration in minutes
   */
  public getDurationMinutes(start: Date | string, end: Date | string): number {
    const startDate = typeof start === 'string' ? parseISO(start) : start;
    const endDate = typeof end === 'string' ? parseISO(end) : end;
    return differenceInMinutes(endDate, startDate);
  }
  
  // ============================================
  // WEEK OPERATIONS
  // ============================================
  
  /**
   * Get start and end of week (Monday to Sunday)
   * @param date - Reference date
   * @returns Object with start and end dates
   */
  public getWeekBounds(date: Date): { start: Date; end: Date } {
    return {
      start: startOfWeek(date, { weekStartsOn: 1 }), // Monday
      end: endOfWeek(date, { weekStartsOn: 1 })      // Sunday
    };
  }
  
  /**
   * Add weeks to a date
   * @param date - Base date
   * @param weeks - Number of weeks to add (can be negative)
   * @returns New date
   */
  public addWeeks(date: Date, weeks: number): Date {
    return addWeeks(date, weeks);
  }

  /**
   * Add months to a date
   * @param date - Base date
   * @param months - Number of months to add (can be negative)
   * @returns New date
   */
  public addMonths(date: Date, months: number): Date {
    return addMonths(date, months);
  }
  
  /**
   * Get ISO week number (1-53)
   * @param date - Date to get week number for
   * @returns ISO week number
   */
  public getWeekNumber(date: Date): number {
    return getISOWeek(date);
  }
  
  /**
   * Get all dates in a full week (7 days starting from given date)
   * @param weekStart - Start date of the week
   * @returns Array of 7 dates
   */
  public getFullWeekDates(weekStart: Date): Date[] {
    const dates: Date[] = [];
    for (let i = 0; i < 7; i++) {
      dates.push(this.addDays(weekStart, i));
    }
    return dates;
  }
  
  /**
   * Get dates for work week using ISO 8601 day numbering (Monday=1, Sunday=7)
   * @param weekStart - Any date in the week
   * @param workDays - Array of ISO day numbers (1=Monday, 7=Sunday)
   * @returns Array of dates for the specified work days
   */
  public getWorkWeekDates(weekStart: Date, workDays: number[]): Date[] {
    const dates: Date[] = [];
    
    // Get Monday of the week
    const weekBounds = this.getWeekBounds(weekStart);
    const mondayOfWeek = this.startOfDay(weekBounds.start);
    
    // Calculate dates for each work day using ISO numbering
    workDays.forEach(isoDay => {
      const date = new Date(mondayOfWeek);
      // ISO day 1=Monday is +0 days, ISO day 7=Sunday is +6 days
      const daysFromMonday = isoDay === 7 ? 6 : isoDay - 1;
      date.setDate(mondayOfWeek.getDate() + daysFromMonday);
      dates.push(date);
    });
    
    return dates;
  }
  
  // ============================================
  // GRID HELPERS
  // ============================================
  
  /**
   * Create a date at a specific time (minutes since midnight)
   * @param baseDate - Base date (date component)
   * @param totalMinutes - Minutes since midnight
   * @returns New date with specified time
   */
  public createDateAtTime(baseDate: Date, totalMinutes: number): Date {
    const hours = Math.floor(totalMinutes / 60);
    const minutes = totalMinutes % 60;
    return setMins(setHours(startOfDay(baseDate), hours), minutes);
  }
  
  /**
   * Snap date to nearest interval
   * @param date - Date to snap
   * @param intervalMinutes - Snap interval in minutes
   * @returns Snapped date
   */
  public snapToInterval(date: Date, intervalMinutes: number): Date {
    const minutes = this.getMinutesSinceMidnight(date);
    const snappedMinutes = Math.round(minutes / intervalMinutes) * intervalMinutes;
    return this.createDateAtTime(date, snappedMinutes);
  }
  
  // ============================================
  // UTILITY METHODS
  // ============================================
  
  /**
   * Check if two dates are the same day
   * @param date1 - First date
   * @param date2 - Second date
   * @returns True if same day
   */
  public isSameDay(date1: Date, date2: Date): boolean {
    return isSameDay(date1, date2);
  }
  
  /**
   * Get start of day
   * @param date - Date
   * @returns Start of day (00:00:00)
   */
  public startOfDay(date: Date): Date {
    return startOfDay(date);
  }
  
  /**
   * Get end of day
   * @param date - Date
   * @returns End of day (23:59:59.999)
   */
  public endOfDay(date: Date): Date {
    return endOfDay(date);
  }
  
  /**
   * Add days to a date
   * @param date - Base date
   * @param days - Number of days to add (can be negative)
   * @returns New date
   */
  public addDays(date: Date, days: number): Date {
    return addDays(date, days);
  }
  
  /**
   * Add minutes to a date
   * @param date - Base date
   * @param minutes - Number of minutes to add (can be negative)
   * @returns New date
   */
  public addMinutes(date: Date, minutes: number): Date {
    return addMinutes(date, minutes);
  }
  
  /**
   * Parse ISO string to date
   * @param isoString - ISO date string
   * @returns Parsed date
   */
  public parseISO(isoString: string): Date {
    return parseISO(isoString);
  }
  
  /**
   * Check if date is valid
   * @param date - Date to check
   * @returns True if valid
   */
  public isValid(date: Date): boolean {
    return isValid(date);
  }
  
  /**
   * Check if event spans multiple days
   * @param start - Start date or ISO string
   * @param end - End date or ISO string
   * @returns True if spans multiple days
   */
  public isMultiDay(start: Date | string, end: Date | string): boolean {
    const startDate = typeof start === 'string' ? this.parseISO(start) : start;
    const endDate = typeof end === 'string' ? this.parseISO(end) : end;
    return !this.isSameDay(startDate, endDate);
  }
}