Calendar/src/utils/TimeFormatter.ts

/**
 * TimeFormatter - Centralized time formatting with timezone support
 * 
 * Handles conversion from UTC/Zulu time to configured timezone (default: Europe/Copenhagen)
 * Supports both 12-hour and 24-hour format configuration
 * 
 * All events in the system are stored in UTC and must be converted to local timezone
 */

export interface TimeFormatSettings {
  timezone: string;
  use24HourFormat: boolean;
  locale: string;
  dateFormat: 'locale' | 'technical';
  showSeconds: boolean;
}

export class TimeFormatter {
  private static settings: TimeFormatSettings = {
    timezone: 'Europe/Copenhagen',  // Default to Denmark
    use24HourFormat: true,          // 24-hour format standard in Denmark
    locale: 'da-DK',                // Danish locale
    dateFormat: 'technical',        // Use technical format yyyy-mm-dd hh:mm:ss
    showSeconds: false              // Don't show seconds by default
  };

  /**
   * Configure time formatting settings
   */
  static configure(settings: Partial<TimeFormatSettings>): void {
    TimeFormatter.settings = { ...TimeFormatter.settings, ...settings };
  }

  /**
   * Get current time format settings
   */
  static getSettings(): TimeFormatSettings {
    return { ...TimeFormatter.settings };
  }

  /**
   * Convert UTC date to configured timezone
   * @param utcDate - Date in UTC (or assumed to be UTC)
   * @returns Date object adjusted to configured timezone
   */
  static convertToLocalTime(utcDate: Date): Date {
    // Create a new date to avoid mutating the original
    const localDate = new Date(utcDate);
    
    // If the date doesn't have timezone info, treat it as UTC
    // This handles cases where mock data doesn't have 'Z' suffix
    if (!utcDate.toISOString().endsWith('Z') && utcDate.getTimezoneOffset() === new Date().getTimezoneOffset()) {
      // Adjust for the fact that we're treating local time as UTC
      localDate.setMinutes(localDate.getMinutes() + localDate.getTimezoneOffset());
    }
    
    return localDate;
  }

  /**
   * Get timezone offset for configured timezone
   * @param date - Reference date for calculating offset (handles DST)
   * @returns Offset in minutes
   */
  static getTimezoneOffset(date: Date = new Date()): number {
    const utc = new Date(date.getTime() + (date.getTimezoneOffset() * 60000));
    const targetTime = new Date(utc.toLocaleString('en-US', { timeZone: TimeFormatter.settings.timezone }));
    return (targetTime.getTime() - utc.getTime()) / 60000;
  }

  /**
   * Format time in 12-hour format
   * @param date - Date to format
   * @returns Formatted time string (e.g., "9:00 AM")
   */
  static format12Hour(date: Date): string {
    const localDate = TimeFormatter.convertToLocalTime(date);
    
    return localDate.toLocaleTimeString(TimeFormatter.settings.locale, {
      timeZone: TimeFormatter.settings.timezone,
      hour: 'numeric',
      minute: '2-digit',
      hour12: true
    });
  }

  /**
   * Format time in 24-hour format
   * @param date - Date to format
   * @returns Formatted time string (e.g., "09:00")
   */
  static format24Hour(date: Date): string {
    const localDate = TimeFormatter.convertToLocalTime(date);
    
    // Always use colon separator, not locale-specific formatting
    let hours = String(localDate.getHours()).padStart(2, '0');
    let minutes = String(localDate.getMinutes()).padStart(2, '0');
    return `${hours}:${minutes}`;
  }

  /**
   * Format time according to current configuration
   * @param date - Date to format
   * @returns Formatted time string
   */
  static formatTime(date: Date): string {
    return TimeFormatter.settings.use24HourFormat 
      ? TimeFormatter.format24Hour(date)
      : TimeFormatter.format12Hour(date);
  }

  /**
   * Format time from total minutes since midnight
   * @param totalMinutes - Minutes since midnight (e.g., 540 for 9:00 AM)
   * @returns Formatted time string
   */
  static formatTimeFromMinutes(totalMinutes: number): string {
    const hours = Math.floor(totalMinutes / 60) % 24;
    const minutes = totalMinutes % 60;
    
    // Create a date object for today with the specified time
    const date = new Date();
    date.setHours(hours, minutes, 0, 0);
    
    return TimeFormatter.formatTime(date);
  }

  /**
   * Format date and time together
   * @param date - Date to format
   * @returns Formatted date and time string
   */
  static formatDateTime(date: Date): string {
    const localDate = TimeFormatter.convertToLocalTime(date);
    
    const dateStr = localDate.toLocaleDateString(TimeFormatter.settings.locale, {
      timeZone: TimeFormatter.settings.timezone,
      year: 'numeric',
      month: '2-digit',
      day: '2-digit'
    });
    
    const timeStr = TimeFormatter.formatTime(date);
    
    return `${dateStr} ${timeStr}`;
  }

  /**
   * Format time range (start - end)
   * @param startDate - Start date
   * @param endDate - End date
   * @returns Formatted time range string (e.g., "09:00 - 10:30")
   */
  static formatTimeRange(startDate: Date, endDate: Date): string {
    const startTime = TimeFormatter.formatTime(startDate);
    const endTime = TimeFormatter.formatTime(endDate);
    return `${startTime} - ${endTime}`;
  }

  /**
   * Check if current timezone observes daylight saving time
   * @param date - Reference date
   * @returns True if DST is active
   */
  static isDaylightSavingTime(date: Date = new Date()): boolean {
    const january = new Date(date.getFullYear(), 0, 1);
    const july = new Date(date.getFullYear(), 6, 1);
    
    const janOffset = TimeFormatter.getTimezoneOffset(january);
    const julOffset = TimeFormatter.getTimezoneOffset(july);
    
    return Math.max(janOffset, julOffset) !== TimeFormatter.getTimezoneOffset(date);
  }

  /**
   * Get timezone abbreviation (e.g., "CET", "CEST")
   * @param date - Reference date
   * @returns Timezone abbreviation
   */
  static getTimezoneAbbreviation(date: Date = new Date()): string {
    const localDate = TimeFormatter.convertToLocalTime(date);
    
    return localDate.toLocaleTimeString('en-US', {
      timeZone: TimeFormatter.settings.timezone,
      timeZoneName: 'short'
    }).split(' ').pop() || '';
  }

  /**
   * Format date in technical format: yyyy-mm-dd
   */
  static formatDateTechnical(date: Date): string {
    let year = date.getFullYear();
    let month = String(date.getMonth() + 1).padStart(2, '0');
    let day = String(date.getDate()).padStart(2, '0');
    return `${year}-${month}-${day}`;
  }

  /**
   * Format time in technical format: hh:mm or hh:mm:ss
   */
  static formatTimeTechnical(date: Date, includeSeconds: boolean = false): string {
    let hours = String(date.getHours()).padStart(2, '0');
    let minutes = String(date.getMinutes()).padStart(2, '0');
    
    if (includeSeconds) {
      let seconds = String(date.getSeconds()).padStart(2, '0');
      return `${hours}:${minutes}:${seconds}`;
    }
    return `${hours}:${minutes}`;
  }

  /**
   * Format date and time in technical format: yyyy-mm-dd hh:mm:ss
   */
  static formatDateTimeTechnical(date: Date): string {
    let localDate = TimeFormatter.convertToLocalTime(date);
    let dateStr = TimeFormatter.formatDateTechnical(localDate);
    let timeStr = TimeFormatter.formatTimeTechnical(localDate, TimeFormatter.settings.showSeconds);
    return `${dateStr} ${timeStr}`;
  }

}