/**
 * DateRange Value Object
 *
 * Represents a validated date range with start and end dates.
 * Value objects are immutable and enforce validation rules.
 *
 * Domain invariants enforced:
 * - Start date must be before or equal to end date
 * - Both dates must be valid
 *
 * @layer Domain
 */

/**
 * DateRange Value Object
 *
 * Immutable representation of a date range.
 */
export class DateRange {
  private readonly startDate: Date;
  private readonly endDate: Date;

  private constructor(startDate: Date, endDate: Date) {
    this.startDate = new Date(startDate);
    this.endDate = new Date(endDate);
    this.validate();
  }

  /**
   * Creates a new DateRange instance
   *
   * @param startDate - Range start date
   * @param endDate - Range end date
   * @returns DateRange value object
   * @throws Error if range is invalid
   */
  static create(startDate: Date | string, endDate: Date | string): DateRange {
    const start = typeof startDate === 'string' ? new Date(startDate) : startDate;
    const end = typeof endDate === 'string' ? new Date(endDate) : endDate;

    return new DateRange(start, end);
  }

  /**
   * Creates a DateRange for the last N days
   *
   * @param days - Number of days
   * @returns DateRange value object
   */
  static lastNDays(days: number): DateRange {
    const endDate = new Date();
    const startDate = new Date();
    startDate.setDate(startDate.getDate() - days);

    return new DateRange(startDate, endDate);
  }

  /**
   * Creates a DateRange for the last N months
   *
   * @param months - Number of months
   * @returns DateRange value object
   */
  static lastNMonths(months: number): DateRange {
    const endDate = new Date();
    const startDate = new Date();
    startDate.setMonth(startDate.getMonth() - months);

    return new DateRange(startDate, endDate);
  }

  /**
   * Creates a DateRange for this month
   *
   * @returns DateRange value object
   */
  static thisMonth(): DateRange {
    const now = new Date();
    const startDate = new Date(now.getFullYear(), now.getMonth(), 1);
    const endDate = new Date(now.getFullYear(), now.getMonth() + 1, 0);

    return new DateRange(startDate, endDate);
  }

  /**
   * Creates a DateRange for this year
   *
   * @returns DateRange value object
   */
  static thisYear(): DateRange {
    const now = new Date();
    const startDate = new Date(now.getFullYear(), 0, 1);
    const endDate = new Date(now.getFullYear(), 11, 31);

    return new DateRange(startDate, endDate);
  }

  /**
   * Validates date range
   *
   * @throws Error if range is invalid
   */
  private validate(): void {
    if (isNaN(this.startDate.getTime())) {
      throw new Error('Invalid start date');
    }

    if (isNaN(this.endDate.getTime())) {
      throw new Error('Invalid end date');
    }

    if (this.startDate > this.endDate) {
      throw new Error('Start date must be before or equal to end date');
    }
  }

  /**
   * Gets start date
   *
   * @returns Start date (copy)
   */
  getStartDate(): Date {
    return new Date(this.startDate);
  }

  /**
   * Gets end date
   *
   * @returns End date (copy)
   */
  getEndDate(): Date {
    return new Date(this.endDate);
  }

  /**
   * Gets duration in milliseconds
   *
   * @returns Duration in milliseconds
   */
  getDurationMs(): number {
    return this.endDate.getTime() - this.startDate.getTime();
  }

  /**
   * Gets duration in days
   *
   * @returns Duration in days (rounded)
   */
  getDurationDays(): number {
    return Math.ceil(this.getDurationMs() / (1000 * 60 * 60 * 24));
  }

  /**
   * Checks if a date is within this range
   *
   * @param date - Date to check
   * @returns true if date is within range (inclusive)
   */
  contains(date: Date): boolean {
    return date >= this.startDate && date <= this.endDate;
  }

  /**
   * Checks if this range overlaps with another range
   *
   * @param other - DateRange to check
   * @returns true if ranges overlap
   */
  overlaps(other: DateRange): boolean {
    return this.startDate <= other.endDate && this.endDate >= other.startDate;
  }

  /**
   * Checks if this range is completely within another range
   *
   * @param other - DateRange to check
   * @returns true if this range is within other
   */
  isWithin(other: DateRange): boolean {
    return this.startDate >= other.startDate && this.endDate <= other.endDate;
  }

  /**
   * Extends range by adding days
   *
   * @param days - Number of days to add to end date
   * @returns New DateRange with extended end date
   */
  extend(days: number): DateRange {
    const newEndDate = new Date(this.endDate);
    newEndDate.setDate(newEndDate.getDate() + days);

    return new DateRange(this.startDate, newEndDate);
  }

  /**
   * Shifts range forward or backward by days
   *
   * @param days - Number of days to shift (positive = forward, negative = backward)
   * @returns New DateRange shifted by days
   */
  shift(days: number): DateRange {
    const newStartDate = new Date(this.startDate);
    newStartDate.setDate(newStartDate.getDate() + days);

    const newEndDate = new Date(this.endDate);
    newEndDate.setDate(newEndDate.getDate() + days);

    return new DateRange(newStartDate, newEndDate);
  }

  /**
   * Checks equality with another DateRange
   *
   * @param other - DateRange to compare
   * @returns true if ranges are equal
   */
  equals(other: DateRange): boolean {
    return (
      this.startDate.getTime() === other.startDate.getTime() &&
      this.endDate.getTime() === other.endDate.getTime()
    );
  }

  /**
   * Converts to string representation
   *
   * @returns String representation of date range
   */
  toString(): string {
    return `${this.startDate.toISOString()} - ${this.endDate.toISOString()}`;
  }

  /**
   * Converts to JSON
   *
   * @returns Object with start and end dates
   */
  toJSON(): { startDate: string; endDate: string } {
    return {
      startDate: this.startDate.toISOString(),
      endDate: this.endDate.toISOString(),
    };
  }
}