/**
 * Date formatting utilities for consistent display across the app.
 * Works in all JavaScript environments (browser, Node.js, Bun, etc.)
 */

type DateInput = string | Date;

/**
 * Safely convert a date input to a Date object.
 */
function toDate(date: DateInput): Date {
  return typeof date === "string" ? new Date(date) : date;
}

/**
 * Calculate the difference in days between two dates.
 */
function daysDiff(from: Date, to: Date): number {
  const diffMs = to.getTime() - from.getTime();
  return Math.floor(diffMs / (1000 * 60 * 60 * 24));
}

/**
 * Format a date for display in tables and lists.
 * @example formatDate("2024-01-15") // "Jan 15, 2024"
 */
export function formatDate(date: DateInput): string {
  const d = toDate(date);
  return d.toLocaleDateString("en-US", {
    month: "short",
    day: "numeric",
    year: "numeric",
  });
}

/**
 * Format a date with time for detailed views.
 * @example formatDateTime("2024-01-15T15:30:00") // "Jan 15, 2024, 3:30 PM"
 */
export function formatDateTime(date: DateInput): string {
  const d = toDate(date);
  return d.toLocaleDateString("en-US", {
    month: "short",
    day: "numeric",
    year: "numeric",
    hour: "numeric",
    minute: "2-digit",
  });
}

/**
 * Format a date in long form.
 * @example formatLongDate("2024-01-15") // "January 15, 2024"
 */
export function formatLongDate(date: DateInput): string {
  const d = toDate(date);
  return d.toLocaleDateString("en-US", {
    month: "long",
    day: "numeric",
    year: "numeric",
  });
}

/**
 * Options for relative date formatting.
 */
export interface FormatRelativeDateOptions {
  /**
   * Reference date to compare against. Defaults to current date.
   */
  now?: Date;
}

/**
 * Format a date as a relative time string.
 * @example
 * formatRelativeDate("2024-01-15") // "Today" (if today is Jan 15)
 * formatRelativeDate("2024-01-14") // "Yesterday" (if today is Jan 15)
 * formatRelativeDate("2024-01-10") // "5 days ago" (if today is Jan 15)
 * formatRelativeDate("2024-01-01") // "2 weeks ago" (if today is Jan 15)
 * formatRelativeDate("2023-06-15") // "Jun 15, 2023" (older dates)
 */
export function formatRelativeDate(
  date: DateInput,
  options?: FormatRelativeDateOptions,
): string {
  const d = toDate(date);
  const now = options?.now ?? new Date();
  const diffDays = daysDiff(d, now);

  if (diffDays === 0) {
    return "Today";
  }
  if (diffDays === 1) {
    return "Yesterday";
  }
  if (diffDays < 7) {
    return `${diffDays.toLocaleString()} days ago`;
  }
  if (diffDays < 30) {
    const weeks = Math.floor(diffDays / 7);
    return weeks === 1 ? "1 week ago" : `${weeks.toLocaleString()} weeks ago`;
  }

  // For older dates, show the actual date
  return d.toLocaleDateString("en-US", {
    month: "short",
    day: "numeric",
    year: d.getFullYear() !== now.getFullYear() ? "numeric" : undefined,
  });
}

/**
 * Format a date as a relative time string, with "Never" for null values.
 * Useful for displaying "last used" timestamps.
 * @example
 * formatRelativeTime("2024-01-15") // "Today"
 * formatRelativeTime(null) // "Never"
 */
export function formatRelativeTime(
  date: DateInput | null | undefined,
  options?: FormatRelativeDateOptions,
): string {
  if (date === null || date === undefined) {
    return "Never";
  }
  return formatRelativeDate(date, options);
}