Assist_Design/packages/domain/toolkit/formatting/date.ts

/**
 * Toolkit - Date Formatting
 *
 * Utilities for formatting dates and times.
 */

export type DateFormatStyle = "short" | "medium" | "long" | "full";

export interface DateFormatOptions {
  locale?: string;
  dateStyle?: DateFormatStyle;
  timeStyle?: DateFormatStyle;
  includeTime?: boolean;
  timezone?: string;
}

/**
 * Format an ISO date string for display
 */
export function formatDate(isoString: string, options: DateFormatOptions = {}): string {
  const {
    locale = "en-US",
    dateStyle = "medium",
    timeStyle = "short",
    includeTime = false,
    timezone,
  } = options;

  try {
    const date = new Date(isoString);

    if (isNaN(date.getTime())) {
      return isoString; // Return original if invalid
    }

    const formatOptions: Intl.DateTimeFormatOptions = {
      dateStyle,
      ...(includeTime && { timeStyle }),
      ...(timezone && { timeZone: timezone }),
    };

    return new Intl.DateTimeFormat(locale, formatOptions).format(date);
  } catch {
    return isoString; // Return original on error
  }
}

/**
 * Format a date relative to now (e.g., "2 days ago", "in 3 hours")
 */
export function formatRelativeDate(isoString: string, options: { locale?: string } = {}): string {
  const { locale = "en-US" } = options;

  try {
    const date = new Date(isoString);
    const now = new Date();
    const diffMs = date.getTime() - now.getTime();
    const diffSeconds = Math.floor(diffMs / 1000);
    const diffMinutes = Math.floor(diffSeconds / 60);
    const diffHours = Math.floor(diffMinutes / 60);
    const diffDays = Math.floor(diffHours / 24);

    // Use Intl.RelativeTimeFormat for proper localization
    const formatter = new Intl.RelativeTimeFormat(locale, { numeric: "auto" });

    if (Math.abs(diffDays) > 0) {
      return formatter.format(diffDays, "day");
    } else if (Math.abs(diffHours) > 0) {
      return formatter.format(diffHours, "hour");
    } else if (Math.abs(diffMinutes) > 0) {
      return formatter.format(diffMinutes, "minute");
    } else {
      return formatter.format(diffSeconds, "second");
    }
  } catch {
    return isoString;
  }
}

/**
 * Check if a date string is valid
 */
export function isValidDate(dateString: string): boolean {
  const date = new Date(dateString);
  return !isNaN(date.getTime());
}