/**
 * Date formatting utilities for the WealthX design system.
 * Uses date-fns for consistent, locale-independent formatting.
 */
import {
  format,
  parseISO,
  startOfDay,
  differenceInCalendarDays,
} from "date-fns";

/**
 * Parse an ISO date string safely, handling both full ISO and date-only strings.
 * Date-only strings ("2026-01-15") are parsed via parseISO to avoid timezone shifts.
 */
function safeParse(iso: string): Date {
  return parseISO(iso);
}

/**
 * Format an ISO date string as "15 Jan 2026".
 * Returns "—" for falsy input, raw string on parse failure.
 */
export function formatDateShort(iso?: string): string {
  if (!iso) return "—";
  try {
    return format(safeParse(iso), "dd MMM yyyy");
  } catch {
    return iso;
  }
}

/**
 * Format an ISO date string as "15 Jan" (day + month only).
 * Returns raw string on parse failure.
 */
export function formatDateDayMonth(iso: string): string {
  try {
    return format(safeParse(iso), "dd MMM");
  } catch {
    return iso;
  }
}

/**
 * Format an ISO date string with weekday: "Wed, 15 Jan 2026".
 * Returns raw string on parse failure.
 */
export function formatDateWithWeekday(iso: string): string {
  try {
    return format(safeParse(iso), "EEE, dd MMM yyyy");
  } catch {
    return iso;
  }
}

/**
 * Format a Date or ISO string as a long human-readable string: "Wednesday, 15 January 2026".
 * Used for booking confirmations and summary displays.
 */
export function formatDateLong(date: Date | string): string {
  try {
    const d = typeof date === "string" ? safeParse(date) : date;
    return format(d, "EEEE, d MMMM yyyy");
  } catch {
    return String(date);
  }
}

/**
 * Current month and year as "June 2026". Used as a default "last updated" label
 * when no real freshness date is supplied (e.g. Policy AI coverage block).
 */
export function formatCurrentMonthYear(): string {
  return format(new Date(), "MMMM yyyy");
}

/**
 * Format a Date or ISO string as an uppercase short weekday: "MON", "TUE", etc.
 * Used for calendar day headers.
 */
export function formatWeekdayShort(date: Date | string): string {
  try {
    const d = typeof date === "string" ? safeParse(date) : date;
    return format(d, "EEE").toUpperCase();
  } catch {
    return String(date);
  }
}

/**
 * Returns the number of calendar days remaining until the given ISO date.
 * Returns 0 if the date has already passed or is today.
 */
export function daysUntil(iso: string): number {
  try {
    const target = startOfDay(parseISO(iso));
    const today = startOfDay(new Date());
    return Math.max(0, differenceInCalendarDays(target, today));
  } catch {
    return 0;
  }
}