/**
 * Formats a date string into a relative, human-readable time.
 * Uses the user's system locale where possible, with a fallback to en-GB.
 */
export function formatRelativeTime(dateString: string): string {
	const date = new Date(dateString);
	const now = new Date();
	const diffMs = now.getTime() - date.getTime();
	const diffMins = Math.floor(diffMs / 60000);
	const diffHours = Math.floor(diffMins / 60);
	const diffDays = Math.floor(diffHours / 24);

	if (diffMins < 1) return 'just now';
	if (diffMins < 60) return `${diffMins}m ago`;
	if (diffHours < 24) return `${diffHours}h ago`;
	if (diffDays < 7) return `${diffDays}d ago`;

	const userLocale = typeof navigator !== 'undefined' ? navigator.language : 'en-GB';

	return date.toLocaleDateString(userLocale, {
		day: 'numeric',
		month: 'short',
		year: date.getFullYear() !== now.getFullYear() ? 'numeric' : undefined
	});
}