export type TWUIRecencyGroup<T> = {
    label: string;
    items: T[];
};

const DAY = 24 * 60 * 60 * 1000;

/**
 * # Group by recency
 * Buckets items into "Today", "Yesterday", "Previous 7 days",
 * "Previous 30 days" and then by month, newest first - the grouping chat
 * apps use for conversation lists. Empty groups are left out.
 */
export default function twuiGroupByRecency<T>(
    items: T[],
    getTime: (item: T) => number,
    now: number = Date.now(),
): TWUIRecencyGroup<T>[] {
    const startOfToday = new Date(now);
    startOfToday.setHours(0, 0, 0, 0);
    const today = startOfToday.getTime();

    const groups = new Map<string, T[]>();

    const label = (time: number) => {
        if (time >= today) return "Today";
        if (time >= today - DAY) return "Yesterday";
        if (time >= today - 7 * DAY) return "Previous 7 days";
        if (time >= today - 30 * DAY) return "Previous 30 days";
        return new Date(time).toLocaleDateString(undefined, {
            month: "long",
            year: "numeric",
        });
    };

    [...items]
        .sort((a, b) => getTime(b) - getTime(a))
        .forEach((item) => {
            const key = label(getTime(item));
            const list = groups.get(key);
            if (list) list.push(item);
            else groups.set(key, [item]);
        });

    return Array.from(groups, ([label, items]) => ({ label, items }));
}