import type { Clock } from "@suaveplan/types";
import { MS_PER_DAY } from "../constants/constants.js";
import { TimeEncodingType } from "../types/license.js";

const defaultClock: Clock = () => Date.now();

/**
 * Convert a `Date` (or now) to days since the Unix epoch. The 18-bit
 * `timeValue` field can hold ~718 years of day numbers.
 */
export function getDayNumber(date?: Date, clock: Clock = defaultClock): number {
    const ms = date !== undefined ? date.getTime() : clock();
    return Math.floor(ms / MS_PER_DAY);
}

/** Inverse of {@link getDayNumber}. */
export function dayNumberToDate(dayNumber: number): Date {
    return new Date(dayNumber * MS_PER_DAY);
}

/**
 * Determine whether a license is expired given its time-encoding metadata.
 * The optional `clock` defaults to `Date.now()` and is read only when
 * `referenceDate` is omitted.
 */
export function checkExpiration(
    timeEncodingType: TimeEncodingType,
    timeValue: number,
    referenceDate?: Date,
    creationDate?: Date,
    clock: Clock = defaultClock
): { isExpired: boolean; expirationDate?: Date } {
    const ref = referenceDate ?? new Date(clock());

    switch (timeEncodingType) {
        case TimeEncodingType.NONE:
            return { isExpired: false };

        case TimeEncodingType.ABSOLUTE_DAYS: {
            const expirationDate = dayNumberToDate(timeValue);
            return { isExpired: ref > expirationDate, expirationDate };
        }

        case TimeEncodingType.RELATIVE_DAYS: {
            const creation = creationDate ?? ref;
            const expirationDate = new Date(
                creation.getTime() + timeValue * MS_PER_DAY
            );
            return { isExpired: ref > expirationDate, expirationDate };
        }

        case TimeEncodingType.ABSOLUTE_TIMESTAMP: {
            const expirationDate = new Date(timeValue * 1000);
            return { isExpired: ref > expirationDate, expirationDate };
        }

        default:
            return { isExpired: false };
    }
}