type Course = {
	id: number;
	start: string; // e.g. "2025-09-24T10:45" (local wall time)
	end: string; // e.g. "2025-09-24T12:45"
	[k: string]: any;
};

import { token } from "./getToken";

const TZ = "Europe/Paris";

/** Format a Date (interpreted in the given time zone) to YYYYMMDD */
function formatYMD(date: Date, timeZone = TZ): string {
	const fmt = new Intl.DateTimeFormat("en-CA", {
		timeZone,
		year: "numeric",
		month: "2-digit",
		day: "2-digit",
	});
	// en-CA gives "YYYY-MM-DD" -> strip dashes
	return fmt.format(date).replaceAll("-", "");
}

/** Return Monday 00:00 and Sunday 23:59:59.999 of the week that contains `now` in TZ */
function getWeekBounds(now: Date, timeZone = TZ): { monday: Date; sunday: Date } {
	// Get the "wall-clock" Y/M/D in TZ
	const parts = new Intl.DateTimeFormat("en-GB", {
		timeZone,
		year: "numeric",
		month: "2-digit",
		day: "2-digit",
		weekday: "short",
	}).formatToParts(now);

	const y = Number(parts.find((p) => p.type === "year")!.value);
	const m = Number(parts.find((p) => p.type === "month")!.value);
	const d = Number(parts.find((p) => p.type === "day")!.value);
	const wk = parts.find((p) => p.type === "weekday")!.value; // "Mon".."Sun"

	// Build a Date that represents midnight in TZ by using UTC as a container
	// (Date.UTC so it's not shifted by the host machine's local tz)
	const midnightInTZ = new Date(Date.UTC(y, m - 1, d, 0, 0, 0, 0));

	// Map Mon..Sun -> 0..6 (offset from Monday)
	const weekdayIdx = ["Mon", "Tue", "Wed", "Thu", "Fri", "Sat", "Sun"].indexOf(wk);
	const monday = new Date(midnightInTZ);
	monday.setUTCDate(monday.getUTCDate() - weekdayIdx);

	const sunday = new Date(monday);
	sunday.setUTCDate(sunday.getUTCDate() + 6);
	sunday.setUTCHours(23, 59, 59, 999);

	return { monday, sunday };
}

/**
 * Returns the course occurring at the moment this function runs.
 * If none is in progress, returns null.
 */
export async function getCurrentCourse(now: Date = new Date()): Promise<Course | null> {
	// Compute Mon..Sun bounds in Europe/Paris, then format as YYYYMMDD for the query.
	const { monday, sunday } = getWeekBounds(now, TZ);
	const startYMD = formatYMD(monday, TZ); // e.g. "20250922"
	const endYMD = formatYMD(sunday, TZ); // e.g. "20250928"

	const url = `https://learning.estia.fr/pegasus/index.php?com=emergement&job=get-cours.json&start=${startYMD}&end=${endYMD}`;

	const res = await fetch(url, {
		credentials: "include",
		headers: {
			"User-Agent": "Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:142.0) Gecko/20100101 Firefox/142.0",
			Accept: "application/json, text/javascript, */*; q=0.01",
			"Accept-Language": "en-US,en;q=0.5",
			"X-Requested-With": "XMLHttpRequest",
			"Sec-GPC": "1",
			"Sec-Fetch-Dest": "empty",
			"Sec-Fetch-Mode": "cors",
			"Sec-Fetch-Site": "same-origin",
			Pragma: "no-cache",
			"Cache-Control": "no-cache",
			cookie: `PHPSESSID=${token}`,
			Referer: "https://learning.estia.fr/pegasus/index.php?com=emergement&job=load-cours-programmes-apprenant",
		},
		method: "GET",
		mode: "cors",
	});

	if (!res.ok) {
		throw new Error(`Failed to fetch courses: ${res.status} ${res.statusText}`);
	}

	const courses: Course[] = (await res.json()) as Course[];

	// Sort by start time just in case (ascending)
	courses.sort((a, b) => new Date(a.start).getTime() - new Date(b.start).getTime());

	// Find the one currently in progress: start <= now < end
	const current = courses.find((c) => {
		const start = new Date(c.start).getTime();
		const end = new Date(c.end).getTime();
		const t = now.getTime();
		return t >= start && t < end;
	});

	console.log("Current course:", current);

	return current ?? null;
}