import { assertExists } from "https://deno.land/std@0.223.0/assert/assert_exists.ts";

import { Client, EmbedBuilder } from "npm:discord.js";

import { _1d, _1min, wait } from "./utils.ts";
import { fetch_feed_channel, format_devoir_title } from "./lib.ts";
import { Storage } from "./storage.ts";

export async function notification_loop(bot: Client, storage: Storage) {
	while (true) {
		const devoirs_to_notify = await get_devoirs_to_notify(storage);
		await delete_obsolete_notifications(devoirs_to_notify, storage, bot);
		await create_missing_messages(storage, bot, devoirs_to_notify);
		await update_existing_notifications(storage, bot);
		await wait(15 * _1min);
	}
}

async function get_devoirs_to_notify(storage: Storage) {
	const devoirs_to_notify = new Set<string>();
	const notification_threshold = 7 * _1d;
	for await (const [devoir_id, devoir] of storage.devoirs.list()) {
		const time_left = devoir.date - Date.now();
		if (time_left < 0) continue; // TODO : delete devoir.
		if (time_left > notification_threshold) continue;
		devoirs_to_notify.add(devoir_id.id);
	}
	return devoirs_to_notify;
}

async function delete_obsolete_notifications(devoirs_to_notify: Set<string>, storage: Storage, bot: Client<boolean>) {
	for await (const [notif_id, notif] of storage.notifications.list()) {
		if (devoirs_to_notify.has(notif.devoir_id)) continue;
		const feed = await storage.feeds.get({ id: notif.feed_id });
		if (feed === null) continue;
		const feed_channel = await fetch_feed_channel(bot, feed);
		try {
			const message = await feed_channel.messages.fetch(notif.message_id);
			await message.delete();
		} catch (_) { /* oki */ }
		await storage.notifications.delete(notif_id);
		await storage.feeds.update({ id: notif.feed_id }, (f) => f.notification_ids.delete(notif_id.id));
	}
}

async function create_missing_messages(storage: Storage, bot: Client<boolean>, devoirs_to_notify: Set<string>) {
	for await (const [feed_id, feed] of storage.feeds.list()) {
		const feed_channel = await fetch_feed_channel(bot, feed);
		// find devoirs needing to create a notification for
		const devoirs_to_notify_in_feed = new Set(devoirs_to_notify.values());
		for (const existing_notification_id of feed.notification_ids.values()) {
			const notification = await storage.notifications.get({ id: existing_notification_id });
			assertExists(notification);
			devoirs_to_notify_in_feed.delete(notification.devoir_id);
		}
		// create notifications
		for (const devoir_id of devoirs_to_notify_in_feed.values()) {
			const devoir = await storage.devoirs.get({ id: devoir_id });
			if (devoir === null) continue;
			const embed = new EmbedBuilder()
				.setTitle(format_devoir_title(devoir))
				.setDescription(devoir.description);
			const message = await feed_channel.send({ embeds: [embed] });
			const notification_id = await storage.notifications.add({
				devoir_id: devoir_id,
				message_id: message.id,
				feed_id: feed_id.id,
			});
			storage.feeds.update(feed_id, (f) => f.notification_ids.add(notification_id.id));
		}
	}
}

async function update_existing_notifications(storage: Storage, bot: Client<boolean>) {
	for await (const [_, notification] of storage.notifications.list()) {
		const devoir = await storage.devoirs.get({ id: notification.devoir_id });
		if (devoir === null) continue;
		const feed = await storage.feeds.get({ id: notification.feed_id });
		if (feed === null) continue;
		const feed_channel = await fetch_feed_channel(bot, feed);
		const message = await feed_channel.messages.fetch(notification.message_id);
		const ms_left = devoir.date - Date.now();
		const days_left = Math.floor(ms_left / _1d);
		const embed = new EmbedBuilder()
			.setTitle(format_devoir_title(devoir) + ` (${days_left} jours)`)
			.setDescription(devoir.description)
			.setColor(0x8888ff);
		if (days_left <= 5) embed.setColor(0xffd726);
		if (days_left <= 3) embed.setColor(0xff8b26);
		if (days_left <= 1) embed.setColor(0xff2626);
		await message.edit({ embeds: [embed], content: "" });
	}
}