import { Agent } from "undici";
import { didTag, handleTag, lookups, type LookupCache } from "#lib/api/lookupCache.ts";

// identity and account events always arrive. these two add a repo's own records
export const LOOKUP_COLLECTIONS = ["org.tangled.repo.manifest", "org.tangled.git.refs"];

// bobbin applies the same event from its own stream. a lookup refetched before it has
// would keep the old answer
const REEVICT_MS = 10_000;
const MIN_RETRY_MS = 1_000;
const MAX_RETRY_MS = 60_000;
const REPORT_MS = 60_000;

interface JetstreamEvent {
	did?: unknown;
	kind?: unknown;
	identity?: { handle?: unknown };
	commit?: { collection?: unknown };
}

export const tagsForEvent = (event: JetstreamEvent): string[] => {
	if (typeof event.did !== "string") return [];
	const tags = [didTag(event.did)];
	switch (event.kind) {
		case "identity":
			if (typeof event.identity?.handle === "string")
				tags.push(handleTag(event.identity.handle));
			return tags;
		case "account":
			return tags;
		case "commit":
			return LOOKUP_COLLECTIONS.includes(String(event.commit?.collection)) ? tags : [];
		default:
			return [];
	}
};

export const subscribeUrl = (url: string): string => {
	const parsed = new URL(url);
	for (const collection of LOOKUP_COLLECTIONS)
		parsed.searchParams.append("wantedCollections", collection);
	return parsed.href;
};

interface Socket {
	onopen: (() => void) | null;
	onmessage: ((message: { data: unknown }) => void) | null;
	onclose: (() => void) | null;
	close(): void;
}

export interface LookupEventsOptions {
	url: string;
	cache?: LookupCache;
	connect?: (url: string) => Socket;
}

export interface LookupEvents {
	readonly connected: boolean;
	close(): void;
}

// the cache is cleared on every open because events missed while down are gone
export const subscribeLookupEvents = ({
	url,
	cache = lookups,
	// node's websocket would use the global dispatcher, whose http/2 can't upgrade
	connect = (target) =>
		new WebSocket(target, { dispatcher: new Agent() } as never) as unknown as Socket
}: LookupEventsOptions): LookupEvents => {
	const target = subscribeUrl(url);
	let socket: Socket | undefined;
	let connected = false;
	let closed = false;
	let unreachable = false;
	let retryMs = MIN_RETRY_MS;

	const evict = (tags: string[]) => {
		cache.evict(tags);
		setTimeout(() => cache.evict(tags), REEVICT_MS).unref?.();
	};

	const open = () => {
		const current = connect(target);
		socket = current;
		current.onopen = () => {
			cache.clear();
			connected = true;
			unreachable = false;
			retryMs = MIN_RETRY_MS;
			console.info(`[lookups] following ${url}`);
		};
		current.onmessage = ({ data }) => {
			if (typeof data !== "string") return;
			let event: JetstreamEvent;
			try {
				event = JSON.parse(data) as JetstreamEvent;
			} catch {
				return;
			}
			const tags = tagsForEvent(event);
			if (tags.length > 0) evict(tags);
		};
		current.onclose = () => {
			if (socket !== current) return;
			if (connected) {
				console.warn(`[lookups] lost ${url}, cached lookups live out their ttl`);
			} else if (!unreachable) {
				console.warn(`[lookups] can't reach ${url}, retrying`);
				unreachable = true;
			}
			connected = false;
			if (closed) return;
			const wait = retryMs / 2 + Math.random() * (retryMs / 2);
			retryMs = Math.min(retryMs * 2, MAX_RETRY_MS);
			setTimeout(open, wait).unref?.();
		};
	};

	open();
	return {
		get connected() {
			return connected;
		},
		close() {
			closed = true;
			socket?.close();
		}
	};
};

export const startLookups = (config: { lookupCacheTtlMs: number; hydrantSubscribeUrl: string }) => {
	lookups.configure(config.lookupCacheTtlMs);
	if (config.lookupCacheTtlMs === 0) return;
	const events = subscribeLookupEvents({ url: config.hydrantSubscribeUrl });
	setInterval(() => {
		const { hits, misses, evictions, clears } = lookups.stats;
		if (hits + misses + evictions + clears === 0) return;
		console.info(
			`[lookups] hits=${hits} misses=${misses} evictions=${evictions} clears=${clears} entries=${lookups.size} connected=${events.connected}`
		);
		lookups.stats = { hits: 0, misses: 0, evictions: 0, clears: 0 };
	}, REPORT_MS).unref?.();
};