/*
	SPDX-FileCopyrightText: © 2025 Hornwitser <code@hornwitser.no>
	SPDX-License-Identifier: AGPL-3.0-or-later
*/
import { readUsers, ServerSession } from "~/server/database";
import type { ApiAccount, ApiEvent } from "~/shared/types/api";
import { serverSessionToApi } from "./utils/session";
import { H3Event } from "h3";

function sendMessage(
	stream: WritableStream<string>,
	message: string,
) {
	const writer = stream.getWriter();
	writer.ready
		.then(() => writer.write(message))
		.catch(console.error)
		.finally(() => writer.releaseLock())
	;
}

function sendMessageAndClose(
	stream: WritableStream<string>,
	message: string,
) {
	const writer = stream.getWriter();
	writer.ready
		.then(() => {
			writer.write(message);
			writer.close();
		}).catch(console.error)
		.finally(() => writer.releaseLock())
	;
}

const streams = new Map<WritableStream<string>, { sessionId?: number, accountId?: number, expiresAtMs: number }>();

let keepaliveInterval: ReturnType<typeof setInterval> | null = null
export async function addStream(
	event: H3Event,
	stream: WritableStream<string>,
	session?: ServerSession,
) {
	if (streams.size === 0) {
		console.log("Starting keepalive")
		keepaliveInterval = setInterval(sendKeepalive, 4000)
	}
	const runtimeConfig = useRuntimeConfig(event);
	streams.set(stream, {
		sessionId: session?.id,
		accountId: session?.accountId,
		expiresAtMs: session?.expiresAtMs ?? Date.now() + runtimeConfig.sessionExpiresTimeout * 1000,
	});
	// Produce a response immediately to avoid the reply waiting for content.
	const update: ApiEvent = {
		type: "connected",
		session: session ? await serverSessionToApi(event, session) : undefined,
	};
	sendMessage(stream, `event: update\ndata: ${JSON.stringify(update)}\n\n`);
}
export function deleteStream(stream: WritableStream<string>) {
	streams.delete(stream);
	if (streams.size === 0) {
		console.log("Ending keepalive")
		clearInterval(keepaliveInterval!);
	}
}

export function cancelAccountStreams(accountId: number) {
	for (const [stream, data] of streams) {
		if (data.accountId === accountId) {
			sendMessageAndClose(stream, `data: cancelled\n\n`);
		}
	}
}

export function cancelSessionStreams(sessionId: number) {
	for (const [stream, data] of streams) {
		if (data.sessionId === sessionId) {
			sendMessageAndClose(stream, `data: cancelled\n\n`);
		}
	}
}

const encodeEventCache = new WeakMap<ApiEvent, Map<ApiAccount["type"] | undefined, string>>();
function encodeEvent(event: ApiEvent, userType: ApiAccount["type"] | undefined) {
	const cache = encodeEventCache.get(event);
	const cacheEntry = cache?.get(userType);
	if (cacheEntry) {
		return cacheEntry;
	}

	let data: string;
	if (event.type === "schedule-update") {
		if (!canSeeCrew(userType)) {
			event = {
				type: event.type,
				updatedFrom: event.updatedFrom,
				data: filterSchedule(event.data),
			};
		}
		data = JSON.stringify(event);
	} else if (event.type === "user-update") {
		if (
			!canSeeCrew(userType)
			|| !event.data.deleted && event.data.type === "anonymous" && !canSeeAnonymous(userType)
		) {
			event = {
				type: event.type,
				data: {
					id: event.data.id,
					updatedAt: event.data.updatedAt,
					deleted: true,
				}
			}
		}
		data = JSON.stringify(event);
	} else {
		throw Error(`encodeEvent cannot encode ${event.type} event`);
	}

	if (cache) {
		cache.set(userType, data);
	} else {
		encodeEventCache.set(event, new Map([[userType, data]]));
	}
	return data;
}

export async function broadcastEvent(event: ApiEvent) {
	const id = Date.now();
	console.log(`broadcasting update to ${streams.size} clients`);
	if (!streams.size) {
		return;
	}

	// Session expiry events cause the streams belonging to that session to be terminated
	if (event.type === "session-expired") {
		cancelSessionStreams(event.sessionId);
		return;
	}

	const users = await readUsers();
	for (const [stream, streamData] of streams) {
		// Account events are specially handled and only sent to the user they belong to.
		if (event.type === "account-update") {
			if (streamData.accountId === event.data.id) {
				sendMessage(stream, `id: ${id}\nevent: update\ndata: ${JSON.stringify(event)}\n\n`);
			}

		} else {
			let userType: ApiAccount["type"] | undefined;
			if (streamData.accountId !== undefined) {
				userType = users.find(a => a.id === streamData.accountId)?.type
			}
			const data = encodeEvent(event, userType)
			sendMessage(stream, `id: ${id}\nevent: update\ndata: ${data}\n\n`);
		}
	}
}

function sendKeepalive() {
	const now = Date.now();
	for (const [stream, streamData] of streams) {
		if (streamData.expiresAtMs > now) {
			sendMessage(stream, ": keepalive\n");
		} else {
			sendMessageAndClose(stream, `data: cancelled\n\n`);
		}
	}
}