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

const keepaliveTimeoutMs = 45e3;
const eventUpdateTimeMs = 1e3;

class EventStream {
	write!: (data: string) => void;
	close!: (reason?: string) => void;

	constructor(
		public sessionId: number | undefined,
		public accountId: number | undefined,
		public userType: ApiUserType | undefined,
		public rotatesAtMs: number ,
		public lastKeepAliveMs: number,
		public lastEventId: number,
	) {
	}
}

export async function createEventStream(
	event: H3Event,
	source: string,
	lastEventId: number,
	session?: ServerSession,
) {
	const runtimeConfig = useRuntimeConfig(event);
	const now = Date.now();
	const events = (readEvents()).filter(e => e.id > lastEventId);
	const users = readUsers();
	const apiSession = session ? await serverSessionToApi(event, session) : undefined;
	let userType: ApiAccount["type"] | undefined;
	if (session?.accountId !== undefined) {
		userType = users.find(a => !a.deleted && a.id === session.accountId)?.type
	}
	const stream = new EventStream(
		session?.id,
		session?.accountId,
		userType,
		session?.rotatesAtMs ?? now + runtimeConfig.sessionRotatesTimeout * 1000,
		now,
		events[events.length - 1]?.id ?? lastEventId,
	);

	const readableStream = new ReadableStream<Uint8Array>({
		start(controller) {
			const encoder = new TextEncoder();
			stream.write = (data: string) => {
				controller.enqueue(encoder.encode(data));
			}
			stream.close = (reason?: string) => {
				const data: ApiDisconnected = {
					type: "disconnect",
					reason,
				};
				stream.write(`data: ${JSON.stringify(data)}\n\n`);
				controller.close();
				deleteStream(stream);
			},
			console.log(`Starting event stream for ${source}`)
			addStream(stream);
		},
		cancel(reason) {
			console.log(`Cancelled event stream for ${source}:`, reason);
			deleteStream(stream);
		}
	});
	// Produce a response immediately to avoid the reply waiting for content.
	const update: ApiEventStreamMessage = {
		type: "connected",
		session: apiSession,
	};
	stream.write(`data: ${JSON.stringify(update)}\n\n`);

	/*
		Send events since the provided lastEventId

		Warning: This have to happen either before addStream(stream) is
		called, or as done here synchronously after it. Otherwise there's a
		possibility of events being delivered out of order, which will break
		the assumption made by the schedule updating logic.
	*/
	if (events.length)
		console.log(`Sending ${events.length} event(s) to ${source}`);
	for (const event of events) {
		if (!sendEventToStream(stream, event)) {
			break;
		}
	}

	return readableStream;
}

let updateInterval: ReturnType<typeof setInterval> | null = null
const streams = new Set<EventStream>();
function addStream(
	stream: EventStream,
) {
	if (streams.size === 0) {
		console.log("Starting event updates")
		updateInterval = setInterval(sendEventUpdates, eventUpdateTimeMs)
	}
	streams.add(stream);
}
function deleteStream(stream: EventStream) {
	streams.delete(stream);
	if (streams.size === 0) {
		console.log("Ending event updates")
		clearInterval(updateInterval!);
		updateInterval = null;
	}
}

export function cancelAccountStreams(accountId: number) {
	for (const stream of streams.values()) {
		if (stream.accountId === accountId) {
			stream.close("cancelled");
		}
	}
}

export function cancelSessionStreams(sessionId: number) {
	for (const stream of streams.values()) {
		if (stream.sessionId === sessionId) {
			stream.close("cancelled");
		}
	}
}

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 = {
				id: event.id,
				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 = {
				id: event.id,
				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 events = readEvents();
	events.push(event);
	writeEvents(events);
}

function sendEventToStream(stream: EventStream, event: ApiEvent) {
	// Session expiry events cause the streams belonging to that session to be terminated
	if (event.type === "session-expired") {
		if (stream.sessionId === event.sessionId) {
			stream.close("session expired");
			return false;
		}
		return true;
	}

	// Account events are specially handled and only sent to the user they belong to.
	if (event.type === "account-update") {
		if (stream.accountId === event.data.id) {
			stream.write(`id: ${event.id}\nevent: event\ndata: ${JSON.stringify(event)}\n\n`);
		}
		return true;
	}

	// All other events are encoded according to the user access level seeing it.
	const data = encodeEvent(event, stream.userType)
	stream.write(`id: ${event.id}\nevent: event\ndata: ${data}\n\n`);
	return true;
}

async function sendEventUpdates() {
	// Cancel streams that need to be rotated.
	const now = Date.now();
	for (const stream of streams.values()) {
		if (stream.rotatesAtMs < now) {
			stream.close("session rotation");
			continue;
		}
	}

	// Send events.
	const skipEventId = Math.min(...[...streams.values()].map(s => s.lastEventId));
	const events = (readEvents()).filter(e => e.id > skipEventId);
	if (events.length)
		console.log(`broadcasting ${events.length} event(s) to ${streams.size} client(s)`);
	for (const stream of streams.values()) {
		for (const event of events) {
			if (event.id > stream.lastEventId) {
				stream.lastEventId = event.id;
				stream.lastKeepAliveMs = now;

				if (!sendEventToStream(stream, event)) {
					break;
				}
			}
		}
	}

	// Send Keepalives to streams with no activity.
	for (const stream of streams.values()) {
		if (stream.lastKeepAliveMs + keepaliveTimeoutMs < now) {
			stream.write(": keepalive\n");
			stream.lastKeepAliveMs = now;
		}
	}
}