import { Inject, Injectable, Logger, Optional } from '@nestjs/common';
import { DiscoveryService, ModulesContainer } from '@nestjs/core';
import { createLazyPromise } from '@wener/utils';
import type { Subscription } from 'nats';
import { App } from '../../app';
import { EXPOSE_SERVICE_METADATA_KEY, ServiceRegistry } from '../../service';
import { NatsConn } from '../NatsModule';
import { handleNatsServiceRequest } from './handleNatsServiceRequest';
import { getSubscribeSubject } from './nats';
import ServerModule from './ServerModule';
import type { NatsServiceServerModuleOptions } from './types';

const { MODULE_OPTIONS_TOKEN } = ServerModule;

@Injectable()
export class NatsServerHandler {
	private subscriptions: Subscription[] = [];
	private readonly log = new Logger(NatsServerHandler.name);
	readonly discoveryService: DiscoveryService;
	private readonly _started = createLazyPromise();

	get started(): Promise<void> {
		return this._started;
	}

	get svc(): ServiceRegistry {
		return this._svc;
	}

	constructor(
		@Inject(ModulesContainer) readonly modulesContainer: ModulesContainer,
		@Inject(ServiceRegistry) readonly _svc: ServiceRegistry,
		@Inject(NatsConn) readonly nc: NatsConn,
		@Optional() @Inject(MODULE_OPTIONS_TOKEN) readonly options: NatsServiceServerModuleOptions = {},
	) {
		this.discoveryService = new DiscoveryService(modulesContainer);
	}

	async close(): Promise<void> {
		const done: Promise<any> = Promise.allSettled(
			this.subscriptions.map(async (v) =>
				v.drain().then(() => {
					v.unsubscribe();
				}),
			),
		);
		this.subscriptions = [];
		return done;
	}

	private subscribeService({ name }: { name: string }) {
		const { getServiceSubject = getSubscribeSubject, queue = App.service } = this.options;
		const { nc, log, svc } = this;

		for (let subject of getServiceSubject({ service: name })) {
			this.log.log(`Subscribe ${subject}`);
			const sub = nc.subscribe(subject, {
				callback(err, msg) {
					if (err) {
						log.error(String(err));
						return;
					}
					if (!msg.reply) {
						log.debug(`No reply subject: ${msg.subject}`);
						return;
					}
					return handleNatsServiceRequest({ msg, registry: svc, logger: log });
				},
				queue,
			});
			this.subscriptions.push(sub);
		}
	}

	listen() {
		const { svc, log } = this;
		for (const { metatype, instance } of this.discoveryService
			.getProviders()
			.filter(({ metatype }) => metatype && Reflect.getMetadata(EXPOSE_SERVICE_METADATA_KEY, metatype))) {
			svc.addService({ service: metatype as any, target: instance });
		}

		const names = svc.getServiceNames();
		log.log(`Register service (${names.length}) ${names.join(', ')}`);
		for (const name of names) {
			this.subscribeService({ name });
		}

		this._started.resolve(true);
	}
}