systemquery/src/lib/SystemQuery.mjs

"use strict";

import { once, EventEmitter } from 'events';

import log from './io/NamespacedLog.mjs'; const l = log("systemquery");

import Agent from './agent/Agent.mjs';
import InfoBroker from './core/InfoBroker.mjs';
import HttpSubsystem from './agent/subsystems/http/HttpSubsystem.mjs';

import ItemQueue from './async/ItemQueue.mjs';


class SystemQuery extends EventEmitter {
	/**
	 * Returns an object representing our local information that looks and
	 * even quacks a bit like a real Peer object, but isn't.
	 * @return	{Object}
	 */
	get peer_local() {
		return {
			id: this.agent.peer_id,
			id_short: (this.agent.peer_id || "").substring(0, 7),
			name: this.agent.peer_name,
			address: this.agent.local_bind_address,
			port: this.agent.local_port,
			self: true
		}
	}
	
	get listening() { return this.agent !== null ? this.agent.listening : false; }
	
	
	// TODO: Handle duplicate connections better by both skipping counting them here, and also implementing a more robust reaper for killing duplicate connections that always kills the newest/oldest connection to avoid issues.

	
	constructor(config, mode = "agent") {
		super();
		
		// The operating mode. Possible values: agent [default], query_client
		// TODO: Is this the best way of doing this? Maybe we should have a separate class for this? I'm not sure.
		this.mode = mode;
		this.config = config;
		this.info = new InfoBroker();
		
		this.http = new HttpSubsystem(this);
	}
	
	/**
	 * Initialises the SystemQuery agent.
	 * @return	{Promise}	A Promise that resolves when initialisation is complete.
	 */
	async init() {
		///
		// 1: Create agent
		///
		this.agent = new Agent(this.config);
		this.http.init(
			this.config.net.http.port,
			this.config.net.http.bind_address
		);
		
		///
		// 2: Attach listeners
		///
		this.agent.on("message-query", this.handle_query.bind(this));
		this.agent.on("message-query-response", this.handle_query_response.bind(this));
		
		///
		// 3: Start agent
		///
		await this.agent.init();
	}
	
	async handle_query(peer, msg) {
		// 1: Validate input
		if(typeof msg.name !== "string"
			|| !this.info.is_valid_table(msg.name)) return;
		
		// 2: Fetch system info
		let table = await this.info.fetch_table(msg.name);
		if(table === null) return;
		
		// 3: Return to requester
		await peer.send("query-response", { name: msg.name, table });
	}
	async handle_query_response(peer, msg) {
		l.log(`query-response from ${peer.id_short}`, msg);
	}
	
	async capture_query_response(event_name, ac) {
		return await once(this.agent, `message-${event_name}`, { signal: ac });
	}
	
	/**
	 * Fetches the table with the given name from all peers in the swarm
	 * (including this local instance).
	 * While this function iteratively yields tables as they are received, it
	 * will wait until all peers respond before finally ending.
	 * If 1 of more peers do not respond, then if no answers are received
	 * within the time limit specified in the config object (supplied at
	 * startup) this function will return.
	 * @param	{string}	name			The name of the table to fetch.
	 * @return	{AsyncGenerator<Object>}	An asynchronous generator that yields the tables as they are received.
	 */
	async *fetch_table(name) {
		// If it isn't valid for us, it ain't gonna be valid for anyone else....
		if(!this.info.is_valid_table(name)) return null;
		
		const queue = new ItemQueue();
		
		const handle_response = (peer, msg) => {
			// Note that multiple fetch_table calls may be running in parallel, so we should not make too much of a fuss if we get the wrong table by accident.
			if(typeof msg !== "object"
				|| typeof msg.table !== "object"
				|| typeof msg.name !== "string") {
					l.debug(`Discarding invalid table from peer ${peer.id_short}`);
					return;
				}
			
			// If it's not the right table, ignore it
			if(msg.name !== name) return;
			
			queue.enqueue({ peer, table: msg.table });
		};
		
		this.agent.on("message-query-response", handle_response);
		
		// Only *after* we have our listeners in place do we then broadcast the
		// query. Note that despite not having entered the below while loop yet,
		// we do not drop any messages due to the use of the ItemQueue.
		this.agent.broadcast(`query`, { name });
		
		
		// Yield our result first
		let table_ours = await this.info.fetch_table(name);
		yield {
			peer: this.peer_local,
			table: table_ours
		};
		
		let peers_seen = [];
		while(peers_seen.length < this.agent.connected_peers.length) {
			l.info(`peers_seen:`, peers_seen, `connected peers:`, this.agent.connected_peers.map(peer => peer.id));
			let next = await queue.dequeue(this.config.net.table_timeout * 1000);
			if(typeof next === "undefined") // We timed out
				break;
			l.log(`fetch table DEBUG`, next);
			if(!peers_seen.includes(next.peer.id))
				peers_seen.push(next.peer.id);
			yield next;
		}
		
		this.agent.off("message-query-response", handle_response);
		
		// FUTURE: Add a cache here? Note that we also do not listen for query responses unless we've asked for a table.
	}
}

SystemQuery.Create = async function(config) {
	let result = new SystemQuery(config);
	await result.init();
	return result;
}

export default SystemQuery;