'use strict';
const {Resolver, V4MAPPED, ADDRCONFIG} = require('dns');
const {promisify} = require('util');
const os = require('os');
const Keyv = require('keyv');

const kCacheableLookupData = Symbol('cacheableLookupData');
const kCacheableLookupInstance = Symbol('cacheableLookupInstance');

const verifyAgent = agent => {
	if (!(agent && typeof agent.createConnection === 'function')) {
		throw new Error('Expected an Agent instance as the first argument');
	}
};

const map4to6 = entries => {
	for (const entry of entries) {
		entry.address = `::ffff:${entry.address}`;
		entry.family = 6;
	}
};

const getIfaceInfo = () => {
	let has4 = false;
	let has6 = false;

	for (const device of Object.values(os.networkInterfaces())) {
		for (const iface of device) {
			if (iface.internal) {
				continue;
			}

			if (iface.family === 'IPv6') {
				has6 = true;
			} else {
				has4 = true;
			}

			if (has4 && has6) {
				break;
			}
		}
	}

	return {has4, has6};
};

class CacheableLookup {
	constructor({cacheAdapter, maxTtl = Infinity, resolver} = {}) {
		this.cache = new Keyv({
			uri: typeof cacheAdapter === 'string' && cacheAdapter,
			store: typeof cacheAdapter !== 'string' && cacheAdapter,
			namespace: 'cached-lookup'
		});

		this.maxTtl = maxTtl;

		this._resolver = resolver || new Resolver();
		this._resolve4 = promisify(this._resolver.resolve4.bind(this._resolver));
		this._resolve6 = promisify(this._resolver.resolve6.bind(this._resolver));

		this._iface = getIfaceInfo();

		this.lookup = this.lookup.bind(this);
		this.lookupAsync = this.lookupAsync.bind(this);
	}

	set servers(servers) {
		this._resolver.setServers(servers);
	}

	get servers() {
		return this._resolver.getServers();
	}

	lookup(hostname, options, callback) {
		if (typeof options === 'function') {
			callback = options;
			options = {};
		}

		// eslint-disable-next-line promise/prefer-await-to-then
		this.lookupAsync(hostname, {...options, throwNotFound: true}).then(result => {
			if (options.all) {
				callback(null, result);
			} else {
				callback(null, result.address, result.family, result.expires, result.ttl);
			}
		}).catch(callback);
	}

	async lookupAsync(hostname, options = {}) {
		let cached;
		if (!options.family && options.all) {
			const [cached4, cached6] = await Promise.all([this.lookupAsync(hostname, {all: true, family: 4}), this.lookupAsync(hostname, {all: true, family: 6})]);
			cached = [...cached4, ...cached6];
		} else {
			cached = await this.query(hostname, options.family || 4);

			if (cached.length === 0 && options.family === 6 && options.hints & V4MAPPED) {
				cached = await this.query(hostname, 4);
				map4to6(cached);
			}
		}

		if (options.hints & ADDRCONFIG) {
			const {_iface} = this;
			cached = cached.filter(entry => entry.family === 6 ? _iface.has6 : _iface.has4);
		}

		if (cached.length === 0 && options.throwNotFound) {
			const error = new Error(`ENOTFOUND ${hostname}`);
			error.code = 'ENOTFOUND';
			error.hostname = hostname;

			throw error;
		}

		const now = Date.now();
		cached = cached.filter(entry => entry.ttl === 0 || now < entry.expires);

		if (options.all) {
			return cached;
		}

		if (cached.length === 1) {
			return cached[0];
		}

		if (cached.length === 0) {
			return undefined;
		}

		return this._getEntry(cached);
	}

	async query(hostname, family) {
		let cached = await this.cache.get(`${hostname}:${family}`);
		if (!cached) {
			cached = await this.queryAndCache(hostname, family);
		}

		return cached;
	}

	async queryAndCache(hostname, family) {
		const resolve = family === 4 ? this._resolve4 : this._resolve6;
		const entries = await resolve(hostname, {ttl: true});

		if (entries === undefined) {
			return [];
		}

		const now = Date.now();

		let cacheTtl = 0;
		for (const entry of entries) {
			cacheTtl = Math.max(cacheTtl, entry.ttl);
			entry.family = family;
			entry.expires = now + (entry.ttl * 1000);
		}

		cacheTtl = Math.min(this.maxTtl, cacheTtl) * 1000;

		if (this.maxTtl !== 0 && cacheTtl !== 0) {
			await this.cache.set(`${hostname}:${family}`, entries, cacheTtl);
		}

		return entries;
	}

	_getEntry(entries) {
		return entries[Math.floor(Math.random() * entries.length)];
	}

	install(agent) {
		verifyAgent(agent);

		if (kCacheableLookupData in agent) {
			throw new Error('CacheableLookup has been already installed');
		}

		agent[kCacheableLookupData] = agent.createConnection;
		agent[kCacheableLookupInstance] = this;

		agent.createConnection = (options, callback) => {
			if (!('lookup' in options)) {
				options.lookup = this.lookup;
			}

			return agent[kCacheableLookupData](options, callback);
		};
	}

	uninstall(agent) {
		verifyAgent(agent);

		if (agent[kCacheableLookupData]) {
			if (agent[kCacheableLookupInstance] !== this) {
				throw new Error('The agent is not owned by this CacheableLookup instance');
			}

			agent.createConnection = agent[kCacheableLookupData];

			delete agent[kCacheableLookupData];
			delete agent[kCacheableLookupInstance];
		}
	}

	updateInterfaceInfo() {
		this._iface = getIfaceInfo();
	}
}

module.exports = CacheableLookup;
module.exports.default = CacheableLookup;