'use strict';
const {
	V4MAPPED,
	ADDRCONFIG,
	ALL,
	promises: {
		Resolver: AsyncResolver
	},
	lookup: dnsLookup
} = require('dns');
const {promisify} = require('util');
const os = require('os');

const kCacheableLookupCreateConnection = Symbol('cacheableLookupCreateConnection');
const kCacheableLookupInstance = Symbol('cacheableLookupInstance');
const kExpires = Symbol('expires');

const supportsALL = typeof ALL === 'number';

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) {
		if (entry.family === 6) {
			continue;
		}

		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) {
				return {has4, has6};
			}
		}
	}

	return {has4, has6};
};

const isIterable = map => {
	return Symbol.iterator in map;
};

const ttl = {ttl: true};
const all = {all: true};

class CacheableLookup {
	constructor({
		cache = new Map(),
		maxTtl = Infinity,
		fallbackDuration = 3600,
		errorTtl = 0.15,
		resolver = new AsyncResolver(),
		lookup = dnsLookup
	} = {}) {
		this.maxTtl = maxTtl;
		this.errorTtl = errorTtl;

		this._cache = cache;
		this._resolver = resolver;
		this._dnsLookup = promisify(lookup);

		if (this._resolver instanceof AsyncResolver) {
			this._resolve4 = this._resolver.resolve4.bind(this._resolver);
			this._resolve6 = this._resolver.resolve6.bind(this._resolver);
		} else {
			this._resolve4 = promisify(this._resolver.resolve4.bind(this._resolver));
			this._resolve6 = promisify(this._resolver.resolve6.bind(this._resolver));
		}

		this._iface = getIfaceInfo();

		this._pending = {};
		this._nextRemovalTime = false;
		this._hostnamesToFallback = new Set();

		if (fallbackDuration < 1) {
			this._fallback = false;
		} else {
			this._fallback = true;

			const interval = setInterval(() => {
				this._hostnamesToFallback.clear();
			}, fallbackDuration * 1000);

			/* istanbul ignore next: There is no `interval.unref()` when running inside an Electron renderer */
			if (interval.unref) {
				interval.unref();
			}
		}

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

	set servers(servers) {
		this.clear();

		this._resolver.setServers(servers);
	}

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

	lookup(hostname, options, callback) {
		if (typeof options === 'function') {
			callback = options;
			options = {};
		} else if (typeof options === 'number') {
			options = {
				family: options
			};
		}

		if (!callback) {
			throw new Error('Callback must be a function.');
		}

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

	async lookupAsync(hostname, options = {}) {
		if (typeof options === 'number') {
			options = {
				family: options
			};
		}

		let cached = await this.query(hostname);

		if (options.family === 6) {
			const filtered = cached.filter(entry => entry.family === 6);

			if (options.hints & V4MAPPED) {
				if ((supportsALL && options.hints & ALL) || filtered.length === 0) {
					map4to6(cached);
				} else {
					cached = filtered;
				}
			} else {
				cached = filtered;
			}
		} else if (options.family === 4) {
			cached = cached.filter(entry => entry.family === 4);
		}

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

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

			throw error;
		}

		if (options.all) {
			return cached;
		}

		return cached[0];
	}

	async query(hostname) {
		let cached = await this._cache.get(hostname);

		if (!cached) {
			const pending = this._pending[hostname];

			if (pending) {
				cached = await pending;
			} else {
				const newPromise = this.queryAndCache(hostname);
				this._pending[hostname] = newPromise;

				try {
					cached = await newPromise;
				} finally {
					delete this._pending[hostname];
				}
			}
		}

		cached = cached.map(entry => {
			return {...entry};
		});

		return cached;
	}

	async _resolve(hostname) {
		const wrap = async promise => {
			try {
				return await promise;
			} catch (error) {
				if (error.code === 'ENODATA' || error.code === 'ENOTFOUND') {
					return [];
				}

				throw error;
			}
		};

		// ANY is unsafe as it doesn't trigger new queries in the underlying server.
		const [A, AAAA] = await Promise.all([
			this._resolve4(hostname, ttl),
			this._resolve6(hostname, ttl)
		].map(promise => wrap(promise)));

		let aTtl = 0;
		let aaaaTtl = 0;
		let cacheTtl = 0;

		const now = Date.now();

		for (const entry of A) {
			entry.family = 4;
			entry.expires = now + (entry.ttl * 1000);

			aTtl = Math.max(aTtl, entry.ttl);
		}

		for (const entry of AAAA) {
			entry.family = 6;
			entry.expires = now + (entry.ttl * 1000);

			aaaaTtl = Math.max(aaaaTtl, entry.ttl);
		}

		if (A.length > 0) {
			if (AAAA.length > 0) {
				cacheTtl = Math.min(aTtl, aaaaTtl);
			} else {
				cacheTtl = aTtl;
			}
		} else {
			cacheTtl = aaaaTtl;
		}

		return {
			entries: [
				...A,
				...AAAA
			],
			cacheTtl
		};
	}

	async _lookup(hostname) {
		try {
			const entries = await this._dnsLookup(hostname, {
				all: true
			});

			return {
				entries,
				cacheTtl: 0
			};
		} catch (_) {
			return {
				entries: [],
				cacheTtl: 0
			};
		}
	}

	async _set(hostname, data, cacheTtl) {
		if (this.maxTtl > 0 && cacheTtl > 0) {
			cacheTtl = Math.min(cacheTtl, this.maxTtl) * 1000;
			data[kExpires] = Date.now() + cacheTtl;

			try {
				await this._cache.set(hostname, data, cacheTtl);
			} catch (error) {
				this.lookupAsync = async () => {
					const cacheError = new Error('Cache Error. Please recreate the CacheableLookup instance.');
					cacheError.cause = error;

					throw cacheError;
				};
			}

			if (isIterable(this._cache)) {
				this._tick(cacheTtl);
			}
		}
	}

	async queryAndCache(hostname) {
		if (this._hostnamesToFallback.has(hostname)) {
			return this._dnsLookup(hostname, all);
		}

		let query = await this._resolve(hostname);

		if (query.entries.length === 0 && this._fallback) {
			query = await this._lookup(hostname);

			if (query.entries.length !== 0) {
				// Use `dns.lookup(...)` for that particular hostname
				this._hostnamesToFallback.add(hostname);
			}
		}

		const cacheTtl = query.entries.length === 0 ? this.errorTtl : query.cacheTtl;
		await this._set(hostname, query.entries, cacheTtl);

		return query.entries;
	}

	_tick(ms) {
		const nextRemovalTime = this._nextRemovalTime;

		if (!nextRemovalTime || ms < nextRemovalTime) {
			clearTimeout(this._removalTimeout);

			this._nextRemovalTime = ms;

			this._removalTimeout = setTimeout(() => {
				this._nextRemovalTime = false;

				let nextExpiry = Infinity;

				const now = Date.now();

				for (const [hostname, entries] of this._cache) {
					const expires = entries[kExpires];

					if (now >= expires) {
						this._cache.delete(hostname);
					} else if (expires < nextExpiry) {
						nextExpiry = expires;
					}
				}

				if (nextExpiry !== Infinity) {
					this._tick(nextExpiry - now);
				}
			}, ms);

			/* istanbul ignore next: There is no `timeout.unref()` when running inside an Electron renderer */
			if (this._removalTimeout.unref) {
				this._removalTimeout.unref();
			}
		}
	}

	install(agent) {
		verifyAgent(agent);

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

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

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

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

	uninstall(agent) {
		verifyAgent(agent);

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

			agent.createConnection = agent[kCacheableLookupCreateConnection];

			delete agent[kCacheableLookupCreateConnection];
			delete agent[kCacheableLookupInstance];
		}
	}

	updateInterfaceInfo() {
		const {_iface} = this;

		this._iface = getIfaceInfo();

		if ((_iface.has4 && !this._iface.has4) || (_iface.has6 && !this._iface.has6)) {
			this._cache.clear();
		}
	}

	clear(hostname) {
		if (hostname) {
			this._cache.delete(hostname);
			return;
		}

		this._cache.clear();
	}
}

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