'use strict';

class LRU {
		constructor (max = 0, ttl = 0) {
			this.first = null;
			this.items = Object.create(null);
			this.last = null;
			this.max = max;
			this.size = 0;
			this.ttl = ttl;
		}

		has (key) {
			return key in this.items;
		}

		clear () {
			this.first = null;
			this.items = Object.create(null);
			this.last = null;
			this.size = 0;

			return this;
		}

		delete (key) {
			if (this.has(key)) {
				const item = this.items[key];

				delete this.items[key];
				this.size--;

				if (item.prev !== null) {
					item.prev.next = item.next;
				}

				if (item.next !== null) {
					item.next.prev = item.prev;
				}

				if (this.first === item) {
					this.first = item.next;
				}

				if (this.last === item) {
					this.last = item.prev;
				}
			}

			return this;
		}

		evict () {
			const item = this.first;

			delete this.items[item.key];
			this.first = item.next;
			this.first.prev = null;
			this.size--;

			return this;
		}

		get (key) {
			let result;

			if (this.has(key)) {
				const item = this.items[key];

				if (this.ttl > 0 && item.expiry <= new Date().getTime()) {
					this.delete(key);
				} else {
					result = item.value;
					this.set(key, result, true);
				}
			}

			return result;
		}

		keys () {
			return Object.keys(this.items);
		}

		set (key, value, bypass = false) {
			let item;

			if (bypass || this.has(key)) {
				item = this.items[key];
				item.value = value;

				if (bypass === false) {
					item.expiry = this.ttl > 0 ? new Date().getTime() + this.ttl : this.ttl;
				}

				if (this.last !== item) {
					const last = this.last,
						next = item.next,
						prev = item.prev;

					if (this.first === item) {
						this.first = item.next;
					}

					item.next = null;
					item.prev = this.last;
					last.next = item;

					if (prev !== null) {
						prev.next = next;
					}

					if (next !== null) {
						next.prev = prev;
					}
				}
			} else {
				if (this.max > 0 && this.size === this.max) {
					this.evict();
				}

				item = this.items[key] = {
					expiry: this.ttl > 0 ? new Date().getTime() + this.ttl : this.ttl,
					key: key,
					prev: this.last,
					next: null,
					value
				};

				if (++this.size === 1) {
					this.first = item;
				} else {
					this.last.next = item;
				}
			}

			this.last = item;

			return this;
		}
	}

	function factory (max = 1000, ttl = 0) {
		if (isNaN(max) || max < 0) {
			throw new TypeError("Invalid max value");
		}

		if (isNaN(ttl) || ttl < 0) {
			throw new TypeError("Invalid ttl value");
		}

		return new LRU(max, ttl);
	}

module.exports = factory;