"use strict";

var indexOf = require("es5-ext/array/#/e-index-of")
  , create  = Object.create;

module.exports = function (length) {
	var lastId = 0, map = [[], []], cache = create(null);
	return {
		get: function (args) {
			var index = 0, set = map, i;
			while (index < length - 1) {
				i = indexOf.call(set[0], args[index]);
				if (i === -1) return null;
				set = set[1][i];
				++index;
			}
			i = indexOf.call(set[0], args[index]);
			if (i === -1) return null;
			return set[1][i] || null;
		},
		set: function (args) {
			var index = 0, set = map, i;
			while (index < length - 1) {
				i = indexOf.call(set[0], args[index]);
				if (i === -1) {
					i = set[0].push(args[index]) - 1;
					set[1].push([[], []]);
				}
				set = set[1][i];
				++index;
			}
			i = indexOf.call(set[0], args[index]);
			if (i === -1) {
				i = set[0].push(args[index]) - 1;
			}
			set[1][i] = ++lastId;
			cache[lastId] = args;
			return lastId;
		},
		delete: function (id) {
			var index = 0, set = map, i, path = [], args = cache[id];
			while (index < length - 1) {
				i = indexOf.call(set[0], args[index]);
				if (i === -1) {
					return;
				}
				path.push(set, i);
				set = set[1][i];
				++index;
			}
			i = indexOf.call(set[0], args[index]);
			if (i === -1) {
				return;
			}
			id = set[1][i];
			set[0].splice(i, 1);
			set[1].splice(i, 1);
			while (!set[0].length && path.length) {
				i = path.pop();
				set = path.pop();
				set[0].splice(i, 1);
				set[1].splice(i, 1);
			}
			delete cache[id];
		},
		clear: function () {
			map = [[], []];
			cache = create(null);
		}
	};
};