"use strict";

var toPosInt = require("../number/to-pos-integer");

var test = function (arg1, arg2) { return arg2; };

var desc, defineProperty, generate, mixin;

try {
	Object.defineProperty(test, "length", {
		configurable: true,
		writable: false,
		enumerable: false,
		value: 1
	});
}
catch (ignore) {}

if (test.length === 1) {
	// ES6
	desc = { configurable: true, writable: false, enumerable: false };
	defineProperty = Object.defineProperty;
	module.exports = function (fn, length) {
		length = toPosInt(length);
		if (fn.length === length) return fn;
		desc.value = length;
		return defineProperty(fn, "length", desc);
	};
} else {
	mixin = require("../object/mixin");
	generate = (function () {
		var cache = [];
		return function (length) {
			var args, i = 0;
			if (cache[length]) return cache[length];
			args = [];
			while (length--) args.push("a" + (++i).toString(36));
			// eslint-disable-next-line no-new-func
			return new Function(
				"fn",
				"return function (" + args.join(", ") + ") { return fn.apply(this, arguments); };"
			);
		};
	})();
	module.exports = function (src, length) {
		var target;
		length = toPosInt(length);
		if (src.length === length) return src;
		target = generate(length)(src);
		try { mixin(target, src); }
		catch (ignore) {}
		return target;
	};
}