'use strict';

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

  , test = function (a, b) {}, 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 (l) {
			var args, i = 0;
			if (cache[l]) return cache[l];
			args = [];
			while (l--) args.push('a' + (++i).toString(36));
			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;
	};
}