function monkeyPatch(name, parentObj, patches) {
	const injId   = Symbol()
	const before  = (patches["before"]  === undefined) ? (...args)=>args     :  patches["before"];
	const instead = (patches["instead"] === undefined) ? (res,...args)=>res(...args) : patches["instead"];
	const after   = (patches["after"]   === undefined) ? (args, res)=>res    :   patches["after"];
	const handler = {
		apply: (target, thisArg, [ctx, args]) => {
			before.apply(ctx, args);
			res = instead(target.bind(ctx), args)
			return after.apply(ctx, args.concat([res]));
		}
	};
	const prox = new Proxy(parentObj[name], handler);
	const orig = parentObj[name];
	parentObj[name] = function() {
		return prox(this, [arguments]);
	};
	const unpatch = () => {
		parentObj[name] = orig;
	}
	parentObj[injId] = {
		name:    name,
		orig:    orig,
		unpatch: unpatch
	};
	return unpatch;
}

function before(name, parentObj, func) {
	return monkeyPatch(name, parentObj, {before: func})
}

function instead(name, parentObj, func) {
	return monkeyPatch(name, parentObj, {instead: func})
}

function after(name, parentObj, func) {
	return monkeyPatch(name, parentObj, {after: func})
}

module.exports = {
	monkeyPatch,
	before,
	instead,
	after
}