/**
 * This function will be stringified and then injected into every rewired module.
 * Then you can set private variables by calling myModule.__set__("myPrivateVar", newValue);
 *
 * All variables within this function are namespaced in the arguments array because every
 * var declaration could possibly clash with a variable in the module scope.
 *
 * @param {String|Object} varName name of the variable to set
 * @param {String} varValue new value
 * @return {Function}
 */
function __set__() {
    arguments.varName = arguments[0];
    arguments.varValue = arguments[1];
    arguments.src = "";
    arguments.snapshot = {};

    if (typeof arguments[0] === "object" && arguments.length === 1) {
        arguments.env = arguments.varName;
        if (!arguments.env || Array.isArray(arguments.env)) {
            throw new TypeError("__set__ expects an object as env");
        }
        for (arguments.varName in arguments.env) {
            if (arguments.env.hasOwnProperty(arguments.varName)) {
                arguments.varValue = arguments.env[arguments.varName];
                arguments.src += arguments.varName + " = arguments.env." + arguments.varName + "; ";
                arguments.snapshot[arguments.varName] = eval(arguments.varName);
            }
        }
    } else if (typeof arguments.varName === "string" && arguments.length === 2) {
        if (!arguments.varName) {
            throw new TypeError("__set__ expects a non-empty string as a variable name");
        }
        arguments.src = arguments.varName + " = arguments.varValue;";
        arguments.snapshot[arguments.varName] = eval(arguments.varName);
    } else {
        throw new TypeError("__set__ expects an environment object or a non-empty string as a variable name");
    }

    eval(arguments.src);

    return function (snapshot) {
        module.exports.__set__(snapshot);
    }.bind(null, arguments.snapshot);
}

module.exports = __set__;
