var App = function () {
    var app_instance;

    app_instance = function () {
        var app         = {},
            definitions = {},
            constants   = {},
            overwrites  = {};

        app.define = function (constant, definition) {
            if (definitions[constant] !== undefined) {
                throw "Constant '" + constant + "' already defined."
            }
            if (typeof definition !== 'function') {
                throw "Definition has to be a function."
            }

            definitions[constant] = definition;
        };

        app.require = function (constant) {
            if (overwrites[constant]) {
                return overwrites[constant]();
            }

            if (constants[constant] === undefined) {
                if (definitions[constant] === undefined) {
                    throw "Constant '" + constant + "' not defined."
                }
                constants[constant] = definitions[constant]();
            }

            return constants[constant];
        };

        app.overwrite = function(constant, definition) {
            overwrites[constant] = definition;
        }

        app.reset = function(constant) {
            delete overwrites[constant];
        }

        app.resetDefinitions = function () {
            constants = {};
        };

        return app;
    }

    return {
        Mediators: {},
        induce: function (scope) {
            scope.app = app_instance();
        }
    };
}();

App.induce(window);