(function () {

    var modules = {};

    // Stack of moduleIds currently being built.

    var requireStack = [];

    // Map of module ID -> index into requireStack of modules currently being built.

    var inProgressModules = {};

    var SEPARATOR = '.';

    function build (module) {

        var factory = module.factory;

        var localRequire = function (id) {

            var resultantId = id;

            // Its a relative path, so lop off the last portion and add the id (minus "./")

            if (id.charAt(0) === '.') {

                resultantId = module.id.slice(0, module.id.lastIndexOf(SEPARATOR)) + SEPARATOR + id.slice(2);

            }

            return require(resultantId);

        };

        module.exports = {};

        delete module.factory;

        factory(localRequire, module.exports, module);

        return module.exports;

    }

    require = function (id) {

        if (!modules[id]) {

            throw 'module ' + id + ' not found';

        } else if (id in inProgressModules) {

            var cycle = requireStack.slice(inProgressModules[id]).join('->') + '->' + id;

            throw 'Cycle in require graph: ' + cycle;

        }

        if (modules[id].factory) {

            try {

                inProgressModules[id] = requireStack.length;

                requireStack.push(id);

                return build(modules[id]);

            } finally {

                delete inProgressModules[id];

                requireStack.pop();

            }

        }

        return modules[id].exports;

    };

    define = function (id, factory) {

        if (modules[id]) {

            throw 'module ' + id + ' already defined';

        }

        modules[id] = {

            id: id,

            factory: factory

        };

    };

    define.remove = function (id) {

        delete modules[id];

    };

    define.moduleMap = modules;

})();