/**
 * @fileoverview Implements the Node.js require.resolve algorithm
 * @author Nicholas C. Zakas
 */

"use strict";

//------------------------------------------------------------------------------
// Requirements
//------------------------------------------------------------------------------

var lodash = require("lodash"),
    Module = require("module");

//------------------------------------------------------------------------------
// Private
//------------------------------------------------------------------------------

var DEFAULT_OPTIONS = {

    /*
     * module.paths is an array of paths to search for resolving things relative
     * to this file. Module.globalPaths contains all of the special Node.js
     * directories that can also be searched for modules.
     *
     * Need to check for existence of module.paths because Jest seems not to
     * include it. See https://github.com/eslint/eslint/issues/5791.
     */
    lookupPaths: module.paths ? module.paths.concat(Module.globalPaths) : Module.globalPaths.concat()
};

/**
 * Resolves modules based on a set of options.
 * @param {Object} options The options for resolving modules.
 * @param {string[]} options.lookupPaths An array of paths to include in the
 *      lookup with the highest priority paths coming first.
 * @constructor
 */
function ModuleResolver(options) {
    options = options || {};

    this.options = lodash.assign({}, DEFAULT_OPTIONS, options);
}

ModuleResolver.prototype = {

    /**
     * Resolves the file location of a given module relative to the configured
     * lookup paths.
     * @param {string} name The module name to resolve.
     * @param {string} extraLookupPath An extra path to look into for the module.
     *      This path is used with the highest priority.
     * @returns {string} The resolved file path for the module.
     * @throws {Error} If the module cannot be resolved.
     */
    resolve: function(name, extraLookupPath) {

        /*
         * First, clone the lookup paths so we're not messing things up for
         * subsequent calls to this function. Then, move the extraLookupPath to the
         * top of the lookup paths list so it will be searched first.
         */
        var lookupPaths = this.options.lookupPaths.concat();

        lookupPaths.unshift(extraLookupPath);

        /**
         * Module._findPath is an internal method to Node.js, then one they use to
         * lookup file paths when require() is called. So, we are hooking into the
         * exact same logic that Node.js uses.
         */
        var result = Module._findPath(name, lookupPaths);   // eslint-disable-line no-underscore-dangle

        if (!result) {
            throw new Error("Cannot find module '" + name + "'");
        }

        return result;

    }

};

//------------------------------------------------------------------------------
// Public API
//------------------------------------------------------------------------------

module.exports = ModuleResolver;
