jaredhanson/locomotive

/**
 * Creates an instance of `Resolver`.
 *
 * A resolver is responsible for resolving a module ID to its corresponding
 * path on the filesystem.
 *
 * Locomotive uses a resolver to locate controller modules, which are loaded
 * and instantiated in order to handle requests.
 *
 * @constructor
 * @api protected
 */
function Resolver() {
  this._mechs = [];
}

/**
 * Resolve `id`.
 *
 * @param {String} id
 * @return {String}
 * @api protected
 */
Resolver.prototype.resolve = function(id) {
  var mechs = this._mechs
    , mech, prefix, mid, rid;
  for (var i = 0, len = mechs.length; i < len; ++i) {
    mech = mechs[i];
    prefix = mech.prefix;
    if (id.indexOf(prefix) !== 0) { continue; }
    mid = id.slice(prefix.length);
    rid = mech.fn(mid);
    if (rid) { return rid; }
  }
  throw new Error("Unable to resolve '" + id + "'");
};

/**
 * Utilize new mechanism `fn`, optionally scoped to `prefix`.
 *
 * @param {String} prefix
 * @param {Function} fn
 * @api protected
 */
Resolver.prototype.use = function(prefix, fn) {
  if (typeof prefix == 'function') {
    fn = prefix;
    prefix = '';
  }
  if (prefix.length && prefix[prefix.length - 1] != '/') { prefix += '/'; }
  this._mechs.push({ prefix: prefix, fn: fn });
};


/**
 * Expose `Resolver`.
 */
module.exports = Resolver;