/*!
 * negotiator
 * Copyright(c) 2012 Federico Romero
 * Copyright(c) 2012-2014 Isaac Z. Schlueter
 * Copyright(c) 2015 Douglas Christopher Wilson
 * MIT Licensed
 */

'use strict';

/**
 * Cached loaded submodules.
 * @private
 */

var modules = Object.create(null);

/**
 * Module exports.
 * @public
 */

module.exports = Negotiator;
module.exports.Negotiator = Negotiator;

/**
 * Create a Negotiator instance from a request.
 * @param {object} request
 * @public
 */

function Negotiator(request) {
  if (!(this instanceof Negotiator)) {
    return new Negotiator(request);
  }

  this.request = request;
}

Negotiator.prototype.charset = function charset(available) {
  var set = this.charsets(available);
  return set && set[0];
};

Negotiator.prototype.charsets = function charsets(available) {
  var preferredCharsets = loadModule('charset').preferredCharsets;
  return preferredCharsets(this.request.headers['accept-charset'], available);
};

Negotiator.prototype.encoding = function encoding(available) {
  var set = this.encodings(available);
  return set && set[0];
};

Negotiator.prototype.encodings = function encodings(available) {
  var preferredEncodings = loadModule('encoding').preferredEncodings;
  return preferredEncodings(this.request.headers['accept-encoding'], available);
};

Negotiator.prototype.language = function language(available) {
  var set = this.languages(available);
  return set && set[0];
};

Negotiator.prototype.languages = function languages(available) {
  var preferredLanguages = loadModule('language').preferredLanguages;
  return preferredLanguages(this.request.headers['accept-language'], available);
};

Negotiator.prototype.mediaType = function mediaType(available) {
  var set = this.mediaTypes(available);
  return set && set[0];
};

Negotiator.prototype.mediaTypes = function mediaTypes(available) {
  var preferredMediaTypes = loadModule('mediaType').preferredMediaTypes;
  return preferredMediaTypes(this.request.headers.accept, available);
};

// Backwards compatibility
Negotiator.prototype.preferredCharset = Negotiator.prototype.charset;
Negotiator.prototype.preferredCharsets = Negotiator.prototype.charsets;
Negotiator.prototype.preferredEncoding = Negotiator.prototype.encoding;
Negotiator.prototype.preferredEncodings = Negotiator.prototype.encodings;
Negotiator.prototype.preferredLanguage = Negotiator.prototype.language;
Negotiator.prototype.preferredLanguages = Negotiator.prototype.languages;
Negotiator.prototype.preferredMediaType = Negotiator.prototype.mediaType;
Negotiator.prototype.preferredMediaTypes = Negotiator.prototype.mediaTypes;

/**
 * Load the given module.
 * @private
 */

function loadModule(moduleName) {
  var module = modules[moduleName];

  if (module !== undefined) {
    return module;
  }

  // This uses a switch for static require analysis
  switch (moduleName) {
    case 'charset':
      module = require('negotiator/lib/charset');
      break;
    case 'encoding':
      module = require('negotiator/lib/encoding');
      break;
    case 'language':
      module = require('negotiator/lib/language');
      break;
    case 'mediaType':
      module = require('negotiator/lib/mediaType');
      break;
    default:
      throw new Error('Cannot find module \'' + moduleName + '\'');
  }

  // Store to prevent invoking require()
  modules[moduleName] = module;

  return module;
}
