/**
   * negotiator
   * Copyright(c) 2012 Isaac Z. Schlueter
   * Copyright(c) 2014 Federico Romero
   * Copyright(c) 2014-2015 Douglas Christopher Wilson
   * MIT Licensed
   */
  
  'use strict';
  
  /**
   * Module exports.
   * @public
   */
  
  module.exports = preferredLanguages;
  module.exports.preferredLanguages = preferredLanguages;
  
  /**
   * Module variables.
   * @private
   */
  
  var simpleLanguageRegExp = /^\s*([^\s\-;]+)(?:-([^\s;]+))?\s*(?:;(.*))?$/;
  
  /**
   * Parse the Accept-Language header.
   * @private
   */
  
  function parseAcceptLanguage(accept) {
    var accepts = accept.split(',');
  
    for (var i = 0, j = 0; i < accepts.length; i++) {
      var langauge = parseLanguage(accepts[i].trim(), i);
  
      if (langauge) {
        accepts[j++] = langauge;
      }
    }
  
    // trim accepts
    accepts.length = j;
  
    return accepts;
  }
  
  /**
   * Parse a language from the Accept-Language header.
   * @private
   */
  
  function parseLanguage(str, i) {
    var match = simpleLanguageRegExp.exec(str);
    if (!match) return null;
  
    var prefix = match[1],
        suffix = match[2],
        full = prefix;
  
    if (suffix) full += "-" + suffix;
  
    var q = 1;
    if (match[3]) {
      var params = match[3].split(';')
      for (var i = 0; i < params.length; i ++) {
        var p = params[i].split('=');
        if (p[0] === 'q') q = parseFloat(p[1]);
      }
    }
  
    return {
      prefix: prefix,
      suffix: suffix,
      q: q,
      i: i,
      full: full
    };
  }
  
  /**
   * Get the priority of a language.
   * @private
   */
  
  function getLanguagePriority(language, accepted, index) {
    var priority = {o: -1, q: 0, s: 0};
  
    for (var i = 0; i < accepted.length; i++) {
      var spec = specify(language, accepted[i], index);
  
      if (spec && (priority.s - spec.s || priority.q - spec.q || priority.o - spec.o) < 0) {
        priority = spec;
      }
    }
  
    return priority;
  }
  
  /**
   * Get the specificity of the language.
   * @private
   */
  
  function specify(language, spec, index) {
    var p = parseLanguage(language)
    if (!p) return null;
    var s = 0;
    if(spec.full.toLowerCase() === p.full.toLowerCase()){
      s |= 4;
    } else if (spec.prefix.toLowerCase() === p.full.toLowerCase()) {
      s |= 2;
    } else if (spec.full.toLowerCase() === p.prefix.toLowerCase()) {
      s |= 1;
    } else if (spec.full !== '*' ) {
      return null
    }
  
    return {
      i: index,
      o: spec.i,
      q: spec.q,
      s: s
    }
  };
  
  /**
   * Get the preferred languages from an Accept-Language header.
   * @public
   */
  
  function preferredLanguages(accept, provided) {
    // RFC 2616 sec 14.4: no header = *
    var accepts = parseAcceptLanguage(accept === undefined ? '*' : accept || '');
  
    if (!provided) {
      // sorted list of all languages
      return accepts
        .filter(isQuality)
        .sort(compareSpecs)
        .map(getFullLanguage);
    }
  
    var priorities = provided.map(function getPriority(type, index) {
      return getLanguagePriority(type, accepts, index);
    });
  
    // sorted list of accepted languages
    return priorities.filter(isQuality).sort(compareSpecs).map(function getLanguage(priority) {
      return provided[priorities.indexOf(priority)];
    });
  }
  
  /**
   * Compare two specs.
   * @private
   */
  
  function compareSpecs(a, b) {
    return (b.q - a.q) || (b.s - a.s) || (a.o - b.o) || (a.i - b.i) || 0;
  }
  
  /**
   * Get full language string.
   * @private
   */
  
  function getFullLanguage(spec) {
    return spec.full;
  }
  
  /**
   * Check if a spec has any quality.
   * @private
   */
  
  function isQuality(spec) {
    return spec.q > 0;
  }