mjackson/mach

var parseMediaValue = require('../utils/parseMediaValue');
var parseMediaValues = require('../utils/parseMediaValues');
var qualityFactorForMediaValue = require('../utils/qualityFactorForMediaValue');
var stringifyMediaValues = require('../utils/stringifyMediaValues');
var stringifyMediaValueWithoutQualityFactor = require('../utils/stringifyMediaValueWithoutQualityFactor');
var Header = require('../Header');

function byHighestPrecedence(a, b) {
  // "*" gets least precedence, all others are compared by specificity
  return a === '*' ? -1 : (b === '*' ? 1 : byMostSpecific(a, b));
}

function byMostSpecific(a, b) {
  return stringifyMediaValueWithoutQualityFactor(b).length - stringifyMediaValueWithoutQualityFactor(a).length;
}

/**
 * Represents an HTTP Accept-Language header and provides several methods
 * for determining acceptable content languages.
 *
 * http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.4
 */
class AcceptLanguage extends Header {

  constructor(value) {
    super('Accept-Language', value);
  }

  /**
   * Returns the value of this header as a string.
   */
  get value() {
    return stringifyMediaValues(this._mediaValues, '-') || '';
  }

  set value(value) {
    this._mediaValues = value ? parseMediaValues(value, '-') : [];
  }

  /**
   * Returns true if the given language is acceptable.
   */
  accepts(language) {
    return this.qualityFactorForLanguage(language) !== 0;
  }

  /**
   * Returns the quality factor for the given language.
   */
  qualityFactorForLanguage(language) {
    var values = this._mediaValues;

    if (!values.length)
      return 1;

    var givenValue = parseMediaValue(language, '-');
    var matchingValues = values.filter(function (value) {
      if (value.type === '*')
        return true;

      if (value.subtype && value.subtype !== givenValue.subtype)
        return false;

      return value.type === givenValue.type;
    }).sort(byHighestPrecedence);

    if (!matchingValues.length)
      return 0;

    return qualityFactorForMediaValue(matchingValues[0]);
  }

}

module.exports = AcceptLanguage;