mjackson/mach

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

function byHighestPrecedence(a, b) {
  // "*" gets least precedence, all others are equal
  return a === '*' ? -1 : (b === '*' ? 1 : 0);
}

/**
 * Represents an HTTP Accept-Charset header and provides several methods
 * for determining acceptable content character sets.
 *
 * http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.2
 */
class AcceptCharset extends Header {

  constructor(value) {
    super('Accept-Charset', 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 charset is acceptable.
   */
  accepts(charset) {
    return this.qualityFactorForCharset(charset) !== 0;
  }

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

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

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

    // From RFC 2616:
    // The special value "*", if present in the Accept-Charset field, matches every character
    // set (including ISO-8859-1) which is not mentioned elsewhere in the Accept-Charset field.
    // If no "*" is present in an Accept-Charset field, then all character sets not explicitly
    // mentioned get a quality value of 0, except for ISO-8859-1, which gets a quality value of
    // 1 if not explicitly mentioned.
    if (givenValue.type === 'iso-8859-1') {
      if (matchingValues.length && matchingValues[0].type === 'iso-8859-1')
        return qualityFactorForMediaValue(matchingValues[0]);

      return 1;
    }

    if (!matchingValues.length)
      return 0;

    return qualityFactorForMediaValue(matchingValues[0]);
  }

}

module.exports = AcceptCharset;