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 paramsMatchIgnoringQualityFactor(params, givenParams) {
  for (var paramName in params)
    if (params.hasOwnProperty(paramName) && paramName !== 'q' && givenParams[paramName] !== params[paramName])
      return false;

  return true;
}

function byHighestPrecedence(a, b) {
  //   Accept: text/*, text/html, text/html;level=1, */*
  //
  // have the following precedence:
  //
  //   1) text/html;level=1
  //   2) text/html
  //   3) text/*
  //   4) */*
  return stringifyMediaValueWithoutQualityFactor(b).length - stringifyMediaValueWithoutQualityFactor(a).length;
}

/**
 * Represents an HTTP Accept header and provides several methods for
 * determining acceptable media types.
 *
 * http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.1
 */
class Accept extends Header {

  constructor(value) {
    super('Accept', 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 media type is acceptable.
   */
  accepts(mediaType) {
    return this.qualityFactorForMediaType(mediaType) !== 0;
  }

  /**
   * Returns the quality factor for the given media type.
   */
  qualityFactorForMediaType(mediaType) {
    var values = this._mediaValues;

    if (!values.length)
      return 1;

    var givenValue = parseMediaValue(mediaType);
    var matchingValues = values.filter(function (value) {
      return (value.type === '*' || value.type === givenValue.type) &&
             (value.subtype === '*' || value.subtype === givenValue.subtype) &&
             paramsMatchIgnoringQualityFactor(value.params, givenValue.params);
    }).sort(byHighestPrecedence);

    if (!matchingValues.length)
      return 0;

    return qualityFactorForMediaValue(matchingValues[0]);
  }

}

module.exports = Accept;