1/**
  2 * negotiator
  3 * Copyright(c) 2012 Isaac Z. Schlueter
  4 * Copyright(c) 2014 Federico Romero
  5 * Copyright(c) 2014-2015 Douglas Christopher Wilson
  6 * MIT Licensed
  7 */
  8
  9'use strict';
 10
 11/**
 12 * Module exports.
 13 * @public
 14 */
 15
 16module.exports = preferredEncodings;
 17module.exports.preferredEncodings = preferredEncodings;
 18
 19/**
 20 * Module variables.
 21 * @private
 22 */
 23
 24var simpleEncodingRegExp = /^\s*([^\s;]+)\s*(?:;(.*))?$/;
 25
 26/**
 27 * Parse the Accept-Encoding header.
 28 * @private
 29 */
 30
 31function parseAcceptEncoding(accept) {
 32  var accepts = accept.split(',');
 33  var hasIdentity = false;
 34  var minQuality = 1;
 35
 36  for (var i = 0, j = 0; i < accepts.length; i++) {
 37    var encoding = parseEncoding(accepts[i].trim(), i);
 38
 39    if (encoding) {
 40      accepts[j++] = encoding;
 41      hasIdentity = hasIdentity || specify('identity', encoding);
 42      minQuality = Math.min(minQuality, encoding.q || 1);
 43    }
 44  }
 45
 46  if (!hasIdentity) {
 47    /*
 48     * If identity doesn't explicitly appear in the accept-encoding header,
 49     * it's added to the list of acceptable encoding with the lowest q
 50     */
 51    accepts[j++] = {
 52      encoding: 'identity',
 53      q: minQuality,
 54      i: i
 55    };
 56  }
 57
 58  // trim accepts
 59  accepts.length = j;
 60
 61  return accepts;
 62}
 63
 64/**
 65 * Parse an encoding from the Accept-Encoding header.
 66 * @private
 67 */
 68
 69function parseEncoding(str, i) {
 70  var match = simpleEncodingRegExp.exec(str);
 71  if (!match) return null;
 72
 73  var encoding = match[1];
 74  var q = 1;
 75  if (match[2]) {
 76    var params = match[2].split(';');
 77    for (var i = 0; i < params.length; i ++) {
 78      var p = params[i].trim().split('=');
 79      if (p[0] === 'q') {
 80        q = parseFloat(p[1]);
 81        break;
 82      }
 83    }
 84  }
 85
 86  return {
 87    encoding: encoding,
 88    q: q,
 89    i: i
 90  };
 91}
 92
 93/**
 94 * Get the priority of an encoding.
 95 * @private
 96 */
 97
 98function getEncodingPriority(encoding, accepted, index) {
 99  var priority = {o: -1, q: 0, s: 0};
100
101  for (var i = 0; i < accepted.length; i++) {
102    var spec = specify(encoding, accepted[i], index);
103
104    if (spec && (priority.s - spec.s || priority.q - spec.q || priority.o - spec.o) < 0) {
105      priority = spec;
106    }
107  }
108
109  return priority;
110}
111
112/**
113 * Get the specificity of the encoding.
114 * @private
115 */
116
117function specify(encoding, spec, index) {
118  var s = 0;
119  if(spec.encoding.toLowerCase() === encoding.toLowerCase()){
120    s |= 1;
121  } else if (spec.encoding !== '*' ) {
122    return null
123  }
124
125  return {
126    i: index,
127    o: spec.i,
128    q: spec.q,
129    s: s
130  }
131};
132
133/**
134 * Get the preferred encodings from an Accept-Encoding header.
135 * @public
136 */
137
138function preferredEncodings(accept, provided) {
139  var accepts = parseAcceptEncoding(accept || '');
140
141  if (!provided) {
142    // sorted list of all encodings
143    return accepts
144      .filter(isQuality)
145      .sort(compareSpecs)
146      .map(getFullEncoding);
147  }
148
149  var priorities = provided.map(function getPriority(type, index) {
150    return getEncodingPriority(type, accepts, index);
151  });
152
153  // sorted list of accepted encodings
154  return priorities.filter(isQuality).sort(compareSpecs).map(function getEncoding(priority) {
155    return provided[priorities.indexOf(priority)];
156  });
157}
158
159/**
160 * Compare two specs.
161 * @private
162 */
163
164function compareSpecs(a, b) {
165  return (b.q - a.q) || (b.s - a.s) || (a.o - b.o) || (a.i - b.i) || 0;
166}
167
168/**
169 * Get full encoding string.
170 * @private
171 */
172
173function getFullEncoding(spec) {
174  return spec.encoding;
175}
176
177/**
178 * Check if a spec has any quality.
179 * @private
180 */
181
182function isQuality(spec) {
183  return spec.q > 0;
184}