Fix matching if a script can only be in one language

Closes GH-70.
Closes GH-72.

packages/franc/index.js

@@ -78,6 +78,8 @@ function detect(value, options) {
 function detectAll(value, options) {
   var settings = options || {}
   var minLength = MIN_LENGTH
+  var whitelist = settings.whitelist || []
+  var blacklist = settings.blacklist || []
   var script
 
   if (settings.minLength !== null && settings.minLength !== undefined) {
@@ -94,19 +96,27 @@ function detectAll(value, options) {
    * in `value`. */
   script = getTopScript(value, expressions)
 
-  /* One languages exists for the most-used script.
-   *
-   * If no matches occured, such as a digit only string,
-   * exit with `und`. */
+  /* One languages exists for the most-used script. */
   if (!(script[0] in data)) {
-    return script[1] === 0 ? und() : singleLanguageTuples(script[0])
+    /* If no matches occured, such as a digit only string,
+     * or because the language is ignored, exit with `und`. */
+    if (script[1] === 0 || !allow(script[0], whitelist, blacklist)) {
+      return und()
+    }
+
+    return singleLanguageTuples(script[0])
   }
 
   /* Get all distances for a given script, and
    * normalize the distance values. */
   return normalize(
     value,
-    getDistances(utilities.asTuples(value), data[script[0]], settings)
+    getDistances(
+      utilities.asTuples(value),
+      data[script[0]],
+      whitelist,
+      blacklist
+    )
   )
 }
 
@@ -181,14 +191,16 @@ function getOccurrence(value, expression) {
  *   array containing trigram--count tuples.
  * @param {Object.<Object>} languages - multiple
  *   trigrams to test against.
- * @param {Object} options - Configuration.
+ * @param {Array.<string>} whitelist - Whitelisted
+ *   languages; if non-empty, only included languages
+ *   are kept.
+ * @param {Array.<string>} blacklist - Blacklisted
+ *   languages; included languages are ignored.
  * @return {Array.<Array.<string, number>>} An array
  *   containing language--distance tuples.
  */
-function getDistances(trigrams, languages, options) {
+function getDistances(trigrams, languages, whitelist, blacklist) {
   var distances = []
-  var whitelist = options.whitelist || []
-  var blacklist = options.blacklist || []
   var language
 
   languages = filterLanguages(languages, whitelist, blacklist)
@@ -261,17 +273,37 @@ function filterLanguages(languages, whitelist, blacklist) {
   filteredLanguages = {}
 
   for (language in languages) {
-    if (
-      (whitelist.length === 0 || whitelist.indexOf(language) !== -1) &&
-      blacklist.indexOf(language) === -1
-    ) {
+    if (allow(language, whitelist, blacklist)) {
       filteredLanguages[language] = languages[language]
     }
   }
 
   return filteredLanguages
 }
 
+/**
+ * Check if `language` can match according to settings.
+ *
+ * @param {string} language - Languages
+ *   to filter
+ * @param {Array.<string>} whitelist - Whitelisted
+ *   languages; if non-empty, only included languages
+ *   are kept.
+ * @param {Array.<string>} blacklist - Blacklisted
+ *   languages; included languages are ignored.
+ * @return {boolean} - Whether `language` can match
+ */
+function allow(language, whitelist, blacklist) {
+  if (whitelist.length === 0 && blacklist.length === 0) {
+    return true
+  }
+
+  return (
+    (whitelist.length === 0 || whitelist.indexOf(language) !== -1) &&
+    blacklist.indexOf(language) === -1
+  )
+}
+
 /* Create a single `und` tuple. */
 function und() {
   return singleLanguageTuples('und')

test/api.js

@@ -54,6 +54,12 @@ test('franc()', function(t) {
     'should accept `blacklist`'
   )
 
+  t.deepEqual(
+    franc(fixtures.aii.fixture, {blacklist: ['aii']}),
+    'und',
+    'should support `blacklist` if the script can only be in that language'
+  )
+
   t.equal(
     franc(fixtureB, {whitelist: [languageA]}),
     languageA,