refactor: move lang detection to library module

Author: marionebl

source/library/ensure-language.js

@@ -0,0 +1,17 @@
+import franc from 'franc';
+
+export default (input, allowed) => {
+	const detected = franc.all(input)
+		.filter(lang => lang[1] >= 0.45)
+		.map(lang => lang[0]);
+
+	// franc spits out ['und'] when unable to
+	// guess any languages, let it through in this case
+	const matches = detected[0] === 'und' ||
+		detected.indexOf(allowed) > -1;
+
+	return {
+		matches,
+		detected
+	};
+};

source/rules/lang.js

@@ -1,15 +1,8 @@
-import franc from 'franc';
+import ensureLanguage from '../library/ensure-language';
 
 export default (parsed, when, value) => {
 	const negated = when === 'never';
-	const detected = franc.all(parsed.subject)
-		.filter(lang => lang[1] >= 0.45)
-		.map(lang => lang[0]);
-
-	// franc spits out ['und'] when unable to
-	// guess any languages, let it through in this case
-	const matches = detected[0] === 'und' ||
-		detected.indexOf(value) > -1;
+	const {matches, detected} = ensureLanguage(parsed.subject, value);
 
 	return [
 		negated ? !matches : matches,