Improvement on the detection of empty lyrics

src/songinfo/ultimatelyricsprovider.cpp

@@ -141,7 +141,7 @@ void UltimateLyricsProvider::LyricsFetched() {
         ApplyExcludeRule(rule, &lyrics);
       }
 
-      if (!content.isEmpty()) {
+      if (!content.isEmpty() and HTMLHasAlphaNumeric(content)) {
         lyrics = content;
         break;
       }
@@ -150,7 +150,7 @@ void UltimateLyricsProvider::LyricsFetched() {
     lyrics = original_content;
   }
 
-  if (!lyrics.isEmpty()) {
+  if (!lyrics.isEmpty() and HTMLHasAlphaNumeric(lyrics)) {
     CollapsibleInfoPane::Data data;
     data.id_ = "ultimatelyrics/" + name_;
     data.title_ = tr("Lyrics from %1").arg(name_);
@@ -317,3 +317,22 @@ QString UltimateLyricsProvider::NoSpace(const QString& text) {
   ret.remove(' ');
   return ret;
 }
+
+// tells whether a html block has alphanumeric characters (skipping tags)
+// TODO: handle special characters (e.g. ® á)
+bool UltimateLyricsProvider::HTMLHasAlphaNumeric(const QString& html) {
+  bool has_alphanumeric = false;
+  for (int i = 0; i < html.size(); )
+    if (html[i] == QChar('<')) {
+      while (i < html.size() and html[i] != QChar('>'))
+        i ++;
+    } else {
+      if (isalnum(html[i].toAscii())) {
+        has_alphanumeric = true;
+        break;
+      }
+      i ++;
+    }
+    
+  return has_alphanumeric;
+}

src/songinfo/ultimatelyricsprovider.h

@@ -73,6 +73,7 @@ private:
   static QString FirstChar(const QString& text);
   static QString TitleCase(const QString& text);
   static QString NoSpace(const QString& text);
+  static bool HTMLHasAlphaNumeric(const QString& html);
 
   void ReplaceField(const QString& tag, const QString& value, QString* text) const;
   void ReplaceFields(const Song& metadata, QString* text) const;