tags: writeID3v2Tags: write comment tag properly

src/tags.cpp

@@ -31,10 +31,12 @@
 #include <vorbisfile.h>
 #include <tag.h>
 #include <textidentificationframe.h>
+#include <commentsframe.h>
 #include <xiphcomment.h>
 
 #include "global.h"
 #include "settings.h"
+#include "utility/string.h"
 #include "utility/wide_string.h"
 
 namespace {//
@@ -151,9 +153,20 @@ void writeID3v2Tags(const MPD::MutableSong &s, TagLib::ID3v2::Tag *tag)
 		tag->removeFrames(type);
 		if (!list.isEmpty())
 		{
-			auto frame = new TagLib::ID3v2::TextIdentificationFrame(type, TagLib::String::UTF8);
-			frame->setText(list);
-			tag->addFrame(frame);
+			if (type == "COMM") // comment needs to be handled separately
+			{
+				auto frame = new TagLib::ID3v2::CommentsFrame(TagLib::String::UTF8);
+				// apparently there can't be multiple comments,
+				// so if there is more than one, join them.
+				frame->setText(join(list, TagLib::String(Config.tags_separator, TagLib::String::UTF8)));
+				tag->addFrame(frame);
+			}
+			else
+			{
+				auto frame = new TagLib::ID3v2::TextIdentificationFrame(type, TagLib::String::UTF8);
+				frame->setText(list);
+				tag->addFrame(frame);
+			}
 		}
 	};
 	writeID3v2("TIT2", tagList(s, &MPD::Song::getTitle));

src/utility/string.h

@@ -31,6 +31,27 @@ template <size_t N> size_t const_strlen(const char (&)[N]) {
 	return N-1;
 }
 
+// it's present in boost for std::string, but we want more general version.
+template <typename CollectionT, typename StringT>
+StringT join(CollectionT &&collection, StringT &&separator)
+{
+	StringT result;
+	auto first = std::begin(collection), last = std::end(collection);
+	if (first != last)
+	{
+		while (true)
+		{
+			result += *first;
+			++first;
+			if (first != last)
+				result += separator;
+			else
+				break;
+		}
+	}
+	return result;
+}
+
 std::string getBasename(const std::string &path);
 std::string getParentDirectory(const std::string &path);
 std::string getSharedDirectory(const std::string &dir1, const std::string &dir2);