DatabaseCommands: "list" allows grouping

src/db/Helpers.cxx

@@ -22,6 +22,7 @@
 #include "Interface.hxx"
 #include "LightSong.hxx"
 #include "tag/Tag.hxx"
+#include "tag/TagBuilder.hxx"
 
 #include <functional>
 #include <set>
@@ -38,13 +39,100 @@ struct StringLess {
 
 typedef std::set<const char *, StringLess> StringSet;
 
+struct TagLess {
+	gcc_pure
+	bool operator()(const Tag &a, const Tag &b) const {
+		if (a.num_items != b.num_items)
+			return a.num_items < b.num_items;
+
+		const unsigned n = a.num_items;
+		for (unsigned i = 0; i < n; ++i) {
+			const TagItem &ai = *a.items[i];
+			const TagItem &bi = *b.items[i];
+			if (ai.type != bi.type)
+				return unsigned(ai.type) < unsigned(bi.type);
+
+			const int cmp = strcmp(ai.value, bi.value);
+			if (cmp != 0)
+				return cmp < 0;
+		}
+
+		return false;
+	}
+};
+
+typedef std::set<Tag, TagLess> TagSet;
+
+/**
+ * Copy all tag items of the specified type.
+ */
 static bool
-CheckUniqueTag(StringSet &set, const Tag &tag, TagType type)
+CopyTagItem(TagBuilder &dest, TagType dest_type,
+	    const Tag &src, TagType src_type)
+{
+	bool found = false;
+	const unsigned n = src.num_items;
+	for (unsigned i = 0; i < n; ++i) {
+		if (src.items[i]->type == src_type) {
+			dest.AddItem(dest_type, src.items[i]->value);
+			found = true;
+		}
+	}
+
+	return found;
+}
+
+/**
+ * Copy all tag items of the specified type.  Fall back to "Artist" if
+ * there is no "AlbumArtist".
+ */
+static void
+CopyTagItem(TagBuilder &dest, const Tag &src, TagType type)
+{
+	if (!CopyTagItem(dest, type, src, type) &&
+	    type == TAG_ALBUM_ARTIST)
+		CopyTagItem(dest, type, src, TAG_ARTIST);
+}
+
+/**
+ * Copy all tag items of the types in the mask.
+ */
+static void
+CopyTagMask(TagBuilder &dest, const Tag &src, uint32_t mask)
+{
+	for (unsigned i = 0; i < TAG_NUM_OF_ITEM_TYPES; ++i)
+		if ((mask & (1u << i)) != 0)
+			CopyTagItem(dest, src, TagType(i));
+}
+
+static void
+InsertUniqueTag(TagSet &set, const Tag &src, TagType type, const char *value,
+		uint32_t group_mask)
+{
+	TagBuilder builder;
+	if (value == nullptr)
+		builder.AddEmptyItem(type);
+	else
+		builder.AddItem(type, value);
+	CopyTagMask(builder, src, group_mask);
+#if defined(__clang__) || GCC_CHECK_VERSION(4,8)
+	set.emplace(builder.Commit());
+#else
+	set.insert(builder.Commit());
+#endif
+}
+
+static bool
+CheckUniqueTag(TagSet &set, TagType dest_type,
+	       const Tag &tag, TagType src_type,
+	       uint32_t group_mask)
 {
 	bool found = false;
 	for (unsigned i = 0; i < tag.num_items; ++i) {
-		if (tag.items[i]->type == type) {
-			set.insert(tag.items[i]->value);
+		if (tag.items[i]->type == src_type) {
+			InsertUniqueTag(set, tag, dest_type,
+					tag.items[i]->value,
+					group_mask);
 			found = true;
 		}
 	}
@@ -53,35 +141,42 @@ CheckUniqueTag(StringSet &set, const Tag &tag, TagType type)
 }
 
 static bool
-CollectTags(StringSet &set, TagType tag_type, const LightSong &song)
+CollectTags(TagSet &set, TagType tag_type, uint32_t group_mask,
+	    const LightSong &song)
 {
+	static_assert(sizeof(group_mask) * 8 >= TAG_NUM_OF_ITEM_TYPES,
+		      "Mask is too small");
+
+	assert((group_mask & (1u << unsigned(tag_type))) == 0);
+
 	assert(song.tag != nullptr);
 	const Tag &tag = *song.tag;
 
-	if (!CheckUniqueTag(set, tag, tag_type) &&
+	if (!CheckUniqueTag(set, tag_type, tag, tag_type, group_mask) &&
 	    (tag_type != TAG_ALBUM_ARTIST ||
 	     /* fall back to "Artist" if no "AlbumArtist" was found */
-	     !CheckUniqueTag(set, tag, TAG_ARTIST)))
-		set.insert("");
+	     !CheckUniqueTag(set, tag_type, tag, TAG_ARTIST, group_mask)))
+		InsertUniqueTag(set, tag, tag_type, nullptr, group_mask);
 
 	return true;
 }
 
 bool
 VisitUniqueTags(const Database &db, const DatabaseSelection &selection,
-		TagType tag_type,
-		VisitString visit_string,
+		TagType tag_type, uint32_t group_mask,
+		VisitTag visit_tag,
 		Error &error)
 {
-	StringSet set;
+	TagSet set;
 
 	using namespace std::placeholders;
-	const auto f = std::bind(CollectTags, std::ref(set), tag_type, _1);
+	const auto f = std::bind(CollectTags, std::ref(set),
+				 tag_type, group_mask, _1);
 	if (!db.Visit(selection, f, error))
 		return false;
 
-	for (auto value : set)
-		if (!visit_string(value, error))
+	for (const auto &value : set)
+		if (!visit_tag(value, error))
 			return false;
 
 	return true;