song/Filter: move each class into a separate source

17 files changed, 683 insertions, 345 deletions

diff --git a/src/db/plugins/ProxyDatabasePlugin.cxx b/src/db/plugins/ProxyDatabasePlugin.cxx
index 7aeb08b4a..1a21f32c0 100644
--- a/src/db/plugins/ProxyDatabasePlugin.cxx
+++ b/src/db/plugins/ProxyDatabasePlugin.cxx
@@ -29,6 +29,9 @@
 #include "song/LightSong.hxx"
 #include "db/Stats.hxx"
 #include "song/Filter.hxx"
+#include "song/UriSongFilter.hxx"
+#include "song/BaseSongFilter.hxx"
+#include "song/TagSongFilter.hxx"
 #include "Compiler.h"
 #include "config/Block.hxx"
 #include "tag/Builder.hxx"
diff --git a/src/db/plugins/upnp/UpnpDatabasePlugin.cxx b/src/db/plugins/upnp/UpnpDatabasePlugin.cxx
index a901a9675..b6ed6fdc5 100644
--- a/src/db/plugins/upnp/UpnpDatabasePlugin.cxx
+++ b/src/db/plugins/upnp/UpnpDatabasePlugin.cxx
@@ -30,6 +30,8 @@
 #include "db/DatabaseError.hxx"
 #include "db/LightDirectory.hxx"
 #include "song/LightSong.hxx"
+#include "song/Filter.hxx"
+#include "song/TagSongFilter.hxx"
 #include "db/Stats.hxx"
 #include "config/Block.hxx"
 #include "tag/Builder.hxx"
@@ -37,7 +39,6 @@
 #include "tag/Mask.hxx"
 #include "fs/Traits.hxx"
 #include "Log.hxx"
-#include "song/Filter.hxx"
 #include "util/SplitString.hxx"
 
 #include <string>
diff --git a/src/song/AndSongFilter.cxx b/src/song/AndSongFilter.cxx
new file mode 100644
index 000000000..f0b9f86df
--- /dev/null
+++ b/src/song/AndSongFilter.cxx
@@ -0,0 +1,63 @@
+/*
+ * Copyright 2003-2018 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include "config.h"
+#include "AndSongFilter.hxx"
+
+ISongFilterPtr
+AndSongFilter::Clone() const noexcept
+{
+	auto result = std::make_unique<AndSongFilter>();
+
+	for (const auto &i : items)
+		result->items.emplace_back(i->Clone());
+
+	return result;
+}
+
+std::string
+AndSongFilter::ToExpression() const noexcept
+{
+	auto i = items.begin();
+	const auto end = items.end();
+
+	if (std::next(i) == end)
+		return (*i)->ToExpression();
+
+	std::string e("(");
+	e += (*i)->ToExpression();
+
+	for (++i; i != end; ++i) {
+		e += " AND ";
+		e += (*i)->ToExpression();
+	}
+
+	e.push_back(')');
+	return e;
+}
+
+bool
+AndSongFilter::Match(const LightSong &song) const noexcept
+{
+	for (const auto &i : items)
+		if (!i->Match(song))
+			return false;
+
+	return true;
+}
diff --git a/src/song/AndSongFilter.hxx b/src/song/AndSongFilter.hxx
new file mode 100644
index 000000000..5c49a98c1
--- /dev/null
+++ b/src/song/AndSongFilter.hxx
@@ -0,0 +1,55 @@
+/*
+ * Copyright 2003-2018 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#ifndef MPD_AND_SONG_FILTER_HXX
+#define MPD_AND_SONG_FILTER_HXX
+
+#include "ISongFilter.hxx"
+#include "Compiler.h"
+
+#include <list>
+
+/**
+ * Combine multiple #ISongFilter instances with logical "and".
+ */
+class AndSongFilter final : public ISongFilter {
+	std::list<ISongFilterPtr> items;
+
+public:
+	const auto &GetItems() const noexcept {
+		return items;
+	}
+
+	template<typename I>
+	void AddItem(I &&_item) {
+		items.emplace_back(std::forward<I>(_item));
+	}
+
+	gcc_pure
+	bool IsEmpty() const noexcept {
+		return items.empty();
+	}
+
+	/* virtual methods from ISongFilter */
+	ISongFilterPtr Clone() const noexcept override;
+	std::string ToExpression() const noexcept override;
+	bool Match(const LightSong &song) const noexcept override;
+};
+
+#endif
diff --git a/src/song/BaseSongFilter.cxx b/src/song/BaseSongFilter.cxx
new file mode 100644
index 000000000..b30527478
--- /dev/null
+++ b/src/song/BaseSongFilter.cxx
@@ -0,0 +1,35 @@
+/*
+ * Copyright 2003-2018 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include "config.h"
+#include "BaseSongFilter.hxx"
+#include "LightSong.hxx"
+#include "util/UriUtil.hxx"
+
+std::string
+BaseSongFilter::ToExpression() const noexcept
+{
+	return "(base \"" + value + "\")";
+}
+
+bool
+BaseSongFilter::Match(const LightSong &song) const noexcept
+{
+	return uri_is_child_or_same(value.c_str(), song.GetURI().c_str());
+}
diff --git a/src/song/BaseSongFilter.hxx b/src/song/BaseSongFilter.hxx
new file mode 100644
index 000000000..d5a049bf2
--- /dev/null
+++ b/src/song/BaseSongFilter.hxx
@@ -0,0 +1,48 @@
+/*
+ * Copyright 2003-2018 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#ifndef MPD_BASE_SONG_FILTER_HXX
+#define MPD_BASE_SONG_FILTER_HXX
+
+#include "ISongFilter.hxx"
+#include "Compiler.h"
+
+class BaseSongFilter final : public ISongFilter {
+	std::string value;
+
+public:
+	BaseSongFilter(const BaseSongFilter &) = default;
+
+	template<typename V>
+	explicit BaseSongFilter(V &&_value)
+		:value(std::forward<V>(_value)) {}
+
+	const char *GetValue() const noexcept {
+		return value.c_str();
+	}
+
+	ISongFilterPtr Clone() const noexcept override {
+		return std::make_unique<BaseSongFilter>(*this);
+	}
+
+	std::string ToExpression() const noexcept override;
+	bool Match(const LightSong &song) const noexcept override;
+};
+
+#endif
diff --git a/src/song/Filter.cxx b/src/song/Filter.cxx
index 6259cefae..2f1e1180c 100644
--- a/src/song/Filter.cxx
+++ b/src/song/Filter.cxx
@@ -19,6 +19,10 @@
 
 #include "config.h"
 #include "Filter.hxx"
+#include "UriSongFilter.hxx"
+#include "BaseSongFilter.hxx"
+#include "TagSongFilter.hxx"
+#include "ModifiedSinceSongFilter.hxx"
 #include "LightSong.hxx"
 #include "tag/ParseName.hxx"
 #include "tag/Tag.hxx"
@@ -75,158 +79,6 @@ locate_parse_type(const char *str) noexcept
 	return tag_name_parse_i(str);
 }
 
-bool
-StringFilter::Match(const char *s) const noexcept
-{
-#if !CLANG_CHECK_VERSION(3,6)
-	/* disabled on clang due to -Wtautological-pointer-compare */
-	assert(s != nullptr);
-#endif
-
-	if (fold_case) {
-		return fold_case.IsIn(s);
-	} else {
-		return StringIsEqual(s, value.c_str());
-	}
-}
-
-std::string
-UriSongFilter::ToExpression() const noexcept
-{
-	return std::string("(" LOCATE_TAG_FILE_KEY " ") + (negated ? "!=" : "==") + " \"" + filter.GetValue() + "\")";
-}
-
-bool
-UriSongFilter::Match(const LightSong &song) const noexcept
-{
-	return filter.Match(song.GetURI().c_str()) != negated;
-}
-
-std::string
-BaseSongFilter::ToExpression() const noexcept
-{
-	return "(base \"" + value + "\")";
-}
-
-bool
-BaseSongFilter::Match(const LightSong &song) const noexcept
-{
-	return uri_is_child_or_same(value.c_str(), song.GetURI().c_str());
-}
-
-std::string
-TagSongFilter::ToExpression() const noexcept
-{
-	const char *name = type == TAG_NUM_OF_ITEM_TYPES
-		? LOCATE_TAG_ANY_KEY
-		: tag_item_names[type];
-
-	return std::string("(") + name + " " + (negated ? "!=" : "==") + " \"" + filter.GetValue() + "\")";
-}
-
-bool
-TagSongFilter::MatchNN(const TagItem &item) const noexcept
-{
-	return (type == TAG_NUM_OF_ITEM_TYPES || item.type == type) &&
-		filter.Match(item.value);
-}
-
-bool
-TagSongFilter::MatchNN(const Tag &tag) const noexcept
-{
-	bool visited_types[TAG_NUM_OF_ITEM_TYPES];
-	std::fill_n(visited_types, size_t(TAG_NUM_OF_ITEM_TYPES), false);
-
-	for (const auto &i : tag) {
-		visited_types[i.type] = true;
-
-		if (MatchNN(i))
-			return true;
-	}
-
-	if (type < TAG_NUM_OF_ITEM_TYPES && !visited_types[type]) {
-		/* If the search critieron was not visited during the
-		   sweep through the song's tag, it means this field
-		   is absent from the tag or empty. Thus, if the
-		   searched string is also empty
-		   then it's a match as well and we should return
-		   true. */
-		if (filter.empty())
-			return true;
-
-		if (type == TAG_ALBUM_ARTIST && visited_types[TAG_ARTIST]) {
-			/* if we're looking for "album artist", but
-			   only "artist" exists, use that */
-			for (const auto &item : tag)
-				if (item.type == TAG_ARTIST &&
-				    filter.Match(item.value))
-					return true;
-		}
-	}
-
-	return false;
-}
-
-bool
-TagSongFilter::Match(const LightSong &song) const noexcept
-{
-	return MatchNN(song.tag) != negated;
-}
-
-std::string
-ModifiedSinceSongFilter::ToExpression() const noexcept
-{
-	return std::string("(modified-since \"") + FormatISO8601(value).c_str() + "\")";
-}
-
-bool
-ModifiedSinceSongFilter::Match(const LightSong &song) const noexcept
-{
-	return song.mtime >= value;
-}
-
-ISongFilterPtr
-AndSongFilter::Clone() const noexcept
-{
-	auto result = std::make_unique<AndSongFilter>();
-
-	for (const auto &i : items)
-		result->items.emplace_back(i->Clone());
-
-	return result;
-}
-
-std::string
-AndSongFilter::ToExpression() const noexcept
-{
-	auto i = items.begin();
-	const auto end = items.end();
-
-	if (std::next(i) == end)
-		return (*i)->ToExpression();
-
-	std::string e("(");
-	e += (*i)->ToExpression();
-
-	for (++i; i != end; ++i) {
-		e += " AND ";
-		e += (*i)->ToExpression();
-	}
-
-	e.push_back(')');
-	return e;
-}
-
-bool
-AndSongFilter::Match(const LightSong &song) const noexcept
-{
-	for (const auto &i : items)
-		if (!i->Match(song))
-			return false;
-
-	return true;
-}
-
 SongFilter::SongFilter(TagType tag, const char *value, bool fold_case)
 {
 	and_filter.AddItem(std::make_unique<TagSongFilter>(tag, value,
diff --git a/src/song/Filter.hxx b/src/song/Filter.hxx
index b627e4b38..e22d96986 100644
--- a/src/song/Filter.hxx
+++ b/src/song/Filter.hxx
@@ -20,13 +20,10 @@
 #ifndef MPD_SONG_FILTER_HXX
 #define MPD_SONG_FILTER_HXX
 
-#include "lib/icu/Compare.hxx"
+#include "AndSongFilter.hxx"
 #include "Compiler.h"
 
-#include <memory>
 #include <string>
-#include <list>
-#include <chrono>
 
 #include <stdint.h>
 
@@ -37,195 +34,7 @@
 
 template<typename T> struct ConstBuffer;
 enum TagType : uint8_t;
-struct Tag;
-struct TagItem;
 struct LightSong;
-class ISongFilter;
-using ISongFilterPtr = std::unique_ptr<ISongFilter>;
-
-class ISongFilter {
-public:
-	virtual ~ISongFilter() noexcept {}
-
-	virtual ISongFilterPtr Clone() const noexcept = 0;
-
-	/**
-	 * Convert this object into an "expression".  This is
-	 * only useful for debugging.
-	 */
-	virtual std::string ToExpression() const noexcept = 0;
-
-	gcc_pure
-	virtual bool Match(const LightSong &song) const noexcept = 0;
-};
-
-class StringFilter {
-	std::string value;
-
-	/**
-	 * This value is only set if case folding is enabled.
-	 */
-	IcuCompare fold_case;
-
-public:
-	template<typename V>
-	StringFilter(V &&_value, bool _fold_case)
-		:value(std::forward<V>(_value)),
-		 fold_case(_fold_case
-			   ? IcuCompare(value.c_str())
-			   : IcuCompare()) {}
-
-	bool empty() const noexcept {
-		return value.empty();
-	}
-
-	const auto &GetValue() const noexcept {
-		return value;
-	}
-
-	bool GetFoldCase() const noexcept {
-		return fold_case;
-	}
-
-	gcc_pure
-	bool Match(const char *s) const noexcept;
-};
-
-class UriSongFilter final : public ISongFilter {
-	StringFilter filter;
-
-	bool negated;
-
-public:
-	template<typename V>
-	UriSongFilter(V &&_value, bool fold_case, bool _negated)
-		:filter(std::forward<V>(_value), fold_case),
-		 negated(_negated) {}
-
-	const auto &GetValue() const noexcept {
-		return filter.GetValue();
-	}
-
-	bool GetFoldCase() const {
-		return filter.GetFoldCase();
-	}
-
-	bool IsNegated() const noexcept {
-		return negated;
-	}
-
-	ISongFilterPtr Clone() const noexcept override {
-		return std::make_unique<UriSongFilter>(*this);
-	}
-
-	std::string ToExpression() const noexcept override;
-	bool Match(const LightSong &song) const noexcept override;
-};
-
-class BaseSongFilter final : public ISongFilter {
-	std::string value;
-
-public:
-	BaseSongFilter(const BaseSongFilter &) = default;
-
-	template<typename V>
-	explicit BaseSongFilter(V &&_value)
-		:value(std::forward<V>(_value)) {}
-
-	const char *GetValue() const noexcept {
-		return value.c_str();
-	}
-
-	ISongFilterPtr Clone() const noexcept override {
-		return std::make_unique<BaseSongFilter>(*this);
-	}
-
-	std::string ToExpression() const noexcept override;
-	bool Match(const LightSong &song) const noexcept override;
-};
-
-class TagSongFilter final : public ISongFilter {
-	TagType type;
-
-	bool negated;
-
-	StringFilter filter;
-
-public:
-	template<typename V>
-	TagSongFilter(TagType _type, V &&_value, bool fold_case, bool _negated)
-		:type(_type), negated(_negated),
-		 filter(std::forward<V>(_value), fold_case) {}
-
-	TagType GetTagType() const {
-		return type;
-	}
-
-	const auto &GetValue() const noexcept {
-		return filter.GetValue();
-	}
-
-	bool GetFoldCase() const {
-		return filter.GetFoldCase();
-	}
-
-	bool IsNegated() const noexcept {
-		return negated;
-	}
-
-	ISongFilterPtr Clone() const noexcept override {
-		return std::make_unique<TagSongFilter>(*this);
-	}
-
-	std::string ToExpression() const noexcept override;
-	bool Match(const LightSong &song) const noexcept override;
-
-private:
-	bool MatchNN(const Tag &tag) const noexcept;
-	bool MatchNN(const TagItem &tag) const noexcept;
-};
-
-class ModifiedSinceSongFilter final : public ISongFilter {
-	std::chrono::system_clock::time_point value;
-
-public:
-	explicit ModifiedSinceSongFilter(std::chrono::system_clock::time_point _value) noexcept
-		:value(_value) {}
-
-	ISongFilterPtr Clone() const noexcept override {
-		return std::make_unique<ModifiedSinceSongFilter>(*this);
-	}
-
-	std::string ToExpression() const noexcept override;
-	bool Match(const LightSong &song) const noexcept override;
-};
-
-/**
- * Combine multiple #ISongFilter instances with logical "and".
- */
-class AndSongFilter final : public ISongFilter {
-	std::list<ISongFilterPtr> items;
-
-public:
-	const auto &GetItems() const noexcept {
-		return items;
-	}
-
-	template<typename I>
-	void AddItem(I &&_item) {
-		items.emplace_back(std::forward<I>(_item));
-	}
-
-	gcc_pure
-	bool IsEmpty() const noexcept {
-		return items.empty();
-	}
-
-	/* virtual methods from ISongFilter */
-	ISongFilterPtr Clone() const noexcept override;
-	std::string ToExpression() const noexcept override;
-	bool Match(const LightSong &song) const noexcept override;
-};
 
 class SongFilter {
 	AndSongFilter and_filter;
diff --git a/src/song/ISongFilter.hxx b/src/song/ISongFilter.hxx
new file mode 100644
index 000000000..22e746148
--- /dev/null
+++ b/src/song/ISongFilter.hxx
@@ -0,0 +1,48 @@
+/*
+ * Copyright 2003-2018 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#ifndef MPD_I_SONG_FILTER_HXX
+#define MPD_I_SONG_FILTER_HXX
+
+#include "Compiler.h"
+
+#include <memory>
+#include <string>
+
+struct LightSong;
+class ISongFilter;
+using ISongFilterPtr = std::unique_ptr<ISongFilter>;
+
+class ISongFilter {
+public:
+	virtual ~ISongFilter() noexcept {}
+
+	virtual ISongFilterPtr Clone() const noexcept = 0;
+
+	/**
+	 * Convert this object into an "expression".  This is
+	 * only useful for debugging.
+	 */
+	virtual std::string ToExpression() const noexcept = 0;
+
+	gcc_pure
+	virtual bool Match(const LightSong &song) const noexcept = 0;
+};
+
+#endif
diff --git a/src/song/ModifiedSinceSongFilter.cxx b/src/song/ModifiedSinceSongFilter.cxx
new file mode 100644
index 000000000..d429e1150
--- /dev/null
+++ b/src/song/ModifiedSinceSongFilter.cxx
@@ -0,0 +1,35 @@
+/*
+ * Copyright 2003-2018 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include "config.h"
+#include "ModifiedSinceSongFilter.hxx"
+#include "LightSong.hxx"
+#include "util/TimeISO8601.hxx"
+
+std::string
+ModifiedSinceSongFilter::ToExpression() const noexcept
+{
+	return std::string("(modified-since \"") + FormatISO8601(value).c_str() + "\")";
+}
+
+bool
+ModifiedSinceSongFilter::Match(const LightSong &song) const noexcept
+{
+	return song.mtime >= value;
+}
diff --git a/src/song/ModifiedSinceSongFilter.hxx b/src/song/ModifiedSinceSongFilter.hxx
new file mode 100644
index 000000000..f0bbe6c12
--- /dev/null
+++ b/src/song/ModifiedSinceSongFilter.hxx
@@ -0,0 +1,42 @@
+/*
+ * Copyright 2003-2018 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#ifndef MPD_MODIFIED_SINCE_SONG_FILTER_HXX
+#define MPD_MODIFIED_SINCE_SONG_FILTER_HXX
+
+#include "ISongFilter.hxx"
+
+#include <chrono>
+
+class ModifiedSinceSongFilter final : public ISongFilter {
+	std::chrono::system_clock::time_point value;
+
+public:
+	explicit ModifiedSinceSongFilter(std::chrono::system_clock::time_point _value) noexcept
+		:value(_value) {}
+
+	ISongFilterPtr Clone() const noexcept override {
+		return std::make_unique<ModifiedSinceSongFilter>(*this);
+	}
+
+	std::string ToExpression() const noexcept override;
+	bool Match(const LightSong &song) const noexcept override;
+};
+
+#endif
diff --git a/src/song/StringFilter.cxx b/src/song/StringFilter.cxx
new file mode 100644
index 000000000..5ef9b33f7
--- /dev/null
+++ b/src/song/StringFilter.cxx
@@ -0,0 +1,39 @@
+/*
+ * Copyright 2003-2018 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include "config.h"
+#include "StringFilter.hxx"
+#include "util/StringCompare.hxx"
+
+#include <assert.h>
+
+bool
+StringFilter::Match(const char *s) const noexcept
+{
+#if !CLANG_CHECK_VERSION(3,6)
+	/* disabled on clang due to -Wtautological-pointer-compare */
+	assert(s != nullptr);
+#endif
+
+	if (fold_case) {
+		return fold_case.IsIn(s);
+	} else {
+		return StringIsEqual(s, value.c_str());
+	}
+}
diff --git a/src/song/StringFilter.hxx b/src/song/StringFilter.hxx
new file mode 100644
index 000000000..da809f3a3
--- /dev/null
+++ b/src/song/StringFilter.hxx
@@ -0,0 +1,60 @@
+/*
+ * Copyright 2003-2018 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#ifndef MPD_STRING_FILTER_HXX
+#define MPD_STRING_FILTER_HXX
+
+#include "lib/icu/Compare.hxx"
+#include "Compiler.h"
+
+#include <string>
+
+class StringFilter {
+	std::string value;
+
+	/**
+	 * This value is only set if case folding is enabled.
+	 */
+	IcuCompare fold_case;
+
+public:
+	template<typename V>
+	StringFilter(V &&_value, bool _fold_case)
+		:value(std::forward<V>(_value)),
+		 fold_case(_fold_case
+			   ? IcuCompare(value.c_str())
+			   : IcuCompare()) {}
+
+	bool empty() const noexcept {
+		return value.empty();
+	}
+
+	const auto &GetValue() const noexcept {
+		return value;
+	}
+
+	bool GetFoldCase() const noexcept {
+		return fold_case;
+	}
+
+	gcc_pure
+	bool Match(const char *s) const noexcept;
+};
+
+#endif
diff --git a/src/song/TagSongFilter.cxx b/src/song/TagSongFilter.cxx
new file mode 100644
index 000000000..35939ee8a
--- /dev/null
+++ b/src/song/TagSongFilter.cxx
@@ -0,0 +1,82 @@
+/*
+ * Copyright 2003-2018 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include "config.h"
+#include "TagSongFilter.hxx"
+#include "LightSong.hxx"
+#include "tag/Tag.hxx"
+
+std::string
+TagSongFilter::ToExpression() const noexcept
+{
+	const char *name = type == TAG_NUM_OF_ITEM_TYPES
+		? "any"
+		: tag_item_names[type];
+
+	return std::string("(") + name + " " + (negated ? "!=" : "==") + " \"" + filter.GetValue() + "\")";
+}
+
+bool
+TagSongFilter::MatchNN(const TagItem &item) const noexcept
+{
+	return (type == TAG_NUM_OF_ITEM_TYPES || item.type == type) &&
+		filter.Match(item.value);
+}
+
+bool
+TagSongFilter::MatchNN(const Tag &tag) const noexcept
+{
+	bool visited_types[TAG_NUM_OF_ITEM_TYPES];
+	std::fill_n(visited_types, size_t(TAG_NUM_OF_ITEM_TYPES), false);
+
+	for (const auto &i : tag) {
+		visited_types[i.type] = true;
+
+		if (MatchNN(i))
+			return true;
+	}
+
+	if (type < TAG_NUM_OF_ITEM_TYPES && !visited_types[type]) {
+		/* If the search critieron was not visited during the
+		   sweep through the song's tag, it means this field
+		   is absent from the tag or empty. Thus, if the
+		   searched string is also empty
+		   then it's a match as well and we should return
+		   true. */
+		if (filter.empty())
+			return true;
+
+		if (type == TAG_ALBUM_ARTIST && visited_types[TAG_ARTIST]) {
+			/* if we're looking for "album artist", but
+			   only "artist" exists, use that */
+			for (const auto &item : tag)
+				if (item.type == TAG_ARTIST &&
+				    filter.Match(item.value))
+					return true;
+		}
+	}
+
+	return false;
+}
+
+bool
+TagSongFilter::Match(const LightSong &song) const noexcept
+{
+	return MatchNN(song.tag) != negated;
+}
diff --git a/src/song/TagSongFilter.hxx b/src/song/TagSongFilter.hxx
new file mode 100644
index 000000000..527339a3a
--- /dev/null
+++ b/src/song/TagSongFilter.hxx
@@ -0,0 +1,75 @@
+/*
+ * Copyright 2003-2018 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#ifndef MPD_TAG_SONG_FILTER_HXX
+#define MPD_TAG_SONG_FILTER_HXX
+
+#include "ISongFilter.hxx"
+#include "StringFilter.hxx"
+
+#include <stdint.h>
+
+template<typename T> struct ConstBuffer;
+enum TagType : uint8_t;
+struct Tag;
+struct TagItem;
+struct LightSong;
+
+class TagSongFilter final : public ISongFilter {
+	TagType type;
+
+	bool negated;
+
+	StringFilter filter;
+
+public:
+	template<typename V>
+	TagSongFilter(TagType _type, V &&_value, bool fold_case, bool _negated)
+		:type(_type), negated(_negated),
+		 filter(std::forward<V>(_value), fold_case) {}
+
+	TagType GetTagType() const {
+		return type;
+	}
+
+	const auto &GetValue() const noexcept {
+		return filter.GetValue();
+	}
+
+	bool GetFoldCase() const {
+		return filter.GetFoldCase();
+	}
+
+	bool IsNegated() const noexcept {
+		return negated;
+	}
+
+	ISongFilterPtr Clone() const noexcept override {
+		return std::make_unique<TagSongFilter>(*this);
+	}
+
+	std::string ToExpression() const noexcept override;
+	bool Match(const LightSong &song) const noexcept override;
+
+private:
+	bool MatchNN(const Tag &tag) const noexcept;
+	bool MatchNN(const TagItem &tag) const noexcept;
+};
+
+#endif
diff --git a/src/song/UriSongFilter.cxx b/src/song/UriSongFilter.cxx
new file mode 100644
index 000000000..4445d8c08
--- /dev/null
+++ b/src/song/UriSongFilter.cxx
@@ -0,0 +1,34 @@
+/*
+ * Copyright 2003-2018 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include "config.h"
+#include "UriSongFilter.hxx"
+#include "LightSong.hxx"
+
+std::string
+UriSongFilter::ToExpression() const noexcept
+{
+	return std::string("(file ") + (negated ? "!=" : "==") + " \"" + filter.GetValue() + "\")";
+}
+
+bool
+UriSongFilter::Match(const LightSong &song) const noexcept
+{
+	return filter.Match(song.GetURI().c_str()) != negated;
+}
diff --git a/src/song/UriSongFilter.hxx b/src/song/UriSongFilter.hxx
new file mode 100644
index 000000000..4c16ee19f
--- /dev/null
+++ b/src/song/UriSongFilter.hxx
@@ -0,0 +1,57 @@
+/*
+ * Copyright 2003-2018 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#ifndef MPD_URI_SONG_FILTER_HXX
+#define MPD_URI_SONG_FILTER_HXX
+
+#include "ISongFilter.hxx"
+#include "StringFilter.hxx"
+
+class UriSongFilter final : public ISongFilter {
+	StringFilter filter;
+
+	bool negated;
+
+public:
+	template<typename V>
+	UriSongFilter(V &&_value, bool fold_case, bool _negated)
+		:filter(std::forward<V>(_value), fold_case),
+		 negated(_negated) {}
+
+	const auto &GetValue() const noexcept {
+		return filter.GetValue();
+	}
+
+	bool GetFoldCase() const {
+		return filter.GetFoldCase();
+	}
+
+	bool IsNegated() const noexcept {
+		return negated;
+	}
+
+	ISongFilterPtr Clone() const noexcept override {
+		return std::make_unique<UriSongFilter>(*this);
+	}
+
+	std::string ToExpression() const noexcept override;
+	bool Match(const LightSong &song) const noexcept override;
+};
+
+#endif