ReplayGainMode: add ToString(), FromString()

Move code from ReplayGainConfig.cxx.

src/ReplayGainMode.cxx

@@ -0,0 +1,63 @@
+/*
+ * Copyright 2003-2016 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 "ReplayGainMode.hxx"
+
+#include <stdexcept>
+
+#include <assert.h>
+#include <string.h>
+
+const char *
+ToString(ReplayGainMode mode)
+{
+	switch (mode) {
+	case ReplayGainMode::AUTO:
+		return "auto";
+
+	case ReplayGainMode::OFF:
+		return "off";
+
+	case ReplayGainMode::TRACK:
+		return "track";
+
+	case ReplayGainMode::ALBUM:
+		return "album";
+	}
+
+	assert(false);
+	gcc_unreachable();
+}
+
+ReplayGainMode
+FromString(const char *s)
+{
+	assert(s != nullptr);
+
+	if (strcmp(s, "off") == 0)
+		return ReplayGainMode::OFF;
+	else if (strcmp(s, "track") == 0)
+		return ReplayGainMode::TRACK;
+	else if (strcmp(s, "album") == 0)
+		return ReplayGainMode::ALBUM;
+	else if (strcmp(s, "auto") == 0)
+		return ReplayGainMode::AUTO;
+	else
+		throw std::invalid_argument("Unrecognized replay gain mode");
+}