lib: replace MuMsgPrio with Mu::MessagePriority

Rework good-old MuMsgPrio into Mu::MessagePriority, which looks a bit more like
modern C++.

lib/mu-message-priority.hh

@@ -0,0 +1,128 @@
+/*
+** Copyright (C) 2022 Dirk-Jan C. Binnema <djcb@djcbsoftware.nl>
+**
+** 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 3, 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 MU_MESSAGE_PRIORITY_HH__
+#define MU_MESSAGE_PRIORITY_HH__
+
+#include <array>
+#include <string>
+#include <string_view>
+
+namespace Mu {
+/**
+ * Message priorities
+ *
+ */
+
+/**
+ * The priority ids
+ *
+ */
+enum struct MessagePriority : char {
+	Low    = 'l', /**< Low priority */
+	Normal = 'n', /**< Normal priority */
+	High   = 'h', /**< High priority */
+};
+
+/**
+ * Sequence of all message priorities.
+ */
+static constexpr std::array<MessagePriority, 3> AllMessagePriorities = {
+    MessagePriority::Low, MessagePriority::Normal, MessagePriority::High};
+
+/**
+ * Get the char for some priority
+ *
+ * @param id an id
+ *
+ * @return the char
+ */
+constexpr char
+to_char(MessagePriority prio)
+{
+	return static_cast<char>(prio);
+}
+
+/**
+ * Get the priority for some character; unknown onws
+ * become Normal.
+ *
+ * @param c some character
+ */
+constexpr MessagePriority
+message_priority_from_char(char c)
+{
+	switch (c) {
+	case 'l':
+		return MessagePriority::Low;
+	case 'h':
+		return MessagePriority::High;
+	case 'n':
+	default:
+		return MessagePriority::Normal;
+	}
+}
+
+/**
+ * Get the name for a given priority
+ *
+ * @return the name
+ */
+constexpr std::string_view
+message_priority_name(MessagePriority prio)
+{
+	switch (prio) {
+	case MessagePriority::Low:
+		return "low";
+	case MessagePriority::High:
+		return "high";
+	case MessagePriority::Normal:
+	default:
+		return "normal";
+	}
+}
+
+/**
+ * Get the name for a given priority (backward compatibility)
+ *
+ * @return the name
+ */
+constexpr const char*
+message_priority_name_c_str(MessagePriority prio)
+{
+	switch (prio) {
+	case MessagePriority::Low: return "low";
+	case MessagePriority::High: return "high";
+	case MessagePriority::Normal:
+	default: return "normal";
+	}
+}
+
+/**
+ * Get a the message priority as a string
+ *
+ * @param prio priority
+ *
+ * @return a string
+ */
+std::string to_string(MessagePriority prio);
+
+} // namespace Mu
+
+#endif /*MU_MESSAGE_PRIORITY_HH_*/