mu-maildir: refactor some duplicate code

mu-flags & mu-maildir were having some duplicate code; refactor it into mu-message-file.{cc,hh}

lib/message/mu-message-file.hh

@@ -0,0 +1,98 @@
+/*
+** Copyright (C) 2022 Dirk-Jan C. Binnema <djcb.bulk@gmail.com>
+**
+** 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_FILE_HH__
+#define MU_MESSAGE_FILE_HH__
+
+#include "mu-flags.hh"
+#include <utils/mu-result.hh>
+
+namespace Mu {
+
+/*
+ * The file-components, ie.
+ *     1631819685.fb7b279bbb0a7b66.evergrey:2,RS
+ *     => {
+ *       "1631819685.fb7b279bbb0a7b66.evergrey",
+ *       ':',
+ *       "2,",
+ *       "RS"
+ *     }
+ */
+struct FileParts {
+	std::string	base;	/**< basename */
+	char		separator; /**< separator */
+	std::string	flags_suffix; /**< suffix (with flags) */
+};
+
+/**
+ * Get the file-parts for some message-file
+ *
+ * @param file path to some message file (does not have to exist)
+ *
+ * @return FileParts for the message file
+ */
+FileParts message_file_parts(const std::string& file);
+
+
+struct DirFile {
+	std::string	dir;
+	std::string	file;
+	bool		is_new;
+};
+
+/**
+ * Get information about the message file componemts
+ *
+ * @param path message path
+ *
+ * @return the components for the message file or an error.
+ */
+Result<DirFile> base_message_dir_file(const std::string& path);
+
+
+
+/**
+ * Get the Maildir flags from the full path of a mailfile. The flags are as
+ * specified in http://cr.yp.to/proto/maildir.html, plus Flag::New for new
+ * messages, ie the ones that live in new/. The flags are logically OR'ed. Note
+ * that the file does not have to exist; the flags are based on the path only.
+ *
+ * @param pathname of a mailfile; it does not have to refer to an
+ * actual message
+ *
+ * @return the message flags or an error
+ */
+Result<Flags> flags_from_path(const std::string& pathname);
+
+/**
+ * get the maildir for a certain message path, ie, the path *before*
+ * cur/ or new/ and *after* the root.
+ *
+ * @param path path for some message
+ * @param root filesystem root for the maildir
+ *
+ * @return the maildir or an Error
+ */
+Result<std::string> maildir_from_path(const std::string& path,
+				      const std::string& root);
+} // Mu
+
+
+#endif /* MU_MESSAGE_FILE_HH__ */