mu/lib: refactor mu(-cmd)-server code

Split off the parsing/handling code from the mu command server into
mu-server, and only leave the external interface (the mu4e repl) in
mu-cmd-server.

lib/Makefile.am

@@ -105,6 +105,8 @@ libmu_la_SOURCES=						\
 	mu-runtime.h						\
 	mu-script.c						\
 	mu-script.h						\
+	mu-server.cc						\
+	mu-server.hh						\
 	mu-store.cc						\
 	mu-store.hh						\
 	mu-threader.c						\

lib/mu-server.hh

@@ -0,0 +1,69 @@
+/*
+** Copyright (C) 2020 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_SERVER_HH__
+#define MU_SERVER_HH__
+
+#include <memory>
+#include <functional>
+
+#include <utils/mu-sexp.hh>
+#include <mu-store.hh>
+
+namespace Mu {
+
+/**
+ * @brief Implements the mu server, as used by mu4e.
+ *
+ */
+class Server {
+public:
+        using Output = std::function<void(Sexp&& sexp)>;
+
+        /**
+         * Construct a new server
+         *
+         * @param store a message store object
+         * @param output callable for the server responses.
+         */
+        Server(Store& store, Output output);
+
+        /**
+         * DTOR
+         */
+        ~Server();
+
+        /**
+         * Invoke a call on the server.
+         *
+         * @param expr the s-expression to call
+         *
+         * @return true if we the server is still ready for more
+         * calls, false when it should quit.
+         */
+        bool invoke(const std::string& expr) noexcept;
+
+private:
+        struct                   Private;
+        std::unique_ptr<Private> priv_;
+};
+} // namespace Mu
+
+#endif /* MU_SERVER_HH__ */