Add Clapper deamon subprocess

Daemon is responsible for starting and later watching over spawned "broadwayd" and "remote" app needed for remote playback control. We cannot use systemd n Flatpak, so we make do with running optional background subprocesses.

clapper_src/daemon.js

@@ -0,0 +1,66 @@
+const { Gio, GLib, GObject } = imports.gi;
+const Debug = imports.clapper_src.debug;
+
+let { debug } = Debug;
+
+var Daemon = GObject.registerClass(
+class ClapperDaemon extends Gio.SubprocessLauncher
+{
+    _init()
+    {
+        /* FIXME: show output when debugging is on */
+        const flags = Gio.SubprocessFlags.STDOUT_SILENCE
+            | Gio.SubprocessFlags.STDERR_SILENCE;
+
+        super._init({ flags });
+
+        this.errMsg = 'exited with error or was forced to close';
+        this.loop = GLib.MainLoop.new(null, false);
+
+        this.broadwayd = this.spawnv(['gtk4-broadwayd', '--port=8086']);
+        this.broadwayd.wait_async(null, this._onBroadwaydClosed.bind(this));
+
+        this.setenv('GDK_BACKEND', 'broadway', true);
+
+        const remoteApp = this.spawnv(['com.github.rafostar.Clapper.Remote']);
+        remoteApp.wait_async(null, this._onRemoteClosed.bind(this));
+
+        this.loop.run();
+    }
+
+    _checkProcResult(proc, result)
+    {
+        let hadError = false;
+
+        try {
+            hadError = proc.wait_finish(result);
+        }
+        catch(err) {
+            debug(err);
+        }
+
+        return hadError;
+    }
+
+    _onBroadwaydClosed(proc, result)
+    {
+        const hadError = this._checkProcResult(proc, result);
+
+        if(hadError)
+            debug(`broadwayd ${this.errMsg}`);
+
+        this.broadwayd = null;
+        this.loop.quit();
+    }
+
+    _onRemoteClosed(proc, result)
+    {
+        const hadError = this._checkProcResult(proc, result);
+
+        if(hadError)
+            debug(`remote app ${this.errMsg}`);
+
+        if(this.broadwayd)
+            this.broadwayd.force_exit();
+    }
+});