imporved option parsing and GUI detection

pulseaudio-tcp

@@ -44,7 +44,7 @@ log() {
 
     if [[ -t 1 ]] && $gui && [[ -n $(type -p zenity) ]] ; then
         case "$level" in
-            ERROR)
+            ERROR|WARNING)
                 zenity --error --text="$msg"
             ;;
             *)
@@ -58,6 +58,10 @@ error() {
     log ERROR "$@"
 }
 
+warning() {
+    log WARNING "$@"
+}
+
 info() {
     log INFO "$@"
 }
@@ -447,9 +451,16 @@ do_stop() {
 # Arguments
 
 operation=
+no_more_options=false
 
 for arg in "$@" ; do
     case "$arg" in
+        --)
+            no_more_options=true
+        ;;
+        --*)
+            "$no_more_options" && { gui=false error "Option arguments may not preceed non-option arguments." ; exit 1 ; }
+        ;;&
         --debug)
             debug_cmdline=true
             ;;
@@ -460,11 +471,11 @@ for arg in "$@" ; do
             help_cmdline=true
         ;;
         start|stop|restart|setup|status)
-            [[ -z $operation ]] || { error "Multiple operations are not supported." ; exit 1 ; }
+            [[ -z $operation ]] || { gui=false error "Multiple operations are not supported." ; exit 1 ; }
             operation=$arg
         ;;
         *)
-            error "Unsupported argument (try \"--help\")"
+            gui=false error "Unsupported argument (try \"--help\")"
             exit 1
         ;;
     esac
@@ -489,6 +500,12 @@ fi
 
 if [[ $gui_cmdline = false ]] ; then
     gui=false
+elif [[ -z $(type -p zenity) ]] ; then
+    gui=false
+    warning "Disabling GUI support, because command \"zenity\" was not found."
+elif ! [[ -v DISPLAY ]] && ! [[ -v XDG_SESSION_TYPE ]] ; then
+    gui=false
+    warning "Disabling GUI support, because neither \"DISPLAY\" not \"XDG_SESSION_TYPE\ is set."
 else
     gui=true
 fi
@@ -523,7 +540,6 @@ else
     fi
 
     required_cmds=( jq pactl ssh )
-    "$gui" && required_cmds+=( zenity )
 
     for exe in "${required_cmds[@]}" ; do
         if [[ -z $(type -p "$exe") ]] ; then