sane-input-handler: add a --help command

hosts/common/programs/sane-input-handler/sane-input-handler

@@ -61,6 +61,24 @@ KEYBOARD="${KEYBOARD:-wvkbd-mobintl}"
 
 action="$1"
 
+showHelp() {
+  echo "usage: sane-input-handler <action>"
+  echo ""
+  echo "where action is one of:"
+  echo "- power_tap_{1,2}"
+  echo "- power_hold"
+  echo "- power_tap_1_hold"
+  echo "- power_and_volup"
+  echo "- power_and_voldown"
+  echo "- power_then_volup"
+  echo "- power_then_voldown"
+  echo "- volup_tap_{1,2,3}"
+  echo "- volup_hold_{1,2,3}"
+  echo "- voldown_tap_{1,2,3}"
+  echo "- voldown_hold_{1,2,3}"
+  echo "- voldown_start"
+}
+
 log() {
   printf "sane-input-handler: %s\n" "$1"
 }
@@ -242,19 +260,31 @@ dispatchInhibited() {
   esac
 }
 
-_isAllOn="$(isAllOn && echo 1 || true)"
+dispatchToplevel() {
+  _isAllOn="$(isAllOn && echo 1 || true)"
 
-if [ -z "$_isAllOn" ]; then
-  dispatchOff
-else
-  _isInhibited="$(isInhibited && echo 1 || true)"
-  if [ -n "$_isInhibited" ]; then
-    dispatchInhibited
+  if [ -z "$_isAllOn" ]; then
+    dispatchOff
   else
-    dispatchOn
+    _isInhibited="$(isInhibited && echo 1 || true)"
+    if [ -n "$_isInhibited" ]; then
+      dispatchInhibited
+    else
+      dispatchOn
+    fi
   fi
-fi
 
-dispatchDefault
+  dispatchDefault
+}
+
+case "$action" in
+  (--help)
+    showHelp
+    exit 0
+    ;;
+  (*)
+    dispatchToplevel
+    handleWith unmapped
+    ;;
+esac
 
-handleWith unmapped