[General+Packages] Add pinentry dynamic switcher wrapper

Dynamically accomodate different desktops

general.nix

@@ -108,6 +108,19 @@ in
       enable = true;
       enableSSHSupport = true;
     };
+    
+    systemd.user.services.gpg-agent = let
+      pinentrySwitcher = pkgs.callPackage ./packages/pinentry.nix {};
+      cfg = config.programs.gnupg;
+    in {
+      restartTriggers = [ pinentrySwitcher ];
+      restartIfChanged = true;
+    
+      serviceConfig.ExecStart = [ "" ''
+        ${cfg.package}/bin/gpg-agent --supervised \
+          --pinentry-program ${pinentrySwitcher}/bin/pinentry
+        '' ];
+    };
 
     documentation.man.generateCaches = true;
 

packages/pinentry.nix

@@ -0,0 +1,36 @@
+{ writeShellScriptBin, pinentry, ... }:
+writeShellScriptBin "pinentry" ''
+  flavor=
+  if [ -n "$XDG_CURRENT_DESKTOP" ]; then
+    case "$XDG_CURRENT_DESKTOP" in
+      KDE|LXQT)
+        flavor="qt" ;;
+      XFCE)
+        flavor="gtk2" ;;
+      Gnome)
+        flavor="gnome3" ;;
+      *)
+        echo "Unknown desktop '$XDG_CURRENT_DESKTOP', use 'gnome3'" >&2
+        flavor="gnome3" ;;
+    esac
+  elif [ -z "$XAUTHORITY" -a -z "$WAYLAND_DISPLAY" ]; then
+    echo "No Xauthority nor Wayland display, using curses" >&2
+    flavor="curses"
+  fi
+
+  if [ -z "$flavor" ]; then
+    echo "WARNING: pinentry flavor could not be detected, use 'curses'" >&2
+    flavor="curses"
+  fi
+
+  declare -A pinentryFlavors
+  pinentryFlavors["qt"]="${pinentry.qt}"
+  pinentryFlavors["gtk2"]="${pinentry.gtk2}"
+  pinentryFlavors["gnome"]="${pinentry.gnome3}"
+  pinentryFlavors["curses"]="${pinentry.curses}"
+
+  echo "Selected flavor: $flavor" >&2
+
+  exec ''${pinentryFlavors[$flavor]}/bin/pinentry
+''
+