state: Use dummy layout command

src/main.rs

@@ -174,6 +174,18 @@ mod c {
                 )
             };
         }
+        
+        if let Some(commands::SetLayout { description }) = msg.layout_selection {
+            dbg!(description);
+        }
+    }
+}
+
+pub mod commands {
+    use crate::animation;
+    #[derive(Clone, Debug)]
+    pub struct SetLayout {
+        pub description: animation::Contents,
     }
 }
 
@@ -184,4 +196,5 @@ pub struct Commands {
     pub panel_visibility: Option<panel::Command>,
     pub layout_hint_set: Option<state::InputMethodDetails>,
     pub dbus_visible_set: Option<bool>,
+    pub layout_selection: Option<commands::SetLayout>,
 }

src/state.rs

@@ -9,6 +9,7 @@ use crate::animation;
 use crate::debug;
 use crate::imservice::{ ContentHint, ContentPurpose };
 use crate::layout::ArrangementKind;
+use crate::main;
 use crate::main::Commands;
 use crate::outputs;
 use crate::outputs::{Millimeter, OutputId, OutputState};
@@ -153,10 +154,34 @@ impl Outcome {
             animation::Outcome::Hidden => (Some(false), Some(panel::Command::Hide)),
         };
 
+        // Compare the old and new states as not to flood with updates,
+        // which may look up in the file system.
+        use animation::Outcome::*;
+        let layout_selection = match &new_state.panel {
+            Visible{ contents: new_contents, ..} => {
+                let same
+                    = if let Visible { contents, .. } = &self.panel {
+                        contents == new_contents
+                    } else {
+                        false
+                    };
+
+                if !same {
+                    Some(main::commands::SetLayout {
+                        description: new_contents.clone()
+                    })
+                } else {
+                    None
+                }
+            },
+            animation::Outcome::Hidden => None,
+        };        
+
         Commands {
             panel_visibility,
             layout_hint_set,
             dbus_visible_set,
+            layout_selection,
         }
     }
 }