Add tick thread and Skirmish state update

Introduce `AppEvent::Tick` and a background thread that emits timed
events. `App` now handles `Tick` by calling a new `update` method,
which advances the board and increments a `turn_counter` in
`SkirmishState`. Add required imports, fields, and the
`spawn_tick_thread` call in `main`.

src/app/app.rs

@@ -65,6 +65,7 @@ impl App {
                         .board
                         .change_resize(&window_area, state.skirmish.side_panel);
                 }
+                AppEvent::Tick => self.update()?,
             }
         }
 
@@ -90,4 +91,11 @@ impl App {
         handle_keybindings(self, key_event);
         Ok(())
     }
+
+    fn update(&mut self) -> Result<()> {
+        if let Some(state) = self.states_mut() {
+            state.skirmish.update(&self.args);
+        }
+        Ok(())
+    }
 }

src/app/state.rs

@@ -35,6 +35,7 @@ impl GameStates {
                     false,
                 ),
                 side_panel: false,
+                turn_counter: 0,
             },
             perk_decks: PerkDecksState {
                 id: 2,

src/app/states/skirmish.rs

@@ -1,4 +1,4 @@
-use crate::app::states::skirmish_states::BoardState;
+use crate::{app::states::skirmish_states::BoardState, cli::Cli};
 
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct SkirmishState {
@@ -6,4 +6,15 @@ pub struct SkirmishState {
     pub name: &'static str,
     pub board: BoardState,
     pub side_panel: bool,
+    pub turn_counter: u64,
+}
+
+impl SkirmishState {
+    pub fn update(&mut self, cli: &Cli) {
+        self.board.advance_turn();
+
+        // if self.board.is_victory() {}
+
+        self.turn_counter += 1;
+    }
 }

src/app/threads/events.rs

@@ -5,6 +5,7 @@ use std::sync::mpsc::Sender;
 pub enum AppEvent {
     Input(KeyEvent),
     Resize(u16, u16),
+    Tick,
 }
 
 /// Reads *all* crossterm events and forwards the ones we care about.

src/app/threads/mod.rs

@@ -1,5 +1,7 @@
 mod audio;
 mod events;
+mod tick;
 
 pub use audio::{AudioCmd, SoundrackParts, Soundtrack, handle_audio};
 pub use events::{AppEvent, handle_events};
+pub use tick::spawn_tick_thread;

src/app/threads/tick.rs

@@ -0,0 +1,22 @@
+use crate::app::threads::AppEvent;
+use std::{
+    sync::mpsc::Sender,
+    thread,
+    time::{Duration, Instant},
+};
+
+pub fn spawn_tick_thread(tx: Sender<AppEvent>, interval_ms: u64) {
+    thread::spawn(move || {
+        let interval: Duration = Duration::from_millis(interval_ms);
+        loop {
+            if tx.send(AppEvent::Tick).is_err() {
+                break;
+            }
+
+            let elapsed: Duration = Instant::now().elapsed();
+            if interval > elapsed {
+                thread::sleep(interval - elapsed);
+            }
+        }
+    });
+}