Add GameStates, typed enums, and App::new constructor

src/app/keybindings/main_menu.rs

@@ -1,5 +1,5 @@
 use crate::app::{
-    App,
+    App, View,
     keybindings::{Action, event_to_action},
 };
 use ratatui::crossterm::event::KeyEvent;
@@ -8,7 +8,35 @@ pub fn main_menu_keybindings(app: &mut App, event: &KeyEvent) {
     if let Some(action) = event_to_action(&event) {
         match action {
             Action::Quit => app.exit = true,
-            _ => (),
+            Action::ScrollUp => {
+                app.game_states.main_menu_state.selected_view = app
+                    .game_states
+                    .main_menu_state
+                    .selected_view
+                    .saturating_sub(1)
+                    .max(1);
+            }
+            Action::ScrollDown => {
+                app.game_states.main_menu_state.selected_view = app
+                    .game_states
+                    .main_menu_state
+                    .selected_view
+                    .saturating_add(1)
+                    .min(4);
+            }
+            Action::Select => {
+                let selected_view: usize = app.game_states.main_menu_state.selected_view;
+
+                if selected_view == 1 {
+                    app.view = View::Skirmish;
+                } else if selected_view == 2 {
+                    app.view = View::PerkDecks;
+                } else if selected_view == 3 {
+                    app.view = View::SkillsConfig;
+                } else if selected_view == 4 {
+                    app.view = View::Settings;
+                }
+            } // _ => (),
         }
     }
 }