From f02ba89a93c9ebd1bca49ce554e2049059d597f4 Mon Sep 17 00:00:00 2001
From: Christian Nieves <cnieves@google.com>
Date: Sun, 8 Dec 2024 02:57:20 -0600
Subject: [PATCH] input system

---
 src/snake/main.rs | 77 ++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 62 insertions(+), 15 deletions(-)

diff --git a/src/snake/main.rs b/src/snake/main.rs
index 7749638..66efd3b 100644
--- a/src/snake/main.rs
+++ b/src/snake/main.rs
@@ -6,8 +6,29 @@ const ARENA_WIDTH: u32 = 20;
 const ARENA_HEIGHT: u32 = 15;
 const WINDOW_WIDTH: f32 = 1280.0;
 
+#[derive(Eq, PartialEq, Copy, Clone)]
+enum Direction {
+    Up,
+    Down,
+    Left,
+    Right,
+}
+
+impl Direction {
+    fn opposite(self) -> Self {
+        match self {
+            Self::Left => Self::Right,
+            Self::Right => Self::Left,
+            Self::Up => Self::Down,
+            Self::Down => Self::Up,
+        }
+    }
+}
+
 #[derive(Component)]
-struct SnakeHead;
+struct SnakeHead {
+    direction: Direction,
+}
 
 #[derive(Component)]
 struct Position {
@@ -33,20 +54,43 @@ impl Size {
 #[derive(Resource)]
 struct MovementTimer(Timer);
 
-fn snake_movement_system(
-    input: Res<ButtonInput<KeyCode>>,
-
-    mut head_transforms: Query<(&SnakeHead, &mut Position)>,
-) {
-    for (_, mut pos) in head_transforms.iter_mut() {
-        if input.pressed(KeyCode::ArrowUp) {
-            pos.y += 1;
+fn snake_movement_input(input: Res<ButtonInput<KeyCode>>, mut heads: Query<(&mut SnakeHead)>) {
+    if let Some(mut head) = heads.iter_mut().next() {
+        let dir: Direction = if input.pressed(KeyCode::ArrowUp) {
+            Direction::Up
         } else if input.pressed(KeyCode::ArrowDown) {
-            pos.y -= 1;
+            Direction::Down
         } else if input.pressed(KeyCode::ArrowLeft) {
-            pos.x -= 1;
+            Direction::Left
         } else if input.pressed(KeyCode::ArrowRight) {
-            pos.x += 1;
+            Direction::Right
+        } else {
+            head.direction
+        };
+        // allow all inputs except turning around
+        if dir != head.direction.opposite() {
+            head.direction = dir;
+        }
+    }
+}
+
+fn snake_movement(
+    input: Res<ButtonInput<KeyCode>>,
+    time: Res<Time>,
+    mut timer: ResMut<MovementTimer>,
+    mut heads: Query<(&SnakeHead, &mut Position)>,
+) {
+    if let Some((head, mut pos)) = heads.iter_mut().next() {
+        if timer.0.tick(time.delta()).just_finished() {
+            if head.direction == Direction::Up {
+                pos.y += 1;
+            } else if head.direction == Direction::Down {
+                pos.y -= 1;
+            } else if head.direction == Direction::Left {
+                pos.x -= 1;
+            } else if head.direction == Direction::Right {
+                pos.x += 1;
+            }
         }
     }
 }
@@ -91,10 +135,12 @@ fn setup_player(mut commands: Commands) {
     commands
         .spawn(Sprite {
             color: SNAKE_HEAD_COLOR,
-            custom_size: Some(Vec2::new(10.0, 10.0)),
+            custom_size: Some(Vec2::new(1.0, 1.0)),
             ..default()
         })
-        .insert(SnakeHead)
+        .insert(SnakeHead {
+            direction: Direction::Right,
+        })
         .insert(Position { x: 0, y: 0 })
         .insert(Size::square(1.0));
 }
@@ -107,7 +153,8 @@ pub struct SnakePlugin;
 impl Plugin for SnakePlugin {
     fn build(&self, app: &mut App) {
         app.add_systems(Startup, (setup_camera, setup_player));
-        app.add_systems(Update, snake_movement_system);
+        app.add_systems(Update, snake_movement_input);
+        app.add_systems(FixedUpdate, snake_movement);
         app.add_systems(PostUpdate, (scale_translation, position_translation));
 
         app.insert_resource(MovementTimer(Timer::from_seconds(