7 files changed, 61 insertions, 5 deletions
diff --git a/src/engine/TheAbstractionEngine.ts b/src/engine/TheAbstractionEngine.ts
index 886b50f..63c6274 100644
--- a/src/engine/TheAbstractionEngine.ts
+++ b/src/engine/TheAbstractionEngine.ts
@@ -12,6 +12,7 @@ import {
   Music,
   Level,
   Modal,
+  RadialObserve,
 } from "./systems";
 
 export class TheAbstractionEngine {
@@ -35,6 +36,7 @@ export class TheAbstractionEngine {
 
     const isDev = document.location.hostname.includes("localhost");
     [
+      new RadialObserve(),
       new Modal(),
       new Level(isDev ? LevelNames.CarCadr : LevelNames.LevelSelection),
       inputSystem,
diff --git a/src/engine/entities/EntityNames.ts b/src/engine/entities/EntityNames.ts
index 17b5519..dd508c9 100644
--- a/src/engine/entities/EntityNames.ts
+++ b/src/engine/entities/EntityNames.ts
@@ -11,4 +11,5 @@ export namespace EntityNames {
   export const Portal = "Portal";
   export const Grass = "Grass";
   export const Sign = "Sign";
+  export const Piston = "Piston";
 }
diff --git a/src/engine/entities/Piston.ts b/src/engine/entities/Piston.ts
new file mode 100644
index 0000000..18b761b
--- /dev/null
+++ b/src/engine/entities/Piston.ts
@@ -0,0 +1,48 @@
+import { Entity, EntityNames } from ".";
+import { Colliding, ComponentNames, FacingDirection, Grid, RadialObserve } from "../components";
+import { Game } from "../Game";
+import { Coord2D, Direction } from "../interfaces";
+
+export class Piston extends Entity {
+  constructor(gridPosition: Coord2D, direction: Direction) {
+    super(EntityNames.Piston);
+
+    const radius = 1 + .001;
+    this.addComponent(new RadialObserve(this.onObservation.bind(this), radius));
+
+    this.addComponent(new FacingDirection(direction));
+
+    this.addComponent(new Grid(gridPosition));
+
+    this.addComponent(new Colliding());
+  }
+
+  private onObservation(_game: Game, entity: Entity) {
+    const facingDirection = this.getComponent<FacingDirection>(ComponentNames.FacingDirection);
+
+    const myPosition = this.getComponent<Grid>(ComponentNames.Grid).gridPosition;
+    const observingGrid = entity.getComponent<Grid>(ComponentNames.Grid);
+    const observingPosition = observingGrid.gridPosition;
+
+    const [dx, dy] = [myPosition.x - observingPosition.x, myPosition.y - observingPosition.y].map(x => Math.round(x));
+    const v: Record<typeof dx, Record<typeof dy, Direction>> = {
+      [-1]: {
+	[dy]: Direction.RIGHT,
+      },
+      [1]: {
+	[dy]: Direction.LEFT,
+      },
+      [0]: {
+	[-1]: Direction.UP,
+	[1]: Direction.DOWN,
+      }
+    };
+
+    if (facingDirection.currentDirection !== v[dx][dy]) {
+      return;
+    }
+
+    observingGrid.movingDirection = facingDirection.currentDirection;
+    entity.addComponent(observingGrid);
+  }
+}
diff --git a/src/engine/levels/CarCadr.ts b/src/engine/levels/CarCadr.ts
index 8875623..ee50ee9 100644
--- a/src/engine/levels/CarCadr.ts
+++ b/src/engine/levels/CarCadr.ts
@@ -9,6 +9,8 @@ import {
   Player,
   Wall,
 } from "../entities";
+import { Piston } from "../entities/Piston";
+import { Direction } from "../interfaces";
 import { Grid, SystemNames } from "../systems";
 import { normalRandom } from "../utils";
 
@@ -58,6 +60,7 @@ export class CarCadr extends Level {
       new Wall({ x: 10, y: 5 }),
       new Wall({ x: 12, y: 5 }),
       new Wall({ x: 12, y: 3 }),
+      new Piston({ x: 10, y: 6 }, Direction.RIGHT),
       new FunctionApplication({ x: 12, y: 6 }, "(_INPUT _KEY)"),
       new Wall({ x: 10, y: 7 }),
       new Wall({ x: 11, y: 7 }),
diff --git a/src/engine/systems/RadialObserve.ts b/src/engine/systems/RadialObserve.ts
index 8d418df..581452c 100644
--- a/src/engine/systems/RadialObserve.ts
+++ b/src/engine/systems/RadialObserve.ts
@@ -1,16 +1,16 @@
 import { System, SystemNames } from ".";
-import { ComponentNames, Grid, RadialObserve } from "../components";
+import { ComponentNames, Grid, RadialObserve as RadialObserveComponent } from "../components";
 import { Entity, EntityNames } from "../entities";
 import { Game } from "../Game";
 import { cartesianDistance } from "../interfaces";
 
 const radialObservations: Record<string, Set<string>> = {
-  TODO: new Set([]),
+  [EntityNames.Piston]: new Set([EntityNames.FunctionBox]),
 };
 
-export class RadialObserver extends System {
+export class RadialObserve extends System {
   constructor() {
-    super(SystemNames.RadialObserver);
+    super(SystemNames.RadialObserve);
   }
 
   public update(_dt: number, game: Game) {
@@ -20,7 +20,7 @@ export class RadialObserver extends System {
       }
       const observable = radialObservations[entity.name];
 
-      const entityObserve = entity.getComponent<RadialObserve>(
+      const entityObserve = entity.getComponent<RadialObserveComponent>(
         ComponentNames.RadialObserve,
       );
       if (!entityObserve.onObservation) {
diff --git a/src/engine/systems/SystemNames.ts b/src/engine/systems/SystemNames.ts
index 430ee48..33e39ac 100644
--- a/src/engine/systems/SystemNames.ts
+++ b/src/engine/systems/SystemNames.ts
@@ -9,4 +9,5 @@ export namespace SystemNames {
   export const Music = "Music";
   export const Level = "Level";
   export const Modal = "Modal";
+  export const RadialObserve = "RadialObserve";
 }
diff --git a/src/engine/systems/index.ts b/src/engine/systems/index.ts
index 16ff911..a8c40b9 100644
--- a/src/engine/systems/index.ts
+++ b/src/engine/systems/index.ts
@@ -10,3 +10,4 @@ export * from "./Life";
 export * from "./Music";
 export * from "./Level";
 export * from "./Modal";
+export * from "./RadialObserve";