4 files changed, 130 insertions, 11 deletions
diff --git a/src/engine/systems/Collision.ts b/src/engine/systems/Collision.ts
new file mode 100644
index 0000000..7b1b963
--- /dev/null
+++ b/src/engine/systems/Collision.ts
@@ -0,0 +1,103 @@
+import { System, SystemNames } from ".";
+import { Game } from "..";
+import { Entity, EntityNames } from "../entities";
+import { BoundingBox, Colliding, ComponentNames, Grid } from "../components";
+
+const collisionMap: Record<string, Set<string>> = {
+  [EntityNames.Key]: new Set([EntityNames.LockedDoor]),
+  [EntityNames.Curry]: new Set([EntityNames.Player]),
+};
+
+export class Collision extends System {
+  static canCollide(entityName: string, otherEntityName: string) {
+    if (collisionMap[entityName]) {
+      return collisionMap[entityName].has(otherEntityName);
+    }
+    return collisionMap[otherEntityName]?.has(entityName) ?? false;
+  }
+
+  constructor() {
+    super(SystemNames.Collision);
+  }
+
+  public update(_dt: number, game: Game) {
+    game.forEachEntityWithComponent(ComponentNames.Colliding, (entity) => {
+      if (!entity.hasComponent(ComponentNames.BoundingBox)) {
+        return;
+      }
+      const collidingBox = entity.getComponent<BoundingBox>(
+        ComponentNames.BoundingBox,
+      );
+      let collidingGrid = entity.hasComponent(ComponentNames.Grid)
+        ? entity.getComponent<Grid>(ComponentNames.Grid)
+        : null;
+
+      const collidingWith: Entity[] = [];
+      game.forEachEntityWithComponent(
+        ComponentNames.BoundingBox,
+        (otherEntity) => {
+          const otherBoundingBox = otherEntity.getComponent<BoundingBox>(
+            ComponentNames.BoundingBox,
+          );
+          let otherGrid = otherEntity.hasComponent(ComponentNames.Grid)
+            ? otherEntity.getComponent<Grid>(ComponentNames.Grid)
+            : null;
+
+          if (collidingGrid && otherGrid) {
+            if (
+              collidingGrid.gridPosition.x === otherGrid.gridPosition.x &&
+              collidingGrid.gridPosition.y === otherGrid.gridPosition.y
+            ) {
+              collidingWith.push(otherEntity);
+            }
+            return;
+          }
+
+          if (collidingBox.isCollidingWith(otherBoundingBox)) {
+            collidingWith.push(otherEntity);
+          }
+        },
+      );
+
+      for (const collision of collidingWith) {
+        this.handleCollision(entity, collision, game);
+      }
+    });
+  }
+
+  private handleCollision(entity: Entity, otherEntity: Entity, game: Game) {
+    if (!Collision.canCollide(entity.name, otherEntity.name)) {
+      return;
+    }
+
+    const keyDoorPair = [EntityNames.Key, EntityNames.LockedDoor].map((x) =>
+      [entity, otherEntity].find((y) => y.name === x),
+    );
+    const [key, door] = keyDoorPair;
+    if (key && door) {
+      this.handleKeyDoorCollision(key, door, game);
+    }
+
+    const curryPlayerPair = [EntityNames.Curry, EntityNames.Player].map((x) =>
+      [entity, otherEntity].find((y) => y.name === x),
+    );
+    const [curry, player] = curryPlayerPair;
+    if (curry && player) {
+      this.handleCurryPlayerCollision(curry, player, game);
+    }
+  }
+
+  private handleKeyDoorCollision(key: Entity, door: Entity, game: Game) {
+    game.removeEntity(key.id);
+    game.removeEntity(door.id);
+  }
+
+  private handleCurryPlayerCollision(
+    curry: Entity,
+    _player: Entity,
+    game: Game,
+  ) {
+    game.removeEntity(curry.id);
+    game.stop();
+  }
+}
diff --git a/src/engine/systems/Grid.ts b/src/engine/systems/Grid.ts
index 8756320..915335b 100644
--- a/src/engine/systems/Grid.ts
+++ b/src/engine/systems/Grid.ts
@@ -1,4 +1,4 @@
-import { System, SystemNames } from ".";
+import { Collision, System, SystemNames } from ".";
 import { Game } from "..";
 import { Entity } from "../entities";
 import { PhysicsConstants } from "../config";
@@ -13,8 +13,8 @@ import { Coord2D, Direction, Dimension2D } from "../interfaces";
 import { clamp } from "../utils";
 
 export class Grid extends System {
-  private dimension: Dimension2D;
-  private grid: Set<string>[][] = [];
+  public dimension: Dimension2D;
+  public grid: Set<string>[][] = [];
 
   constructor(
     { width: columns, height: rows }: Dimension2D,
@@ -108,10 +108,10 @@ export class Grid extends System {
       grid.movingDirection = Direction.NONE;
       entity.addComponent(grid); // default to not moving
 
-      let nextGridPosition = this.getNewGridPosition(
+      let [currentPosition, nextGridPosition] = [
         gridPosition,
-        movingDirection,
-      );
+        this.getNewGridPosition(gridPosition, movingDirection),
+      ];
 
       const moving = new Set<string>();
       moving.add(entity.id);
@@ -122,11 +122,24 @@ export class Grid extends System {
           (id) => game.getEntity(id)!,
         );
 
-        if (
-          entities.some((entity) =>
-            entity.hasComponent(ComponentNames.Colliding),
+        const collidingEntities = entities.filter((entity) =>
+          entity.hasComponent(ComponentNames.Colliding),
+        );
+
+        if (collidingEntities.length > 0) {
+          // i.e. key going into a door or function going into an application
+          const allEntitiesInPreviousCellCanCollide = Array.from(
+            this.grid[currentPosition.y][currentPosition.x],
           )
-        ) {
+            .map((id) => game.getEntity(id)!)
+            .every((entity) =>
+              collidingEntities.every((collidingEntity) =>
+                Collision.canCollide(entity.name, collidingEntity.name),
+              ),
+            );
+          if (allEntitiesInPreviousCellCanCollide) {
+            break;
+          }
           moving.clear();
           break;
         }
@@ -148,6 +161,7 @@ export class Grid extends System {
           moving.add(pushableEntity.id);
         }
 
+        currentPosition = nextGridPosition;
         nextGridPosition = this.getNewGridPosition(
           nextGridPosition,
           movingDirection,
@@ -324,7 +338,7 @@ export class Grid extends System {
     this.grid.forEach((row) =>
       row.forEach((cell) => {
         for (const id of cell) {
-          if (movedEntities.has(id)) {
+          if (movedEntities.has(id) || !game.getEntity(id)) {
             cell.delete(id);
           }
         }
diff --git a/src/engine/systems/SystemNames.ts b/src/engine/systems/SystemNames.ts
index 85d1539..c96dc48 100644
--- a/src/engine/systems/SystemNames.ts
+++ b/src/engine/systems/SystemNames.ts
@@ -4,4 +4,5 @@ export namespace SystemNames {
   export const FacingDirection = "FacingDirection";
   export const Grid = "Grid";
   export const LambdaFactory = "LambdaFactory";
+  export const Collision = "Collision";
 }
diff --git a/src/engine/systems/index.ts b/src/engine/systems/index.ts
index 4490ee2..6ee5392 100644
--- a/src/engine/systems/index.ts
+++ b/src/engine/systems/index.ts
@@ -5,3 +5,4 @@ export * from "./Input";
 export * from "./FacingDirection";
 export * from "./Grid";
 export * from "./LambdaFactory";
+export * from "./Collision";