From 8ec7f5368232d59f344e1067e1bad5e48dbcb7ae Mon Sep 17 00:00:00 2001
From: Elizabeth Hunt <elizabeth@simponic.xyz>
Date: Sat, 7 Sep 2024 20:20:07 -0700
Subject: get "cats" up there

---
 static/src/engine/game.ts | 112 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 112 insertions(+)
 create mode 100644 static/src/engine/game.ts

(limited to 'static/src/engine/game.ts')

diff --git a/static/src/engine/game.ts b/static/src/engine/game.ts
new file mode 100644
index 0000000..64f63b5
--- /dev/null
+++ b/static/src/engine/game.ts
@@ -0,0 +1,112 @@
+import { System, SystemType } from "./system";
+import { Entity } from "./entity";
+import { ComponentType } from "./component";
+
+export class Game {
+  private running: boolean;
+  private last_update: number;
+
+  private readonly entities: Map<string, Entity> = new Map();
+  private readonly component_entities: Map<ComponentType, Set<string>> =
+    new Map();
+  private readonly systems: Map<SystemType, System> = new Map();
+  private readonly system_order: SystemType[];
+
+  constructor(
+    public readonly client_id: string,
+    systems: System[],
+  ) {
+    this.last_update = performance.now();
+    this.running = false;
+
+    systems.forEach((system) => this.systems.set(system.system_type, system));
+    this.system_order = systems.map(({ system_type }) => system_type);
+  }
+
+  public start() {
+    if (this.running) return;
+
+    console.log("starting game");
+    this.running = true;
+    this.last_update = performance.now();
+
+    const game_loop = (timestamp: number) => {
+      if (!this.running) return;
+
+      // rebuild component -> { entity } map
+      this.component_entities.clear();
+      Array.from(this.entities.values()).forEach((entity) =>
+        Object.values(entity.components).forEach((component) => {
+          const set =
+            this.component_entities.get(component.name) ?? new Set<string>();
+          set.add(entity.id);
+          this.component_entities.set(component.name, set);
+        }),
+      );
+
+      const dt = timestamp - this.last_update;
+
+      this.system_order.forEach((system_type) =>
+        this.systems.get(system_type)!.update(dt, this),
+      );
+
+      this.last_update = timestamp;
+      requestAnimationFrame(game_loop); // tail call recursion! /s
+    };
+    requestAnimationFrame(game_loop);
+  }
+
+  public stop() {
+    if (!this.running) return;
+    this.running = false;
+  }
+
+  public for_each_entity_with_component(
+    component: ComponentType,
+    callback: (entity: Entity) => void,
+  ) {
+    this.component_entities.get(component)?.forEach((entity_id) => {
+      const entity = this.entities.get(entity_id);
+      if (!entity) return;
+
+      callback(entity);
+    });
+  }
+
+  public get_entity(id: string) {
+    return this.entities.get(id);
+  }
+
+  public put_entity(entity: Entity) {
+    const old_entity = this.entities.get(entity.id);
+    if (old_entity) this.clear_entity_components(old_entity);
+
+    Object.values(entity.components).forEach((component) => {
+      const set =
+        this.component_entities.get(component.name) ?? new Set<string>();
+      set.add(entity.id);
+      this.component_entities.set(component.name, set);
+    });
+    this.entities.set(entity.id, entity);
+  }
+
+  public remove_entity(id: string) {
+    const entity = this.entities.get(id);
+    if (typeof entity === "undefined") return;
+
+    this.clear_entity_components(entity);
+    this.entities.delete(id);
+  }
+
+  private clear_entity_components(entity: Entity) {
+    Object.values(entity.components).forEach((component) => {
+      const set = this.component_entities.get(component.name);
+      if (typeof set === "undefined") return;
+      set.delete(entity.id);
+    });
+  }
+
+  public get_system<T extends System>(system_type: SystemType): T | undefined {
+    return this.systems.get(system_type) as T;
+  }
+}
-- 
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