Add scene creation and active scene switching commands

src/commands/set-active-scene-command.ts

@@ -0,0 +1,48 @@
+import { createOpaqueId } from "../core/ids";
+
+import type { EditorCommand } from "./command";
+
+export function createSetActiveSceneCommand(nextSceneId: string): EditorCommand {
+  let previousSceneId: string | null = null;
+
+  return {
+    id: createOpaqueId("command"),
+    label: "Switch active scene",
+    execute(context) {
+      const currentProjectDocument = context.getProjectDocument();
+
+      if (currentProjectDocument.scenes[nextSceneId] === undefined) {
+        throw new Error(`Cannot activate missing scene ${nextSceneId}.`);
+      }
+
+      if (previousSceneId === null) {
+        previousSceneId = currentProjectDocument.activeSceneId;
+      }
+
+      context.setProjectDocument({
+        ...currentProjectDocument,
+        activeSceneId: nextSceneId
+      });
+      context.setSelection({ kind: "none" });
+      context.setToolMode("select");
+    },
+    undo(context) {
+      if (previousSceneId === null) {
+        return;
+      }
+
+      const currentProjectDocument = context.getProjectDocument();
+
+      if (currentProjectDocument.scenes[previousSceneId] === undefined) {
+        throw new Error(`Cannot restore missing scene ${previousSceneId}.`);
+      }
+
+      context.setProjectDocument({
+        ...currentProjectDocument,
+        activeSceneId: previousSceneId
+      });
+      context.setSelection({ kind: "none" });
+      context.setToolMode("select");
+    }
+  };
+}