Add command for importing background image asset

src/commands/import-background-image-asset-command.ts

@@ -0,0 +1,56 @@
+import { createOpaqueId } from "../core/ids";
+import { cloneWorldSettings, type WorldSettings } from "../document/world-settings";
+import { cloneProjectAssetRecord, type ImageAssetRecord } from "../assets/project-assets";
+
+import type { EditorCommand } from "./command";
+
+interface ImportBackgroundImageAssetCommandOptions {
+  asset: ImageAssetRecord;
+  world: WorldSettings;
+  label?: string;
+}
+
+export function createImportBackgroundImageAssetCommand(options: ImportBackgroundImageAssetCommandOptions): EditorCommand {
+  const nextAsset = cloneProjectAssetRecord(options.asset);
+  const nextWorld = cloneWorldSettings(options.world);
+  let previousWorld: WorldSettings | null = null;
+
+  return {
+    id: createOpaqueId("command"),
+    label: options.label ?? `Import ${nextAsset.sourceName} as background`,
+    execute(context) {
+      const currentDocument = context.getDocument();
+
+      if (currentDocument.assets[nextAsset.id] !== undefined) {
+        throw new Error(`Asset ${nextAsset.id} already exists.`);
+      }
+
+      if (previousWorld === null) {
+        previousWorld = cloneWorldSettings(currentDocument.world);
+      }
+
+      context.setDocument({
+        ...currentDocument,
+        assets: {
+          ...currentDocument.assets,
+          [nextAsset.id]: cloneProjectAssetRecord(nextAsset)
+        },
+        world: cloneWorldSettings(nextWorld)
+      });
+    },
+    undo(context) {
+      const currentDocument = context.getDocument();
+      const nextAssets = {
+        ...currentDocument.assets
+      };
+
+      delete nextAssets[nextAsset.id];
+
+      context.setDocument({
+        ...currentDocument,
+        assets: nextAssets,
+        world: previousWorld === null ? cloneWorldSettings(currentDocument.world) : cloneWorldSettings(previousWorld)
+      });
+    }
+  };
+}