Add box brush command helpers and implementations

src/commands/brush-command-helpers.ts

@@ -0,0 +1,47 @@
+import { cloneEditorSelection, type EditorSelection } from "../core/selection";
+import type { BoxBrush } from "../document/brushes";
+import type { SceneDocument } from "../document/scene-document";
+
+export function getBoxBrushOrThrow(document: SceneDocument, brushId: string): BoxBrush {
+  const brush = document.brushes[brushId];
+
+  if (brush === undefined) {
+    throw new Error(`Box brush ${brushId} does not exist.`);
+  }
+
+  if (brush.kind !== "box") {
+    throw new Error(`Brush ${brushId} is not a supported box brush.`);
+  }
+
+  return brush;
+}
+
+export function setSingleBrushSelection(brushId: string): EditorSelection {
+  return {
+    kind: "brushes",
+    ids: [brushId]
+  };
+}
+
+export function cloneSelectionForCommand(selection: EditorSelection): EditorSelection {
+  return cloneEditorSelection(selection);
+}
+
+export function replaceBrush(document: SceneDocument, brush: BoxBrush): SceneDocument {
+  return {
+    ...document,
+    brushes: {
+      ...document.brushes,
+      [brush.id]: brush
+    }
+  };
+}
+
+export function removeBrush(document: SceneDocument, brushId: string): SceneDocument {
+  const { [brushId]: _removedBrush, ...remainingBrushes } = document.brushes;
+
+  return {
+    ...document,
+    brushes: remainingBrushes
+  };
+}