Initial commit: DSH mind-map canvas monorepo

Co-authored-by: Cursor <cursoragent@cursor.com>

apps/web/src/drag-subtree.ts

@@ -0,0 +1,56 @@
+import type { MindEdge } from "@mind-map/shared";
+
+/** Primary-hierarchy descendants including root. */
+export function collectSubtreeIds(
+  rootId: string,
+  edges: MindEdge[],
+): string[] {
+  const kids = new Map<string, string[]>();
+  for (const e of edges) {
+    if (e.deletedAt || e.kind !== "hierarchy" || !e.isPrimaryParent) continue;
+    const list = kids.get(e.from) ?? [];
+    list.push(e.to);
+    kids.set(e.from, list);
+  }
+  const out: string[] = [rootId];
+  const seen = new Set<string>([rootId]);
+  const queue = [rootId];
+  while (queue.length) {
+    const cur = queue.shift()!;
+    for (const c of kids.get(cur) ?? []) {
+      if (seen.has(c)) continue;
+      seen.add(c);
+      out.push(c);
+      queue.push(c);
+    }
+  }
+  return out;
+}
+
+export function isDescendantOrSelf(
+  candidateId: string,
+  rootId: string,
+  edges: MindEdge[],
+): boolean {
+  return collectSubtreeIds(rootId, edges).includes(candidateId);
+}
+
+export type DragGhost = {
+  rootId: string;
+  /** World delta from positions at pointer-down. */
+  dx: number;
+  dy: number;
+  ids: string[];
+};
+
+export function ghostPos(
+  id: string,
+  base: { x: number; y: number } | undefined,
+  ghost: DragGhost | null,
+): { x: number; y: number } | undefined {
+  if (!base) return undefined;
+  if (ghost && ghost.ids.includes(id)) {
+    return { x: base.x + ghost.dx, y: base.y + ghost.dy };
+  }
+  return base;
+}