refactor(server): extract shared task graph utilities (#839)

* refactor(server): extract checkout status projection

* refactor(server): extract shared task graph utilities

packages/server/src/tasks/task-graph.ts

@@ -0,0 +1,66 @@
+import type { Task, TaskStore } from "./types.js";
+
+export interface TaskGraph {
+  allTasks: Task[];
+  candidates: Task[];
+  taskMap: Map<string, Task>;
+  childrenMap: Map<string, Task[]>;
+  candidateIds: Set<string>;
+}
+
+type TaskGraphStore = Pick<TaskStore, "list" | "get" | "getDescendants">;
+
+export function sortByPriorityThenCreated(a: Task, b: Task): number {
+  if (a.priority !== undefined && b.priority === undefined) return -1;
+  if (a.priority === undefined && b.priority !== undefined) return 1;
+  if (a.priority !== undefined && b.priority !== undefined) {
+    if (a.priority !== b.priority) return a.priority - b.priority;
+  }
+  return a.created.localeCompare(b.created);
+}
+
+export function buildTaskMap(tasks: Task[]): Map<string, Task> {
+  return new Map(tasks.map((task) => [task.id, task]));
+}
+
+export function buildChildrenMap(tasks: Task[]): Map<string, Task[]> {
+  const childrenMap = new Map<string, Task[]>();
+  for (const task of tasks) {
+    if (task.parentId) {
+      const siblings = childrenMap.get(task.parentId) ?? [];
+      siblings.push(task);
+      childrenMap.set(task.parentId, siblings);
+    }
+  }
+  return childrenMap;
+}
+
+export async function loadScopedTaskGraph(
+  store: TaskGraphStore,
+  scopeId?: string,
+): Promise<TaskGraph> {
+  const allTasks = await store.list();
+  const candidates = await loadScopedCandidates(store, allTasks, scopeId);
+
+  return {
+    allTasks,
+    candidates,
+    taskMap: buildTaskMap(allTasks),
+    childrenMap: buildChildrenMap(allTasks),
+    candidateIds: new Set(candidates.map((task) => task.id)),
+  };
+}
+
+async function loadScopedCandidates(
+  store: TaskGraphStore,
+  allTasks: Task[],
+  scopeId?: string,
+): Promise<Task[]> {
+  if (!scopeId) {
+    return allTasks;
+  }
+
+  const scopeTask = await store.get(scopeId);
+  const descendants = await store.getDescendants(scopeId);
+  return scopeTask ? [scopeTask, ...descendants] : descendants;
+}