// 长任务（例如 Agent 生成报表）的前端状态机：用 reducer 管理，所有状态转换集中在一处，便于测试。
// 自检：node taskReducer-demo.ts

export type TaskStatus = "queued" | "running" | "waiting_input" | "succeeded" | "failed" | "cancelled";

export interface TaskState {
  id: string | null;
  status: TaskStatus | "idle";
  steps: { name: string; done: boolean }[];
  result: { title: string; url: string } | null;
  error: string | null;
  version: number; // 服务端事件的序号：丢弃过期 / 乱序的事件
}

export type TaskEvent =
  | { type: "submitted"; id: string }
  | { type: "progress"; seq: number; step: string; done: boolean }
  | { type: "need_input"; seq: number; question: string }
  | { type: "succeeded"; seq: number; result: { title: string; url: string } }
  | { type: "failed"; seq: number; error: string; retryable: boolean }
  | { type: "cancel" }
  | { type: "retry" };

export const initialState: TaskState = { id: null, status: "idle", steps: [], result: null, error: null, version: 0 };

const FINAL: ReadonlySet<TaskState["status"]> = new Set(["succeeded", "failed", "cancelled"]);

export function taskReducer(s: TaskState, e: TaskEvent): TaskState {
  switch (e.type) {
    case "submitted":
      return { ...initialState, id: e.id, status: "queued" };
    case "cancel":
      return FINAL.has(s.status) ? s : { ...s, status: "cancelled" };
    case "retry":
      return s.status === "failed" ? { ...s, status: "queued", error: null } : s;
    default:
      // 服务端事件：终态之后、或者序号不大于当前版本的事件一律丢弃（重连后可能收到重复事件）
      if (FINAL.has(s.status) || e.seq <= s.version) return s;
  }
  switch (e.type) {
    case "progress": {
      const steps = s.steps.some((x) => x.name === e.step)
        ? s.steps.map((x) => (x.name === e.step ? { ...x, done: e.done } : x))
        : [...s.steps, { name: e.step, done: e.done }];
      return { ...s, status: "running", steps, version: e.seq };
    }
    case "need_input":
      return { ...s, status: "waiting_input", version: e.seq };
    case "succeeded":
      return { ...s, status: "succeeded", result: e.result, version: e.seq };
    case "failed":
      return { ...s, status: "failed", error: e.retryable ? `${e.error}（可重试）` : e.error, version: e.seq };
  }
}