/**
 * 按 `operation_id` 聚合 Agent 任务进度的纯状态机。
 *
 * 同一任务的更新只替换最新投影，避免聊天时间线因进度变化无限新增卡片；取消请求也必须
 * 经过受限状态跃迁。
 */
import type { TaskProgress, TaskStatus } from "@/runtime/protocol/lineup-v1";

export type TaskRecord = TaskProgress & {
  conversation_id: string;
  updated_at: string;
  cancel_requested_at?: string;
};

export type TaskTransition =
  | { disposition: "accepted"; record: TaskRecord }
  | { disposition: "missing" | "invalid_transition"; record?: TaskRecord };

/**
 * Platform-neutral task projection. It has no DOM, storage, transport, or
 * side-effect handler. M1-04 records a user cancellation request locally;
 * M1-06 later owns durable delivery to the Agent.
 */
export class TaskStateMachine {
  private readonly tasks = new Map<string, TaskRecord>();

  public receive(update: TaskProgress, conversationID: string, updatedAt: string): TaskRecord {
    const current = this.tasks.get(update.operation_id);
    const next: TaskRecord = {
      ...update,
      conversation_id: conversationID,
      updated_at: updatedAt,
      ...(current?.cancel_requested_at && update.status !== "cancelled" ? { cancel_requested_at: current.cancel_requested_at } : {}),
    };
    this.tasks.set(next.operation_id, next);
    return copy(next);
  }

  public requestCancel(operationID: string, updatedAt: string): TaskTransition {
    const record = this.tasks.get(operationID);
    if (!record) return { disposition: "missing" };
    if (!record.cancellable || isTerminal(record.status) || record.cancel_requested_at) return { disposition: "invalid_transition", record: copy(record) };
    record.cancel_requested_at = updatedAt;
    record.updated_at = updatedAt;
    return { disposition: "accepted", record: copy(record) };
  }

  public get(operationID: string): TaskRecord | undefined {
    const record = this.tasks.get(operationID);
    return record ? copy(record) : undefined;
  }

  public snapshot(): readonly TaskRecord[] { return [...this.tasks.values()].map(copy); }
  public reset(): void { this.tasks.clear(); }
  public restore(records: readonly TaskRecord[]): void {
    this.tasks.clear();
    for (const record of records) {
      if (!isRestoreable(record) || this.tasks.has(record.operation_id)) continue;
      this.tasks.set(record.operation_id, copy(record));
    }
  }
}

function isTerminal(status: TaskStatus): boolean { return status === "completed" || status === "failed" || status === "cancelled"; }

function isRestoreable(value: unknown): value is TaskRecord {
  if (!value || typeof value !== "object" || Array.isArray(value)) return false;
  const record = value as Partial<TaskRecord>;
  return typeof record.operation_id === "string" && Boolean(record.operation_id)
    && typeof record.conversation_id === "string" && Boolean(record.conversation_id)
    && typeof record.title === "string" && typeof record.percent === "number" && Number.isFinite(record.percent)
    && TASK_STATUS_VALUES.has(record.status as TaskStatus) && typeof record.cancellable === "boolean"
    && typeof record.updated_at === "string" && !Number.isNaN(Date.parse(record.updated_at));
}

const TASK_STATUS_VALUES = new Set<TaskStatus>(["running", "waiting", "completed", "failed", "cancelled"]);
function copy(record: TaskRecord): TaskRecord { return { ...record }; }