import type { DownloadStatus, PauseReason } from "@umt/contracts";
import type { DownloadTaskStatus as DomainDownloadStatus } from "@umt/domain";

// 下载状态:domain 只描述"下载器里看到的状态"(mapQbState 的结果),
// contracts / download_task.status 还叠加业务阶段(submitting / stalled / importing / imported)和 pauseReason。

export type { DomainDownloadStatus };

export interface ContractDownloadState {
  status: DownloadStatus;
  pauseReason: PauseReason | null;
}

const TO_CONTRACT: Record<DomainDownloadStatus, ContractDownloadState> = {
  queued: { status: "queued", pauseReason: null },
  downloading: { status: "downloading", pauseReason: null },
  paused_by_threshold: { status: "paused", pauseReason: "threshold" },
  paused_by_user: { status: "paused", pauseReason: "user" },
  completed: { status: "completed", pauseReason: null },
  error: { status: "failed", pauseReason: null },
  missing_files: { status: "missing", pauseReason: null },
  removed: { status: "removed", pauseReason: null },
};

/** contracts 状态 → 下载器层面的 domain 状态(业务叠加态折回其底层下载状态) */
const TO_DOMAIN: Record<DownloadStatus, DomainDownloadStatus | "by_pause_reason"> = {
  queued: "queued",
  // 提交中:下载器里还没有/刚出现,按排队处理
  submitting: "queued",
  downloading: "downloading",
  paused: "by_pause_reason",
  // 无进展是业务判定(detectNoProgress),下载器里仍是 downloading
  stalled: "downloading",
  completed: "completed",
  // 入库阶段:下载本身已完成
  importing: "completed",
  imported: "completed",
  failed: "error",
  removed: "removed",
  missing: "missing_files",
};

/** 暂停原因 → domain 状态:只有 threshold 会被阈值恢复自动恢复,其余都按用户暂停对待(REQ §8.4.1) */
const PAUSE_TO_DOMAIN: Record<PauseReason, DomainDownloadStatus> = {
  threshold: "paused_by_threshold",
  user: "paused_by_user",
  policy: "paused_by_user",
  agent: "paused_by_user",
};

export const DOMAIN_DOWNLOAD_STATUSES = Object.keys(TO_CONTRACT) as DomainDownloadStatus[];

export function toContractDownloadState(s: DomainDownloadStatus): ContractDownloadState {
  return { ...TO_CONTRACT[s] };
}

export function toDomainDownloadStatus(status: DownloadStatus, pauseReason: PauseReason | null): DomainDownloadStatus {
  const d = TO_DOMAIN[status];
  if (d !== "by_pause_reason") return d;
  return PAUSE_TO_DOMAIN[pauseReason ?? "user"];
}

/**
 * 同步轮询时合并"下载器观察"与"当前业务状态":
 * - 业务叠加态在其底层下载状态不变时保留(importing/imported 遇 completed、stalled 遇 downloading、submitting 遇 queued);
 * - 暂停原因为 policy/agent 且下载器仍是暂停时保留原因,不被改写成 user;
 * - 其余以观察为准。
 */
export function mergeObservedDownloadState(
  current: ContractDownloadState,
  observed: DomainDownloadStatus,
): ContractDownloadState {
  const next = TO_CONTRACT[observed];
  const keep =
    ((current.status === "importing" || current.status === "imported") && observed === "completed") ||
    (current.status === "stalled" && observed === "downloading") ||
    (current.status === "submitting" && observed === "queued");
  if (keep) return { ...current };
  if (
    current.status === "paused" &&
    observed === "paused_by_user" &&
    (current.pauseReason === "policy" || current.pauseReason === "agent")
  ) {
    return { ...current };
  }
  return { ...next };
}