// 本项目新增(REQ §8.2 挂载根哨兵);MP 无对应实现。
import { lstat, stat, writeFile } from "node:fs/promises";
import { join } from "node:path";
import { errnoOf } from "./errors.ts";

export const DEFAULT_ROOT_SENTINEL = ".uhd-root";

export interface FileFacts {
  size: number;
  mtimeMs: number;
  ino: number;
  dev: number;
  nlink: number;
  isFile: boolean;
  isDirectory: boolean;
  isSymbolicLink: boolean;
}

export type StatResult =
  | { kind: "ok"; facts: FileFacts }
  | { kind: "missing" }
  | { kind: "permission_denied" }
  /** 挂载根哨兵不存在/不可读:不能据此判定文件缺失 */
  | { kind: "root_offline"; root: string; reason: string }
  | { kind: "error"; code: string; message: string };

export type RootHealth =
  | { kind: "online"; dev: number }
  | { kind: "offline"; reason: "sentinel_missing" | "root_missing" | "permission_denied" | "error"; code?: string };

/** 检查库根/缓存根是否在线:根目录存在且哨兵文件存在。 */
export async function checkRoot(root: string, sentinel: string = DEFAULT_ROOT_SENTINEL): Promise<RootHealth> {
  let dev: number;
  try {
    const st = await stat(root);
    dev = st.dev;
  } catch (e) {
    const code = errnoOf(e);
    if (code === "ENOENT") return { kind: "offline", reason: "root_missing" };
    if (code === "EACCES" || code === "EPERM") return { kind: "offline", reason: "permission_denied", code };
    return { kind: "offline", reason: "error", code: code ?? "UNKNOWN" };
  }
  try {
    await stat(join(root, sentinel));
    return { kind: "online", dev };
  } catch (e) {
    const code = errnoOf(e);
    if (code === "ENOENT") return { kind: "offline", reason: "sentinel_missing" };
    if (code === "EACCES" || code === "EPERM") return { kind: "offline", reason: "permission_denied", code };
    return { kind: "offline", reason: "error", code: code ?? "UNKNOWN" };
  }
}

/** 在根目录写入哨兵文件(首次登记库根时调用)。 */
export async function writeRootSentinel(root: string, sentinel: string = DEFAULT_ROOT_SENTINEL): Promise<void> {
  await writeFile(join(root, sentinel), `uhd-media-tool root sentinel\ncreated=${new Date().toISOString()}\n`, {
    flag: "wx",
  }).catch((e) => {
    if (errnoOf(e) !== "EEXIST") throw e;
  });
}

function facts(st: Awaited<ReturnType<typeof lstat>>): FileFacts {
  return {
    size: Number(st.size),
    mtimeMs: Number(st.mtimeMs),
    ino: Number(st.ino),
    dev: Number(st.dev),
    nlink: Number(st.nlink),
    isFile: st.isFile(),
    isDirectory: st.isDirectory(),
    isSymbolicLink: st.isSymbolicLink(),
  };
}

/**
 * 区分 ENOENT / EACCES / 挂载根离线的 stat。给出 root 时先检查哨兵,
 * 根离线返回 root_offline 而不是 missing(REQ §8.2)。不抛异常。
 */
export async function statSafe(path: string, opts: { root?: string; sentinel?: string } = {}): Promise<StatResult> {
  if (opts.root) {
    const h = await checkRoot(opts.root, opts.sentinel);
    if (h.kind === "offline") return { kind: "root_offline", root: opts.root, reason: h.reason };
  }
  try {
    return { kind: "ok", facts: facts(await lstat(path)) };
  } catch (e) {
    const code = errnoOf(e);
    if (code === "ENOENT" || code === "ENOTDIR") return { kind: "missing" };
    if (code === "EACCES" || code === "EPERM") return { kind: "permission_denied" };
    return { kind: "error", code: code ?? "UNKNOWN", message: (e as Error)?.message ?? String(e) };
  }
}