import { randomUUID } from "node:crypto";
import { link, open, rename, rm, stat } from "node:fs/promises";
import { basename, dirname, join } from "node:path";

export interface AtomicWriteOptions {
  /** 目标存在时是否原子替换；为 false 时以 EEXIST 拒绝覆盖。 */
  overwrite?: boolean;
  /** 新文件权限；目标已存在时优先继承原权限。 */
  mode?: number;
}

/** 判断未知错误是否具有指定 Node.js 文件系统错误码。 */
function hasErrorCode(error: unknown, code: string): boolean {
  return error instanceof Error && (error as NodeJS.ErrnoException).code === code;
}

/** 读取现有目标权限；目标不存在时使用调用方提供的默认权限。 */
async function resolveMode(path: string, fallback: number): Promise<number> {
  try {
    return (await stat(path)).mode & 0o777;
  } catch (error) {
    if (hasErrorCode(error, "ENOENT")) {
      return fallback;
    }
    throw error;
  }
}

/**
 * 在目标同目录写入并同步临时文件，再通过 rename/link 原子提交。
 * overwrite=false 时不会覆盖提交期间由其他进程创建的目标。
 */
export async function writeTextFileAtomic(
  path: string,
  content: string,
  options: AtomicWriteOptions = {},
): Promise<void> {
  const overwrite = options.overwrite ?? true;
  const mode = await resolveMode(path, options.mode ?? 0o600);
  const tempPath = join(dirname(path), `.${basename(path)}.${process.pid}.${randomUUID()}.tmp`);
  let handle;

  try {
    handle = await open(tempPath, "wx", mode);
    await handle.writeFile(content, "utf8");
    await handle.sync();
    await handle.close();
    handle = undefined;

    if (overwrite) {
      await rename(tempPath, path);
    } else {
      await link(tempPath, path);
      await rm(tempPath, { force: true });
    }
  } catch (error) {
    await handle?.close().catch(() => undefined);
    await rm(tempPath, { force: true }).catch(() => undefined);
    throw error;
  }
}