import { existsSync, readFileSync, renameSync, unlinkSync, writeFileSync } from "node:fs";

/**
 * Writes data to a JSON file atomically using a temp-file-and-rename strategy.
 * This prevents file corruption if the process crashes or is killed during writing.
 * 
 * @param filePath Path to the target file.
 * @param data Data to be JSON-serialized and written.
 */
export function writeJsonAtomic(filePath: string, data: any): void {
  const tmpPath = filePath + ".tmp";
  try {
    writeFileSync(tmpPath, JSON.stringify(data, null, 2), "utf-8");
    renameSync(tmpPath, filePath);
  } catch (err) {
    // Attempt cleanup if rename failed
    try {
      if (existsSync(tmpPath)) unlinkSync(tmpPath);
    } catch {
      // ignore cleanup errors
    }
    throw err;
  }
}

/**
 * Reads data from a JSON file. Returns undefined if the file doesn't exist or is corrupt.
 */
export function readJsonSafe<T>(filePath: string): T | undefined {
  if (!existsSync(filePath)) return undefined;
  try {
    return JSON.parse(readFileSync(filePath, "utf-8")) as T;
  } catch {
    return undefined;
  }
}