import { stat } from "node:fs/promises";

/** Default maximum file size: 100 MB */
export const MAX_FILE_SIZE_BYTES = 100 * 1024 * 1024;

function formatBytes(bytes: number): string {
  if (bytes < 1024) {
    return `${bytes} B`;
  }
  if (bytes < 1024 * 1024) {
    return `${(bytes / 1024).toFixed(1)} KB`;
  }
  return `${(bytes / (1024 * 1024)).toFixed(1)} MB`;
}

/**
 * Check whether a file on disk exceeds the size limit.
 * Returns an error string if the file is too large, or undefined if OK.
 */
export async function checkFileSizeOnDisk(
  filePath: string,
  limit: number = MAX_FILE_SIZE_BYTES,
): Promise<string | undefined> {
  const fileStat = await stat(filePath);
  if (fileStat.size > limit) {
    return `File size (${formatBytes(fileStat.size)}) exceeds the ${formatBytes(
      limit,
    )} limit: ${filePath}`;
  }
  return undefined;
}

/**
 * Check whether content to be written exceeds the size limit.
 * Returns an error string if the content is too large, or undefined if OK.
 */
export function checkContentSize(
  content: string,
  filePath: string,
  limit: number = MAX_FILE_SIZE_BYTES,
): string | undefined {
  const size = Buffer.byteLength(content, "utf-8");
  if (size > limit) {
    return `Content size (${formatBytes(size)}) exceeds the ${formatBytes(
      limit,
    )} limit for: ${filePath}`;
  }
  return undefined;
}