DanielRowe/nmr-datastream

/**
 * openDatastream
 *
 * Opens a datastream (DSMEMBER.DAT) either in its self extracting
 * exe format or in it's extracted .DAT format.
 *
 * You do not need to utilise this function to use anything else
 * it is simply a helper.
 *
 * It can open from either a path or a buffer.
 *
 * @param file: file path or string
 *
 * @returns string
 *
 */

import { promises as fs } from 'fs';
import FileType from 'file-type';
import AdmZip from 'adm-zip';
import { URL } from 'url';

export const openDatastream = async (file: string | Buffer | URL | fs.FileHandle) => {
  // Handle applicably if buffer passed to opener.
  if (Buffer.isBuffer(file)) {
    const fileFormat = await FileType.fromBuffer(file);
    if (fileFormat?.ext === 'exe') {
      const zip = new AdmZip(file); // Extract contents of exe.
      let result = '';
      zip.getEntries().map((zipFile) => {
        if (zipFile.entryName === 'DSMEMBER.DAT') { // Providing we find the right file - return.
          result = zipFile.getData().toString('utf-8');
        }
        return result; // Get data and convert to string.
      });
      if (result === '') {
        throw new Error('DSMember.DAT not found within EXE');
      }
      return result;
    }
    const fileContents = file.toString(); // Convert to string
    if (fileContents.substring(0, 3) === 'H1,') { // Check first few digits match standard datastream - Very basic check.
      return fileContents;
    }
    throw new Error('Invalid file type');
  } else if (typeof file === 'string') { // Handle if string (hopefully file path)
    // Determine file extension
    const fileFormat = await FileType.fromFile(file);
    if (fileFormat?.ext === 'exe') {
      const zip = new AdmZip(file);
      let result = '';
      zip.getEntries().map((zipFile) => {
        if (zipFile.entryName === 'DSMEMBER.DAT') { // Providing we find the right file - return.
          result = zipFile.getData().toString('utf-8');
        }
        return result;
      });
      if (result === '') {
        throw new Error('DSMember.DAT not found within EXE');
      }
      return result;
    }
    if (file.split('.')?.pop()?.toLocaleLowerCase() === 'dat') { // Check the file format is a .dat
      const output = await fs.readFile(file, 'utf-8');
      return output;
    }
    throw new Error('Invalid file provided');
  } else {
    throw new Error('File not provided as a path or buffer');
  }
};

export default openDatastream;