import crypto from 'crypto';
import * as openpgp from 'openpgp';
import { Transform, TransformCallback } from 'stream';

interface EncryptorOptions {
  signingKey?: string;
  password?: string;
  encryptionKeys: string[];
}

class PGPEncryptor extends Transform {
  private _messageChunks: Uint8Array[] = [];
  private _messageLength = 0;
  private _signingKey?: string;
  private _password?: string;

  private _encryptionKeys: string[];

  constructor(options: EncryptorOptions) {
    super();
    this._signingKey = options.signingKey;
    this._password = options.password;
    this._encryptionKeys = options.encryptionKeys;
  }

  // just save the whole message
  _transform = (
    chunk: any,
    _encoding: BufferEncoding,
    callback: TransformCallback
  ): void => {
    this._messageChunks.push(chunk);
    this._messageLength += chunk.length;
    callback();
  };

  // Actually do stuff
  _flush = async (callback: TransformCallback): Promise<void> => {
    // Reconstruct message as buffer
    const message = Buffer.concat(this._messageChunks, this._messageLength);
    const validPublicKeys = await Promise.all(
      this._encryptionKeys.map((armoredKey) => openpgp.readKey({ armoredKey }))
    );
    let privateKey: openpgp.Key | undefined;

    // Just return the message if there is no one to encrypt for
    if (!validPublicKeys.length) {
      this.push(message);
      return callback();
    }

    // Only sign the message if private key and password exist
    if (this._signingKey && this._password) {
      privateKey = await openpgp.readKey({
        armoredKey: this._signingKey,
      });

      await openpgp.decryptKey({ privateKey, passphrase: this._password });
    }

    const emailPartDelimiter = '\r\n\r\n';
    const messageParts = message.toString().split(emailPartDelimiter);

    /**
     * In this loop original headers are split up into two parts,
     * one for the email that is sent
     * and one for the encrypted content
     */
    const header = messageParts.shift() as string;
    const emailHeaders: string[][] = [];
    const contentHeaders: string[][] = [];
    const linesInHeader = header.split('\r\n');
    let previousHeader: string[] = [];
    for (let i = 0; i < linesInHeader.length; i++) {
      const line = linesInHeader[i];
      /**
       * If it is a multi-line header (current line starts with whitespace)
       * or it's the first line in the iteration
       * add the current line with previous header and move on
       */
      if (/^\s/.test(line) || i === 0) {
        previousHeader.push(line);
        continue;
      }

      /**
       * This is done to prevent the last header
       * from being missed
       */
      if (i === linesInHeader.length - 1) {
        previousHeader.push(line);
      }

      /**
       * We need to seperate the actual content headers
       * so that we can add it as a header for the encrypted content
       * So that the content will be displayed properly after decryption
       */
      if (
        /^(content-type|content-transfer-encoding):/i.test(previousHeader[0])
      ) {
        contentHeaders.push(previousHeader);
      } else {
        emailHeaders.push(previousHeader);
      }
      previousHeader = [line];
    }

    // Generate a new boundary for the email content
    const boundary = 'nm_' + crypto.randomBytes(14).toString('hex');
    /**
     * Concatenate everything into single strings
     * and add pgp headers to the email headers
     */
    const emailHeadersRaw =
      emailHeaders.map((line) => line.join('\r\n')).join('\r\n') +
      '\r\n' +
      'Content-Type: multipart/encrypted; protocol="application/pgp-encrypted";' +
      '\r\n' +
      ' boundary="' +
      boundary +
      '"' +
      '\r\n' +
      'Content-Description: OpenPGP encrypted message' +
      '\r\n' +
      'Content-Transfer-Encoding: 7bit';
    const contentHeadersRaw = contentHeaders
      .map((line) => line.join('\r\n'))
      .join('\r\n');

    const encryptedMessage = await openpgp.encrypt({
      message: await openpgp.createMessage({
        text:
          contentHeadersRaw +
          emailPartDelimiter +
          messageParts.join(emailPartDelimiter),
      }),
      publicKeys: validPublicKeys,
      privateKeys: privateKey,
    });

    const body =
      '--' +
      boundary +
      '\r\n' +
      'Content-Type: application/pgp-encrypted\r\n' +
      'Content-Transfer-Encoding: 7bit\r\n' +
      '\r\n' +
      'Version: 1\r\n' +
      '\r\n' +
      '--' +
      boundary +
      '\r\n' +
      'Content-Type: application/octet-stream; name=encrypted.asc\r\n' +
      'Content-Disposition: inline; filename=encrypted.asc\r\n' +
      'Content-Transfer-Encoding: 7bit\r\n' +
      '\r\n' +
      encryptedMessage +
      '\r\n--' +
      boundary +
      '--\r\n';

    this.push(Buffer.from(emailHeadersRaw + emailPartDelimiter + body));
    callback();
  };
}

export const openpgpEncrypt = (options: EncryptorOptions) => {
  return function (mail: any, callback: () => unknown): void {
    if (!options.encryptionKeys.length) {
      setImmediate(callback);
    }
    mail.message.transform(
      () =>
        new PGPEncryptor({
          signingKey: options.signingKey,
          password: options.password,
          encryptionKeys: options.encryptionKeys,
        })
    );
    setImmediate(callback);
  };
};