import * as fs from 'fs';
import * as http from 'http';

export default function saveResponse(
  filePath: string,
  resolve: (fileName: string) => void,
  reject: (reason: string) => void,
  response: http.IncomingMessage,
) {
  //Check that file exists (200 HTTP status code)
  if (response.statusCode !== 200) {
    return reject(`Expected status code 200 but received ${response.statusCode}.`);
  }

  //Remember file size
  const headerLength = Number(response.headers['content-length']);

  const writeStream = fs.createWriteStream(filePath);

  //If we receive a part of the response, write it to disk
  let totalLength = 0;
  const chunkPromises: Array<Promise<void>> = [];
  response.on('data', (chunk: Buffer) => {
    totalLength += chunk.length;

    //Exit early if we received too much data
    if (totalLength > headerLength) {
      return reject(`Expected length ${headerLength} but received at least ${totalLength}.`);
    }

    //Write chunk to disk
    chunkPromises.push(new Promise((writeResolve) => {
      writeStream.write(chunk, () => {
        writeResolve();
      });
    }));
  });

  //If we finished reading response, check for correctness, then return it
  response.on('end', () => {
    //Check that length is correct
    if (totalLength !== headerLength) {
      return reject(`Expected length ${headerLength} but received ${totalLength}.`);
    }

    //wait until everything is written to disk, then return file name
    //TODO: need to automatically delete file once it is no longer used
    //TODO: need to provide methods to seek through file
    Promise.all(chunkPromises).then(() => {
      resolve(filePath);
    });
  });
}