/**
 * Promises are promises and streams are streams, and ne'er the twain shall
 * meet.
 * @module
 */
'use strict'

const BPromise = require('bluebird')
const zlib = require('zlib')
const { WritableBuffer, ReadableString } = require('@overleaf/stream-utils')
const { pipeline } = require('stream')

/**
 * Pipe a read stream to a write stream. The promise resolves when the write
 * stream finishes.
 *
 * @function
 * @param {stream.Readable} readStream
 * @param {stream.Writable} writeStream
 * @return {Promise}
 */
function promisePipe(readStream, writeStream) {
  return new BPromise(function (resolve, reject) {
    pipeline(readStream, writeStream, function (err) {
      if (err) {
        reject(err)
      } else {
        resolve()
      }
    })
  })
}

exports.promisePipe = promisePipe

/**
 * Create a promise for the result of reading a stream to a buffer.
 *
 * @function
 * @param {stream.Readable} readStream
 * @return {Promise.<Buffer>}
 */
function readStreamToBuffer(readStream) {
  return new BPromise(function (resolve, reject) {
    const bufferStream = new WritableBuffer()
    pipeline(readStream, bufferStream, function (err) {
      if (err) {
        reject(err)
      } else {
        resolve(bufferStream.contents())
      }
    })
  })
}

exports.readStreamToBuffer = readStreamToBuffer

/**
 * Create a promise for the result of un-gzipping a stream to a buffer.
 *
 * @function
 * @param {stream.Readable} readStream
 * @return {Promise.<Buffer>}
 */
function gunzipStreamToBuffer(readStream) {
  const gunzip = zlib.createGunzip()
  const bufferStream = new WritableBuffer()
  return new BPromise(function (resolve, reject) {
    pipeline(readStream, gunzip, bufferStream, function (err) {
      if (err) {
        reject(err)
      } else {
        resolve(bufferStream.contents())
      }
    })
  })
}

exports.gunzipStreamToBuffer = gunzipStreamToBuffer

/**
 * Create a write stream that gzips the given string.
 *
 * @function
 * @param {string} string
 * @return {Promise.<stream.Readable>}
 */
function gzipStringToStream(string) {
  return new BPromise(function (resolve, reject) {
    zlib.gzip(Buffer.from(string), function (error, result) {
      if (error) {
        reject(error)
      } else {
        resolve(new ReadableString(result))
      }
    })
  })
}

exports.gzipStringToStream = gzipStringToStream