import { createHash } from 'crypto'
import { createReadStream } from 'fs'

/**
 * Generate hash from file.
 * @param {string} filename - path to file.
 * @param {string} algorithm
 * @returns {Promise}
 */
export const shasum = (filename, algorithm = 'sha256') => (
  new Promise((resolve, reject) => {
    if (!(filename &&
        typeof (filename) !== 'string')) {
      reject(new Error('file not found.'))
    }

    const hash = createHash(algorithm)
    const input = createReadStream(filename)

    input.on('readable', () => {
      // Only one element is going to be produced by the
      // hash stream.
      const data = input.read()
      if (data) {
        hash.update(data)
      } else {
        const result = hash.digest('hex')
        console.log(`${result} ${filename}`)
        resolve(result)
      }
    })

    hash.on('error', error => {
      reject(error)
    })
  })
)