spotify.js

const request = require('request')
const Task = require('data.task')
const Either = require('data.either')

const httpGet = url =>
  new Task((rej, res) =>
  request(url, (error, response, body) =>
    error ? rej(error) : res(body)))

const getJSON = url =>
  httpGet(url)
  .map(parse)
  .chain(eitherToTask)

const first = xs =>
  Either.fromNullable(xs[0])

const eitherToTask = e =>
  e.fold(Task.rejected, Task.of)

const parse = Either.try(JSON.parse)

const findArtist = name =>
  getJSON(`https://api.spotify.com/v1/search?q=${name}&type=artist`)
  .map(result => result.artists.items)
  .map(first)
  .chain(eitherToTask)

const relatedArtists = id =>
  getJSON(`https://api.spotify.com/v1/artists/${id}/related-artists`)
  .map(result => result.artists)

module.exports = {findArtist, relatedArtists}