import DataLoader from 'dataloader'
import LRUCache from 'lru-cache'

const debug = require('debug')('graphbrainz:extensions/fanart-tv')

export default function createLoader (options) {
  const { client } = options
  const cache = LRUCache({
    max: options.cacheSize,
    maxAge: options.cacheTTL,
    dispose (key) {
      debug(`Removed from cache. key=${key}`)
    }
  })
  // Make the cache Map-like.
  cache.delete = cache.del
  cache.clear = cache.reset

  const loader = new DataLoader(keys => {
    return Promise.all(keys.map(key => {
      const [ entityType, id ] = key
      return client.musicEntity(entityType, id)
        .catch(err => {
          if (err.statusCode === 404) {
            // 404s are OK, just return empty data.
            return {
              artistbackground: [],
              artistthumb: [],
              musiclogo: [],
              hdmusiclogo: [],
              musicbanner: [],
              musiclabel: [],
              albums: {}
            }
          }
          throw err
        }).then(body => {
          if (entityType === 'artist') {
            const releaseGroupIDs = Object.keys(body.albums)
            debug(`Priming album cache with ${releaseGroupIDs.length} album(s).`)
            releaseGroupIDs.forEach(key => loader.prime(['release-group', key], body))
          }
          return body
        })
    }))
  }, {
    cacheKeyFn: ([ entityType, id ]) => `${entityType}/${id}`,
    cacheMap: cache
  })
  return loader
}