import DataLoader from 'dataloader'
import LRUCache from 'lru-cache'
import { toPlural } from './types/helpers'

const debug = require('debug')('graphbrainz:loaders')
const ONE_DAY = 24 * 60 * 60 * 1000

export default function createLoaders (client) {
  // All loaders share a single LRU cache that will remember 8192 responses,
  // each cached for 1 day.
  const cache = LRUCache({
    max: parseInt(process.env.GRAPHBRAINZ_CACHE_SIZE || 8192, 10),
    maxAge: parseInt(process.env.GRAPHBRAINZ_CACHE_TTL || ONE_DAY, 10),
    dispose (key) {
      debug(`Removed '${key}' from cache.`)
    }
  })
  // Make the cache Map-like.
  cache.delete = cache.del
  cache.clear = cache.reset

  const lookup = new DataLoader(keys => {
    return Promise.all(keys.map(key => {
      const [ entityType, id, params ] = key
      return client.lookup(entityType, id, params).then(entity => {
        if (entity) {
          // Store the entity type so we can determine what type of object this
          // is elsewhere in the code.
          entity._type = entityType
          entity._inc = params.inc
        }
        return entity
      })
    }))
  }, {
    cacheKeyFn: (key) => client.getLookupURL(...key),
    cacheMap: cache
  })

  const browse = new DataLoader(keys => {
    return Promise.all(keys.map(key => {
      const [ entityType, params ] = key
      return client.browse(entityType, params).then(list => {
        list[toPlural(entityType)].forEach(entity => {
          // Store the entity type so we can determine what type of object this
          // is elsewhere in the code.
          entity._type = entityType
          entity._inc = params.inc
        })
        return list
      })
    }))
  }, {
    cacheKeyFn: (key) => client.getBrowseURL(...key),
    cacheMap: cache
  })

  const search = new DataLoader(keys => {
    return Promise.all(keys.map(key => {
      const [ entityType, query, params ] = key
      return client.search(entityType, query, params).then(list => {
        list[toPlural(entityType)].forEach(entity => {
          // Store the entity type so we can determine what type of object this
          // is elsewhere in the code.
          entity._type = entityType
          entity._inc = params.inc
        })
        return list
      })
    }))
  }, {
    cacheKeyFn: (key) => client.getSearchURL(...key),
    cacheMap: cache
  })

  return { lookup, browse, search }
}