import coerceSelection from './coerceSelection'
import type { KeysT, SubstyleT } from './types'

const EMPTY = {}

const memoize =
  (substyle: SubstyleT): SubstyleT =>
  (select: KeysT, defaultStyle?: Object) => {
    const cacheKey = defaultStyle || EMPTY
    substyle.memoize = substyle.memoize || new WeakMap()
    let mapEntry
    if (!substyle.memoize.has(cacheKey)) {
      mapEntry = {}
      substyle.memoize.set(cacheKey, mapEntry)
    } else {
      mapEntry = substyle.memoize.get(cacheKey)
    }
    const selectHash = coerceSelection(select).join(' ')
    return selectHash in mapEntry
      ? mapEntry[selectHash]
      : (mapEntry[selectHash] = substyle(select || [], defaultStyle))
  }

export default memoize