bdn-pocket/src/selector/selector.js

pocket tools for managing redux and redux-saga

import stampit from '@stamp/it'
import equals from 'ramda/src/equals'
import pathOr from 'ramda/src/pathOr'
import propOr from 'ramda/src/propOr'

import MakeReqMessenger from '../messenger/make_req_messenger'

import SelectorDef, { makeIsCacheValid } from './selector_def'

const Selector = stampit(SelectorDef)
  .methods({
    getPag(pags, id) {
      const { defaultState } = MakeReqMessenger.compose.deepProperties
      if (pags === undefined) {
        throw new Error(`
          pags parameter is undefined -
          expected an object indexed by id
          `)
      }
      const getter = Array.isArray(id) ? pathOr : propOr
      return getter(defaultState, id, pags)
    }
  })

  .init(({ reducer }, { stamp, instance }) => {
    const { PropTypes } = stamp.compose.staticProperties
    const {
      getSubState,
    } = instance
    const isPropsCacheValid = makeIsCacheValid(equals)
    const boundReducer = reducer.bind(instance)
    const isSubStateCacheValid = makeIsCacheValid((r, l) => r === l)
    let lastResult
    let lastPartialReducer

    /**
     * propsReducer generate a partial reducer function
     * that is memoized (lastPartialReducer)
     * if props is sent, propsReducer execute the partial reducer
     * else it return the partial reducer
     */
    return function propsReducer(state, props) {
      const subStates = getSubState(state)
      // memoize partial reducer
      // this partial reducer will be reused in next call if args remains equal
      if (!isSubStateCacheValid(subStates)) {
        // invalidate props cache to ensure reducer to run next time
        isPropsCacheValid(undefined)
        lastPartialReducer = (props = {}) => {
          PropTypes(props)
          if ( !isPropsCacheValid(props) ) {
            lastResult = boundReducer(subStates, props, { instance })
          }
          return lastResult
        }
      }

      return props === undefined ?
        lastPartialReducer :
        lastPartialReducer(props)
    }
  })

export default Selector