freeCodeCamp/common/app/routes/challenges/redux/reducer.js

import { handleActions } from 'redux-actions';
import { createPoly } from '../../../../utils/polyvinyl';

import types from './types';
import { BONFIRE, HTML, JS } from '../../../utils/challengeTypes';
import { arrayToString, buildSeed, createTests, getPath } from '../utils';

const initialState = {
  challenge: '',
  currentStep: 0,
  previousStep: -1,
  filter: '',
  files: {},
  superBlocks: []
};

const mainReducer = handleActions(
  {
    [types.fetchChallengeCompleted]: (state, { payload = '' }) => ({
      ...state,
      challenge: payload
    }),
    [types.updateCurrentChallenge]: (state, { payload: challenge }) => ({
      ...state,
      refresh: true,
      challenge: challenge.dashedName,
      path: getPath(challenge),
      tests: createTests(challenge)
    }),

    // map
    [types.updateFilter]: (state, { payload = ''}) => ({
      ...state,
      filter: payload
    }),
    [types.clearFilter]: (state) => ({
      ...state,
      filter: ''
    }),
    [types.fetchChallengesCompleted]: (state, { payload = [] }) => ({
      ...state,
      superBlocks: payload
    }),

    // step
    [types.resetStep]: () => initialState,
    [types.goToStep]: (state, { payload: step = 0 }) => ({
      ...state,
      currentStep: step,
      previousStep: state.currentStep
    })
  },
  initialState
);

const filesReducer = handleActions(
  {
    [types.updateFile]: (state, { payload: file }) => ({
      ...state,
      [file.path]: file
    }),
    [types.updateFiles]: (state, { payload: files }) => {
      return files
        .reduce((files, file) => {
          files[file.path] = file;
          return files;
        }, { ...state });
    },
    [types.updateCurrentChallenge]: (state, { payload: challenge }) => {
      if (challenge.type === 'mod') {
        return challenge.files;
      }
      if (
        challenge.challengeType !== HTML &&
        challenge.challengeType !== JS &&
        challenge.challengeType !== BONFIRE
      ) {
        return {};
      }
      const path = getPath(challenge);
      return {
        ...state,
        [path]: createPoly({
          path,
          contents: buildSeed(challenge),
          head: arrayToString(challenge.head),
          tail: arrayToString(challenge.tail)
        })
      };
    }
  },
  {}
);

export default function challengeReducers(state, action) {
  const newState = mainReducer(state, action);
  const files = filesReducer(state && state.files || {}, action);
  return newState.files !== files ? { ...newState, files } : newState;
}