import {
  INCREMENT,
  ADD_CHILD,
  REMOVE_CHILD,
  CREATE_NODE,
  DELETE_NODE,
} from '../actions';

const childIds = (state, action) => {
  switch (action.type) {
    case ADD_CHILD:
      return [...state, action.childId];

    case REMOVE_CHILD:
      return state.filter(id => id !== action.childId);

    default:
      return state;
  }
};

const node = (state, action) => {
  switch (action.type) {
    case CREATE_NODE:
      return {
        id: action.nodeId,
        counter: 0,
        childIds: [],
      };

    case INCREMENT:
      return {
        ...state,
        counter: state.counter + 1,
      };

    case ADD_CHILD:
    case REMOVE_CHILD:
      return {
        ...state,
        childIds: childIds(state.childIds, action),
      };

    default:
      return state;
  }
};

const getAllDescendantIds = (state, nodeId) =>
  state[nodeId].childIds.reduce(
    (acc, childId) => [...acc, childId, ...getAllDescendantIds(state, childId)],
    [],
  );

const deleteMany = (state, ids) => {
  state = {
    ...state,
  };
  ids.forEach(id => delete state[id]);

  return state;
};

export default (state = {}, action) => {
  const { nodeId } = action;

  if (typeof nodeId === 'undefined') {
    return state;
  }

  if (action.type === DELETE_NODE) {
    const descendantIds = getAllDescendantIds(state, nodeId);

    return deleteMany(state, [nodeId, ...descendantIds]);
  }

  return {
    ...state,
    [nodeId]: node(state[nodeId], action),
  };
};