// import * as R from 'ramda';
// import { Observable } from 'rxjs';
// // import { combineLatest } from 'rxjs/observable/combineLatest';
// // import { Book } from '../models/models';
// export type Book = { id: string };
// import { ActionTypes as bookActions } from '../actions/book';
// import { ActionTypes as collActions } from '../actions/collection';
// import { combineSelectors } from '../reducers/reducers';
// let { SEARCH_COMPLETE, LOAD, SELECT } = bookActions;
// let { LOAD_SUCCESS } = collActions;

// export interface State {
//   ids: string[];
//   entities: { [id: string]: Book };
//   selectedBookId: string | null;
// };

// export const initialState: State = {
//   ids: [],
//   entities: {},
//   selectedBookId: null,
// };

// // T[] -> { [k]: T }, by a certain property as key
// let byProp = (k: string) => R.pipe(R.map(<T>(v: T) => [R.prop(k, v), v]), R.fromPairs);
// // (state, action: book.Actions | collection.Actions): State

// let mergeBooks = (state: State, books: Book[]) => {
//   const newBooks = books.filter((book: Book) => !state.entities[book.id]);
//   const newBookIds = newBooks.map(R.prop('id'));
//   const newBookEntities = byProp('id')(newBooks);
//   return {
//     ids: [ ...state.ids, ...newBookIds ],
//     entities: R.merge(state.entities, newBookEntities),
//     selectedBookId: state.selectedBookId,
//   };
// }

// export let reducers = {
//   [SEARCH_COMPLETE]: mergeBooks,
//   [LOAD_SUCCESS]: mergeBooks,

//   [LOAD]: (state: State, book: Book) => state.ids.includes(book.id) ? state : {
//     ids: [ ...state.ids, book.id ],
//     entities: R.merge(state.entities, {
//       [book.id]: book,
//     }),
//     selectedBookId: state.selectedBookId,
//   },

//   [SELECT]: (state: State, selectedBookId: number) => ({
//     ids: state.ids,
//     entities: state.entities,
//     selectedBookId,
//   }),
// }

// let getBookEntities = R.map(R.prop('entities'));
// let getBookIds = R.map(R.prop('ids'));
// let getSelectedBookId = R.map(R.prop('selectedBookId'));

// export let selectors = {
//   selectedBook: combineSelectors(
//     [getBookEntities, getSelectedBookId],
//     ([books, id]) => books[id]
//   ),
//   allBooks: combineSelectors(
//     [getBookEntities, getBookIds],
//     ([entities, ids]) => ids.map((id: string) => entities[id])
//   ),
//   // // works even without Ramda typings:
//   // selectedBook(state$: Observable<State>) {
//   //   return combineLatest<{ [id: string]: Book }, string>(
//   //     state$.let(getBookEntities),
//   //     state$.let(getSelectedBookId)
//   //   )
//   //   .map(([ entities, selectedBookId ]) => entities[selectedBookId])
//   // },
//   // allBooks(state$: Observable<State>) {
//   //   return combineLatest<{ [id: string]: Book }, string[]>(
//   //     state$.let(getBookEntities),
//   //     state$.let(getBookIds)
//   //   )
//   //   .map(([ entities, ids ]) => ids.map(id => entities[id]));
//   // },
// };