Cart.reducer.ts

import {
  CartItem,
  Product
} from '../Components/ProductItem/ProductItem.component';

const ADD_TO_CART = 'ADD_TO_CART';
const REMOVE_FROM_CART = 'REMOVE_FROM_CART';
const ADD_QUANTITY = 'ADD_QUANTITY';
const SUB_QUANTITY = 'SUB_QUANTITY';
const RESET_CART = 'RESET_CART';

export const constants = {
  ADD_TO_CART,
  REMOVE_FROM_CART,
  ADD_QUANTITY,
  SUB_QUANTITY,
  RESET_CART
};

export interface CartState {
  products: Array<CartItem>;
  total: number;
}

export const initialState: CartState = {
  products: [],
  total: 0
};

const addToCart = (product: Product) => ({
  type: ADD_TO_CART,
  payload: product
});
const removeFromCart = (productId: number) => ({
  type: REMOVE_FROM_CART,
  payload: productId
});
const addQuantity = (productId: number) => ({
  type: ADD_QUANTITY,
  payload: productId
});
const subQuantity = (productId: number) => ({
  type: SUB_QUANTITY,
  payload: productId
});
const resetCart = () => ({ type: RESET_CART });

export const actions = {
  addToCart,
  removeFromCart,
  addQuantity,
  subQuantity,
  resetCart
};

const _findProductById = (state: CartState, productId: number) =>
  state.products.find(item => item.id === productId);

const _updateProduct = (
  products: Array<CartItem>,
  product: CartItem
): Array<CartItem> =>
  products.map((item) => {
    if (item.id === product.id) {
      return product;
    }

    return item;
  });

const _mapAddQuantityState = (
  state: CartState,
  existingProduct: CartItem
): CartState => ({
  ...state,
  products: _updateProduct(state.products, {
    ...existingProduct,
    quantity: existingProduct.quantity + 1
  }),
  total: state.total + Number(existingProduct.price)
});

const _mapRemoveFromCartState = (
  state: CartState,
  existingProduct: CartItem
): CartState => ({
  ...state,
  products: state.products.filter(item => item.id !== existingProduct.id),
  total: state.total - Number(existingProduct.price) * existingProduct.quantity
});

const addQuantityHandler = (state: CartState, productId: number): CartState => {
  const existingProduct = _findProductById(state, productId);

  if (existingProduct) {
    return _mapAddQuantityState(state, existingProduct);
  }

  return state;
};

const addToCartHandler = (state: CartState, product: Product): CartState => {
  const existingProduct = _findProductById(state, product.id);

  if (existingProduct) {
    return _mapAddQuantityState(state, existingProduct);
  }

  return {
    ...state,
    products: [
      ...state.products,
      {
        ...product,
        quantity: 1
      }
    ],
    total: state.total + Number(product.price)
  };
};

const removeFromCartHandler = (
  state: CartState,
  productId: number
): CartState => {
  const existingProduct = _findProductById(state, productId);

  if (existingProduct) {
    return _mapRemoveFromCartState(state, existingProduct);
  }

  return state;
};

const subQuantityHandler = (state: CartState, productId: number): CartState => {
  const existingProduct = _findProductById(state, productId);

  if (existingProduct) {
    if (existingProduct.quantity <= 1) {
      return _mapRemoveFromCartState(state, existingProduct);
    }

    return {
      ...state,
      products: _updateProduct(state.products, {
        ...existingProduct,
        quantity: existingProduct.quantity - 1
      }),
      total: state.total - Number(existingProduct.price)
    };
  }

  return state;
};

const resetCartHandler = (): CartState => initialState;

const cartReducer = (
  state = initialState,
  action: { type: string; payload: Product & number }
) => {
  switch (action.type) {
    case ADD_TO_CART:
      return addToCartHandler(state, action.payload);
    case REMOVE_FROM_CART:
      return removeFromCartHandler(state, action.payload);
    case ADD_QUANTITY:
      return addQuantityHandler(state, action.payload);
    case SUB_QUANTITY:
      return subQuantityHandler(state, action.payload);
    case RESET_CART:
      return resetCartHandler();
    default:
      return initialState;
  }
};

export default cartReducer;