Cart Reducer

CartReducer.jsx

const cartReducer = (state = {
    cartItems: 0,
    items: products,
    cartContents: [],
}, action) => {
    switch (action.type) {
        case "ADD_TO_CART": {
            const existingItem = state.cartContents.find(item => {
                return item.id === Number(action.payload);
            })
            let newCartContents;
            if (existingItem) {
                newCartContents = state.cartContents.map(item => {
                    if (item.id === Number(action.payload)) {
                        return { ...item, count: item.count + 1 }
                    }
                    return item;
                });
            } else {
                newCartContents = [
                    ...state.cartContents,
                    state.items[action.payload],
                ];
            }
            state = {
                ...state,
                cartItems: state.cartItems + 1,
                cartContents: newCartContents,
            };
        }
            break;
        case "SUBTRACT_ITEM": {
            let subtractItem = state.cartContents.map(item => {
                if (item.id === Number(action.payload)) {
                    return { ...item, count: item.count - 1 }
                }
                return item;
            });
            state = {
                ...state,
                cartItems: state.cartItems - 1,
                cartContents: subtractItem,
            };
        };
        break;
        case "ADD_ITEM": {
            let addItem = state.cartContents.map(item => {
                if (item.id === Number(action.payload)) {
                    return { ...item, count: item.count + 1 }
                }
                return item;
            });
            state = {
                ...state,
                cartItems: state.cartItems + 1,
                cartContents: addItem,
            };
        };
        break;
        default:
    }
    return state;
};