BeerController.java

public with sharing class BeerController {
    public BeerController() {

    }

    public static String generateCardId(){
        String CharList = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789_';
        Integer position;
        Integer LengthRequired = 30;
        String Res = '';
        for(Integer i = 0; i <= LengthRequired; i++) {
            position = Integer.valueof(String.valueof(Math.roundToLong(CharList.length()*Math.random()))) -1;
            Res += CharList.substring(position,position+1);
        }
        return Res;
    }

    public static String getCouponInformation(String name){
        Coupon__c couponRec = [Select Id, Name, 
                                Price__c 
                                FROM Coupon__c 
                                Where Expired__c = false
                                AND Name =: name];
        return couponRec.Id;
    }

    @AuraEnabled
    public static string createCartItems(String CartId, String BeerId, Decimal Amount){
        Cart_Item__c item = new Cart_Item__c();
        Map<Id, Cart_Item__c> cartItemsMap = getCartItems(CartId);
        if ( cartItemsMap.containsKey(BeerId) ) {
            item = cartItemsMap.get(BeerId);
            item.Item_Amount__c = item.Item_Amount__c + Amount;
            item.Item_Quantity__c = item.Item_Quantity__c + 1;
            update item;
        } else {
            item.Beer__c = BeerId;
            item.Cart__c = CartId;
            item.Item_Quantity__c = 1;
            item.Item_Amount__c = Amount;
            insert item;
        }
        
        return item.Id;
    }

    public Static Map<Id, Cart_Item__c> getCartItems(String cartId){
        /* beerId, Cart_Iems*/
        Map<Id, Cart_Item__c> cartItemsMap = new Map<Id, Cart_Item__c>();
        for ( Cart_Item__c cart : [Select Id, Name, Beer__c, Cart__c, 
                                Item_Quantity__c, Item_Amount__c
                                FROM Cart_Item__c
                                Where Cart__c =: cartId]) {
            cartItemsMap.put(cart.Beer__c, cart);
        }
        return cartItemsMap;
    }

    @AuraEnabled(cacheable=false)
    public static string getCartId(){
        List<Cart__c> cartInfo = [ Select Id, Name 
                                FROM Cart__c 
                                Where User__c =: UserInfo.getUserId()
                                AND Cart_Status__c = 'Open'
                                AND Is_Active__c = true];
        if (cartInfo != null && cartInfo.size() > 0) {
            List<Cart_Item__c> cartItems = new list<Cart_Item__c>();
            cartItems = [Select Id, Name, Beer__c, Cart__c, Item_Quantity__c, Item_Amount__c
                                FROM Cart_Item__c
                                Where Cart__c =: cartInfo.get(0).Id];
            
            Decimal itemQnty = 0;
            for (Cart_Item__c item : cartItems) {
                itemQnty = itemQnty + item.Item_Quantity__c;
            }
            CartWrapper wrapper = new CartWrapper();
            wrapper.CartId = cartInfo.get(0).Id;
            wrapper.items = cartItems;
            wrapper.Count = itemQnty;
            return JSON.serialize(wrapper);
        } else { 
            Cart__c defaultCart = new Cart__c();
            String couponId = getCouponInformation('Default');
            defaultCart.Cart_Id__c = String.valueOf(Math.random());
            defaultCart.Cart_Status__c = 'Open';
            defaultCart.Is_Active__c = true;
            defaultCart.Coupon__c = couponId;
            defaultCart.User__c = UserInfo.getUserId();
            insert defaultCart;
            CartWrapper wrapper = new CartWrapper();
            wrapper.CartId = defaultCart.Id;
            wrapper.items = null;
            wrapper.Count = 0;
            return JSON.serialize(wrapper);
        }                        
    }

    @AuraEnabled(cacheable=true)
    public static List<sObject> searchBeer(String searchParam){
        String likeParam = '%' +searchParam+'%';
        String Query = '';
        /*
            Select Id, Name From beer__c Where Name Like '%aa%'
        */
        if(searchParam != null){
           Query  = 'Select Id, Name, Alcohol__c,brewery_id__c, brewery_Name__c, Id__c, Price__c,Image__c,Remaining_Quantity__c, Tags__c, Total_Quantity__c From Beer__c Where Name Like :likeParam LIMIT 50 ';
        }else{
           Query  = 'Select Id, Name, Alcohol__c,brewery_id__c, brewery_Name__c, Id__c, Price__c,Image__c,Remaining_Quantity__c, Tags__c, Total_Quantity__c From Beer__c LIMIT 50 '; 
        }
        
        List<SObject> sObjectList = Database.query(Query);
        return sObjectList;
    }

    public class CartWrapper {
        @AuraEnabled
        public String CartId                { get; set; }
        @AuraEnabled
        public Decimal Count                { get; set; }
        @AuraEnabled
        public List<Cart_Item__c> items     { get; set; }
    }
}

BeerList.html

<template>
    <div style="background: white; border-radius: 10px;">
        
        <div style="border: 2px solid red; width: 30px; height: 30px; border-radius: 50%; 
                margin-left: 1313px;
                margin-bottom: -30px;
                text-align: center;
                font-size: 19px;"
            > 
            <strong class="slds-m-top_small" style="text-align:center; vertical-align:center;">{itemsinCart}</strong>
        </div>
        <div style="margin-left: 1300px;" >
            <img src={cart} height="70" width="80" /> 
        </div>
        
        <div class="slds-m-left_small slds-m-right_small slds-m-bottom_small">
            <c-beer-search onsearch={handleEvent} ></c-beer-search>
        </div>
        <div class="slds-m-left_small slds-m-right_small slds-m-bottom_small">
            <template if:true={beerRecords} >
                <div class="slds-grid slds-wrap">
                    <template for:each={beerRecords} for:item="item">
                            <div class="slds-col slds-size_1-of-3 " key={item.Id}>
                                <c-beer-tile beer-record={item} oncart={addToCart}></c-beer-tile>
                            </div> 
                    </template>
                </div>
            </template>
        </div>
    </div>
</template>

BeerList.Js

/* eslint-disable radix */
/* eslint-disable no-alert */
/* eslint-disable no-console */
import { LightningElement, track, wire } from 'lwc';
import searchBeer from '@salesforce/apex/BeerController.searchBeer';
import cartIco from '@salesforce/resourceUrl/cart';
import getCartId from '@salesforce/apex/BeerController.getCartId';
import createCartItems from '@salesforce/apex/BeerController.createCartItems';
import { ShowToastEvent } from 'lightning/platformShowToastEvent';
export default class BeerList extends LightningElement {

    @track beerRecords;
    @track errros;
    @track cart = cartIco;
    @track cartId;
    @track itemsinCart = 0;

    connectedCallback(){
        this.defaultCartId();
    } 

    defaultCartId(){
        getCartId()
        .then(data => {
            const wrapper = JSON.parse(data);
            if ( wrapper ){
                this.itemsinCart = wrapper.Count;
                this.cartId = wrapper.CartId;
            }
        })
        .catch(error => {
            this.cartId = undefined;
            console.log(error);
        });
    }

    addToCart(event){
        const selectBeerId = event.detail;

        const selectBeerRecord = this.beerRecords.find(
            record => record.Id === selectBeerId
        );
        /*
            for(Beer__c beer : beerRecords ){
                if(beer.Id == selectBeerId ){
                    return beer;
                }
            }
        */
        createCartItems({
            CartId : this.cartId,
            BeerId : selectBeerId,
            Amount : selectBeerRecord.Price__c
        })
        .then(data => {
            console.log(' Cart Item Id ', data);
            this.itemsinCart = this.itemsinCart + 1;
            const toast = new ShowToastEvent({
                'title' : 'Success!!',
                "message" : selectBeerRecord.Name +' Added into Cart!',
                "variant" : "success", 
            });
            this.dispatchEvent(toast);
        })
        .catch(error => {
            console.log(error);
            const toast = new ShowToastEvent({
                'title' : 'Error!!',
                "message" : JSON.stringify(error),
                "variant" : "error", 
            });
            this.dispatchEvent(toast);
        });

    }
    

    @wire(searchBeer)
        wiredRecords({error, data}){
            
            if ( data ) {
                this.beerRecords = data;
                this.errors = undefined;
            }
            if( error ) {
                this.beerRecords = undefined;
                this.errors = error;
            }
        }

    handleEvent(event){
        const eventVal = event.detail;
        
        searchBeer({
            searchParam : eventVal
        })
        .then(result => {
            
            this.beerRecords = result;
            this.errros = undefined;
        })
        .catch(error => {
            
            this.errors = error;
            this.beerRecords = undefined;
        })
    }
}