Project: LWC Calling a Secure External REST Service

A currencyConverter component that calls an external exchange-rate API to convert an amount between currencies:

1. A Named Credential (Exchange_Rate_API, Lesson 2) storing the endpoint and authentication.
2. A thin Controller and a Service class (Module 16's layering) making the callout and mapping the response.
3. Robust status code and CalloutException handling (Lesson 4), surfaced as a clear AuraHandledException.
4. A component with a loading state and toast feedback (Module 8) for the conversion action.

// Service — the actual integration logic
public inherited sharing class ExchangeRateService {
    public static Decimal convert(String fromCurrency, String toCurrency, Decimal amount) {
        HttpRequest request = new HttpRequest();
        request.setEndpoint('callout:Exchange_Rate_API/convert?from=' + fromCurrency + '&to=' + toCurrency);
        request.setMethod('GET');

        HttpResponse response;
        try {
            response = new Http().send(request);
        } catch (CalloutException e) {
            throw new AuraHandledException('Could not reach the exchange rate service. Please try again.');
        }

        if (response.getStatusCode() != 200) {
            throw new AuraHandledException('Exchange rate service returned an unexpected response.');
        }

        ExchangeRateResponse rate = (ExchangeRateResponse) JSON.deserialize(response.getBody(), ExchangeRateResponse.class);
        return amount * rate.rate;
    }
}

public class ExchangeRateResponse {
    public Decimal rate;
}

// Controller — thin, LWC-facing
public with sharing class CurrencyConverterController {
    @AuraEnabled
    public static Decimal convert(String fromCurrency, String toCurrency, Decimal amount) {
        return ExchangeRateService.convert(fromCurrency, toCurrency, amount);
    }
}

import { LightningElement } from 'lwc';
import convert from '@salesforce/apex/CurrencyConverterController.convert';
import { ShowToastEvent } from 'lightning/platformShowToastEvent';

export default class CurrencyConverter extends LightningElement {
    fromCurrency = 'USD';
    toCurrency = 'ZAR';
    amount = 0;
    convertedAmount;
    isConverting = false;

    async handleConvert() {
        this.isConverting = true;
        try {
            this.convertedAmount = await convert({
                fromCurrency: this.fromCurrency,
                toCurrency: this.toCurrency,
                amount: this.amount,
            });
        } catch (error) {
            this.dispatchEvent(new ShowToastEvent({
                title: 'Conversion Failed',
                message: error.body?.message ?? 'An unexpected error occurred.',
                variant: 'error',
            }));
        } finally {
            this.isConverting = false;
        }
    }
}

This method is called imperatively (Module 7's decision table), not via @wire — it's triggered by a specific user action (clicking "Convert"), not something that should load automatically on render. Every module referenced here — DTOs (Module 7), Controller/Service layering (Module 16), loading states and toasts (Module 8) — comes together in one realistic feature.