Pulls current rates and updates CurrencyType records in SFDC

CurrencyUpdater

public class CurrencyUpdater {

	list <CurrencyType> ctl = new list<CurrencyType>([SELECT Id,IsoCode,ConversionRate FROM CurrencyType WHERE IsActive = TRUE AND IsCorporate = FALSE]);
	map <string, CurrencyType> ctMap = new map<String, CurrencyType>();

    public CurrencyUpdater () {
         for (CurrencyType ct : ctl){
        ctMap.put(ct.IsoCode,ct);
    	}   
    }

    public class CurrentRate {
            string IsoCode;
            decimal value;
        }
    
    public class myJSONClass{
        public string disclaimer;
        public string license;
        public string timestamp;
        public string base;
  //      public currentRate[] rates = new list<currentRate>();
        public map<string,decimal> rates = new map<string,decimal>();
    }
        
    public list<CurrencyType> callEndpoint() {
        
      	list <currencyType> ctUpdateList = new list <currencyType>();
        
          HttpRequest req = new HttpRequest(); 
          //Set HTTPRequest Method
          req.setMethod('GET');
        
          //Set HTTPRequest header properties
          req.setEndpoint('callout:OpenExchangeRates');
         
          //Set the HTTPRequest body	
          //req.setBody(body); 	
        
          Http http = new Http();
          
           try {
         
                //Execute web service call here		
                HTTPResponse res = http.send(req);	
        
                //Helpful debug messages
                //System.debug('res to string' + res.toString());
                System.debug('STATUS:'+res.getStatus());
                System.debug('STATUS_CODE:'+res.getStatusCode());
               
                string responseText = res.getBody();
               	//system.debug('responseText = ' + responseText);
               
               	myJSONClass obj = (myJSONClass)JSON.deserialize(responseText, myJSONClass.class);   
               // system.debug(obj.rates.keySet());

               
               FOR (currencyType ct : ctl){
                   //system.debug('old rate = ' + ct.IsoCode +' ' +ct.ConversionRate);
                   IF (obj.rates.get(ct.IsoCode) != null ){
                   		ct.ConversionRate = obj.rates.get(ct.IsoCode);
                        ct.IsActive = TRUE;                                                
                   		//system.debug('new rate = ' + ct.IsoCode + ' ' + ct.ConversionRate);
                        ctUpdateList.add(ct); 
                       string ctJSON = JSON.serialize(ct);
                       callSFDCAPI(ctJSON, ct.Id);
                       
                   }
                  // system.debug('ctid = ' + ct.id);
               }
               
               // update(ctUpdateList);  ILLEGAL!! try this instead -->
               // https://salesforce.stackexchange.com/questions/13294/patch-request-using-apex-httprequest/13300#13300
               
               
        } catch(System.CalloutException e) {
            //Exception handling goes here....
        }
                        
	return ctUpdateList;                       
    } 
    
    /* no dice
    public class runFlow{        
   //Instance of the Flow
	   public Flow.Interview.UpdateCurrencyTypes myFlow {get; set;}
   
       public void start(list<CurrencyType> input) {
          list<CurrencyType> ctList = new list<CurrencyType>();
          ctList.addAll(input);
          Map<String, Object> params = new Map<String, Object>();
			params.put('socCurrencyTypes', ctList);
         // https://andyinthecloud.com/2014/10/26/calling-flow-from-apex/
          myFlow = new Flow.Interview.UpdateCurrencyTypes(params);
          myFlow.start();
       }
	}
    */  
        
    
    
    public void callSFDCAPI(string input, id recId) {
        
        string inputJSON = input;
        id crId = recId;
        system.debug('inputJSON = ' + inputJSON);
        
        Http h = new Http();
        HttpRequest req = new HttpRequest();
        req.setEndpoint(URL.getSalesforceBaseUrl().toExternalForm() + '/services/data/v41.0/sobjects/CurrencyType/' + crId + '?_HttpMethod=PATCH' );
        req.setMethod('POST');
        req.setBody(inputJSON);
        req.setHeader('Authorization', 'OAuth ' + UserInfo.getSessionId());
        req.setHeader('Content-Type', 'application/json');
        req.setHeader('X-HTTP-Method-Override', 'PATCH');
        HttpResponse res = h.send(req);
        }
}