public with sharing class opportunityFulfillmentEmail {

@InvocableMethod 
public static void sentCsmEmail(List <flowInput> requests ) {
     
    
    flowInput req = requests[0];
    
    
      List<string> toAddress = new List<string>(req.primaryEmail);
      List<string> toCCAddress = new List<string>(req.CcEmail);
      ID conId = req.contactId;
    
    // Query the fields we need to merge 
      Opportunity opp = [SELECT Id, Billing_Contact_FirstName__c,Buying_Contact_FirstName__c 
                          FROM Opportunity 
                          WHERE Id=:req.oppId];
    // Query the email template
      EmailTemplate emailTemplate = [SELECT Id,Subject,Body,HtmlValue
                                      FROM EmailTemplate
                                      WHERE Id=:req.templateId
                                      LIMIT 1];
    // Process the merge fields  
      String plainBody = emailTemplate.Body;
      plainBody = plainBody.replace('{!Opportunity.Billing_Contact_FirstName__c}', opp.Billing_Contact_FirstName__c);                             
      plainBody = plainBody.replace('{!Opportunity.Buying_Contact_FirstName__c}', opp.Buying_Contact_FirstName__c); 
      
      String htmlBody = emailTemplate.HtmlValue;
      htmlBody = htmlBody.replace('{!Opportunity.Billing_Contact_FirstName__c}', opp.Billing_Contact_FirstName__c);
      htmlBody = htmlBody.replace('{!Opportunity.Buying_Contact_FirstName__c}', opp.Buying_Contact_FirstName__c);

    // Build the email message
      Messaging.SingleEmailMessage message = new Messaging.SingleEmailMessage();
     
      message.setTemplateID(emailTemplate.Id);
      message.setSubject(emailTemplate.Subject);
      message.setPlainTextBody(plainBody);
      message.setHTMLBody(htmlBody);
      message.setToAddresses(toAddress);          
      message.setCcAddresses(toCCAddress);
      message.setTargetObjectId(conId);
      
      Messaging.sendEmail(new Messaging.SingleEmailMessage[] { Message });


  }
  // Input details which comes to Apex class from flow 
 public class flowInput {

    @InvocableVariable(required=true)
    public List<string> primaryEmail;

    @InvocableVariable(required=true)
    public List<string> CcEmail;
    
    @InvocableVariable(required=true)
    public id oppId;

    @InvocableVariable(required=true)
    public id contactId;  

    @InvocableVariable(required=true)
    public id templateId;  

 }