trigger CaseEmail on Case (after insert, after update,before delete) {
    
   If((Trigger.isUpdate || Trigger.isinsert) && Trigger.isafter){//This line will allow only if the record is created or edited
	CaseEmailHandler.sendemailforInsrtupdate(Trigger.new);
   }
    if(Trigger.isDelete && Trigger.isBefore){// if the case is deleted we have to send an email so using this line and we used before because after deletion we cannot send email 
	CaseEmailHandler.sendemailfordelete(Trigger.old);
}
    }

public class CaseEmailHandler {

    public static void sendemailforInsrtupdate(List<Case> caselist){
            Set<Id> conIds = new Set<Id>();
    List<Messaging.SingleEmailMessage> mails = new List<Messaging.SingleEmailMessage>();
    for (Case c: caselist) {
        conIds.add(c.ContactId);//adding the contact id so we can get the contact email for the case
   }
    Map<Id, Contact> conMap = new Map<Id, Contact>([SELECT Id, Email FROM Contact WHERE Id In :conIds]);// quering the contact so we get the contact email
    
    for (Case c : caselist) {
        if (c.status == 'Closed') {// checking if the status is closed in case of create or edit scenerio
            Contact relatedCaseContact = conMap.get(c.ContactId);//getting the contact information related to particular case
            
            Messaging.SingleEmailMessage CaseNotificationmail = new Messaging.SingleEmailMessage();  
            CaseNotificationmail.setToAddresses(new List<String> { relatedCaseContact.Email });//adding to address
            CaseNotificationmail.setReplyTo('sample@salesforce.com');//adding reply to  address
            CaseNotificationmail.setSenderDisplayName('Salesforce');  //adding display name          
            
            CaseNotificationmail.setSubject(' Case Status updation  ' + 'Changed to ' + c.status + ' Case Number:' + c.CaseNumber);//adding subject
            CaseNotificationmail.setPlainTextBody(' Your case Status for Case Number: ' + c.CaseNumber + '  Related Case Contact:' +c.ContactId +' has been closed '); //adding body of the email
            mails.add(CaseNotificationmail); //adding the notification to the list so all the emails can be sent once
        }
        
        if(Trigger.isinsert && Trigger.isafter){// as we need a notification when a case is craeted
            Contact relatedCaseContact = conMap.get(c.ContactId);
                   Messaging.SingleEmailMessage mail =  new Messaging.SingleEmailMessage();
        mail.setToAddresses(new List<String> { relatedCaseContact.Email });
        mail.setSubject('New Case Create: '+ c.CaseNumber);
        String body = 'Case is created. Thank you for contacting us';
        mail.setHtmlBody(body);
        mails.add(mail);
        }
    }
 Messaging.sendEmail(mails);//sending the emails at once   
    }
    public static void sendemailfordelete(List<Case> caselist){
               Set<Id> conIds = new Set<Id>();
         for (Case c: caselist) {
        conIds.add(c.ContactId);
   }
      List<Messaging.SingleEmailMessage> emails = new List<Messaging.SingleEmailMessage>();
         Map<Id, Contact> conMp = new Map<Id, Contact>([SELECT Id, Email FROM Contact WHERE Id In :conIds]);
        
    for (Case cs : caselist) {
         Contact relatedCaseContact = conMp.get(cs.ContactId);
        Messaging.SingleEmailMessage email = new Messaging.SingleEmailMessage();
        
        email.setToAddresses(new List<String> { relatedCaseContact.Email  });
        email.setSubject('Case Deleted');
        email.setPlainTextBody('This message is to alert you that the Case number' + cs.CaseNumber + ' has been deleted. Thank you for contacting us.');
        emails.add(email);
    }
    Messaging.sendEmail(emails);
    }
    
}