public class contactActivityHandler {

public static void updateContact(List<Task> tks){ // Trigger.New comes as List here
    Set <Id> ContactIds = new Set<Id>();
    List <Contact> ContactList = new List<Contact>();

    for(Task t :tks)
    {
        if(t.whoId!=null)
        {
            Schema.SObjectType tType= t.whoId.getSObjectType();
            if(tType == Contact.Schema.SObjectType)
            {
                ContactIds.add(t.WhoId);
            }
        }
    }
    //Querying the related Contacts based on whoId on Task
    Map<Id,Contact> ContactMap =  new Map<Id,Contact>([select id, Last_Contact_Date__c,Name, Last_Activity_TypeOfInteraction__c, LastActivityDate, Last_Activity_Subject__c,Last_Activity_Date__c, Last_Activity_Name__c from Contact where id in:ContactIds]);
    for(Task t :tks)
    {
        If((!t.Subject.contains('DFP sent')))
        {
            for(Contact l : ContactMap.Values())
            {
              If(t.ActivityDate >=l.Last_Contact_Date__c)
                {
                l.Last_Activity_Subject__c = t.subject;
                l.Last_Activity_Date__c = t.ActivityDate;
                l.Last_Activity_Name__c = l.Name;
                l.Last_Activity_TypeOfInteraction__c = t.Type_of_Interaction__c;
                ContactList.add(l);
                }
             }
        }
    }
    // updating the Lead
    if(ContactList.size()>0)
    {

        update ContactList;
    }
}//End of Update Contact

public static void updateOldContact(List<Task> tks, List<Task>tksOld){ // Trigger.New comes as List here

    Set<Id> ContactIds = new Set<Id>();
    Set<Id> OldContactIds = new Set<Id>(); //to get old contact ids
    List<Contact> ContactList = new List<Contact>();
    List<Contact> OldContactList = new List<Contact>();
    List<Contact> AllUpdateContactList = new List<Contact>();

    for(Task t :tks) // looping through Ids and saves as Contacts Ids?
    {
        if(t.whoId!=null)
        {
            Schema.SObjectType tType= t.whoId.getSObjectType();
            if(tType == Contact.Schema.SObjectType)
            {

                ContactIds.add(t.WhoId);
            }
        }
    }//End of First loop

    for(Task ot :tksOld) // looping through Ids and saves as Contacts Ids?
    {
        if(ot.whoId!=null)
        {
            Schema.SObjectType otType= ot.whoId.getSObjectType();
            if(otType == Contact.Schema.SObjectType)
            {

                OldContactIds.add(ot.WhoId); //Get old contact Id
            }
        }
    }//End of Second loop


    //Querying the related Contacts based on whoId on Task
    for(Id conold : OldContactIds){
        if(ContactIds.contains(conold)==false){ //Check old id with new id
            Map<Id,Contact> OldContactMap =  new Map<Id,Contact>([select id, Last_Contact_Date__c,Name, Last_Activity_TypeOfInteraction__c, LastActivityDate, Last_Activity_Subject__c,Last_Activity_Date__c, Last_Activity_Name__c from Contact where id in:OldContactIds]);
            Map<Id,Contact> NewContactMap =  new Map<Id,Contact>([select id,Last_Contact_Date__c,Name, Last_Activity_TypeOfInteraction__c, LastActivityDate, Last_Activity_Subject__c,Last_Activity_Date__c, Last_Activity_Name__c from Contact where id in:ContactIds]);
            List<Task>  tskrecs = [select id,Subject,ActivityDate,Type_of_Interaction__c  from task where WhoId =: ContactIds Order By lastmodifieddate DESC LIMIT 1];
            List<Task>  Oldtskrecs = [select id,Subject,ActivityDate,Type_of_Interaction__c  from task where WhoId =: OldContactIds Order By lastmodifieddate DESC LIMIT 1];
            for(Task t :tskrecs)
            {
                If((!t.Subject.contains('DFP sent')))
                {
                    for(Contact l : OldContactMap.Values())
                    {
                        If(t.ActivityDate != null)
                        {
                            for(Contact nl : NewContactMap.values()){

                                nl.Last_Activity_Subject__c= t.subject;
                                nl.Last_Activity_Date__c = t.ActivityDate;
                                nl.Last_Activity_Name__c = l.Name;
                                nl.Last_Activity_TypeOfInteraction__c = t.Type_of_Interaction__c;
                                AllUpdateContactList.add(nl);
                             }
                        }
                    }
                }
            }
            for(Task t :Oldtskrecs){
                If((!t.Subject.contains('DFP sent')))
                {
                    for(Contact l : OldContactMap.Values())
                    {
                        If(t.ActivityDate != null)
                        {
                            l.Last_Activity_Subject__c = t.subject;
                            l.Last_Activity_Date__c = t.ActivityDate;
                            l.Last_Activity_Name__c = l.Name;
                            l.Last_Activity_TypeOfInteraction__c = t.Type_of_Interaction__c;
                            AllUpdateContactList.add(l);
                        }

                    }
                }

            }
            update AllUpdateContactList;
        }else if(ContactIds.contains(conold)== true ){
            updateContact(tks);
        }
    }
}//End of Update Old Contact