trigger CreateContract on Opportunity (after insert, after update) {

    List<Contract> conttoinsert = new List<Contract>();
	
	List<opportunity> LstUpdOpp = new List<opportunity>();
	
	Map<String,opportunity> mapOpp = new Map<String,opportunity> ();
	
	if(Trigger.IsInsert || Trigger.Isupdate)
	{
		//Intialising mapOpp
		for(opportunity opp: Trigger.new)
		{
			mapOpp.put(opp.name,opp);
		}
		
		if(Trigger.Isupdate)
		{
			List<opportunity> lstOppNoCont = new List <opportunity>();
			//Removing duplicate creation of contract records.
			for(opportunity opp: Trigger.new)
			{
				if(opp.contract == null)
					lstOppNoCont.add(opp);// list holds the opp records for which contract records are not created.
			}
			
			//if the opportunity doesnt have contract records then will create new contract
			if(!lstOppNoCont.isEmpty())
			{
				// Fetching the contract records to be insert for valid opportunities.
				conttoinsert.addall(newContract(lstOppNoCont));
			}
		}
			
		//It create the contract records for eligible opportunity
		if(Trigger.IsInsert)
		{
			// Fetching the contract records to be insert for valid opportunities.
			conttoinsert.addall(newContract(Trigger.new));
		}
		
		//Create contract records if the list is not empty. also update the opportunity records with the new contract records.
		if ( !conttoinsert.isEmpty()) {
			
			//create contracts.
			insert conttoinsert;
			
			//Update Opportunity with the contract record.
			for(contract Rec: conttoinsert)
			{
				Opportunity oppRec = new Opportunity();
				oppRec = mapOpp.get(Rec.name);
				oppRec.contractid = rec.id;
				oppRec.id = oppRec.id;
				LstUpdOpp.add(oppRec);
				
			}
			
			if(!LstUpdOpp.isEmpty()){
				update LstUpdOpp;
			}
        }
	}
	
	//Create the contract records for eligible opportunity and returns list of contract.
	public list <contract> newContract (list<opportunity> Lstopp)
	{
		List<Contract> lstNewCon = new List<Contract>();
		
		for (Opportunity opp : Lstopp) {
		
			if (opp.StageName == 'Closed Won' && opp.RecordTypeID == '012N00000004pSi' && opp.Record_Complete__c == TRUE) {
				Contract con = new Contract();
				con.Name                  = opp.name;
				con.Account               = opp.Account;
				con.CurrencyIsoCode       = opp.CurrencyIsoCode;
				con.AccountId             = opp.AccountId;
				con.StartDate             = opp.Service_Start_Date__c;
				con.Contract_Value__c     = opp.Total_Performance__c;
				con.Description           = opp.Opportunity_Description__c;
				con.Sales_Lead__c         = opp.OwnerID;
				lstNewCon.add(con);
			} 
		}
		return lstNewCon;
	}
	
	
	
    
}