logic help - check if event already exists

I have code that fires when an opportunity is moved to a closed won status.  When this condition is met, it will create a series of events on a related oject (Project_Requst__c).  This all works fine, but I am trying to make the existing code a little more intelligent and check if an event already exists on the date before adding a new event.  I'm just trying to prevent double booking of events.

So, I'm trying to determine how I can check if an existing event is already on the calendar that has the same record type id and same owner id.  I've created a list of Events with the same ownerId and recordTypeId. Next, I've created a set of the existing event startDateTimes that I can check to see if that start date exists already within the for loop.  However, if it finds that the startDateTime already exists, I can add a day to the current startDateTime, but how do I check if the next day on the calendar already has an event that exists?

So, for example, my iterator is 7 and I'm looping 7 times to create 7 events. I check the startDateTime in the first iteration and determine that an event already exists so I add one day.  However, I won't know if an event exists on the calendar date that was added to by one day.

How can I prevent the double booking of events?

See my method and helper method in the code below.

Please note, the code I'm using is APEX (Salesforce coding language). Its closest relative is Java, which is why I'm requesting help in this zone.  The logic should apply across any programming language.

Thanks in advance for any help.
Regards.

private static void doResourceEventsInsert(List<Opportunity> inNew, Map<Id, Opportunity> inOld) {
	
		//Gather all Data
 		List<Opportunity> lstOpps = new List<Opportunity>([Select Id, StageName, Name, Project_Number__c, (Select Id From Project_Request_and_Follow_up__r) From Opportunity o Where (Opportunity_Record_Type_Name_Static__c = 'WithintheContractProject' OR Opportunity_Record_Type_Name_Static__c = 'BillableProject') and isWon = true and id in :inNew]);

		if (lstOpps.size() > 0) {
        	Map<Id,Pricing__c> mapPricing = new Map<Id,Pricing__c>([Select Id,  (Select Id From Product_Management__r)  From Pricing__c Where isPrimaryPricing__c = true and Opportunity__c in :lstOpps]);  
 			Map<Id,ProductManagement__c> mapCS = new Map<Id,ProductManagement__c>([Select Id, (Select Id, Hours__c, DateOfWorkAllocation__c, Month_Index__c, Resource__r.Id, Resource__r.User_Id__c From Scheduling1__r) from ProductManagement__c Where Pricing__c in :mapPricing.values()]);

			RecordType rt = [Select Id From RecordType Where Name = 'Service Delivery Event' and sObjectType = 'Event'];
			List<Event> lstEvent = new List<Event>();
            
			//Loop through Data 	
			for(Opportunity opp : lstOpps) {
				if (inOld.get(opp.Id).isWon == false && opp.Project_Request_and_Follow_up__r.size() > 0) { 
					for(Pricing__c p : mapPricing.values()){
						for (ProductManagement__c cs : mapPricing.get(p.Id).Product_Management__r) {
							for (Scheduling__c s : mapCS.get(cs.Id).Scheduling1__r) {
								if (s.Hours__c != null && s.Resource__r.User_Id__c != null) {
									lstEvent = doResourceEventsStage(lstEvent,s.Resource__r.User_Id__c, opp.Project_Request_and_Follow_up__r.get(0).Id, rt.Id, s.DateOfWorkAllocation__c.year(), s.DateOfWorkAllocation__c.month(), s.Hours__c, opp.Name, opp.Project_Number__c);
					            }
							}
						}
					}
				}
				if (lstEvent.size() > 0) { 
					insert lstEvent;
				}
			}
		}
	}
 

	public static List<Event> doResourceEventsStage(List<Event> lstEvent, Id idEventOwner, Id idProjectRequest, Id idRecordType, Integer intYear, Integer intMonth, Decimal decHours, String oppName, String projectCode) {
		
        Integer recurrenceInterval = ((math.ceil(decHours / 8)) - 1).intValue();
        Integer currentMonth = system.today().month();
        Datetime startDate = Datetime.newInstance(intYear, intMonth, system.today().day(), 8, 0, 0);
        Date firstDayOfMonth = LibCommonFunctions.doConvertDateTimeToDate(startDate);
        
        if (currentMonth > intMonth) {
            firstDayOfMonth = firstDayOfMonth.toStartOfMonth();
        }
        
        Datetime firstWorkDayOfMonth = LibCommonFunctions.doConvertDateToDateTime(firstDayOfMonth, 8, 0, 0);
        Integer intStart = LibCommonFunctions.skipToNextBusinessDay(firstWorkDayOfMonth);
        
        if (intStart == 1) {
            firstWorkDayOfMonth = firstWorkDayOfMonth.addDays(1);
        }
        else if (intStart == 2) {
            firstWorkDayOfMonth = firstWorkDayOfMonth.addDays(2);
        }
        
        Datetime dt = LibCommonFunctions.doCalculateEndDate(firstWorkDayOfMonth, recurrenceInterval);
        Date endDate = LibCommonFunctions.doConvertDateTimeToDate(dt);
        
        List<Event> existingEvents = [Select Id, StartDateTime From Event Where ownerId =: idEventOwner AND RecordTypeId =: idRecordType];
        
        Set<DateTime> EventStartTimes = new Set<DateTime>();
		for(Event ev : existingEvents){
   			EventStartTimes.add(ev.StartDateTime);
		}
	
		for (Integer i = 0; i <= recurrenceInterval; i++){
			if (EventStartTimes.contains(firstWorkDayOfMonth)){
				firstWorkDayOfMonth = firstWorkDayOfMonth.addDays(1);
				firstWorkDayOfMonth = firstWorkDayOfMonth.addDays(LibCommonFunctions.skipToNextBusinessDay(firstWorkDayOfMonth));
			}	
			Event e = new Event();
			e.OwnerId = idEventOwner;
			e.RecordTypeId = idRecordType;
			e.Subject = oppName + ' - ' + projectCode;
			e.WhatId = idProjectRequest;
			e.StartDateTime = firstWorkDayOfMonth;
			e.EndDateTime = firstWorkDayOfMonth.addHours(8);
			firstWorkDayOfMonth = firstWorkDayOfMonth.addDays(1);
			firstWorkDayOfMonth = firstWorkDayOfMonth.addDays(LibCommonFunctions.skipToNextBusinessDay(firstWorkDayOfMonth));
			lstEvent.add(e);
		}
		
		return lstEvent;
		
	}

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