I've been staring at this code too long and I think something obvious isn't jumping out at me.  I have a recursive trigger causing me to hit the maximum trigger depth but I can't think of how to fix it.  If anyone can help I am posting the trigger in it's entirety and the error.

THANKS!

The scenario is a user updates a custom revenue object.  This fires a trigger to update the record with the "Prior Year Revenue"  and also update the next year's "Prior Year Revenue".

trigger RollUpPriorYear_AIAU on Revenue__c (before insert, before update, after update, after insert){
    Set<String> pastKeys = new Set<String>();
    Set<String> futureKeys = new Set<String>();
    
    Map<String, Revenue__c> currentRevs = new Map<String, Revenue__c>();
    Map<String, Revenue__c> futureRevs = new Map<String, Revenue__c>();
     
    // key: Internal id corrected to last year, total prior year amount 
    Map<String, Integer> pastTotalPriors = new Map<String, Integer>();
    List<Revenue__c> priorRevs = new List<Revenue__c>();
    
    // revenue to be updated
    List<Revenue__c> futurePlaceHolders = new List<Revenue__c>(); 
    List<Revenue__c> futureRevsToBeUpdated = new List<Revenue__c>();
    
    for(Revenue__c r: trigger.new){    
        // gather the internal ids
        
        // current 
        currentRevs.put(makeKey(r, 0), r);
        
        // past
        pastKeys.add(makeKey(r, -1));
        
        // future
        futureKeys.add(makeKey(r, 1));  
    }
    
    // retrieve all the past total forecasted
    for(Revenue__c re: [SELECT Account__c,Team__c,User__c,Total_Forecast__c,Quarter__c,Fiscal_Year__c,Platform__c FROM Revenue__c WHERE InternalId__c IN : pastKeys]){
        String reKey = makeKey(re, 0);
        if(pastTotalPriors.containsKey(reKey)){
            Integer aTotal = pastTotalPriors.get(reKey);
            aTotal += Integer.ValueOf(re.Total_Forecast__c);
            pastTotalPriors.put(reKey,aTotal); 
        }
        else{
            pastTotalPriors.put(reKey,Integer.ValueOf(re.Total_Forecast__c));
        }
        
        priorRevs.add(re);
    }
    
    // create placeholders if no current rev exists to hold prior rev
    for(Revenue__c pr : trigger.new){
        if(!futureRevs.containsKey(makeKey(pr,0))){
            Revenue__c ph = new Revenue__c();
            ph.Account__c = pr.Account__c;
            ph.Team__c = pr.Team__c;
            ph.Platform__c = pr.Platform__c;
            ph.Fiscal_Year__c = String.ValueOf(Integer.ValueOf(pr.Fiscal_Year__c.substring(0, 4)) + 1); 
            ph.Fiscal_Year__c += '-';
            ph.Fiscal_Year__c += String.ValueOf(Integer.ValueOf(pr.Fiscal_Year__c.substring(5, 7)) + 1);
            ph.Quarter__c = pr.Quarter__c;
            ph.User__c = pr.User__c;
            ph.Date__c = pr.Date__c;
            futurePlaceHolders.add(ph);
        }
    }
    
    if(trigger.isBefore){
        // this deals with updating past revenue records
        for(Revenue__c r: trigger.new){
            system.debug('*** updating the following pastTotalPriors: ' + pastTotalPriors);  
            r.Final_Prior_Year__c = pastTotalPriors.get(makeKey(r,-1));
        }
    }  
    
    if(trigger.isAfter){
        // this deals with updating future revenue records - so they also fire this trigger
        for(Revenue__c rev: [SELECT id FROM Revenue__c WHERE InternalId__c IN : futureKeys]){
            futureRevsToBeUpdated.add(rev);
            futureRevs.put(makeKey(rev,0),rev);
        }
        update futureRevsToBeUpdated;
        
        // this creates placeholders for prior year revenue values sitting on the current year revenue records
        // THIS IS GIVING ME THE ERRORS
        insert futurePlaceHolders; 
    }
    
// utility method    
    private String makeKey(Revenue__c rev, Integer yrAdj){
        //Account__c + Team__c + TEXT( Platform__c ) + Fiscal_Year__c + TEXT( Quarter__c ) + User__c
        String theKey = String.ValueOf(rev.Account__c).substring(0, 15);
        theKey += String.ValueOf(rev.Team__c).substring(0, 15);
        theKey += rev.Platform__c;
        theKey += Integer.ValueOf(rev.Fiscal_Year__c.substring(0, 4)) + yrAdj;
        theKey += '-';
        theKey += Integer.ValueOf(rev.Fiscal_Year__c.substring(5, 7)) + yrAdj;
        theKey += rev.Quarter__c;
        theKey += String.ValueOf(rev.User__c).substring(0, 15);
        System.debug(' *** theKey: ' + theKey);
        return theKey;
    }
}

Error: Invalid Data. 
Review all error messages below to correct your data.
Apex trigger RollUpPriorYear_AIAU caused an unexpected exception, contact your administrator: RollUpPriorYear_AIAU: execution of AfterInsert caused by: System.DmlException: Insert failed. First exception on row 0; first error: CANNOT_INSERT_UPDATE_ACTIVATE_ENTITY, RollUpPriorYear_AIAU: maximum trigger depth exceeded Revenue trigger event AfterInsert for [a06c0000000Y7Ds] Revenue trigger event AfterInsert for [a06c0000000Y7Dt] Revenue trigger event AfterInsert for [a06c0000000Y7Du] Revenue trigger event AfterInsert for [a06c0000000Y7Dv] Revenue trigger event AfterInsert for [a06c0000000Y7Dw] Revenue trigger event AfterInsert for [a06c0000000Y7Dx] Revenue trigger event AfterInsert for [a06c0000000Y7Dy] Revenue trigger event AfterInsert for [a06c0000000Y7Dz] Revenue trigger event AfterInsert for [a06c0000000Y7E0] Revenue trigger event AfterInsert for [a06c0000000Y7E1] Revenue trigger event AfterInsert for [a06c0000000Y7E2] Revenue trigger event AfterInsert for [a06c0000000Y7E3] Revenue trigger event AfterInsert for [a06c0000000Y7E4] Revenue trigger event AfterInsert for [a06c0000000Y7E5] Revenue trigger event AfterInsert for [a06c0000000Y7E6] Revenue trigger event AfterInsert for [a06c0000000Y7E7]: []: Trigger.RollUpPriorYear_AIAU: line 79, column 1