Hi everyone 

I would appreciate if anyone can help me with transforming the following trigger in to an apex batch 

trigger ListingRankingManagementTrigger on pba__Listing__c (after insert, after update) {
  
  
    // To avoid exceeding governor limits,
   // use a float to reorder and have an unattended process (batch) pass it to integers again
  
    List<pba__Listing__c> listings = Trigger.new;

    Map<Id, pba__Listing__c> oldListings = null;
    if (!Trigger.isInsert) {
      oldListings = Trigger.oldMap;
    }

    for (pba__Listing__c listing : listings) {

      boolean doMove = true;
      integer addFactor = 0;

     / * If we move the ranking we have to locate the listing that had the new ranking before and - If the new ranking is lower than the old one, add one - If the new ranking is higher than the old one, subtract one
   * /
      
      if (!Trigger.isInsert) {
        pba__Listing__c oldListing = oldListings.get(listing.Id);
        doMove = (oldListing.Ranking__c != listing.Ranking__c );
        if (oldListing.Ranking__c == null || listing.Ranking__c < oldListing.Ranking__c) {
          addFactor = 1;
        } else {
          addFactor = -1;
        }
      } else {    
         // If it is an insert, it is as if the previous ranking was the highest
        addFactor = 1;
      }
      
      if (listing.Ranking__c == null) {
       // If ranking has not been included, we do not move
        doMove = false;
      }
      
      if (doMove) {
        List<pba__Listing__c> prevListings = [Select Id, Ranking__c from pba__Listing__c l where l.Ranking__c =:listing.Ranking__c AND l.id != :listing.id];
        if (prevListings.size()>0) {
          pba__Listing__c prevListing = prevListings.get(0);
         // We have the listing that was previously in our Ranking. We are going to insert it between us and the following ranking
          pba__Listing__c nextListing = null;
          if (addFactor > 0) {
            nextListing = [Select Ranking__c from pba__Listing__c l where l.Ranking__c > :listing.Ranking__c order by Ranking__c ASC LIMIT 1];
          } else {
            nextListing = [Select Ranking__c from pba__Listing__c l where l.Ranking__c < :listing.Ranking__c order by Ranking__c DESC LIMIT 1];
          }
          if (nextListing != null) {
            prevListing.Ranking__c = (prevListing.Ranking__c + nextListing.Ranking__c) / 2;
            update prevListing;
          }
          
        }
          
      }
    }
  

}