//A Utility class to process Stock Item records from the Stock Item Handler
public with sharing class StockItemHandler {

    //Default Constructor
    public void StockItemHandler() {
    }

    //Check for duplicate stock items before insert and display an error to user if a duplicate is found
    public void OnBeforeInsert(List<Stock_Item__c> stockItems){

        //Create a set to hold new stock items being inserted
        Set<String> newStockSet = new Set<String>();

        //Create a set to hold stock items in the database (db)
        Set<String> dbStockSet = new Set<String>();

        //Create an error variable and assign value
        String errorMsg = 'This item name is already entered in the system. Please enter a unique item name.';

        for (Stock_Item__c s : stockItems)                           // Loop through all of the records for insert
            newStockSet.add(s.Item_Name__c);                         // Add each item name to the newStockSet

        for (Stock_Item__c dbStock : [SELECT Item_Name__c            //Loop through stock items in the database
                                      FROM Stock_Item__c
                                      WHERE Item_Name__c IN :newStockSet]){
            dbStockSet.add(dbStock.Item_Name__c.toUpperCase());      // Add values to the dbStockSet that match an item being inserted
        }

        for (Stock_Item__c s : stockItems){                          // Loop through all of the records for insert
            if(dbStockSet.contains(s.Item_Name__c.toUpperCase()))    // If the item name is already in the dbStockSet, we have a duplicate item
                s.addError(errorMsg);                                // So, add an error to the record
        }
    }

    //Check stock on hand before a stock item can be deleted
    public void OnBeforeDelete(List<Stock_Item__c> stockItems){

        // Create a list to hold new cases for insertion.
        List<Case> casesToCreate = new List<Case>();

        for(Stock_Item__c s : stockItems){                            // Loop through all of the records being deleted
            if(s.Stock_on_Hand__c <> 0){                              // If the stock on hand is greater than zero, we need to alert someone
                Case newCase = new Case();                            // So, create a new case for the deleted item
                newCase.Status = 'New';
                newCase.Subject = 'Item with Stock on Hand DELETED';  // Set the field values for the new case record
                newCase.Description = 'Item Name: ' + s.Item_Name__c + '; Stock Item Id: ' + s.Id + '; Number on Hand: ' + s.Stock_on_Hand__c;
                casesToCreate.add(newCase);                           // Add new case to the casesToCreate list
            }
        }
        insert casesToCreate;                                         //DML call to insert list of new case records
    }
}