trigger AccountTrigger on Account (before insert) {
    // Generate current year
    Integer currentYear = System.today().year();
    
    // Query existing Account records with the current year
    List<Account> existingAccounts = [SELECT Account_Number_c FROM Account WHERE Account_Number_c LIKE 'ACCT-' + String.valueOf(currentYear) + '-%'];
    
    // Create a map to store the sequential numbers for each year
    Map<Integer, Integer> yearSequentialNumberMap = new Map<Integer, Integer>();
    
    // Iterate through existing Account records and populate the map
    for (Account acc : existingAccounts) {
        String accountNumber = acc.Account_Number__c;
        Integer year = Integer.valueOf(accountNumber.split('-')[1]);
        Integer sequentialNumber = Integer.valueOf(accountNumber.split('-')[2]);
        
        if (!yearSequentialNumberMap.containsKey(year) || sequentialNumber > yearSequentialNumberMap.get(year)) {
            yearSequentialNumberMap.put(year, sequentialNumber);
        }
    }
    
    // Generate account numbers for new Account records
    Integer sequentialNumber = yearSequentialNumberMap.containsKey(currentYear) ? yearSequentialNumberMap.get(currentYear) + 1 : 1;
    
    for (Account acc : Trigger.new) {
        acc.Account_Number__c = 'ACCT-' + String.valueOf(currentYear) + '-' + String.format('%04d', sequentialNumber);
        sequentialNumber++;
    }
}