global class UpdateAccount implements Database.Batchable<sObject>

{
    List<Id> failedUpdates; 
    global Database.QueryLocator start(Database.BatchableContext BC)
    {
        String query1 = 'SELECT Id,Description,	NumberOfEmployees,(SELECT LastName FROM Contacts) FROM Account';
        
        return Database.getQueryLocator(query1);
        
        
    }
    
    global void execute(Database.BatchableContext BC, List<Account> scope)
    {
        for(Account a : scope)
        {
            a.Description = 'New Description from batch class';
            a.NumberOfEmployees =500;
            
            for(Contact con:a.Contacts){
                con.LastName= 'newLAstNAme';
            }
        }
        List<Database.SaveResult> results = Database.update(scope, false);
        for (Database.SaveResult result : results) {
            if (!result.isSuccess()) {
                failedUpdates.add(result.getId());
            }
        }
    }
    
    global void finish(Database.BatchableContext BC){
        if (!failedUpdates.isEmpty()) {
            Messaging.SingleEmailMessage mail = new Messaging.SingleEmailMessage();
            mail.setToAddresses(new String[] {'himanshu.s@hicglobalsolutions.com'});
            mail.setSubject('Batch Apex Failure');
            String messageBody = 'The following records failed to update: ';
            for (Id failedId : failedUpdates) {
                messageBody += failedId + ', ';
                
            }
            mail.setPlainTextBody(messageBody);
            
            Messaging.sendEmail(new Messaging.SingleEmailMessage[] {mail});
        }
    }
    /*global void execute(SchedulableContext SC) {
        UpdateAccount batchJob = new UpdateAccount();
        Database.executeBatch(batchJob);
    }

    public static void scheduleJob() {
        UpdateAccount batchJob = new UpdateAccount();
        String cronExpression = '0 0 0 ? * MON *'; // Every Monday at midnight
        System.schedule('Update Account Batch', cronExpression, batchJob);
    }*/
}