global class SendNotificationBatch implements Database.Batchable<sObject>, Schedulable, Database.Stateful {

//Variable Section
global FINAL String strQuery;
global List<String> errorMessages = new List<String>();

global SendNotificationBatch() {
    this.strQuery = getBatchQuery();
}

//Returns the Query String to Batch constructor to fetch right records.
private String getBatchQuery() {
    String strQuery = 'SELECT Id, CloseDate, Owner.Email FROM Opportunity WHERE CloseDate < TODAY';
    return strQuery;
}

//Batch Start method
global Database.QueryLocator start(Database.BatchableContext BC) {
    return Database.getQueryLocator(strQuery);
}

//Batch Execute method calls findCostForWoD method
global void execute(Database.BatchableContext BC, List<sObject> scopeList) {
    System.debug(LoggingLevel.INFO, '== scopeList size ==' + scopeList.size());

    List<Opportunity> oppList = (List<Opportunity>) scopeList;
    if(!oppList.isEmpty()) {
        List<Messaging.SingleEmailMessage> mailList = new List<Messaging.SingleEmailMessage>();
        for (Opportunity prod : oppList)
        {

            Messaging.SingleEmailMessage message = new Messaging.SingleEmailMessage();
            String[] toAddresses = new String[] {prod.Owner.Email};
            Message.setToAddresses(toAddresses);
            Message.SaveAsActivity = false;
            mailList.add(Message);

        }
        if(!mailList.isEmpty()) {
            try{
                Messaging.sendEmail(mailList);
            }
            catch (Exception ex) {
                errorMessages.add('Unable to send email to Tech: '+ ex.getStackTraceString());
            }
        }
    }
}

//Batch Finish method for after execution of batch work
global void finish(Database.BatchableContext BC) {
    AsyncApexJob aaj = [Select Id, Status, NumberOfErrors, JobItemsProcessed, MethodName, TotalJobItems, CreatedBy.Email from AsyncApexJob where Id =:BC.getJobId()];

    // Send an email to the Apex job's submitter notifying of job completion.
    Messaging.SingleEmailMessage mail = new Messaging.SingleEmailMessage();
    String[] toAddresses = new String[] {aaj.CreatedBy.Email};
    mail.setToAddresses(toAddresses);
    mail.setSubject('JOB Salesforce Send Notification Batch: ' + aaj.Status);
    String bodyText='Total Job Items ' + aaj.TotalJobItems + ' Number of records processed ' + aaj.JobItemsProcessed + ' with '+ aaj.NumberOfErrors + ' failures.n';
    bodyText += 'Number of Error Messages ' + errorMessages.size() + 'n';
    bodyText += 'Error Message' + String.join(errorMessages, 'n');
    mail.setPlainTextBody(bodyText);
    Messaging.sendEmail(new Messaging.SingleEmailMessage[] { mail });
}

//Method which schedules the ProductDownloadBatch
global void execute(SchedulableContext sc) {
    SendNotificationBatch snInstance = new SendNotificationBatch();
    ID batchprocessid = Database.executeBatch(snInstance);
}