public with sharing class ReportExportQueueable implements Queueable {

    private Report_Export_Job__c exportJob;
    private Integer paginationColumn;
    private String paginationField;

    public ReportExportQueueable(Report_Export_Job__c exportJob) {
        this.exportJob = exportJob;
        if(exportJob.Total_Rows__c == null) {
            exportJob.Total_Rows__c = 0;
        }
    }

    private String getFileSoFar() {
        // Get content from the attachment
    }

    private void writeFile(String data) {
        // Write to the attachment
    }

    private Reports.ReportMetadata reportMetadata;

    private Reports.ReportMetadata getReportMetadata() {
        // Get the metadata from  Reports.ReportManager.describeReport(exportJob.Report_Id__c)
        // Set the report params so that it is exportable e.g. make sure we include the field
        // to paginate on
    }

    public void execute(QueueableContext context) {
        if(exportJob.Report_Instance_Id__c == null) {
            exportJob.Report_Instance_Id__c = Reports.ReportManager.runAsyncReport(exportJob.Report_Id__c, getReportMetadata(), true).getId();
            update exportJob;
            System.enqueueJob(new ReportExportQueueable(exportJob));
            System.debug('Starting first instance of report');
            return;
        }
        Reports.ReportInstance instance = Reports.ReportManager.getReportInstance(exportJob.Report_Instance_Id__c);
        String instanceStatus = instance.getStatus();
        System.debug('instanceStatus: ' + instanceStatus);
        if(instanceStatus == 'Running' || instanceStatus == 'New') {
            System.enqueueJob(new ReportExportQueueable(exportJob));
            System.debug('Report is still running, re-queueing self');
            return;
        } else if(instanceStatus == 'Error') {
            exportJob.Status__c = 'Error';
            update exportJob;
            System.debug('Report has errors, exiting');
            return;
        }

        System.debug('Getting results...');

        Reports.ReportResults results = instance.getReportResults();

        Reports.ReportFactWithDetails factDetails =
                (Reports.ReportFactWithDetails) results.getFactMap().get('T!T');

        List<Reports.ReportDetailRow> reportRows = factDetails.getRows();
        if(reportRows.isEmpty()) {
            exportJob.Status__c = 'Complete';
            update exportJob;
            System.debug('Report has no results, exiting');
        } else {
            System.debug('Processing results...');

            // Get the data dn write to the Attachment
            writeFile(fileSoFar);

            exportJob.Total_Rows__c += reportRows.size();

            String paginationValue = (String) reportRows[reportRows.size() - 1].getDataCells()[paginationColumn].getValue();

            if(reportRows.size() == 2000) {
                // Add filters to the metadata, using paginationValue
                
                exportJob.Report_Instance_Id__c = Reports.ReportManager.runAsyncReport(exportJob.Report_Id__c, reportMetadata, true).getId();
                update exportJob;
                requeue();
                System.debug('Starting next instance of report');
            } else {
                exportJob.Status__c = 'Complete';
                update exportJob;
                System.debug('Less than 2000 rows returned, report complete');
            }
        }
    }

    private void requeue() {
        if(!(Test.isRunningTest() && System.isQueueable())) {
            System.enqueueJob(new ReportExportQueueable(exportJob));
        }
    }
}