package eu.openaire.urls_controller.components;

import eu.openaire.urls_controller.services.FullTextsServiceImpl;
import eu.openaire.urls_controller.util.GenericUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.scheduling.annotation.Scheduled;
import org.springframework.stereotype.Component;

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.CancellationException;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;


@Component
public class ScheduledTasks {

    private static final Logger logger = LoggerFactory.getLogger(ScheduledTasks.class);


    @Scheduled(fixedDelay = 3_600_000)  // Execute this method 1 hour after the last execution, in order for some tasks to have been gathered.
    //@Scheduled(fixedDelay = 20_000)    // Just for testing (every 20 secs).
    public void executeBackgroundTasks()
    {
        List<Callable<Boolean>> tempList = new ArrayList<>(FullTextsServiceImpl.backgroundCallableTasks);   // Copy the list in order to know what was executed and delete only that data later.
        // So the items added while this execution happens, will be left in the list, while the other will be deleted.
        int numOfTasks = tempList.size();   // Since the temp-list is a deep-copy and not a reference, new tasks that are added will not be executed.
        if ( numOfTasks == 0 )
            return;

        logger.debug(numOfTasks + " background tasks were found inside the \"backgroundCallableTasks\" list and are about to be executed.");
        // Execute the tasks and wait for them to finish.
        try {
            List<Future<Boolean>> futures = FullTextsServiceImpl.backgroundExecutor.invokeAll(tempList);
            int sizeOfFutures = futures.size();
            for ( int i = 0; i < sizeOfFutures; ++i ) {
                try {
                    Boolean value = futures.get(i).get();	// Get and see if an exception is thrown..
                    // Add check for the value, if wanted.. (we don't care at the moment)
                } catch (ExecutionException ee) {
                    String stackTraceMessage = GenericUtils.getSelectiveStackTrace(ee, null, 15);	// These can be serious errors like an "out of memory exception" (Java HEAP).
                    logger.error("Task_" + (i+1) + " failed with: " + ee.getMessage() + "\n" + stackTraceMessage);
                } catch (CancellationException ce) {
                    logger.error("Task_" + (i+1) + " was cancelled: " + ce.getMessage());
                } catch (IndexOutOfBoundsException ioobe) {
                    logger.error("IOOBE for task_" + i + " in the futures-list! " + ioobe.getMessage());
                } finally {
                    FullTextsServiceImpl.backgroundCallableTasks.remove(tempList.get(i));   // Remove this object from the global list. Do not use indexes, since they will be different after each deletion and addition.
                }
            }
        } catch (Exception e) {
            logger.error("", e);
        }
    }

}