// License: GPL. For details, see LICENSE file.
package org.openstreetmap.josm.actions.downloadtasks;

import java.awt.Component;
import java.lang.reflect.InvocationTargetException;
import java.net.URL;
import java.util.HashSet;
import java.util.Set;
import java.util.concurrent.Future;

import javax.swing.SwingUtilities;

import org.openstreetmap.josm.Main;
import org.openstreetmap.josm.data.Bounds;
import org.openstreetmap.josm.data.osm.Changeset;
import org.openstreetmap.josm.data.osm.ChangesetCache;
import org.openstreetmap.josm.gui.PleaseWaitRunnable;
import org.openstreetmap.josm.gui.progress.ProgressMonitor;
import org.openstreetmap.josm.io.OsmServerChangesetReader;
import org.openstreetmap.josm.tools.ExceptionUtil;
import org.openstreetmap.josm.tools.bugreport.BugReportExceptionHandler;

/**
 * Common abstract implementation of other changeset download tasks.
 * @since 10124
 */
public abstract class AbstractChangesetDownloadTask extends AbstractDownloadTask<Set<Changeset>> {

    abstract class RunnableDownloadTask extends PleaseWaitRunnable {
        /** the reader object used to read changesets from the API */
        protected final OsmServerChangesetReader reader = new OsmServerChangesetReader();
        /** the set of downloaded changesets */
        protected final Set<Changeset> downloadedChangesets = new HashSet<>();
        /** keeps the last exception thrown in the task, if any */
        protected Exception lastException;

        RunnableDownloadTask(Component parent, String title) {
            super(parent, title, false /* don't ignore exceptions */);
        }

        @Override
        protected void cancel() {
            setCanceled(true);
            synchronized (this) {
                if (reader != null) {
                    reader.cancel();
                }
            }
        }

        protected final void rememberLastException(Exception e) {
            lastException = e;
            setFailed(true);
        }

        protected final void updateChangesets() {
            // update the global changeset cache with the downloaded changesets.
            // this will trigger change events which views are listening to. They
            // will update their views accordingly.
            //
            // Run on the EDT because UI updates are triggered.
            //
            Runnable r = () -> ChangesetCache.getInstance().update(downloadedChangesets);
            if (SwingUtilities.isEventDispatchThread()) {
                r.run();
            } else {
                try {
                    SwingUtilities.invokeAndWait(r);
                } catch (InterruptedException e) {
                    Main.warn("InterruptedException in "+getClass().getSimpleName()+" while updating changeset cache");
                    Thread.currentThread().interrupt();
                } catch (InvocationTargetException e) {
                    Throwable t = e.getTargetException();
                    if (t instanceof RuntimeException) {
                        BugReportExceptionHandler.handleException(t);
                    } else if (t instanceof Exception) {
                        ExceptionUtil.explainException(e);
                    } else {
                        BugReportExceptionHandler.handleException(t);
                    }
                }
            }
        }
    }

    private RunnableDownloadTask downloadTaskRunnable;

    protected final void setDownloadTask(RunnableDownloadTask downloadTask) {
        this.downloadTaskRunnable = downloadTask;
    }

    @Override
    public final Future<?> download(boolean newLayer, Bounds downloadArea, ProgressMonitor progressMonitor) {
        return download();
    }

    /**
     * Asynchronously launches the changeset download task. This is equivalent to {@code download(false, null, null)}.
     *
     * You can wait for the asynchronous download task to finish by synchronizing on the returned
     * {@link Future}, but make sure not to freeze up JOSM. Example:
     * <pre>
     *    Future<?> future = task.download();
     *    // DON'T run this on the Swing EDT or JOSM will freeze
     *    future.get(); // waits for the dowload task to complete
     * </pre>
     *
     * The following example uses a pattern which is better suited if a task is launched from the Swing EDT:
     * <pre>
     *    final Future<?> future = task.download();
     *    Runnable runAfterTask = new Runnable() {
     *       public void run() {
     *           // this is not strictly necessary because of the type of executor service
     *           // Main.worker is initialized with, but it doesn't harm either
     *           //
     *           future.get(); // wait for the download task to complete
     *           doSomethingAfterTheTaskCompleted();
     *       }
     *    }
     *    Main.worker.submit(runAfterTask);
     * </pre>
     *
     * @return the future representing the asynchronous task
     */
    public final Future<?> download() {
        return downloadTaskRunnable != null ? Main.worker.submit(downloadTaskRunnable) : null;
    }

    @Override
    public final Future<?> loadUrl(boolean newLayer, String url, ProgressMonitor progressMonitor) {
        return downloadTaskRunnable != null ? Main.worker.submit(downloadTaskRunnable) : null;
    }

    @Override
    public final void cancel() {
        if (downloadTaskRunnable != null) {
            downloadTaskRunnable.cancel();
        }
    }

    @Override
    public String getConfirmationMessage(URL url) {
        return null;
    }
}