Downloader thread

CachesMapDownloader.java

package cgeo.geocaching.maps;

import cgeo.geocaching.Settings;
import cgeo.geocaching.cgBase;
import cgeo.geocaching.cgSearch;
import cgeo.geocaching.geopoint.Geopoint;

import org.apache.commons.lang3.StringUtils;

import android.os.Handler;
import android.util.Log;

import java.util.concurrent.LinkedBlockingQueue;

/**
 * Worker thread downloading caches from the internet.
 */

class CachesMapDownloader extends Thread {

    class ViewPortBox {
        public final Geopoint topLeft;
        public final Geopoint bottomRight;
        public final Runnable refreshCallback;
        public final Handler noMapTokenHandler;

        public ViewPortBox(final Geopoint topLeft, final Geopoint bottomRight, final Runnable refreshCallback, final Handler noMapTokenHandler) {
            this.topLeft = topLeft;
            this.bottomRight = bottomRight;
            this.refreshCallback = refreshCallback;
            this.noMapTokenHandler = noMapTokenHandler;
        }
    }

    private final cgBase base;

    private static CachesMapDownloader instance;

    private CachesMapDownloader(final cgBase base) {
        this.base = base;
    }

    public static CachesMapDownloader getInstance(final cgBase base) {
        if (instance == null) {
            synchronized (CachesMapDownloader.class) {
                if (instance == null) {
                    instance = new CachesMapDownloader(base);
                    instance.start();
                }
            }
        }
        return instance;
    }

    private final LinkedBlockingQueue<ViewPortBox> queue = new LinkedBlockingQueue<ViewPortBox>(1);

    public synchronized void getCaches(final Geopoint topLeft, final Geopoint bottomRight, final Runnable refreshCallback, final Handler noMapTokenHandler) {
        queue.clear();
        queue.offer(new ViewPortBox(topLeft, bottomRight, refreshCallback, noMapTokenHandler));
    }

    @Override
    public void run() {
        String token = null;

        while (true) {
            ViewPortBox viewPort;
            try {
                viewPort = queue.take();
            } catch (InterruptedException e) {
                // This should not happen
                continue;
            }

            if (StringUtils.isBlank(token)) {
                Log.d(Settings.tag, "CachesMapDownloader: requesting map user token");
                token = cgBase.getMapUserToken(viewPort.noMapTokenHandler);
                if (StringUtils.isBlank(token)) {
                    continue;
                }
            }

            final double latMin = viewPort.bottomRight.getLatitude();

            final double latMax = viewPort.topLeft.getLatitude();
            final double lonMin = viewPort.topLeft.getLongitude();
            final double lonMax = viewPort.bottomRight.getLongitude();
            final cgSearch search = base.searchByViewport(token, latMin, latMax, lonMin, lonMax, 0);
            if (search != null && viewPort.refreshCallback != null) {
                viewPort.refreshCallback.run();
            }
        }
    }

}