package cgeo.geocaching;

import cgeo.geocaching.enumerations.LocationProviderType;
import cgeo.geocaching.geopoint.Geopoint;
import cgeo.geocaching.go4cache.Go4Cache;
import cgeo.geocaching.utils.Log;
import cgeo.geocaching.utils.MemorySubject;

import org.apache.commons.lang3.StringUtils;

import android.content.Context;
import android.location.GpsSatellite;
import android.location.GpsStatus;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.os.Bundle;

import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.TimeUnit;

/**
 * Provide information about the user location. This class should be instantiated only once per application.
 */
class GeoDataProvider extends MemorySubject<IGeoData> {

    private static final String LAST_LOCATION_PSEUDO_PROVIDER = "last";
    private final LocationManager geoManager;
    private final GpsStatus.Listener gpsStatusListener = new GpsStatusListener();
    private final LocationData gpsLocation = new LocationData();
    private final LocationData netLocation = new LocationData();
    private final Listener networkListener = new Listener(LocationManager.NETWORK_PROVIDER, netLocation);
    private final Listener gpsListener = new Listener(LocationManager.GPS_PROVIDER, gpsLocation);
    private final Unregisterer unregisterer = new Unregisterer();
    public boolean gpsEnabled = false;
    public int satellitesVisible = 0;
    public int satellitesFixed = 0;

    private static class LocationData {
        public Location location;
        public long timestamp = 0;

        public void update(final Location location) {
            this.location = location;
            timestamp = System.currentTimeMillis();
        }

        public boolean isRecent() {
            return isValid() && System.currentTimeMillis() < timestamp + 30000;
        }

        public boolean isValid() {
            return location != null;
        }
    }

    private static class GeoData extends Location implements IGeoData {
        public boolean gpsEnabled = false;
        public int satellitesVisible = 0;
        public int satellitesFixed = 0;

        GeoData(final Location location, final boolean gpsEnabled, final int satellitesVisible, final int satellitesFixed) {
            super(location);
            this.gpsEnabled = gpsEnabled;
            this.satellitesVisible = satellitesVisible;
            this.satellitesFixed = satellitesFixed;
        }

        @Override
        public Location getLocation() {
            return this;
        }

        private static LocationProviderType getLocationProviderType(final String provider) {
            if (provider.equals(LocationManager.GPS_PROVIDER)) {
                return LocationProviderType.GPS;
            }
            if (provider.equals(LocationManager.NETWORK_PROVIDER)) {
                return LocationProviderType.NETWORK;
            }
            return LocationProviderType.LAST;
        }

        @Override
        public LocationProviderType getLocationProvider() {
            return getLocationProviderType(getProvider());
        }

        @Override
        public Geopoint getCoords() {
            return new Geopoint(this);
        }

        @Override
        public boolean getGpsEnabled() {
            return gpsEnabled;
        }

        @Override
        public int getSatellitesVisible() {
            return satellitesVisible;
        }

        @Override
        public int getSatellitesFixed() {
            return satellitesFixed;
        }

        @Override
        public boolean isPseudoLocation() {
            return StringUtils.equals(getProvider(), GeoDataProvider.LAST_LOCATION_PSEUDO_PROVIDER);
        }
    }

    private class Unregisterer extends Thread {

        private boolean unregisterRequested = false;
        private final ArrayBlockingQueue<Boolean> queue = new ArrayBlockingQueue<Boolean>(1);

        public void cancelUnregister() {
            try {
                queue.put(false);
            } catch (final InterruptedException e) {
                // Do nothing
            }
        }

        public void lateUnregister() {
            try {
                queue.put(true);
            } catch (final InterruptedException e) {
                // Do nothing
            }
        }

        @Override
        public void run() {
            try {
                while (true) {
                    if (unregisterRequested) {
                        final Boolean element = queue.poll(2500, TimeUnit.MILLISECONDS);
                        if (element == null) {
                            // Timeout
                            unregisterListeners();
                            unregisterRequested = false;
                        } else {
                            unregisterRequested = element;
                        }
                    } else {
                        unregisterRequested = queue.take();
                    }
                }
            } catch (final InterruptedException e) {
                // Do nothing
            }
        }

    }

    /**
     * Build a new geo data provider object.
     * <p/>
     * There is no need to instantiate more than one such object in an application, as observers can be added
     * at will.
     *
     * @param context the context used to retrieve the system services
     */
    GeoDataProvider(final Context context) {
        geoManager = (LocationManager) context.getSystemService(Context.LOCATION_SERVICE);
        unregisterer.start();

        final Location initialLocation = new Location(LAST_LOCATION_PSEUDO_PROVIDER);
        try {
            // Try to find a sensible initial location from the last locations known to Android.
            final Location lastGpsLocation = geoManager.getLastKnownLocation(LocationManager.GPS_PROVIDER);
            final Location lastNetworkLocation = geoManager.getLastKnownLocation(LocationManager.NETWORK_PROVIDER);

            // If both providers are non-null, take the most recent one
            if (lastGpsLocation != null && lastNetworkLocation != null) {
                if (lastGpsLocation.getTime() >= lastNetworkLocation.getTime()) {
                    copyCoords(initialLocation, lastGpsLocation);
                } else {
                    copyCoords(initialLocation, lastNetworkLocation);
                }
            } else if (lastGpsLocation != null) {
                copyCoords(initialLocation, lastGpsLocation);
            } else if (lastNetworkLocation != null) {
                copyCoords(initialLocation, lastNetworkLocation);
            } else {
                Log.i("GeoDataProvider: no last known location available");
            }
        } catch (final Exception e) {
            // This error is non-fatal as its only consequence is that we will start with a dummy location
            // instead of a previously known one.
            Log.e("GeoDataProvider: error when retrieving last known location", e);
        }
        // Start with an historical GeoData just in case someone queries it before we get
        // a chance to get any information.
        notifyObservers(new GeoData(initialLocation, false, 0, 0));
    }

    private static void copyCoords(final Location target, final Location source) {
        target.setLatitude(source.getLatitude());
        target.setLongitude(source.getLongitude());
    }
    private void registerListeners() {
        geoManager.addGpsStatusListener(gpsStatusListener);

        for (final Listener listener : new Listener[] { networkListener, gpsListener }) {
            try {
                geoManager.requestLocationUpdates(listener.locationProvider, 0, 0, listener);
            } catch (final Exception e) {
                Log.w("There is no location provider " + listener.locationProvider);
            }
        }
    }

    private synchronized void unregisterListeners() {
        // This method must be synchronized because it will be called asynchronously from the Unregisterer thread.
        // We check that no observers have been re-added to prevent a race condition.
        if (sizeObservers() == 0) {
            geoManager.removeUpdates(networkListener);
            geoManager.removeUpdates(gpsListener);
            geoManager.removeGpsStatusListener(gpsStatusListener);
        }
    }

    @Override
    protected void onFirstObserver() {
        unregisterer.cancelUnregister();
        registerListeners();
    }

    @Override
    protected void onLastObserver() {
        unregisterer.lateUnregister();
    }

    private class Listener implements LocationListener {
        private final String locationProvider;
        private final LocationData locationData;

        Listener(final String locationProvider, final LocationData locationData) {
            this.locationProvider = locationProvider;
            this.locationData = locationData;
        }

        @Override
        public void onStatusChanged(final String provider, final int status, final Bundle extras) {
            // nothing
        }

        @Override
        public void onProviderDisabled(final String provider) {
            // nothing
        }

        @Override
        public void onProviderEnabled(final String provider) {
            // nothing
        }

        @Override
        public void onLocationChanged(final Location location) {
            locationData.update(location);
            selectBest();
        }
    }

    private final class GpsStatusListener implements GpsStatus.Listener {

        @Override
        public void onGpsStatusChanged(final int event) {
            boolean changed = false;
            switch (event) {
                case GpsStatus.GPS_EVENT_SATELLITE_STATUS: {
                    final GpsStatus status = geoManager.getGpsStatus(null);
                    int visible = 0;
                    int fixed = 0;
                    for (final GpsSatellite satellite : status.getSatellites()) {
                        if (satellite.usedInFix()) {
                            fixed++;
                        }
                        visible++;
                    }
                    if (visible != satellitesVisible || fixed != satellitesFixed) {
                        satellitesVisible = visible;
                        satellitesFixed = fixed;
                        changed = true;
                    }
                    break;
                }
                case GpsStatus.GPS_EVENT_STARTED:
                    if (!gpsEnabled) {
                        gpsEnabled = true;
                        changed = true;
                    }
                    break;
                case GpsStatus.GPS_EVENT_STOPPED:
                    if (gpsEnabled) {
                        gpsEnabled = false;
                        satellitesFixed = 0;
                        satellitesVisible = 0;
                        changed = true;
                    }
                    break;
            }

            if (changed) {
                selectBest();
            }
        }
    }

    private LocationData best() {
        if (gpsLocation.isRecent() || !netLocation.isValid()) {
            return gpsLocation.isValid() ? gpsLocation : null;
        }
        if (!gpsLocation.isValid()) {
            return netLocation;
        }
        return gpsLocation.timestamp > netLocation.timestamp ? gpsLocation : netLocation;
    }

    private void selectBest() {
        assign(best());
    }

    private void assign(final LocationData locationData) {
        if (locationData == null) {
            return;
        }

        // We do not necessarily get signalled when satellites go to 0/0.
        final int visible = gpsLocation.isRecent() ? satellitesVisible : 0;
        final IGeoData current = new GeoData(locationData.location, gpsEnabled, visible, satellitesFixed);
        notifyObservers(current);

        Go4Cache.signalCoordinates(current.getCoords());
    }

}