package org.litesoft.GWT.client.pavsupport.internal;

import com.google.gwt.event.shared.*;
import com.google.gwt.place.shared.*;
import com.google.gwt.user.client.ui.*;
import org.litesoft.GWT.client.pavsupport.*;
import org.litesoft.commonfoundation.typeutils.Objects;

import java.util.*;

public class PanelPlaceActivityHelper<CommonActivityParam extends CommonActivityParameter> extends ActivityFactoryRegistry
{
    private static final Activity NULL_ACTIVITY = new Activity()
    {
        @Override
        public String mayStop()
        {
            return null;
        }

        @Override
        public void onCancel()
        {
        }

        @Override
        public void onStop()
        {
        }

        @Override
        public void start( AcceptsOneWidget panel )
        {
            panel.setWidget( new Label( "!" ) );
        }
    };

    private final AcceptsOneWidget mPanel;
    private final CommonActivityParam mCommonActivityParam;
    private Activity mCurrentActivity = NULL_ACTIVITY;
    private Activity mPendingActivity;
    private Place mCurrentPlace = Place.NOWHERE;
    private Place mPendingAsyncPlace;
    private PlaceChangeListener.Source mPlaceChangerRequestedPlaceSource;
    private Place mPlaceChangerRequestedPlace;
    private PlaceChangeListener mPlaceChangeListener;

    public PanelPlaceActivityHelper( AcceptsOneWidget pPanel, CommonActivityParam pCommonActivityParam )
    {
        mPanel = pPanel;
        mCommonActivityParam = pCommonActivityParam;
    }

    public void add( PlaceChangeListener pPlaceChangeListener )
    {
        mPlaceChangeListener = pPlaceChangeListener;
    }

    public void placeChangeRequested( Place pPlace, PlaceChangeListener.Source pSource )
    {
        mPlaceChangerRequestedPlace = pPlace;
        mPlaceChangerRequestedPlaceSource = pSource;
    }

    public Place getCurrentPlace()
    {
        return mCurrentPlace;
    }

    public boolean isPendingAsync( Place pPlace )
    {
        return pPlace.equals( mPendingAsyncPlace );
    }

    public void clearPendingAsync()
    {
        mPendingAsyncPlace = null;
    }

    public ActivityFactory get( Place pPlace )
    {
        return get( PlaceIdExtractor.getPlaceId( pPlace ) );
    }

    public String getCurrentActivityMayStop()
    {
        return mCurrentActivity.mayStop();
    }

    public boolean activate( Place pNewPlace )
    {
        if ( !isPendingAsync( pNewPlace ) )
        {
            mPendingAsyncPlace = null;
            ActivityFactory zFactory = get( pNewPlace );
            if ( zFactory == null )
            {
                return false;
            }
            if ( zFactory instanceof ActivityFactory.Asynchronous ) // Un-Happy Case!
            {
                loadSyncFactory( (ActivityFactory.Asynchronous) zFactory, mPendingAsyncPlace = pNewPlace );
            }
            else
            {
                activate( pNewPlace, (ActivityFactory.Synchronous) zFactory );
            }
        }
        return true;
    }

    /**
     * Activate the New Place and it's associated Activity (deactivating the current activity.
     */
    public void activate( Place pNewPlace, ActivityFactory.Synchronous pSyncFactory )
    {
        Set<Throwable> zIssues = new LinkedHashSet<Throwable>();

        notifyPlaceChangeListener( pNewPlace );
        mCurrentPlace = pNewPlace;

        Activity zNewActivity = Objects.deNull( createActivity( zIssues, pSyncFactory, pNewPlace ), NULL_ACTIVITY );

        if ( (mPendingActivity != null) && (mPendingActivity != zNewActivity) ) // The place changed again before the new Activity showed its widget
        {
            tryCancel( zIssues, mPendingActivity );
        }
        mPendingActivity = zNewActivity;

        // Wrap the actual panel with a per-call instance that protects the actual panel from canceled or stopped activities, and
        // which handles the Pending Activity becoming the Current Activity.
        AcceptsOneWidget zPanel = new ProtectedDisplay( zIssues, mPendingActivity );

        if ( !canStart( zIssues, mPendingActivity, zPanel ) )
        {
            NULL_ACTIVITY.start( new ProtectedDisplay( zIssues, mPendingActivity = NULL_ACTIVITY ) ); // Can NOT fail!
        }
    }

    private void notifyPlaceChangeListener( Place pNewPlace )
    {
        if ( mPlaceChangeListener != null )
        {
            if ( (mPlaceChangerRequestedPlaceSource == null) || //
                 ((mPlaceChangerRequestedPlaceSource == PlaceChangeListener.Source.Forward) && //
                  !Objects.areNonArraysEqual( mPlaceChangerRequestedPlace, pNewPlace )) )
            {
                mPlaceChangerRequestedPlaceSource = PlaceChangeListener.Source.Unexpected;
            }
            mPlaceChangeListener.placeChange( mPlaceChangerRequestedPlaceSource, mCurrentPlace, pNewPlace );
        }
        mPlaceChangerRequestedPlaceSource = null;
        mPlaceChangerRequestedPlace = null;
    }

    @SuppressWarnings({"unchecked"})
    protected Activity createActivity( Collection<Throwable> pIssues, ActivityFactory.Synchronous pFactory, Place pPlace )
    {
        try
        {
            return pFactory.createActivity( mCommonActivityParam, pFactory.getView(), pPlace );
        }
        catch ( Exception e )
        {
            pIssues.add( e );
        }
        return null;
    }

    private boolean canStart( Set<Throwable> pIssues, Activity pActivity, AcceptsOneWidget pPanel )
    {
        try
        {
            pActivity.start( pPanel );
            return true;
        }
        catch ( Exception e )
        {
            pIssues.add( e );
        }
        return false;
    }

    private void tryCancel( Collection<Throwable> pIssues, Activity pActivity )
    {
        try
        {
            pActivity.onCancel();
        }
        catch ( Exception e )
        {
            pIssues.add( e );
        }
    }

    private void tryStop( Collection<Throwable> pIssues, Activity pActivity )
    {
        try
        {
            pActivity.onStop();
        }
        catch ( Exception e )
        {
            pIssues.add( e );
        }
    }

    private void possiblyUpdateActivityAndShowWidget( Set<Throwable> pIssues, Activity pActivity, IsWidget pWidget )
    {
        if ( mPendingActivity == null ) // Normal? Happy case when No Pending Activity and request is from Current Activity
        {
            if ( pActivity == mCurrentActivity )
            {
                showWidget( pWidget );
            }
            return;
        }
        if ( pActivity != mPendingActivity ) // Is a Pending Activity, but the request is NOT from it!
        {
            return;
        }
        tryStop( pIssues, mCurrentActivity );
        mCurrentActivity = mPendingActivity;
        mPendingActivity = null;
        showWidget( pWidget );
        if ( !pIssues.isEmpty() )
        {
            throw new UmbrellaException( pIssues );
        }
    }

    private void showWidget( IsWidget pWidget )
    {
        if ( mPanel != null )
        {
            mPanel.setWidget( pWidget );
        }
    }

    @SuppressWarnings({"unchecked"})
    private void loadSyncFactory( final ActivityFactory.Asynchronous pAsyncFactory, final Place pPlace )
    {
        pAsyncFactory.load( mCommonActivityParam, new ActivityFactory.Asynchronous.Callback<CommonActivityParam, IsWidget, Place>()
        {
            @Override
            public void loaded( ActivityFactory.Synchronous<CommonActivityParam, IsWidget, Place> pSynchronousFactory )
            {
                switchAsyncToSync( pPlace, pAsyncFactory, pSynchronousFactory );
            }
        } );
    }

    private void switchAsyncToSync( Place pPlace, ActivityFactory.Asynchronous pAsyncFactory, ActivityFactory.Synchronous pSyncFactory )
    {
        System.out.println( "Switched " + Objects.justSimpleName( pPlace ) + " from Async to Sync" );
        boolean zStillGoing = pPlace.equals( mPendingAsyncPlace );
        mPendingAsyncPlace = null;
        if ( replace( pAsyncFactory, pSyncFactory ) && zStillGoing )
        {
            activate( pPlace, pSyncFactory );
        }
    }

    /**
     * Wraps our real display to prevent an Activity from taking it over if it is
     * not the currentActivity.
     */
    private class ProtectedDisplay implements AcceptsOneWidget
    {
        private final Set<Throwable> mIssues;
        private final Activity mExpectedActivity;

        ProtectedDisplay( Set<Throwable> pIssues, Activity pExpectedActivity )
        {
            mIssues = pIssues;
            mExpectedActivity = pExpectedActivity;
        }

        @Override
        public void setWidget( IsWidget pWidget )
        {
            possiblyUpdateActivityAndShowWidget( mIssues, mExpectedActivity, pWidget );
        }
    }
}