package org.simantics.ui.workbench.handler.e4;

import org.eclipse.swt.widgets.Display;
import org.eclipse.ui.PlatformUI;
import org.eclipse.ui.contexts.IContextActivation;
import org.eclipse.ui.contexts.IContextService;
import org.simantics.DatabaseJob;
import org.simantics.Simantics;
import org.simantics.db.Session;
import org.simantics.db.UndoContext;
import org.simantics.db.exception.DatabaseException;
import org.simantics.db.management.ISessionContext;
import org.simantics.db.service.UndoRedoSupport;
import org.simantics.ui.SimanticsUI;
import org.simantics.utils.ui.ErrorLogger;
import org.simantics.utils.ui.SWTUtils;

public class UndoRedoTester {

    private static final boolean DEBUG = false;
    private static final String SIMANTICS_UNDO_CONTEXT = "org.simantics.ui.undoContext";
    public static final String UNDO_ENABLED = "org.simantics.undo.enabled";
    
    private static UndoRedoSupport undoSupport = null;
    private static UndoChangeListener changeListener = new UndoChangeListener();
    private static IContextActivation activation = null;
    
    private static class UndoChangeListener implements UndoRedoSupport.ChangeListener {

        private int oldUndo = 0;
        private int oldRedo = 0;
        
        @Override
        public void onChanged() {
            if (DEBUG)
                System.out.println("UndoPropertyTester: on change.");
            Display display = PlatformUI.getWorkbench().getDisplay();
            SWTUtils.asyncExec(display, new Runnable() {
                @Override
                public void run() {
                    handleChange();
                }
            });
        }
        
        private void handleChange() {
            int newUndo = oldUndo;
            int newRedo = oldRedo;
            try {
                ISessionContext ctx = Simantics.getSessionContext();
                if (DEBUG)
                    System.out.println("UndoPropertyTester: handle change, ctx=" + ctx);
                if (ctx == null)
                    return;
                Session session = ctx.peekSession();
                if (DEBUG)
                    System.out.println("UndoPropertyTester: handle change, session=" + session);
                if (session == null)
                    return;
                UndoContext uc = undoSupport.getUndoContext(session);
                if (uc == null)
                    return;
                newUndo = uc.getAll().size();
                newRedo = uc.getRedoList().size();
                if (DEBUG) {
                    System.out.println("on undo change: " + oldUndo + "->" + newUndo);
                    System.out.println("on redo change: " + oldRedo + "->" + newRedo);
                }
                boolean undoOn = oldUndo == 0 && newUndo == 1;
                boolean undoOff = oldUndo > 0 && newUndo == 0;
                boolean redoOn = oldRedo == 0 && newRedo == 1;
                boolean redoOff = oldRedo > 0 && newRedo == 0;
                if (undoOn || undoOff || redoOn || redoOff)
                    toggleContext();
            } catch (DatabaseException e) {
                ErrorLogger.getDefault().logError("Undo/Redo support failed.", e);
            }
            oldUndo = newUndo;
            oldRedo = newRedo;
        }
        private void toggleContext() {
            IContextService contextService = (IContextService)PlatformUI.getWorkbench().getService(IContextService.class);
            if (null != activation) {
                if (DEBUG)
                    System.out.println("UndoPropertyTester: deactivate.");
                try {
                    contextService.deactivateContext(activation);
                } catch (Throwable t) {
                    ErrorLogger.getDefault().logError("Undo/Redo support failed.", t);
                }
                activation = null;
                if (DEBUG)
                    System.out.println("UndoPropertyTester: deactivated.");
            } else {
                if (DEBUG)
                    System.out.println("UndoPropertyTester: activate.");
                try {
                    activation = contextService.activateContext(SIMANTICS_UNDO_CONTEXT);
                } catch (Throwable t) {
                    ErrorLogger.getDefault().logError("Undo/Redo support failed.", t);
                    activation = null;
                }
                if (DEBUG)
                    System.out.println("UndoPropertyTester: activated=" + activation);
            }
        }
        
    }
    
    private UndoRedoTester() {
    }
    
    public static boolean canUndo() {
        String undoEnabled = System.getProperty(UNDO_ENABLED);
        if(undoEnabled != null && "false".equals(undoEnabled))
            return false;
        
        ISessionContext ctx = Simantics.getSessionContext();
        if (ctx == null) {
            if (DEBUG)
                System.out.println("UndoPropertyTester: no can do undo.");
            return false;
        }
        try {
            Session s = ctx.peekSession();
            if (null == s) {
                if (DEBUG)
                    System.out.println("UndoPropertyTester: session is null, no can do undo.");
                return false;
            }
            if (DatabaseJob.inProgress())
                return true;
            if (null == undoSupport) {
                undoSupport = s.getService(UndoRedoSupport.class);
                undoSupport.subscribe(changeListener);
            }
            UndoContext uc = undoSupport.getUndoContext(s);
            if (uc == null)
                return false;
            boolean ret = !uc.getAll().isEmpty();
            if (DEBUG)
                System.out.println("UndoPropertyTester: " + (ret ? "" : "no ")+ "can do undo.");
            return ret;
        } catch (Exception e) {
            ErrorLogger.getDefault().logError("Undo/Redo support failed.", e);
            if (DEBUG)
                System.out.println("UndoPropertyTester: no can do undo");
            return false;
        }
    }
    
    public static boolean canRedo() {
        ISessionContext ctx = Simantics.getSessionContext();
        if (ctx == null) {
            if (DEBUG)
                System.out.println("UndoPropertyTester: no can do redo.");
            return false;
        }
        try {
            Session s = ctx.peekSession();
            if (null == s) {
                if (DEBUG)
                    System.out.println("UndoPropertyTester: session is null, no can do redo.");
                return false;
            }
            if (DatabaseJob.inProgress())
                return true;
            if (null == undoSupport) {
                undoSupport = s.getService(UndoRedoSupport.class);
                undoSupport.subscribe(changeListener);
            }
            UndoContext uc = undoSupport.getUndoContext(s);
            if (uc == null)
                return false;
            boolean ret = !uc.getRedoList().isEmpty();
            if (DEBUG)
                System.out.println("UndoPropertyTester: " + (ret ? "" : "no ")+ "can do redo.");
            return ret;
        } catch (Exception e) {
            ErrorLogger.getDefault().logError("Undo/Redo support failed.", e);
            if (DEBUG)
                System.out.println("UndoPropertyTester: no can do redo.");
            return false;
        }
    }

}