import java.beans.PropertyChangeListener;
import java.beans.PropertyChangeSupport;
import java.util.Iterator;

import org.eclipse.core.databinding.DataBindingContext;
import org.eclipse.core.databinding.UpdateValueStrategy;
import org.eclipse.core.databinding.beans.BeanProperties;
import org.eclipse.core.databinding.observable.Realm;
import org.eclipse.core.databinding.observable.list.WritableList;
import org.eclipse.core.databinding.observable.value.ComputedValue;
import org.eclipse.jface.databinding.swt.SWTObservables;
import org.eclipse.jface.databinding.viewers.ViewerSupport;
import org.eclipse.jface.layout.GridDataFactory;
import org.eclipse.jface.viewers.TableViewer;
import org.eclipse.swt.SWT;
import org.eclipse.swt.events.SelectionAdapter;
import org.eclipse.swt.events.SelectionEvent;
import org.eclipse.swt.layout.GridLayout;
import org.eclipse.swt.widgets.Button;
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Shell;
import org.eclipse.swt.widgets.Table;
import org.eclipse.swt.widgets.TableColumn;
import org.eclipse.swt.widgets.Text;

/**
 * Binds a TableViewer to a Collection and displays the sum of the shown column
 * in a text field.
 */
public class SnippetTableViewerSum {

	public static void main(String[] args) {
		final Display display = Display.getDefault();
		Realm.runWithDefault(SWTObservables.getRealm(display), new Runnable() {
			public void run() {
				ViewModel viewModel = new ViewModel();
				Shell shell = new View(viewModel).createShell();
				while (!shell.isDisposed()) {
					if (!display.readAndDispatch()) {
						display.sleep();
					}
				}
			}
		});
	}

	public static abstract class AbstractModelObject {
		private PropertyChangeSupport propertyChangeSupport = new PropertyChangeSupport(
				this);

		public void addPropertyChangeListener(PropertyChangeListener listener) {
			propertyChangeSupport.addPropertyChangeListener(listener);
		}

		public void addPropertyChangeListener(String propertyName,
				PropertyChangeListener listener) {
			propertyChangeSupport.addPropertyChangeListener(propertyName,
					listener);
		}

		public void removePropertyChangeListener(PropertyChangeListener listener) {
			propertyChangeSupport.removePropertyChangeListener(listener);
		}

		public void removePropertyChangeListener(String propertyName,
				PropertyChangeListener listener) {
			propertyChangeSupport.removePropertyChangeListener(propertyName,
					listener);
		}

		protected void firePropertyChange(String propertyName, Object oldValue,
				Object newValue) {
			propertyChangeSupport.firePropertyChange(propertyName, oldValue,
					newValue);
		}
	}

	static class Task extends AbstractModelObject {
		Double timeTaken = null;

		public Task(Double timeTaken) {
			this.timeTaken = timeTaken;
		}

		public Double getTimeTaken() {
			return timeTaken;
		}

		public void setTimeTaken(Double timeTaken) {
			Double oldValue = this.timeTaken;
			this.timeTaken = timeTaken;
			firePropertyChange("timeTaken", oldValue, timeTaken);
		}
	}

	static class ViewModel {
		private WritableList tasks = new WritableList();

		{
			tasks.add(new Task(Math.random()));
			tasks.add(new Task(Math.random()));
			tasks.add(new Task(Math.random()));
			tasks.add(new Task(Math.random()));
			tasks.add(new Task(Math.random()));
			tasks.add(new Task(Math.random()));
			tasks.add(new Task(Math.random()));
		}

		public WritableList getTasks() {
			return tasks;
		}
	}

	static class View {
		private ViewModel viewModel;
		private Table tasks;
		private Button addTask;
		private TableColumn column;
		private SumValue sumValue;

		public View(ViewModel viewModel) {
			this.viewModel = viewModel;
		}

		public Shell createShell() {

			Display display = Display.getDefault();

			DataBindingContext dbc = new DataBindingContext();

			Shell shell = new Shell(display);
			shell.setLayout(new GridLayout(2, false));

			GridDataFactory gdf = GridDataFactory.swtDefaults()
					.align(SWT.FILL, SWT.FILL).grab(true, true);

			tasks = new Table(shell, SWT.BORDER | SWT.FULL_SELECTION);
			gdf.applyTo(tasks);
			tasks.setLinesVisible(true);
			column = new TableColumn(tasks, SWT.NONE);

			TableViewer tasksViewer = new TableViewer(tasks);
			ViewerSupport.bind(tasksViewer, viewModel.getTasks(),
					BeanProperties.value(Task.class, "timeTaken"));

			column.pack();

			GridDataFactory gdf2 = GridDataFactory.swtDefaults().align(
					SWT.FILL, SWT.BEGINNING);
			addTask = new Button(shell, SWT.PUSH);
			gdf2.applyTo(addTask);
			addTask.setText("Add Task");
			addTask.addSelectionListener(new SelectionAdapter() {
				@Override
				public void widgetSelected(SelectionEvent e) {
					viewModel.getTasks().add(new Task(Math.random()));
					column.pack();
				}

			});

			GridDataFactory gdf3 = GridDataFactory.swtDefaults()
					.align(SWT.FILL, SWT.BEGINNING).grab(true, false);
			Text sum = new Text(shell, SWT.BORDER);
			gdf3.applyTo(sum);
			sumValue = new SumValue(viewModel.getTasks());
			dbc.bindValue(SWTObservables.observeText(sum, SWT.None), sumValue,
					new UpdateValueStrategy(false,
							UpdateValueStrategy.POLICY_NEVER), null);

			shell.setSize(300, 300);
			shell.open();
			return shell;
		}
	}

	// The computed value which calculates the sum
	static class SumValue extends ComputedValue {
		private WritableList tasks;

		SumValue(WritableList tasks) {
			this.tasks = tasks;
		}

		protected Object calculate() {
			double sum = 0;
			Iterator<Task> iterator = tasks.iterator();
			while (iterator.hasNext()) {
				Task task = (Task) iterator.next();
				sum += task.getTimeTaken();
			}
			return String.valueOf(sum);
		}
	}
}