/*******************************************************************************
 * Copyright (c) 2006, 2007 IBM Corporation and others.
 *
 * This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License 2.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-2.0/
 *
 * SPDX-License-Identifier: EPL-2.0
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.debug.internal.ui.model.elements;

import org.eclipse.core.runtime.CoreException;
import org.eclipse.core.runtime.IProgressMonitor;
import org.eclipse.core.runtime.IStatus;
import org.eclipse.core.runtime.Status;
import org.eclipse.core.runtime.jobs.ISchedulingRule;
import org.eclipse.core.runtime.jobs.Job;
import org.eclipse.debug.internal.ui.viewers.model.provisional.IChildrenCountUpdate;
import org.eclipse.debug.internal.ui.viewers.model.provisional.IChildrenUpdate;
import org.eclipse.debug.internal.ui.viewers.model.provisional.IElementContentProvider;
import org.eclipse.debug.internal.ui.viewers.model.provisional.IHasChildrenUpdate;
import org.eclipse.debug.internal.ui.viewers.model.provisional.IPresentationContext;
import org.eclipse.debug.internal.ui.viewers.model.provisional.IViewerUpdate;

/**
 * @since 3.3
 */
public abstract class ElementContentProvider implements IElementContentProvider {

	protected static final Object[] EMPTY = new Object[0];

	protected abstract static class ElementContentProviderJob extends Job {

		public ElementContentProviderJob(String name) {
			super(name);
			setSystem(true);
			setUser(false);
		}

		@Override
		public boolean belongsTo(Object family) {
			return family == ElementContentProvider.class;
		}

	}

	@Override
	public void update(final IChildrenUpdate[] updates) {
		Job job = new ElementContentProviderJob("Debug children update") { //$NON-NLS-1$
			@Override
			protected IStatus run(IProgressMonitor monitor) {
				for (IChildrenUpdate update : updates) {
					if (!update.isCanceled()) {
						retrieveChildren(update);
					}
					update.done();
				}
				return Status.OK_STATUS;
			}
		};
		job.setRule(getRule(updates));
		job.schedule();
	}

	@Override
	public void update(final IChildrenCountUpdate[] updates) {
		Job job = new ElementContentProviderJob("Debug child count update") { //$NON-NLS-1$
			@Override
			protected IStatus run(IProgressMonitor monitor) {
				for (IChildrenCountUpdate update : updates) {
					if (!update.isCanceled()) {
						retrieveChildCount(update);
					}
					update.done();
				}
				return Status.OK_STATUS;
			}
		};
		job.setRule(getRule(updates));
		job.schedule();
	}

	/**
	 * Computes the children for the given parent in the specified context.
	 *
	 * @param update update request
	 */
	protected void retrieveChildren(IChildrenUpdate update) {
		if (!update.isCanceled()) {
			IStatus status = Status.OK_STATUS;
			try {
				IPresentationContext context = update.getPresentationContext();
				if (supportsContext(context)) {
					int offset = update.getOffset();
					Object[] children = getChildren(update.getElement(), offset, update.getLength(), context, update);
					if (!update.isCanceled() && children != null) {
						for (int i = 0; i < children.length; i++) {
							update.setChild(children[i], offset + i);
						}
					}
				}
			} catch (CoreException e) {
				status = e.getStatus();
			}
			update.setStatus(status);
		}
	}

	/**
	 * Computes whether the given element is a container.
	 */
	protected void retrieveChildCount(IChildrenCountUpdate update) {
		if (!update.isCanceled()) {
			IStatus status = Status.OK_STATUS;
			try {
				IPresentationContext context = update.getPresentationContext();
				if (supportsContext(context)) {
					int childCount = getChildCount( update.getElement(), context, update);
					if (!update.isCanceled()) {
						update.setChildCount(childCount);
					}
				} else {
					update.setChildCount(0);
				}
			} catch (CoreException e) {
				status = e.getStatus();
			}
			update.setStatus(status);
		}
	}

	/**
	 * Returns the children for the given parent at the specified index in the specified context
	 * or <code>null</code> if none.
	 *
	 * @param parent element to retrieve children for
	 * @param index child index
	 * @param length number of children to retrieve
	 * @param context context children will be presented in
	 * @return child or <code>null</code>
	 * @throws CoreException if an exception occurs retrieving child
	 */
	protected abstract Object[] getChildren(Object parent, int index, int length, IPresentationContext context, IViewerUpdate monitor) throws CoreException;

	/**
	 * Returns the number of children for the given element.
	 *
	 * @param element element that may have children
	 * @param context context element will be presented in
	 * @return number of children
	 * @throws CoreException if an exception occurs determining child count
	 */
	protected abstract int getChildCount(Object element, IPresentationContext context, IViewerUpdate monitor) throws CoreException;

	/**
	 * Returns whether this adapter supports the given context.
	 *
	 * @param context
	 * @return whether this adapter supports the given context
	 */
	protected boolean supportsContext(IPresentationContext context) {
		return supportsContextId(context.getId());
	}

	/**
	 * Returns whether this adapter provides content in the specified context id.
	 *
	 * @param id part id
	 * @return whether this adapter provides content in the specified context id
	 */
	protected abstract boolean supportsContextId(String id);

	/**
	 * Returns the range of elements from <code>index</code> to <code>index + length</code>
	 * or <code>null</code> if the index and range is outside the bounds of the original element array.
	 *
	 * @param elements the original element array
	 * @param index the initial index to start copying from
	 * @param length the number of elements we want to copy into the returned array
	 * @return element or <code>null</code>
	 */
	protected Object[] getElements(Object[] elements, int index, int length) {
		int max = elements.length;
		if (index < max && ((index + length) > max)) {
			length = max - index;
		}
		if ((index + length) <= elements.length) {
			Object[] sub = new Object[length];
			System.arraycopy(elements, index, sub, 0, length);
			return sub;
		}
		return null;
	}

	@Override
	public void update(final IHasChildrenUpdate[] updates) {
		Job job = new ElementContentProviderJob("Debug has children update") { //$NON-NLS-1$
			@Override
			protected IStatus run(IProgressMonitor monitor) {
				for (IHasChildrenUpdate update : updates) {
					if (!update.isCanceled()) {
						updateHasChildren(update);
					}
					update.done();
				}
				return Status.OK_STATUS;
			}
		};
		job.setRule(getRule(updates));
		job.schedule();
	}

	/**
	 * Updates whether the given elements have children.
	 *
	 * @param update specifies element and progress monitor
	 */
	protected void updateHasChildren(IHasChildrenUpdate update) {
		if (!update.isCanceled()) {
			IStatus status = Status.OK_STATUS;
			try {
				IPresentationContext context = update.getPresentationContext();
				if (supportsContext(context)) {
					boolean hasChildren = hasChildren(update.getElement(), context, update);
					if (!update.isCanceled()) {
						update.setHasChilren(hasChildren);
					}
				} else {
					update.setHasChilren(false);
				}
			} catch (CoreException e) {
				status = e.getStatus();
			}
			update.setStatus(status);
		}

	}

	/**
	 * Returns whether the given element has children in the specified context.
	 * Subclasses can override to be more efficient.
	 *
	 * @param element
	 * @param context
	 * @param monitor
	 * @return
	 */
	protected boolean hasChildren(Object element, IPresentationContext context, IViewerUpdate monitor) throws CoreException {
		return getChildCount(element, context, monitor) > 0;
	}

	/**
	 * Returns a scheduling rule to use when performing the given updates or
	 * <code>null</code> if none.
	 *
	 * @param updates
	 * @return scheduling rule or <code>null</code> if none
	 */
	protected ISchedulingRule getRule(IChildrenCountUpdate[] updates) {
		return null;
	}

	/**
	 * Returns a scheduling rule to use when performing the given updates or
	 * <code>null</code> if none.
	 *
	 * @param updates
	 * @return scheduling rule or <code>null</code> if none
	 */
	protected ISchedulingRule getRule(IChildrenUpdate[] updates) {
		return null;
	}

	/**
	 * Returns a scheduling rule to use when performing the given updates or
	 * <code>null</code> if none.
	 *
	 * @param updates
	 * @return scheduling rule or <code>null</code> if none
	 */
	protected ISchedulingRule getRule(IHasChildrenUpdate[] updates) {
		return null;
	}

}
