/*******************************************************************************
 * Copyright (c) 2007, 2012 Wind River Systems 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:
 *     Wind River Systems - initial API and implementation
 *******************************************************************************/
package org.eclipse.cdt.dsf.ui.viewmodel;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import org.eclipse.cdt.dsf.concurrent.ConfinedToDsfExecutor;
import org.eclipse.cdt.dsf.concurrent.CountingRequestMonitor;
import org.eclipse.cdt.dsf.concurrent.DataRequestMonitor;
import org.eclipse.cdt.dsf.concurrent.MultiRequestMonitor;
import org.eclipse.cdt.dsf.ui.concurrent.ViewerCountingRequestMonitor;
import org.eclipse.cdt.dsf.ui.concurrent.ViewerDataRequestMonitor;
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.IViewerUpdate;

/**
 * The default strategy for implementing the IElementContentProvider
 * functionality for an IVMProvider. It implements an algorithm to populate
 * contents of the view in accordance with the tree structure of the view model
 * nodes configured in the view model provider.
 * <p/>
 * This class may be used by an <code>IVMProvider</code> directly, or it may be
 * be extended to customize for the provider's needs.
 * <p/>
 * This class is closely linked with a view model provider which is required for
 * the constructor. The view model provider is used to access the correct
 * executor and the node hierarchy.
 *
 * @since 1.0
 */
@ConfinedToDsfExecutor("#getExecutor()")
public class DefaultVMContentProviderStrategy implements IElementContentProvider {

	private final AbstractVMProvider fVMProvider;

	public DefaultVMContentProviderStrategy(AbstractVMProvider provider) {
		fVMProvider = provider;
	}

	/**
	 * Returns the view model provider that this strategy is configured for.
	 *
	 * @return
	 */
	protected AbstractVMProvider getVMProvider() {
		return fVMProvider;
	}

	@Override
	public void update(final IHasChildrenUpdate[] updates) {
		if (updates.length == 0)
			return;

		// Optimization: if all the updates belong to the same node, avoid
		// creating any new lists/arrays.
		boolean allNodesTheSame = true;
		IVMNode firstNode = getNodeForElement(updates[0].getElement());
		for (int i = 1; i < updates.length; i++) {
			if (firstNode != getNodeForElement(updates[i].getElement())) {
				allNodesTheSame = false;
				break;
			}
		}

		if (allNodesTheSame) {
			updateNodeChildren(firstNode, updates);
		} else {
			// Sort the updates by the node.
			Map<IVMNode, List<IHasChildrenUpdate>> nodeUpdatesMap = new HashMap<>();
			for (IHasChildrenUpdate update : updates) {
				// Get the VM Context for last element in path.
				IVMNode node = getNodeForElement(update.getElement());
				if (node == null) {
					// Stale update, most likely as a result of the nodes being
					// changed. Just ignore it.
					update.done();
					continue;
				}
				if (!nodeUpdatesMap.containsKey(node)) {
					nodeUpdatesMap.put(node, new ArrayList<IHasChildrenUpdate>());
				}
				nodeUpdatesMap.get(node).add(update);
			}

			// Iterate through the nodes in the sorted map.
			for (IVMNode node : nodeUpdatesMap.keySet()) {
				updateNodeChildren(node,
						nodeUpdatesMap.get(node).toArray(new IHasChildrenUpdate[nodeUpdatesMap.get(node).size()]));
			}
		}
	}

	/**
	 * @param node
	 *            the type of element (thread, variable, frame, e.g,) that's in
	 *            the update requests. All the given requests contain the same
	 *            type of element.
	 * @param updates
	 *            the has-children requests
	 */
	private void updateNodeChildren(IVMNode node, final IHasChildrenUpdate[] updates) {
		final IVMNode[] childNodes = getVMProvider().getChildVMNodes(node);
		if (childNodes.length == 0) {
			// If parent element's node has no children, just set the
			// result and continue to next element.
			for (IHasChildrenUpdate update : updates) {
				update.setHasChilren(false);
				update.done();
			}
		} else if (childNodes.length == 1) {
			// Optimization: if there is only one child node, just pass on the
			// update to the child node.
			getVMProvider().updateNode(childNodes[0], updates);
		} else {
			// Create a matrix of element updates:
			// The first dimension "i" is the list of children updates that came
			// from the viewer. For each of these updates, there are "j" number
			// of element updates corresponding to the number of child nodes in
			// this node. Each children update from the viewer is complete when
			// all the child nodes fill in their elements update. Once the
			// matrix is constructed, the child nodes are given the list of
			// updates equal to the updates requested by the viewer.
			VMHasChildrenUpdate[][] elementsUpdates = new VMHasChildrenUpdate[childNodes.length][updates.length];
			for (int i = 0; i < updates.length; i++) {
				final IHasChildrenUpdate update = updates[i];

				final MultiRequestMonitor<DataRequestMonitor<Boolean>> hasChildrenMultiRequestMon = new MultiRequestMonitor<DataRequestMonitor<Boolean>>(
						getVMProvider().getExecutor(), null) {
					@Override
					protected void handleCompleted() {
						// Status is OK, only if all request monitors are OK.
						if (isSuccess()) {
							boolean isContainer = false;
							for (DataRequestMonitor<Boolean> hasElementsDone : getRequestMonitors()) {
								isContainer |= hasElementsDone.isSuccess() && hasElementsDone.getData().booleanValue();
							}
							update.setHasChilren(isContainer);
						} else {
							update.setStatus(getStatus());
						}
						update.done();
					}
				};
				hasChildrenMultiRequestMon.requireDoneAdding();

				for (int j = 0; j < childNodes.length; j++) {
					elementsUpdates[j][i] = new VMHasChildrenUpdate(update, hasChildrenMultiRequestMon
							.add(new ViewerDataRequestMonitor<Boolean>(getVMProvider().getExecutor(), update) {
								@Override
								protected void handleCompleted() {
									hasChildrenMultiRequestMon.requestMonitorDone(this);
								}
							}));
				}
				hasChildrenMultiRequestMon.doneAdding();
			}

			for (int j = 0; j < childNodes.length; j++) {
				getVMProvider().updateNode(childNodes[j], elementsUpdates[j]);
			}
		}
	}

	@Override
	public void update(final IChildrenCountUpdate[] updates) {
		for (final IChildrenCountUpdate update : updates) {
			IVMNode node = getNodeForElement(update.getElement());

			if (node != null && !update.isCanceled()) {
				IVMNode[] childNodes = getVMProvider().getChildVMNodes(node);

				if (childNodes.length == 0) {
					// If there is no child nodes, logically the child count is 0.
					update.setChildCount(0);
					update.done();
				} else if (childNodes.length == 1) {
					// Optimization: there is only one child node, just pass on the child count to it.
					getVMProvider().updateNode(childNodes[0], update);
				} else {
					getChildrenCountsForNode(update, node,
							new ViewerDataRequestMonitor<Integer[]>(getVMProvider().getExecutor(), update) {
								@Override
								protected void handleCompleted() {
									if (isSuccess()) {
										int numChildren = 0;
										for (Integer count : getData()) {
											numChildren += count.intValue();
										}
										update.setChildCount(numChildren);
									} else {
										update.setChildCount(0);
									}
									update.done();
								}
							});
				}
			} else {
				update.done();
			}

		}
	}

	@Override
	public void update(final IChildrenUpdate[] updates) {
		for (final IChildrenUpdate update : updates) {
			// Get the VM Context for last element in path.
			final IVMNode node = getNodeForElement(update.getElement());
			if (node != null && !update.isCanceled()) {
				IVMNode[] childNodes = getVMProvider().getChildVMNodes(node);
				if (childNodes.length == 0) {
					// Invalid update, just mark done.
					update.done();
				} else if (childNodes.length == 1) {
					// Optimization: there is only one child node, pass the updates to it.
					getVMProvider().updateNode(childNodes[0], update);
				} else {
					getChildrenCountsForNode(update, node,
							new ViewerDataRequestMonitor<Integer[]>(getVMProvider().getExecutor(), update) {
								@Override
								protected void handleCompleted() {
									if (!isSuccess()) {
										update.done();
										return;
									}

									updateChildrenWithCounts(update, node, getData());
								}
							});
				}
			} else {
				// Stale update. Just ignore.
				update.done();
			}

		}
	}

	/**
	 * Calculates the number of elements in each child node for the element in
	 * update. These counts are then used to delegate the children update to the
	 * correct nodes.
	 */
	private void getChildrenCountsForNode(IViewerUpdate update, IVMNode updateNode,
			final DataRequestMonitor<Integer[]> rm) {

		IVMNode[] childNodes = getVMProvider().getChildVMNodes(updateNode);

		// Check for an invalid call
		assert childNodes.length != 0;

		// Get the mapping of all the counts.
		final Integer[] counts = new Integer[childNodes.length];
		final CountingRequestMonitor crm = new CountingRequestMonitor(getVMProvider().getExecutor(), rm) {
			@Override
			protected void handleSuccess() {
				rm.setData(counts);
				rm.done();
			}
		};
		int countRM = 0;

		for (int i = 0; i < childNodes.length; i++) {
			final int nodeIndex = i;
			getVMProvider().updateNode(childNodes[i], new VMChildrenCountUpdate(update,
					new DataRequestMonitor<Integer>(getVMProvider().getExecutor(), crm) {
						@Override
						protected void handleSuccess() {
							counts[nodeIndex] = getData();
							crm.done();
						}
					}));
			countRM++;
		}
		crm.setDoneCount(countRM);
	}

	/**
	 * Splits the given children update among the configured child nodes. Then
	 * calls each child node to complete the update.
	 */
	private void updateChildrenWithCounts(final IChildrenUpdate update, IVMNode node, Integer[] nodeElementCounts) {
		// Create the multi request monitor to mark update when querying all
		// children nodes is finished.
		CountingRequestMonitor multiRm = new ViewerCountingRequestMonitor(getVMProvider().getExecutor(), update) {
			@Override
			protected void handleCompleted() {
				update.done();
			}
		};
		int multiRmCount = 0;

		// Iterate through all child nodes and if requested range matches, call
		// them to get their elements.
		int updateStartIdx = update.getOffset();
		if (updateStartIdx < 0) {
			updateStartIdx = 0;
		}
		int updateEndIdx;
		int length = update.getLength();
		if (length <= 0) {
			updateEndIdx = Integer.MAX_VALUE;
		} else {
			updateEndIdx = updateStartIdx + length;
		}
		int idx = 0;
		IVMNode[] nodes = getVMProvider().getChildVMNodes(node);
		for (int i = 0; i < nodes.length; i++) {
			final int nodeStartIdx = idx;
			final int nodeEndIdx = idx + nodeElementCounts[i];
			idx = nodeEndIdx;

			// Check if update range overlaps the node's range.
			if (updateStartIdx <= nodeEndIdx && updateEndIdx > nodeStartIdx) {
				final int elementsStartIdx = Math.max(updateStartIdx - nodeStartIdx, 0);
				final int elementsEndIdx = Math.min(updateEndIdx - nodeStartIdx, nodeElementCounts[i]);
				final int elementsLength = elementsEndIdx - elementsStartIdx;
				if (elementsLength > 0) {
					getVMProvider().updateNode(nodes[i], new VMChildrenUpdate(update, elementsStartIdx, elementsLength,
							new DataRequestMonitor<List<Object>>(getVMProvider().getExecutor(), multiRm) {
								@Override
								protected void handleCompleted() {
									// Workaround for a bug caused by an
									// optimization in the viewer:
									// The viewer may request more children then
									// there are at a given level.
									// This causes the update to return with an
									// error.
									// See
									// https://bugs.eclipse.org/bugs/show_bug.cgi?id=202109
									// Instead of checking isSuccess(), check
									// getData() != null.
									if (getData() != null) {
										for (int i = 0; i < elementsLength && i < getData().size(); i++) {
											Object child = getData().get(i);
											if (child != null) {
												update.setChild(getData().get(i), elementsStartIdx + nodeStartIdx + i);
											}
										}
									}
									super.handleCompleted();
								}
							}));
					multiRmCount++;
				}
			}
		}

		// Guard against invalid queries.
		multiRm.setDoneCount(multiRmCount);
	}

	/**
	 * Convenience method that finds the VM node corresponding to given element.
	 * It returns the root node if the element is not a VM Context or if it was
	 * created by another view.
	 *
	 * @param element Element to find the VM Node for.
	 * @return View Model Node that this element was created by.
	 */
	protected IVMNode getNodeForElement(Object element) {
		if (element instanceof IVMContext) {
			IVMNode node = ((IVMContext) element).getVMNode();
			if (isOurNode(((IVMContext) element).getVMNode())) {
				return node;
			}
		}
		return getVMProvider().getRootVMNode();
	}

	/**
	 * Convenience method which checks whether given layout node is a node that
	 * is configured in this ViewModelProvider.
	 * <br>
	 * Note: isOurNode() will also return true if the given node was previously
	 * configured in the VM provider but was later disposed.
	 */
	private boolean isOurNode(IVMNode node) {
		return node.getVMProvider() == getVMProvider();
	}

}
