/*****************************************************************************
 * Copyright (c) 2019 CEA LIST, and others.
 *
 * All rights reserved. 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:
 *   Nicolas FAUVERGUE (CEA LIST) nicolas.fauvergue@cea.fr - Initial API and implementation
 *
 *****************************************************************************/
package org.eclipse.papyrus.gitlight.compare.internal;

import com.google.common.collect.LinkedHashMultimap;

import java.util.List;
import java.util.Set;

import org.eclipse.emf.common.notify.Adapter;
import org.eclipse.emf.compare.Comparison;
import org.eclipse.emf.compare.Diff;
import org.eclipse.emf.compare.DifferenceSource;
import org.eclipse.emf.compare.merge.ResourceChangeAdapter;
import org.eclipse.emf.compare.merge.ResourceChangeAdapter.IResourceChangeParticipant;
import org.eclipse.emf.ecore.util.EcoreUtil;

/**
 * This class materializes the post-comparison treatment. This treatment manages relations between notation
 * changes and UML semantic changes when such changes should be linked. For instance, when the target of a
 * connector is changed in the representation, it is also changed in the UML model. This treatment also
 * installs a {@link IResourceChangeParticipant} on the comparison to make sure Papyrus resources are
 * created/deleted together.
 */
public class PapyrusDiagramPostComparison implements Runnable {
	/** The comparison. */
	private final Comparison comparison;

	/** The indexer. */
	private final DiffIndexer indexer;

	/**
	 * Constructor.
	 * 
	 * @param comparison
	 *            The comparison
	 */
	public PapyrusDiagramPostComparison(Comparison comparison) {
		this.comparison = comparison;
		indexer = new DiffIndexer();
	}

	/**
	 * Executes the treatment.
	 * <p>
	 * In a first step, a participant is registered on the comparison to deal with resources to delete.
	 * </p>
	 * <p>
	 * In a second step, implications are created. The algorithm takes 2 passes:
	 * <ol>
	 * <li>Index all {@link Diff}s that may be related with another {@link Diff}, using specific keys</li>
	 * <li>for each key in the index, create bi-directional implication links between the concerned diffs</li>
	 * </ol>
	 * This algorithm is linear, indexing in the first pass prevents fancy searches in the comparison model
	 * which may impede scalability.
	 * </p>
	 */
	public void run() {
		registerResourceChangeParticipant();
		IDiffHandler handler = getHandler();
		for (Diff diff : comparison.getDifferences()) {
			handler.handle(diff);
		}
		linkEquivalentDiffsWithRequiresRelations();
	}

	/**
	 * Register a {@link IResourceChangeParticipant} on the comparison for Papyrus resources.
	 */
	protected void registerResourceChangeParticipant() {
		final Adapter adapter = EcoreUtil.getAdapter(comparison.eAdapters(), ResourceChangeAdapter.class);
		if (adapter instanceof ResourceChangeAdapter) {
			((ResourceChangeAdapter)adapter)
					.addParticipant(new PapyrusResourceChangeParticipant((ResourceChangeAdapter)adapter));
		}
	}

	/**
	 * Once all related differences are indexed, walk through the index and create the implication links
	 * between all concerned {@link Diff}s. The indexing of {@link Diff}s must have been done before calling
	 * this method.
	 */
	private void linkEquivalentDiffsWithRequiresRelations() {
		for (Object key : indexer.getEquivalentDiffsKeySet()) {
			Set<Diff> diffs = indexer.getEquivalentDiffs(key);
			if (diffs.size() > 1) {
				// Keep a map of equivalent diffs based on having the same source.
				LinkedHashMultimap<DifferenceSource, Diff> sourceDiffs = LinkedHashMultimap.create();
				try {
					for (Diff diff : diffs) {
						sourceDiffs.put(diff.getSource(), diff);
						// Turn off notification delivery because we can end up populating very large
						// relations; processing all those notifications is unnecessary at this point in time,
						// because the reference involved is bi-directional, cross referencers don't need to
						// monitor it.
						diff.eSetDeliver(false);
					}

					for (DifferenceSource differenceSource : sourceDiffs.keySet()) {
						Set<Diff> equivalentDiffs = sourceDiffs.get(differenceSource);
						for (Diff diff : equivalentDiffs) {
							List<Diff> requires = diff.getRequires();
							requires.addAll(equivalentDiffs);
							// Remove the circular requirement.
							requires.remove(diff);
						}
					}
				} finally {
					for (Diff diff : diffs) {
						// Turn notification delivery back on after updating the requires references.
						diff.eSetDeliver(true);
					}
				}
			}
		}
	}

	/**
	 * Provide the {@link IDiffHandler} for the comparison used by this instance.
	 * 
	 * @return An indexer that manages 3-way comparisons if the comparison is 3-way, or an indexer that
	 *         manages 2-way comparisons otherwise.
	 */
	protected IDiffHandler getHandler() {
		if (comparison.isThreeWay()) {
			return new PapyrusDiagram3WayDiffHandler(indexer);
		} else {
			return new PapyrusDiagram2WayDiffHandler(indexer);
		}
	}
}