/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
package org.eclipse.aether.util.graph.traverser;

import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.LinkedHashSet;
import java.util.Set;

import org.eclipse.aether.collection.DependencyCollectionContext;
import org.eclipse.aether.collection.DependencyTraverser;
import org.eclipse.aether.graph.Dependency;

import static java.util.Objects.requireNonNull;

/**
 * A dependency traverser that combines zero or more other traversers using a logical {@code AND}. The resulting
 * traverser enables processing of child dependencies if and only if all constituent traversers request traversal.
 */
public final class AndDependencyTraverser implements DependencyTraverser {

    private final Set<? extends DependencyTraverser> traversers;

    private int hashCode;

    /**
     * Creates a new traverser from the specified traversers. Prefer
     * {@link #newInstance(DependencyTraverser, DependencyTraverser)} if any of the input traversers might be
     * {@code null}.
     *
     * @param traversers The traversers to combine, may be {@code null} but must not contain {@code null} elements.
     */
    public AndDependencyTraverser(DependencyTraverser... traversers) {
        if (traversers != null && traversers.length > 0) {
            this.traversers = new LinkedHashSet<>(Arrays.asList(traversers));
        } else {
            this.traversers = Collections.emptySet();
        }
    }

    /**
     * Creates a new traverser from the specified traversers.
     *
     * @param traversers The traversers to combine, may be {@code null} but must not contain {@code null} elements.
     */
    public AndDependencyTraverser(Collection<? extends DependencyTraverser> traversers) {
        if (traversers != null && !traversers.isEmpty()) {
            this.traversers = new LinkedHashSet<>(traversers);
        } else {
            this.traversers = Collections.emptySet();
        }
    }

    private AndDependencyTraverser(Set<DependencyTraverser> traversers) {
        if (traversers != null && !traversers.isEmpty()) {
            this.traversers = traversers;
        } else {
            this.traversers = Collections.emptySet();
        }
    }

    /**
     * Creates a new traverser from the specified traversers.
     *
     * @param traverser1 The first traverser to combine, may be {@code null}.
     * @param traverser2 The second traverser to combine, may be {@code null}.
     * @return The combined traverser or {@code null} if both traversers were {@code null}.
     */
    public static DependencyTraverser newInstance(DependencyTraverser traverser1, DependencyTraverser traverser2) {
        if (traverser1 == null) {
            return traverser2;
        } else if (traverser2 == null || traverser2.equals(traverser1)) {
            return traverser1;
        }
        return new AndDependencyTraverser(traverser1, traverser2);
    }

    @Override
    public boolean traverseDependency(Dependency dependency) {
        requireNonNull(dependency, "dependency cannot be null");
        for (DependencyTraverser traverser : traversers) {
            if (!traverser.traverseDependency(dependency)) {
                return false;
            }
        }
        return true;
    }

    @Override
    public DependencyTraverser deriveChildTraverser(DependencyCollectionContext context) {
        requireNonNull(context, "context cannot be null");
        int seen = 0;
        Set<DependencyTraverser> childTraversers = null;

        for (DependencyTraverser traverser : traversers) {
            DependencyTraverser childTraverser = traverser.deriveChildTraverser(context);
            if (childTraversers != null) {
                if (childTraverser != null) {
                    childTraversers.add(childTraverser);
                }
            } else if (traverser != childTraverser) {
                childTraversers = new LinkedHashSet<>();
                if (seen > 0) {
                    for (DependencyTraverser s : traversers) {
                        if (childTraversers.size() >= seen) {
                            break;
                        }
                        childTraversers.add(s);
                    }
                }
                if (childTraverser != null) {
                    childTraversers.add(childTraverser);
                }
            } else {
                seen++;
            }
        }

        if (childTraversers == null) {
            return this;
        }
        if (childTraversers.size() <= 1) {
            if (childTraversers.isEmpty()) {
                return null;
            }
            return childTraversers.iterator().next();
        }
        return new AndDependencyTraverser(childTraversers);
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        } else if (null == obj || !getClass().equals(obj.getClass())) {
            return false;
        }

        AndDependencyTraverser that = (AndDependencyTraverser) obj;
        return traversers.equals(that.traversers);
    }

    @Override
    public int hashCode() {
        if (hashCode == 0) {
            int hash = 17;
            hash = hash * 31 + traversers.hashCode();
            hashCode = hash;
        }
        return hashCode;
    }
}