/*
 * 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.visitor;

import org.eclipse.aether.graph.DependencyFilter;
import org.eclipse.aether.graph.DependencyNode;
import org.eclipse.aether.graph.DependencyVisitor;

import static java.util.Objects.requireNonNull;

/**
 * A dependency visitor that delegates to another visitor if nodes match a filter. Note that in case of a mismatching
 * node, the children of that node are still visited and presented to the filter.
 */
public final class FilteringDependencyVisitor implements DependencyVisitor {

    private final DependencyFilter filter;

    private final DependencyVisitor visitor;

    private final Stack<Boolean> accepts;

    private final Stack<DependencyNode> parents;

    /**
     * Creates a new visitor that delegates traversal of nodes matching the given filter to the specified visitor.
     *
     * @param visitor the visitor to delegate to, must not be {@code null}
     * @param filter the filter to apply, may be {@code null} to not filter
     */
    public FilteringDependencyVisitor(DependencyVisitor visitor, DependencyFilter filter) {
        this.visitor = requireNonNull(visitor, "dependency visitor delegate cannot be null");
        this.filter = filter;
        this.accepts = new Stack<>();
        this.parents = new Stack<>();
    }

    /**
     * Gets the visitor to which this visitor delegates to.
     *
     * @return the visitor being delegated to, never {@code null}
     */
    public DependencyVisitor getVisitor() {
        return visitor;
    }

    /**
     * Gets the filter being applied before delegation.
     *
     * @return the filter being applied or {@code null} if none
     */
    public DependencyFilter getFilter() {
        return filter;
    }

    @Override
    public boolean visitEnter(DependencyNode node) {
        boolean accept = filter == null || filter.accept(node, parents);

        accepts.push(accept);

        parents.push(node);

        if (accept) {
            return visitor.visitEnter(node);
        } else {
            return true;
        }
    }

    @Override
    public boolean visitLeave(DependencyNode node) {
        parents.pop();

        Boolean accept = accepts.pop();

        if (accept) {
            return visitor.visitLeave(node);
        } else {
            return true;
        }
    }
}
