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/*
 * 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.repository;

import java.io.File;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.LinkedHashSet;
import java.util.List;

import org.eclipse.aether.artifact.Artifact;
import org.eclipse.aether.repository.WorkspaceReader;
import org.eclipse.aether.repository.WorkspaceRepository;

import static java.util.Objects.requireNonNull;

/**
 * A workspace reader that delegates to a chain of other readers, effectively aggregating their contents.
 */
public final class ChainedWorkspaceReader implements WorkspaceReader {

    private final List readers = new ArrayList<>();

    private WorkspaceRepository repository;

    /**
     * Creates a new workspace reader by chaining the specified readers.
     *
     * @param readers The readers to chain, may be {@code null}.
     * @see #newInstance(WorkspaceReader, WorkspaceReader)
     */
    public ChainedWorkspaceReader(WorkspaceReader... readers) {
        if (readers != null) {
            Collections.addAll(this.readers, readers);
        }

        StringBuilder buffer = new StringBuilder();
        for (WorkspaceReader reader : this.readers) {
            if (buffer.length() > 0) {
                buffer.append('+');
            }
            buffer.append(reader.getRepository().getContentType());
        }

        repository = new WorkspaceRepository(buffer.toString(), new Key(this.readers));
    }

    /**
     * Creates a new workspace reader by chaining the specified readers. In contrast to the constructor, this factory
     * method will avoid creating an actual chained reader if one of the specified readers is actually {@code null}.
     *
     * @param reader1 The first workspace reader, may be {@code null}.
     * @param reader2 The second workspace reader, may be {@code null}.
     * @return The chained reader or {@code null} if no workspace reader was supplied.
     */
    public static WorkspaceReader newInstance(WorkspaceReader reader1, WorkspaceReader reader2) {
        if (reader1 == null) {
            return reader2;
        } else if (reader2 == null) {
            return reader1;
        }
        return new ChainedWorkspaceReader(reader1, reader2);
    }

    public File findArtifact(Artifact artifact) {
        requireNonNull(artifact, "artifact cannot be null");
        File file = null;

        for (WorkspaceReader reader : readers) {
            file = reader.findArtifact(artifact);
            if (file != null) {
                break;
            }
        }

        return file;
    }

    public List findVersions(Artifact artifact) {
        requireNonNull(artifact, "artifact cannot be null");
        Collection versions = new LinkedHashSet<>();

        for (WorkspaceReader reader : readers) {
            versions.addAll(reader.findVersions(artifact));
        }

        return Collections.unmodifiableList(new ArrayList<>(versions));
    }

    public WorkspaceRepository getRepository() {
        Key key = new Key(readers);
        if (!key.equals(repository.getKey())) {
            repository = new WorkspaceRepository(repository.getContentType(), key);
        }
        return repository;
    }

    private static class Key {

        private final List