gradle-master/subprojects/file-collections/src/main/java/org/gradle/api/internal/file/FileCollectionStructureVisitor.java
/*
 * Copyright 2016 the original author or authors.
 *
 * Licensed 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.gradle.api.internal.file;

import org.gradle.api.file.FileCollection;
import org.gradle.api.internal.file.collections.FileSystemMirroringFileTree;
import org.gradle.api.tasks.util.PatternSet;

import java.io.File;

/**
 * Used with {@link FileCollectionInternal#visitStructure(FileCollectionStructureVisitor)} this visitor
 * is called for each element in a file collection that is an atomic source of files.
 */
public interface FileCollectionStructureVisitor {
    enum VisitType {
        // Visitor is interested in the contents of the collection
        Visit,
        // Visitor is not interested in the contents of the collection, but would like to receive the source and other metadata
        NoContents
    }

    /**
     * Called when starting to visit a file collection. Can return true to continue with visiting or false to skip this collection and its contents.
     *
     * <p>When a file collection represents a container of file collections, the children of the file collection are visited in order. Visiting a child works in the
     * same way as visiting this collection, starting with a call to {@link #startVisit(FileCollectionInternal.Source, FileCollectionInternal)}.
     *
     * <p>When the file collection contains some other source of files then {@link #prepareForVisit(FileCollectionInternal.Source)} is called for each source in order.
     */
    default boolean startVisit(FileCollectionInternal.Source source, FileCollectionInternal fileCollection) {
        return true;
    }

    /**
     * Called prior to visiting a file source with the given spec, and allows this visitor to skip these files.
     * A "file source" is some opaque source of files that is not a full {@link FileCollection}.
     *
     * <p>Note that this method is not necessarily called immediately before one of the visit methods, as some collections may be
     * resolved in parallel. However, all visiting is performed sequentially and in order.
     * This method is also called sequentially and in order.
     *
     * @return how should the collection be visited?
     */
    default VisitType prepareForVisit(FileCollectionInternal.Source source) {
        return VisitType.Visit;
    }

    /**
     * Visits an opaque file source that cannot be visited in further detail.
     */
    void visitCollection(FileCollectionInternal.Source source, Iterable<File> contents);

    /**
     * Visits a file tree at a root file on the file system (potentially filtered).
     */
    void visitFileTree(File root, PatternSet patterns, FileTreeInternal fileTree);

    /**
     * Visits a file tree whose content is generated from the contents of a file.
     */
    void visitFileTreeBackedByFile(File file, FileTreeInternal fileTree, FileSystemMirroringFileTree sourceTree);
}
