gradle-master/subprojects/core/src/main/java/org/gradle/api/internal/file/CachingTaskInputFileCollection.java
/*
 * Copyright 2017 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 com.google.common.collect.ImmutableSet;
import org.gradle.api.internal.file.collections.DefaultConfigurableFileCollection;
import org.gradle.api.internal.file.collections.FileCollectionAdapter;
import org.gradle.api.internal.file.collections.ListBackedFileSet;
import org.gradle.api.internal.provider.PropertyHost;
import org.gradle.api.internal.tasks.TaskDependencyFactory;
import org.gradle.api.internal.tasks.properties.LifecycleAwareValue;
import org.gradle.api.tasks.util.PatternSet;
import org.gradle.internal.Factory;
import org.gradle.internal.file.PathToFileResolver;

import java.io.File;
import java.util.function.Consumer;

/**
 * A {@link org.gradle.api.file.ConfigurableFileCollection} that can be used as a task input property. Caches the matching set of files during task execution, and discards the result after task execution.
 *
 * TODO - disallow further changes to this collection once task has started
 * TODO - keep the file entries to snapshot later, to avoid a stat on each file during snapshot
 */
public class CachingTaskInputFileCollection extends DefaultConfigurableFileCollection implements LifecycleAwareValue {
    private boolean canCache;
    private FileCollectionInternal cachedValue;

    // TODO - display name
    public CachingTaskInputFileCollection(PathToFileResolver fileResolver, Factory<PatternSet> patternSetFactory, TaskDependencyFactory taskDependencyFactory, PropertyHost propertyHost) {
        super(null, fileResolver, taskDependencyFactory, patternSetFactory, propertyHost);
    }

    @Override
    protected void visitChildren(Consumer<FileCollectionInternal> visitor) {
        if (canCache) {
            if (cachedValue == null) {
                ImmutableSet.Builder<File> files = ImmutableSet.builder();
                super.visitChildren(files::addAll);
                this.cachedValue = new FileCollectionAdapter(new ListBackedFileSet(files.build()), taskDependencyFactory, patternSetFactory);
            }
            visitor.accept(cachedValue);
        } else {
            super.visitChildren(visitor);
        }
    }

    @Override
    public void prepareValue() {
        canCache = true;
    }

    @Override
    public void cleanupValue() {
        // Keep the files and discard the origin values instead?
        canCache = false;
        cachedValue = null;
    }
}
