/*
 * Copyright 2013-present Facebook, Inc.
 *
 * 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 com.facebook.buck.rules;

/**
 * Object that has in-memory data structures that need to be populated as a result of executing its
 * steps. An object that implements this interface will <em>always</em> have its internal data
 * structures initialized through this interface, regardless of whether it was built locally or read
 * from cache. This ensures that a rule is always in the same state once {@code isRuleBuilt()}
 * returns {@code true}.
 * <p>
 * Objects that implement this interface should create getter methods that delegate to
 * {@link BuildOutputInitializer#getBuildOutput()} to access the in-memory data structures rather
 * than have clients invoke {@link BuildOutputInitializer#getBuildOutput()} directly. This ensures
 * that all getters go through any protections provided by
 * {@link BuildOutputInitializer#getBuildOutput()}.
 * <p>
 */
public interface InitializableFromDisk<T> {

  /**
   * @param onDiskBuildInfo can be used to read metadata from disk to help initialize the rule.
   * @return an object that has the in-memory data structures that need to be populated as a result
   *     of executing this object's steps.
   */
  public T initializeFromDisk(OnDiskBuildInfo onDiskBuildInfo);

  public BuildOutputInitializer<T> getBuildOutputInitializer();
}