// Copyright 2014 The Bazel Authors. All rights reserved.
//
// 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.google.devtools.build.lib.actions;

import com.google.common.collect.ImmutableList;
import com.google.devtools.build.lib.cmdline.Label;
import com.google.devtools.build.lib.concurrent.ThreadSafety.Immutable;
import com.google.devtools.build.lib.util.Preconditions;

/**
 * An action that depends on a set of inputs and creates a single output file whenever it
 * runs. This is useful for bundling up a bunch of dependencies that are shared
 * between individual targets in the action graph; for example generated header files.
 */
@Immutable
public final class MiddlemanAction extends AbstractAction {

  public static final String MIDDLEMAN_MNEMONIC = "Middleman";
  private final String description;
  private final MiddlemanType middlemanType;

  /**
   * Constructs a new {@link MiddlemanAction}.
   *
   * @param owner the owner of the action, usually a {@code ConfiguredTarget}
   * @param inputs inputs of the middleman, i.e. the files it acts as a placeholder for
   * @param stampFile the output of the middleman expansion; must be a middleman artifact (see
   *        {@link Artifact#isMiddlemanArtifact()})
   * @param description a short description for the action, for progress messages
   * @param middlemanType the type of the middleman
   * @throws IllegalArgumentException if {@code stampFile} is not a middleman artifact
   */
  public MiddlemanAction(ActionOwner owner, Iterable<Artifact> inputs, Artifact stampFile,
      String description, MiddlemanType middlemanType) {
    super(owner, inputs, ImmutableList.of(stampFile));
    Preconditions.checkNotNull(middlemanType);
    Preconditions.checkArgument(stampFile.isMiddlemanArtifact(), stampFile);
    this.description = description;
    this.middlemanType = middlemanType;
  }

  @Override
  public final void execute(
      ActionExecutionContext actionExecutionContext) {
    throw new IllegalStateException("MiddlemanAction should never be executed");
  }

  @Override
  protected String computeKey() {
    // TODO(bazel-team): Need to take middlemanType into account here.
    // Only the set of inputs matters, and the dependency checker is
    // responsible for considering those.
    return "";
  }

  /**
   * Returns the type of the middleman.
   */
  @Override
  public MiddlemanType getActionType() {
    return middlemanType;
  }

  @Override
  public boolean canRemoveAfterExecution() {
    // Aggregating middleman actions' inputs are needed by their output artifacts, and the type of
    // the middleman isn't known without having the action, so we just make sure it stays.
    return false;
  }

  @Override
  protected String getRawProgressMessage() {
    return null; // users don't really want to know about Middlemen.
  }

  @Override
  public String prettyPrint() {
    return description + " for " + Label.print(getOwner().getLabel());
  }

  @Override
  public String getMnemonic() {
    return MIDDLEMAN_MNEMONIC;
  }

  /**
   * Creates a new middleman action.
   */
  public static Action create(ActionRegistry env, ActionOwner owner,
      Iterable<Artifact> inputs, Artifact stampFile, String purpose, MiddlemanType middlemanType) {
    MiddlemanAction action = new MiddlemanAction(owner, inputs, stampFile, purpose, middlemanType);
    env.registerAction(action);
    return action;
  }
}