// Copyright 2017 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.skyframe;

import com.google.devtools.build.lib.util.Preconditions;
import com.google.devtools.build.skyframe.SkyKey;
import com.google.devtools.build.skyframe.SkyValue;
import java.util.Objects;
import javax.annotation.Nullable;

/**
 * A value that solely represents the 'name' of a Bazel workspace, as defined in the WORKSPACE file.
 *
 * <p>This is a separate value with trivial change pruning so as to not necessitate a dependency
 * from every {@link PackageValue} to the //external {@link PackageValue}, since such a
 * hypothetical design would necessitate reloading all packages whenever there's a benign change to
 * the WORKSPACE file.
 */
public class WorkspaceNameValue implements SkyValue {
  private static final SkyKey KEY =
      SkyKey.create(SkyFunctions.WORKSPACE_NAME, DummyArgument.INSTANCE);
  private static final WorkspaceNameValue ERROR = new WorkspaceNameValue(null);

  @Nullable
  private final String workspaceName;

  private WorkspaceNameValue(@Nullable String workspaceName) {
    this.workspaceName = workspaceName;
  }

  /**
   * Returns the name of the workspace, or {@code null} if there was an error in the WORKSPACE file.
   */
  @Nullable
  public String maybeGetName() {
    return workspaceName;
  }

  /** Returns the (singleton) {@link SkyKey} for {@link WorkspaceNameValue}s. */
  public static SkyKey key() {
    return KEY;
  }

  /** Returns a {@link WorkspaceNameValue} for a workspace whose WORKSPACE file is in error. */
  public static WorkspaceNameValue withError() {
    return WorkspaceNameValue.ERROR;
  }

  /** Returns a {@link WorkspaceNameValue} for a workspace with the given name. */
  public static WorkspaceNameValue withName(String workspaceName) {
    return new WorkspaceNameValue(Preconditions.checkNotNull(workspaceName));
  }

  @Override
  public boolean equals(Object obj) {
    if (!(obj instanceof WorkspaceNameValue)) {
      return false;
    }
    WorkspaceNameValue other = (WorkspaceNameValue) obj;
    return Objects.equals(workspaceName, other.workspaceName);
  }

  @Override
  public int hashCode() {
    return Objects.hash(workspaceName);
  }

  @Override
  public String toString() {
    return String.format("WorkspaceNameValue[name=%s]", workspaceName);
  }

  /** Singleton class used as the {@link SkyKey#argument} for {@link WorkspaceNameValue#key}. */
  public static final class DummyArgument {
    public static final int HASHCODE = DummyArgument.class.getCanonicalName().hashCode();
    public static final DummyArgument INSTANCE = new DummyArgument();

    private DummyArgument() {
    }

    @Override
    public boolean equals(Object obj) {
      return obj instanceof DummyArgument;
    }

    @Override
    public int hashCode() {
      return HASHCODE;
    }

    @Override
    public String toString() {
      return "#";
    }
  }
}
