// 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.analysis.actions;

import com.google.common.base.Preconditions;
import com.google.common.collect.ImmutableSet;
import com.google.devtools.build.lib.actions.AbstractAction;
import com.google.devtools.build.lib.actions.ActionExecutionContext;
import com.google.devtools.build.lib.actions.ActionExecutionException;
import com.google.devtools.build.lib.actions.ActionKeyContext;
import com.google.devtools.build.lib.actions.ActionOwner;
import com.google.devtools.build.lib.actions.ActionResult;
import com.google.devtools.build.lib.actions.Artifact;
import com.google.devtools.build.lib.actions.Artifact.ArtifactExpander;
import com.google.devtools.build.lib.collect.nestedset.NestedSetBuilder;
import com.google.devtools.build.lib.collect.nestedset.Order;
import com.google.devtools.build.lib.server.FailureDetails;
import com.google.devtools.build.lib.server.FailureDetails.FailureDetail;
import com.google.devtools.build.lib.server.FailureDetails.SymlinkAction.Code;
import com.google.devtools.build.lib.util.DetailedExitCode;
import com.google.devtools.build.lib.util.Fingerprint;
import com.google.devtools.build.lib.vfs.Path;
import com.google.devtools.build.lib.vfs.PathFragment;
import java.io.IOException;
import javax.annotation.Nullable;

/**
 * Action to create a symlink to a known-to-exist target with alias semantics similar to a true copy
 * of the input (if any).
 */
public final class SymlinkAction extends AbstractAction {
  private static final String GUID = "7f4fab4d-d0a7-4f0f-8649-1d0337a21fee";

  /** Null when {@link #getPrimaryInput} is the target of the symlink. */
  @Nullable private final PathFragment inputPath;
  @Nullable private final String progressMessage;

  enum TargetType {
    /**
     * The symlink points into a Fileset.
     *
     * <p>If this is set, the action also updates the mtime for its target thus forcing actions
     * depending on it to be re-executed. This would not be necessary in an ideal world, but
     * dependency checking for Filesets output trees is unsound because they are directories, so we
     * need to force them to be considered changed this way. Yet Another Reason why Filests should
     * go away.
     */
    FILESET,

    /**
     * The symlink should point to an executable.
     *
     * <p>Blaze will verify that the target is indeed executable.
     */
    EXECUTABLE,

    /** Just a vanilla symlink. Don't do anything else other than creating the symlink. */
    OTHER,
  }

  private final TargetType targetType;

  public static SymlinkAction toArtifact(
      ActionOwner owner, Artifact input, Artifact output, String progressMessage) {
    return toArtifact(owner, input, output, progressMessage, /*useExecRootForSource=*/ false);
  }

  /**
   * Creates an action that creates a symlink pointing to an artifact.
   *
   * @param owner the action owner.
   * @param input the {@link Artifact} the symlink will point to
   * @param output the {@link Artifact} that will be created by executing this Action.
   * @param progressMessage the progress message.
   * @param useExecRootForSource whether to link source artifacts to exec root as opposed to the
   *     artifact itself. This indirection makes sure that the symlink is always in sync with exec
   *     root, which could go out of sync with it when re-planting the symlink tree and the header
   *     was unchanged.
   */
  public static SymlinkAction toArtifact(
      ActionOwner owner,
      Artifact input,
      Artifact output,
      String progressMessage,
      boolean useExecRootForSource) {
    return new SymlinkAction(
        owner,
        useExecRootForSource && input.isSourceArtifact() ? input.getExecPath() : null,
        input,
        output,
        progressMessage,
        TargetType.OTHER);
  }

  public static SymlinkAction toExecutable(
      ActionOwner owner, Artifact input, Artifact output, String progressMessage) {
    return new SymlinkAction(owner, null, input, output, progressMessage, TargetType.EXECUTABLE);
  }

  private SymlinkAction(
      ActionOwner owner,
      PathFragment inputPath,
      Artifact primaryInput,
      Artifact primaryOutput,
      String progressMessage,
      TargetType targetType) {
    super(
        owner,
        primaryInput != null
            ? NestedSetBuilder.create(Order.STABLE_ORDER, primaryInput)
            : NestedSetBuilder.emptySet(Order.STABLE_ORDER),
        ImmutableSet.of(primaryOutput));
    this.inputPath = inputPath;
    this.progressMessage = progressMessage;
    this.targetType = targetType;
  }

  /**
   * Creates a symlink to a Fileset.
   *
   * <p>This is different from a regular {@link SymlinkAction} in that the target is in the output
   * tree but not an artifact and that when running this action, the mtime of its target is updated
   * (necessary because dependency checking of Filesets is unsound). For more information, see the
   * Javadoc of {@code TargetType.FILESET}.
   *
   * <p><b>WARNING:</b>Do not use this for anything else other than Filesets. If you do, your
   * correctness will depend on a subtle interaction between various parts of Blaze.
   *
   * @param owner the action owner.
   * @param execPath where the symlink will point to
   * @param primaryInput the {@link Artifact} that is required to build the inputPath.
   * @param primaryOutput the {@link Artifact} that will be created by executing this Action.
   * @param progressMessage the progress message.
   */
  public static SymlinkAction toFileset(
      ActionOwner owner,
      PathFragment execPath,
      Artifact primaryInput,
      Artifact primaryOutput,
      String progressMessage) {
    Preconditions.checkState(!execPath.isAbsolute());
    return new SymlinkAction(
        owner, execPath, primaryInput, primaryOutput, progressMessage, TargetType.FILESET);
  }

  /**
   * Creates a new SymlinkAction instance, where an input artifact is not present. This is useful
   * when dealing with special cases where input paths that are outside the exec root directory
   * tree. Currently, the only instance where this happens is for FDO builds where the profile file
   * is outside the exec root structure.
   *
   * <p>Do <b>NOT</b> use this method unless there is no other way; unconditionally executed actions
   * are costly: even if change pruning kicks in and downstream actions are not re-executed, they
   * trigger unconditional Skyframe invalidation of their reverse dependencies.
   *
   * @param owner the action owner.
   * @param absolutePath where the symlink will point to
   * @param output the Artifact that will be created by executing this Action.
   * @param progressMessage the progress message.
   */
  public static SymlinkAction toAbsolutePath(ActionOwner owner, PathFragment absolutePath,
      Artifact output, String progressMessage) {
    Preconditions.checkState(absolutePath.isAbsolute());
    return new SymlinkAction(owner, absolutePath, null, output, progressMessage, TargetType.OTHER);
  }

  public PathFragment getInputPath() {
    return inputPath == null ? getPrimaryInput().getExecPath() : inputPath;
  }

  public Path getOutputPath(ActionExecutionContext actionExecutionContext) {
    return actionExecutionContext.getInputPath(getPrimaryOutput());
  }

  @Override
  public ActionResult execute(ActionExecutionContext actionExecutionContext)
      throws ActionExecutionException {
    maybeVerifyTargetIsExecutable(actionExecutionContext);

    Path srcPath;
    if (inputPath == null) {
      srcPath = actionExecutionContext.getInputPath(getPrimaryInput());
    } else {
      srcPath = actionExecutionContext.getExecRoot().getRelative(inputPath);
    }

    Path outputPath = getOutputPath(actionExecutionContext);

    try {
      // Delete the empty output directory created prior to the action execution when the output is
      // a tree artifact. All other actions that produce tree artifacts expect it to exist prior to
      // their execution. It's not worth complicating ActionOutputDirectoryHelper just to avoid this
      // small amount of overhead.
      outputPath.delete();

      outputPath.createSymbolicLink(srcPath);
    } catch (IOException e) {
      String message =
          String.format(
              "failed to create symbolic link '%s' to '%s' due to I/O error: %s",
              getPrimaryOutput().getExecPathString(), printInputs(), e.getMessage());
      DetailedExitCode code = createDetailedExitCode(message, Code.LINK_CREATION_IO_EXCEPTION);
      throw new ActionExecutionException(message, e, this, false, code);
    }

    updateInputMtimeIfNeeded(actionExecutionContext);
    return ActionResult.EMPTY;
  }

  private void maybeVerifyTargetIsExecutable(ActionExecutionContext actionExecutionContext)
      throws ActionExecutionException {
    if (targetType != TargetType.EXECUTABLE) {
      return;
    }

    Path inputPath = actionExecutionContext.getInputPath(getPrimaryInput());
    try {
      // Validate that input path is a file with the executable bit set.
      if (!inputPath.isFile()) {
        String message = String.format("'%s' is not a file", getPrimaryInput().getExecPathString());
        throw new ActionExecutionException(
            message, this, false, createDetailedExitCode(message, Code.EXECUTABLE_INPUT_NOT_FILE));
      }
      if (!inputPath.isExecutable()) {
        String message =
            String.format(
                "failed to create symbolic link '%s': file '%s' is not executable",
                getPrimaryOutput().getExecPathString(), getPrimaryInput().getExecPathString());
        throw new ActionExecutionException(
            message, this, false, createDetailedExitCode(message, Code.EXECUTABLE_INPUT_IS_NOT));
      }
    } catch (IOException e) {
      String message =
          String.format(
              "failed to create symbolic link '%s' to the '%s' due to I/O error: %s",
              getPrimaryOutput().getExecPathString(),
              getPrimaryInput().getExecPathString(),
              e.getMessage());
      DetailedExitCode detailedExitCode =
          createDetailedExitCode(message, Code.EXECUTABLE_INPUT_CHECK_IO_EXCEPTION);
      throw new ActionExecutionException(message, e, this, false, detailedExitCode);
    }
  }

  private void updateInputMtimeIfNeeded(ActionExecutionContext actionExecutionContext)
      throws ActionExecutionException {
    if (targetType != TargetType.FILESET) {
      return;
    }

    try {
      // Update the mtime of the target of the symlink to force downstream re-execution of actions.
      // This is needed because dependency checking of Fileset output trees is unsound (it's a
      // directory).
      // Note that utime() on a symlink actually changes the mtime of its target.
      Path linkPath = getOutputPath(actionExecutionContext);
      if (linkPath.exists()) {
        linkPath.setLastModifiedTime(Path.NOW_SENTINEL_TIME);
      } else {
        // Should only happen if the Fileset included no links.
        actionExecutionContext
            .getExecRoot()
            .getRelative(getInputPath())
            .createDirectoryAndParents();
      }
    } catch (IOException e) {
      String message =
          String.format(
              "failed to touch symbolic link '%s' to the '%s' due to I/O error: %s",
              getPrimaryOutput().getExecPathString(),
              getPrimaryInput().getExecPathString(),
              e.getMessage());
      DetailedExitCode code = createDetailedExitCode(message, Code.LINK_TOUCH_IO_EXCEPTION);
      throw new ActionExecutionException(message, e, this, false, code);
    }
  }

  private String printInputs() {
    if (getInputs().isEmpty()) {
      return inputPath.getPathString();
    } else if (getInputs().isSingleton()) {
      return getPrimaryInput().getExecPathString();
    } else {
      throw new IllegalStateException(
          "Inputs unexpectedly contains more than 1 element: " + getInputs());
    }
  }

  @Override
  protected void computeKey(
      ActionKeyContext actionKeyContext,
      @Nullable ArtifactExpander artifactExpander,
      Fingerprint fp) {
    fp.addString(GUID);
    // We don't normally need to add inputs to the key. In this case, however, the inputPath can be
    // different from the actual input artifact.
    if (inputPath != null) {
      fp.addPath(inputPath);
    }
  }

  @Override
  public String getMnemonic() {
    return targetType == TargetType.EXECUTABLE ? "ExecutableSymlink" : "Symlink";
  }

  @Override
  public boolean isVolatile() {
    return inputPath != null && inputPath.isAbsolute();
  }

  @Override
  public boolean executeUnconditionally() {
    // If the SymlinkAction points to an absolute path, we can't verify that its output artifact did
    // not change purely by looking at the output tree. Thus, we re-execute the action just to be
    // safe. Change pruning will take care of not re-running dependent actions and this is used only
    // in very rare cases (only C++ FDO and even then, only twice per build at most) anyway.
    return inputPath != null && inputPath.isAbsolute();
  }

  @Override
  protected String getRawProgressMessage() {
    return progressMessage;
  }

  @Override
  public boolean mayInsensitivelyPropagateInputs() {
    return true;
  }

  private static DetailedExitCode createDetailedExitCode(String message, Code detailedCode) {
    return DetailedExitCode.of(
        FailureDetail.newBuilder()
            .setMessage(message)
            .setSymlinkAction(FailureDetails.SymlinkAction.newBuilder().setCode(detailedCode))
            .build());
  }
}