// Copyright 2016 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.common.base.Function;
import com.google.common.base.MoreObjects;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Iterables;
import com.google.common.collect.Maps;
import com.google.devtools.build.lib.actions.Artifact;
import com.google.devtools.build.lib.actions.Artifact.TreeFileArtifact;
import com.google.devtools.build.lib.actions.FileArtifactValue;
import com.google.devtools.build.lib.actions.cache.DigestUtils;
import com.google.devtools.build.lib.skyframe.serialization.autocodec.AutoCodec;
import com.google.devtools.build.lib.util.BigIntegerFingerprint;
import com.google.devtools.build.lib.vfs.Dirent;
import com.google.devtools.build.lib.vfs.Dirent.Type;
import com.google.devtools.build.lib.vfs.Path;
import com.google.devtools.build.lib.vfs.PathFragment;
import com.google.devtools.build.lib.vfs.Symlinks;
import com.google.devtools.build.skyframe.SkyValue;
import java.io.IOException;
import java.math.BigInteger;
import java.util.Arrays;
import java.util.Collection;
import java.util.Map;
import java.util.Set;
import javax.annotation.Nullable;

/**
 * Value for TreeArtifacts, which contains a digest and the {@link FileArtifactValue}s of its child
 * {@link TreeFileArtifact}s.
 */
@AutoCodec
public class TreeArtifactValue implements SkyValue {
  private static final Function<Artifact, PathFragment> PARENT_RELATIVE_PATHS =
      new Function<Artifact, PathFragment>() {
        @Override
        public PathFragment apply(Artifact artifact) {
            return artifact.getParentRelativePath();
        }
      };

  private final byte[] digest;
  private final Map<TreeFileArtifact, FileArtifactValue> childData;
  private BigInteger valueFingerprint;

  @AutoCodec.VisibleForSerialization
  TreeArtifactValue(byte[] digest, Map<TreeFileArtifact, FileArtifactValue> childData) {
    this.digest = digest;
    this.childData = ImmutableMap.copyOf(childData);
  }

  /**
   * Returns a TreeArtifactValue out of the given Artifact-relative path fragments
   * and their corresponding FileArtifactValues.
   */
  static TreeArtifactValue create(Map<TreeFileArtifact, FileArtifactValue> childFileValues) {
    Map<String, FileArtifactValue> digestBuilder =
        Maps.newHashMapWithExpectedSize(childFileValues.size());
    for (Map.Entry<TreeFileArtifact, FileArtifactValue> e : childFileValues.entrySet()) {
      digestBuilder.put(e.getKey().getParentRelativePath().getPathString(), e.getValue());
    }

    return new TreeArtifactValue(
        DigestUtils.fromMetadata(digestBuilder).getDigestBytesUnsafe(),
        ImmutableMap.copyOf(childFileValues));
  }

  FileArtifactValue getSelfData() {
    return FileArtifactValue.createProxy(digest);
  }

  FileArtifactValue getMetadata() {
    return getSelfData();
  }

  Set<PathFragment> getChildPaths() {
    return ImmutableSet.copyOf(Iterables.transform(childData.keySet(), PARENT_RELATIVE_PATHS));
  }

  @Nullable
  byte[] getDigest() {
    return digest.clone();
  }

  Iterable<TreeFileArtifact> getChildren() {
    return childData.keySet();
  }

  Map<TreeFileArtifact, FileArtifactValue> getChildValues() {
    return childData;
  }

  @Override
  public BigInteger getValueFingerprint() {
    if (valueFingerprint == null) {
      BigIntegerFingerprint fp = new BigIntegerFingerprint();
      fp.addDigestedBytes(digest);
      valueFingerprint = fp.getFingerprint();
    }
    return valueFingerprint;
  }

  @Override
  public int hashCode() {
    return Arrays.hashCode(digest);
  }

  @Override
  public boolean equals(Object other) {
    if (this == other) {
      return true;
    }

    if (!(other instanceof TreeArtifactValue)) {
      return false;
    }

    TreeArtifactValue that = (TreeArtifactValue) other;
    if (!Arrays.equals(digest, that.digest)) {
      return false;
    }

    return childData.equals(that.childData);
  }

  @Override
  public String toString() {
    return MoreObjects.toStringHelper(TreeArtifactValue.class)
        .add("digest", digest)
        .add("childData", childData)
        .toString();
  }

  /**
   * A TreeArtifactValue that represents a missing TreeArtifact. This is occasionally useful because
   * Java's concurrent collections disallow null members.
   */
  static final TreeArtifactValue MISSING_TREE_ARTIFACT =
      new TreeArtifactValue(null, ImmutableMap.<TreeFileArtifact, FileArtifactValue>of()) {
        @Override
        FileArtifactValue getSelfData() {
          throw new UnsupportedOperationException();
        }

        @Override
        Iterable<TreeFileArtifact> getChildren() {
          throw new UnsupportedOperationException();
        }

        @Override
        Map<TreeFileArtifact, FileArtifactValue> getChildValues() {
          throw new UnsupportedOperationException();
        }

        @Override
        FileArtifactValue getMetadata() {
          throw new UnsupportedOperationException();
        }

        @Override
        Set<PathFragment> getChildPaths() {
          throw new UnsupportedOperationException();
        }

        @Nullable
        @Override
        byte[] getDigest() {
          throw new UnsupportedOperationException();
        }

        @Override
        public int hashCode() {
          return 24; // my favorite number
        }

        @Override
        public boolean equals(Object other) {
          return this == other;
        }

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

  private static void explodeDirectory(Path treeArtifactPath,
      PathFragment pathToExplode, ImmutableSet.Builder<PathFragment> valuesBuilder)
      throws IOException {
    Path dir = treeArtifactPath.getRelative(pathToExplode);
    Collection<Dirent> dirents = dir.readdir(Symlinks.NOFOLLOW);
    for (Dirent dirent : dirents) {
      PathFragment canonicalSubpathFragment = pathToExplode.getChild(dirent.getName());
      if (dirent.getType() == Type.DIRECTORY) {
        explodeDirectory(treeArtifactPath, canonicalSubpathFragment, valuesBuilder);
      } else if (dirent.getType() == Type.SYMLINK) {
        Path subpath = dir.getRelative(dirent.getName());
        PathFragment linkTarget = subpath.readSymbolicLinkUnchecked();
        valuesBuilder.add(canonicalSubpathFragment);
        if (linkTarget.isAbsolute()) {
          // We tolerate absolute symlinks here. They will probably be dangling if any downstream
          // consumer tries to read them, but let that be downstream's problem.
          continue;
        }
        // We visit each path segment of the link target to catch any path traversal outside of the
        // TreeArtifact root directory. For example, for TreeArtifact a/b/c, it is possible to have
        // a symlink, a/b/c/sym_link that points to ../outside_dir/../c/link_target. Although this
        // symlink points to a file under the TreeArtifact, the link target traverses outside of the
        // TreeArtifact into a/b/outside_dir.
        PathFragment intermediatePath = canonicalSubpathFragment.getParentDirectory();
        for (String pathSegment : linkTarget.getSegments()) {
          intermediatePath = intermediatePath.getRelative(pathSegment);
          if (intermediatePath.containsUplevelReferences()) {
            String errorMessage = String.format(
                "A TreeArtifact may not contain relative symlinks whose target paths traverse "
                + "outside of the TreeArtifact, found %s pointing to %s.",
                subpath,
                linkTarget);
            throw new IOException(errorMessage);
          }
        }
      } else if (dirent.getType() == Type.FILE) {
        valuesBuilder.add(canonicalSubpathFragment);
      } else {
        // We shouldn't ever reach here.
        Path subpath = dir.getRelative(dirent.getName());
        throw new IllegalStateException("Could not determine type of file " + subpath);
      }
    }
  }

  /**
   * Recursively get all child files in a directory (excluding child directories themselves, but
   * including all files in them).
   *
   * @throws IOException if there is any problem reading or validating outputs under the given tree
   *     artifact.
   */
  public static Set<PathFragment> explodeDirectory(Path treeArtifactPath) throws IOException {
    ImmutableSet.Builder<PathFragment> explodedDirectory = ImmutableSet.builder();
    explodeDirectory(treeArtifactPath, PathFragment.EMPTY_FRAGMENT, explodedDirectory);
    return explodedDirectory.build();
  }
}