// Copyright 2019 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.exec;

import com.google.common.collect.ImmutableMap;
import com.google.devtools.build.lib.actions.Artifact;
import com.google.devtools.build.lib.actions.ExecException;
import com.google.devtools.build.lib.actions.RunfilesSupplier;
import com.google.devtools.build.lib.analysis.RunfilesSupport;
import com.google.devtools.build.lib.runtime.CommandEnvironment;
import com.google.devtools.build.lib.util.io.OutErr;
import com.google.devtools.build.lib.vfs.DigestUtils;
import com.google.devtools.build.lib.vfs.Path;
import com.google.devtools.build.lib.vfs.PathFragment;
import com.google.devtools.build.lib.vfs.XattrProvider;
import java.io.IOException;
import java.util.Arrays;
import java.util.Map;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ConcurrentHashMap;
import javax.annotation.concurrent.ThreadSafe;

/**
 * Utility used in local execution to create a runfiles tree if {@code --nobuild_runfile_links} has
 * been specified.
 *
 * <p>It is safe to call {@link #updateRunfiles} concurrently.
 */
@ThreadSafe
public class RunfilesTreeUpdater {
  private final Path execRoot;
  private final BinTools binTools;
  private final XattrProvider xattrProvider;

  /**
   * Deduplicates multiple attempts to update the same runfiles tree.
   *
   * <p>Attempts may occur concurrently, e.g. if multiple local actions have the same input.
   *
   * <p>The presence of an entry in the map signifies that an earlier attempt to update the
   * corresponding runfiles tree was started, and will (have) set the future upon completion.
   */
  private final ConcurrentHashMap<PathFragment, CompletableFuture<Void>> updatedTrees =
      new ConcurrentHashMap<>();

  public static RunfilesTreeUpdater forCommandEnvironment(CommandEnvironment env) {
    return new RunfilesTreeUpdater(
        env.getExecRoot(), env.getBlazeWorkspace().getBinTools(), env.getXattrProvider());
  }

  public RunfilesTreeUpdater(Path execRoot, BinTools binTools, XattrProvider xattrProvider) {
    this.execRoot = execRoot;
    this.binTools = binTools;
    this.xattrProvider = xattrProvider;
  }

  /** Creates or updates input runfiles trees for a spawn. */
  public void updateRunfiles(
      RunfilesSupplier runfilesSupplier, ImmutableMap<String, String> env, OutErr outErr)
      throws ExecException, IOException, InterruptedException {
    for (Map.Entry<PathFragment, Map<PathFragment, Artifact>> runfiles :
        runfilesSupplier.getMappings().entrySet()) {
      PathFragment runfilesDir = runfiles.getKey();
      if (runfilesSupplier.isBuildRunfileLinks(runfilesDir)) {
        continue;
      }

      var freshFuture = new CompletableFuture<Void>();
      CompletableFuture<Void> priorFuture = updatedTrees.putIfAbsent(runfilesDir, freshFuture);

      if (priorFuture == null) {
        // We are the first attempt; update the runfiles tree and mark the future complete.
        try {
          updateRunfilesTree(
              runfilesDir, env, outErr, !runfilesSupplier.isRunfileLinksEnabled(runfilesDir));
          freshFuture.complete(null);
        } catch (Exception e) {
          freshFuture.completeExceptionally(e);
          throw e;
        }
      } else {
        // There was a previous attempt; wait for it to complete.
        priorFuture.join();
      }
    }
  }

  private void updateRunfilesTree(
      PathFragment runfilesDir,
      ImmutableMap<String, String> env,
      OutErr outErr,
      boolean manifestOnly)
      throws IOException, ExecException, InterruptedException {
    Path runfilesDirPath = execRoot.getRelative(runfilesDir);
    Path inputManifest = RunfilesSupport.inputManifestPath(runfilesDirPath);
    if (!inputManifest.exists()) {
      return;
    }

    Path outputManifest = RunfilesSupport.outputManifestPath(runfilesDirPath);
    try {
      // Avoid rebuilding the runfiles directory if the manifest in it matches the input manifest,
      // implying the symlinks exist and are already up to date. If the output manifest is a
      // symbolic link, it is likely a symbolic link to the input manifest, so we cannot trust it as
      // an up-to-date check.
      if (!outputManifest.isSymbolicLink()
          && Arrays.equals(
              DigestUtils.getDigestWithManualFallbackWhenSizeUnknown(outputManifest, xattrProvider),
              DigestUtils.getDigestWithManualFallbackWhenSizeUnknown(
                  inputManifest, xattrProvider))) {
        return;
      }
    } catch (IOException e) {
      // Ignore it - we will just try to create runfiles directory.
    }

    if (!runfilesDirPath.exists()) {
      runfilesDirPath.createDirectoryAndParents();
    }

    SymlinkTreeHelper helper =
        new SymlinkTreeHelper(inputManifest, runfilesDirPath, /* filesetTree= */ false);
    helper.createSymlinks(execRoot, outErr, binTools, env, manifestOnly);
  }
}