// Copyright (C) 2013 The Android Open Source Project
//
// 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.gerrit.server.index.change;

import static com.google.common.base.Preconditions.checkState;
import static com.google.common.util.concurrent.Futures.successfulAsList;
import static com.google.common.util.concurrent.Futures.transform;
import static com.google.common.util.concurrent.MoreExecutors.directExecutor;
import static com.google.gerrit.server.git.QueueProvider.QueueType.BATCH;

import com.google.common.base.Stopwatch;
import com.google.common.flogger.FluentLogger;
import com.google.common.primitives.Ints;
import com.google.common.util.concurrent.ListenableFuture;
import com.google.common.util.concurrent.ListeningExecutorService;
import com.google.common.util.concurrent.UncheckedExecutionException;
import com.google.gerrit.entities.Change;
import com.google.gerrit.entities.Project;
import com.google.gerrit.entities.RefNames;
import com.google.gerrit.index.SiteIndexer;
import com.google.gerrit.server.git.GitRepositoryManager;
import com.google.gerrit.server.git.MultiProgressMonitor;
import com.google.gerrit.server.git.MultiProgressMonitor.Task;
import com.google.gerrit.server.index.IndexExecutor;
import com.google.gerrit.server.index.OnlineReindexMode;
import com.google.gerrit.server.notedb.ChangeNotes;
import com.google.gerrit.server.notedb.ChangeNotes.Factory.ChangeNotesResult;
import com.google.gerrit.server.project.ProjectCache;
import com.google.gerrit.server.query.change.ChangeData;
import com.google.inject.Inject;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Objects;
import java.util.concurrent.Callable;
import java.util.concurrent.RejectedExecutionException;
import java.util.concurrent.atomic.AtomicBoolean;
import org.eclipse.jgit.errors.RepositoryNotFoundException;
import org.eclipse.jgit.lib.ProgressMonitor;
import org.eclipse.jgit.lib.Repository;
import org.eclipse.jgit.lib.TextProgressMonitor;

/**
 * Implementation that can index all changes on a host or within a project. Used by Gerrit's
 * initialization and upgrade programs as well as by REST API endpoints that offer this
 * functionality.
 */
public class AllChangesIndexer extends SiteIndexer<Change.Id, ChangeData, ChangeIndex> {
  private static final FluentLogger logger = FluentLogger.forEnclosingClass();
  private static final int PROJECT_SLICE_MAX_REFS = 1000;

  private final ChangeData.Factory changeDataFactory;
  private final GitRepositoryManager repoManager;
  private final ListeningExecutorService executor;
  private final ChangeIndexer.Factory indexerFactory;
  private final ChangeNotes.Factory notesFactory;
  private final ProjectCache projectCache;

  @Inject
  AllChangesIndexer(
      ChangeData.Factory changeDataFactory,
      GitRepositoryManager repoManager,
      @IndexExecutor(BATCH) ListeningExecutorService executor,
      ChangeIndexer.Factory indexerFactory,
      ChangeNotes.Factory notesFactory,
      ProjectCache projectCache) {
    this.changeDataFactory = changeDataFactory;
    this.repoManager = repoManager;
    this.executor = executor;
    this.indexerFactory = indexerFactory;
    this.notesFactory = notesFactory;
    this.projectCache = projectCache;
  }

  private static class ProjectSlice {
    private final Project.NameKey name;
    private final int slice;
    private final int slices;

    ProjectSlice(Project.NameKey name, int slice, int slices) {
      this.name = name;
      this.slice = slice;
      this.slices = slices;
    }

    public Project.NameKey getName() {
      return name;
    }

    public int getSlice() {
      return slice;
    }

    public int getSlices() {
      return slices;
    }
  }

  @Override
  public Result indexAll(ChangeIndex index) {
    ProgressMonitor pm = new TextProgressMonitor();
    pm.beginTask("Collecting projects", ProgressMonitor.UNKNOWN);
    List<ProjectSlice> projectSlices = new ArrayList<>();
    int changeCount = 0;
    Stopwatch sw = Stopwatch.createStarted();
    int projectsFailed = 0;
    for (Project.NameKey name : projectCache.all()) {
      try (Repository repo = repoManager.openRepository(name)) {
        // The simplest approach to distribute indexing would be to let each thread grab a project
        // and index it fully. But if a site has one big project and 100s of small projects, then
        // in the beginning all CPUs would be busy reindexing projects. But soon enough all small
        // projects have been reindexed, and only the thread that reindexes the big project is
        // still working. The other threads would idle. Reindexing the big project on a single
        // thread becomes the critical path. Bringing in more CPUs would not speed up things.
        //
        // To avoid such situations, we split big repos into smaller parts and let
        // the thread pool index these smaller parts. This splitting introduces an overhead in the
        // workload setup and there might be additional slow-downs from multiple threads
        // concurrently working on different parts of the same project. But for Wikimedia's Gerrit,
        // which had 2 big projects, many middle sized ones, and lots of smaller ones, the
        // splitting of repos into smaller parts reduced indexing time from 1.5 hours to 55 minutes
        // in 2020.
        int size = estimateSize(repo);
        changeCount += size;
        int slices = 1 + size / PROJECT_SLICE_MAX_REFS;
        if (slices > 1) {
          verboseWriter.println("Submitting " + name + " for indexing in " + slices + " slices");
        }
        for (int slice = 0; slice < slices; slice++) {
          projectSlices.add(new ProjectSlice(name, slice, slices));
        }
      } catch (IOException e) {
        logger.atSevere().withCause(e).log("Error collecting project %s", name);
        projectsFailed++;
        if (projectsFailed > projectCache.all().size() / 2) {
          logger.atSevere().log("Over 50%% of the projects could not be collected: aborted");
          return Result.create(sw, false, 0, 0);
        }
      }
      pm.update(1);
    }
    pm.endTask();
    setTotalWork(changeCount);

    // projectSlices are currently grouped by projects. First all slices for project1, followed
    // by all slices for project2, and so on. As workers pick tasks sequentially, multiple threads
    // would typically work concurrently on different slices of the same project. While this is not
    // a big issue, shuffling the list beforehand helps with ungrouping the project slices, so
    // different slices are less likely to be worked on concurrently.
    // This shuffling gave a 6% runtime reduction for Wikimedia's Gerrit in 2020.
    Collections.shuffle(projectSlices);
    return indexAll(index, projectSlices);
  }

  private int estimateSize(Repository repo) throws IOException {
    // Estimate size based on IDs that show up in ref names. This is not perfect, since patch set
    // refs may exist for changes whose metadata was never successfully stored. But that's ok, as
    // the estimate is just used as a heuristic for sorting projects.
    long size =
        repo.getRefDatabase().getRefsByPrefix(RefNames.REFS_CHANGES).stream()
            .map(r -> Change.Id.fromRef(r.getName()))
            .filter(Objects::nonNull)
            .distinct()
            .count();
    return Ints.saturatedCast(size);
  }

  private SiteIndexer.Result indexAll(ChangeIndex index, List<ProjectSlice> projectSlices) {
    Stopwatch sw = Stopwatch.createStarted();
    MultiProgressMonitor mpm = new MultiProgressMonitor(progressOut, "Reindexing changes");
    Task projTask = mpm.beginSubTask("project-slices", projectSlices.size());
    checkState(totalWork >= 0);
    Task doneTask = mpm.beginSubTask(null, totalWork);
    Task failedTask = mpm.beginSubTask("failed", MultiProgressMonitor.UNKNOWN);

    List<ListenableFuture<?>> futures = new ArrayList<>();
    AtomicBoolean ok = new AtomicBoolean(true);

    for (ProjectSlice projectSlice : projectSlices) {
      Project.NameKey name = projectSlice.getName();
      int slice = projectSlice.getSlice();
      int slices = projectSlice.getSlices();
      ListenableFuture<?> future =
          executor.submit(
              reindexProject(
                  indexerFactory.create(executor, index),
                  name,
                  slice,
                  slices,
                  doneTask,
                  failedTask));
      String description = "project " + name + " (" + slice + "/" + slices + ")";
      addErrorListener(future, description, projTask, ok);
      futures.add(future);
    }

    try {
      mpm.waitFor(
          transform(
              successfulAsList(futures),
              x -> {
                mpm.end();
                return null;
              },
              directExecutor()));
    } catch (UncheckedExecutionException e) {
      logger.atSevere().withCause(e).log("Error in batch indexer");
      ok.set(false);
    }
    // If too many changes failed, maybe there was a bug in the indexer. Don't
    // trust the results. This is not an exact percentage since we bump the same
    // failure counter if a project can't be read, but close enough.
    int nFailed = failedTask.getCount();
    int nDone = doneTask.getCount();
    int nTotal = nFailed + nDone;
    double pctFailed = ((double) nFailed) / nTotal * 100;
    if (pctFailed > 10) {
      logger.atSevere().log(
          "Failed %s/%s changes (%s%%); not marking new index as ready",
          nFailed, nTotal, Math.round(pctFailed));
      ok.set(false);
    }
    return Result.create(sw, ok.get(), nDone, nFailed);
  }

  public Callable<Void> reindexProject(
      ChangeIndexer indexer, Project.NameKey project, Task done, Task failed) {
    return reindexProject(indexer, project, 0, 1, done, failed);
  }

  public Callable<Void> reindexProject(
      ChangeIndexer indexer,
      Project.NameKey project,
      int slice,
      int slices,
      Task done,
      Task failed) {
    return new ProjectIndexer(indexer, project, slice, slices, done, failed);
  }

  private class ProjectIndexer implements Callable<Void> {
    private final ChangeIndexer indexer;
    private final Project.NameKey project;
    private final int slice;
    private final int slices;
    private final ProgressMonitor done;
    private final ProgressMonitor failed;

    private ProjectIndexer(
        ChangeIndexer indexer,
        Project.NameKey project,
        int slice,
        int slices,
        ProgressMonitor done,
        ProgressMonitor failed) {
      this.indexer = indexer;
      this.project = project;
      this.slice = slice;
      this.slices = slices;
      this.done = done;
      this.failed = failed;
    }

    @Override
    public Void call() throws Exception {
      try (Repository repo = repoManager.openRepository(project)) {
        OnlineReindexMode.begin();

        // Order of scanning changes is undefined. This is ok if we assume that packfile locality is
        // not important for indexing, since sites should have a fully populated DiffSummary cache.
        // It does mean that reindexing after invalidating the DiffSummary cache will be expensive,
        // but the goal is to invalidate that cache as infrequently as we possibly can. And besides,
        // we don't have concrete proof that improving packfile locality would help.
        notesFactory.scan(repo, project, id -> (id.get() % slices) == slice).forEach(r -> index(r));
      } catch (RepositoryNotFoundException rnfe) {
        logger.atSevere().log(rnfe.getMessage());
      } finally {
        OnlineReindexMode.end();
      }
      return null;
    }

    private void index(ChangeNotesResult r) {
      if (r.error().isPresent()) {
        fail("Failed to read change " + r.id() + " for indexing", true, r.error().get());
        return;
      }
      try {
        indexer.index(changeDataFactory.create(r.notes()));
        done.update(1);
        verboseWriter.format(
            "Reindexed change %d (project: %s)\n", r.id().get(), r.notes().getProjectName().get());
      } catch (RejectedExecutionException e) {
        // Server shutdown, don't spam the logs.
        failSilently();
      } catch (Exception e) {
        fail("Failed to index change " + r.id(), true, e);
      }
    }

    private void fail(String error, boolean failed, Exception e) {
      if (failed) {
        this.failed.update(1);
      }

      logger.atWarning().withCause(e).log(error);
      verboseWriter.println(error);
    }

    private void failSilently() {
      this.failed.update(1);
    }

    @Override
    public String toString() {
      return "Index all changes of project " + project.get();
    }
  }
}