// Copyright (C) 2020 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.plugins.codeowners.backend;

import static com.google.common.base.Preconditions.checkState;
import static com.google.common.collect.ImmutableSet.toImmutableSet;
import static java.util.Objects.requireNonNull;

import com.google.common.collect.ImmutableSet;
import com.google.common.flogger.FluentLogger;
import com.google.gerrit.entities.Account;
import com.google.gerrit.entities.BranchNameKey;
import com.google.gerrit.entities.Change;
import com.google.gerrit.entities.PatchSetApproval;
import com.google.gerrit.entities.Project;
import com.google.gerrit.exceptions.StorageException;
import com.google.gerrit.extensions.restapi.ResourceConflictException;
import com.google.gerrit.plugins.codeowners.api.CodeOwnerStatus;
import com.google.gerrit.plugins.codeowners.config.CodeOwnersPluginConfiguration;
import com.google.gerrit.plugins.codeowners.config.RequiredApproval;
import com.google.gerrit.server.ApprovalsUtil;
import com.google.gerrit.server.git.GitRepositoryManager;
import com.google.gerrit.server.logging.Metadata;
import com.google.gerrit.server.logging.TraceContext;
import com.google.gerrit.server.logging.TraceContext.TraceTimer;
import com.google.gerrit.server.notedb.ChangeNotes;
import com.google.gerrit.server.notedb.ReviewerStateInternal;
import com.google.gerrit.server.patch.PatchListNotAvailableException;
import com.google.gerrit.server.permissions.PermissionBackend;
import com.google.gerrit.server.permissions.PermissionBackendException;
import com.google.gerrit.server.permissions.ProjectPermission;
import com.google.inject.Inject;
import com.google.inject.Provider;
import com.google.inject.Singleton;
import java.io.IOException;
import java.nio.file.Path;
import java.util.Collections;
import java.util.Optional;
import java.util.concurrent.atomic.AtomicReference;
import java.util.stream.Stream;
import java.util.stream.StreamSupport;
import org.eclipse.jgit.lib.ObjectId;
import org.eclipse.jgit.lib.Ref;
import org.eclipse.jgit.lib.Repository;
import org.eclipse.jgit.revwalk.RevWalk;

/**
 * Class to check code owner approvals on a change.
 *
 * <p>Every file, or rather touched path, in a change needs to be approved by a code owner:
 *
 * <ul>
 *   <li>New file: requires approval on the new path
 *   <li>Modified file: requires approval on the old/new path (old path == new path)
 *   <li>Deleted file: requires approval on the old path
 *   <li>Renamed file: requires approval on the old and new path (equivalent to delete old path +
 *       add new path)
 *   <li>Copied file: requires approval on the new path (an approval on the old path is not needed
 *       since the file at this path was not touched)
 * </ul>
 */
@Singleton
public class CodeOwnerApprovalCheck {
  private static final FluentLogger logger = FluentLogger.forEnclosingClass();

  private final PermissionBackend permissionBackend;
  private final GitRepositoryManager repoManager;
  private final CodeOwnersPluginConfiguration codeOwnersPluginConfiguration;
  private final ChangedFiles changedFiles;
  private final CodeOwnerConfigScanner.Factory codeOwnerConfigScannerFactory;
  private final CodeOwnerConfigHierarchy codeOwnerConfigHierarchy;
  private final Provider<CodeOwnerResolver> codeOwnerResolver;
  private final ApprovalsUtil approvalsUtil;

  @Inject
  CodeOwnerApprovalCheck(
      PermissionBackend permissionBackend,
      GitRepositoryManager repoManager,
      CodeOwnersPluginConfiguration codeOwnersPluginConfiguration,
      ChangedFiles changedFiles,
      CodeOwnerConfigScanner.Factory codeOwnerConfigScannerFactory,
      CodeOwnerConfigHierarchy codeOwnerConfigHierarchy,
      Provider<CodeOwnerResolver> codeOwnerResolver,
      ApprovalsUtil approvalsUtil) {
    this.permissionBackend = permissionBackend;
    this.repoManager = repoManager;
    this.codeOwnersPluginConfiguration = codeOwnersPluginConfiguration;
    this.changedFiles = changedFiles;
    this.codeOwnerConfigScannerFactory = codeOwnerConfigScannerFactory;
    this.codeOwnerConfigHierarchy = codeOwnerConfigHierarchy;
    this.codeOwnerResolver = codeOwnerResolver;
    this.approvalsUtil = approvalsUtil;
  }

  /**
   * Whether the given change has sufficient code owner approvals to be submittable.
   *
   * @param changeNotes the change notes
   * @return whether the given change has sufficient code owner approvals to be submittable
   */
  public boolean isSubmittable(ChangeNotes changeNotes)
      throws ResourceConflictException, IOException, PatchListNotAvailableException {
    requireNonNull(changeNotes, "changeNotes");
    logger.atFine().log(
        "checking if change %d in project %s is submittable",
        changeNotes.getChangeId().get(), changeNotes.getProjectName());
    boolean isSubmittable =
        !getFileStatuses(changeNotes)
            .anyMatch(
                fileStatus ->
                    (fileStatus.newPathStatus().isPresent()
                            && fileStatus.newPathStatus().get().status()
                                != CodeOwnerStatus.APPROVED)
                        || (fileStatus.oldPathStatus().isPresent()
                            && fileStatus.oldPathStatus().get().status()
                                != CodeOwnerStatus.APPROVED));
    logger.atFine().log(
        "change %d in project %s %s submittable",
        changeNotes.getChangeId().get(),
        changeNotes.getProjectName(),
        isSubmittable ? "is" : "is not");
    return isSubmittable;
  }

  /**
   * Gets the code owner statuses for all files/paths that were changed in the current revision of
   * the given change.
   *
   * <p>The code owner statuses tell the user which code owner approvals are still missing in order
   * to make the change submittable.
   *
   * <p>Computing the code owner statuses for non-current revisions is not supported since the
   * semantics are unclear, e.g.:
   *
   * <ul>
   *   <li>non-current revisions are never submittable, hence asking which code owner approvals are
   *       still missing in order to make the revision submittable makes no sense
   *   <li>the code owner status {@link CodeOwnerStatus#PENDING} doesn't make sense for an old
   *       revision, from the perspective of the change owner this status looks like the change is
   *       waiting for the code owner to approve, but since voting on old revisions is not possible
   *       the code-owner is not able to provide this approval
   *   <li>the code owner statuses are computed from the approvals that were given by code owners,
   *       the UI always shows the current approval even when looking at an old revision, showing
   *       code owner statuses that mismatch the shown approvals (because they are computed from
   *       approvals that were present on an old revision) would only confuse users
   * </ul>
   *
   * @param changeNotes the notes of the change for which the current code owner statuses should be
   *     returned
   */
  public Stream<FileCodeOwnerStatus> getFileStatuses(ChangeNotes changeNotes)
      throws ResourceConflictException, IOException, PatchListNotAvailableException {
    requireNonNull(changeNotes, "changeNotes");
    try (TraceTimer traceTimer =
        TraceContext.newTimer(
            "Compute file statuses",
            Metadata.builder()
                .projectName(changeNotes.getProjectName().get())
                .changeId(changeNotes.getChangeId().get())
                .build())) {
      RequiredApproval requiredApproval =
          codeOwnersPluginConfiguration.getRequiredApproval(changeNotes.getProjectName());
      logger.atFine().log("requiredApproval = %s", requiredApproval);

      ImmutableSet<RequiredApproval> overrideApprovals =
          codeOwnersPluginConfiguration.getOverrideApproval(changeNotes.getProjectName());
      boolean hasOverride = hasOverride(overrideApprovals, changeNotes);
      logger.atFine().log(
          "hasOverride = %s (overrideApprovals = %s)", hasOverride, overrideApprovals);

      BranchNameKey branch = changeNotes.getChange().getDest();
      ObjectId revision = getDestBranchRevision(changeNotes.getChange());
      logger.atFine().log("dest branch %s has revision %s", branch.branch(), revision.name());

      boolean enableImplicitApprovalFromUploader =
          codeOwnersPluginConfiguration.areImplicitApprovalsEnabled(changeNotes.getProjectName());
      Account.Id patchSetUploader = changeNotes.getCurrentPatchSet().uploader();
      logger.atFine().log(
          "patchSetUploader = %d, implicit approval from uploader is %s",
          patchSetUploader.get(), enableImplicitApprovalFromUploader ? "enabled" : "disabled");

      CodeOwnerResolverResult globalCodeOwners =
          codeOwnerResolver
              .get()
              .enforceVisibility(false)
              .resolveGlobalCodeOwners(changeNotes.getProjectName());
      logger.atFine().log("global code owners = %s", globalCodeOwners);

      // If the branch doesn't contain any code owner config file yet, we apply special logic
      // (project
      // owners count as code owners) to allow bootstrapping the code owner configuration in the
      // branch.
      boolean isBootstrapping =
          !codeOwnerConfigScannerFactory.create().containsAnyCodeOwnerConfigFile(branch);
      logger.atFine().log("isBootstrapping = %s", isBootstrapping);

      ImmutableSet<Account.Id> reviewerAccountIds = getReviewerAccountIds(changeNotes);
      ImmutableSet<Account.Id> approverAccountIds =
          getApproverAccountIds(requiredApproval, changeNotes);
      logger.atFine().log("reviewers = %s, approvers = %s", reviewerAccountIds, approverAccountIds);

      return changedFiles
          .compute(changeNotes.getProjectName(), changeNotes.getCurrentPatchSet().commitId())
          .stream()
          .map(
              changedFile ->
                  getFileStatus(
                      branch,
                      revision,
                      globalCodeOwners,
                      enableImplicitApprovalFromUploader,
                      patchSetUploader,
                      reviewerAccountIds,
                      approverAccountIds,
                      hasOverride,
                      isBootstrapping,
                      changedFile));
    }
  }

  private FileCodeOwnerStatus getFileStatus(
      BranchNameKey branch,
      ObjectId revision,
      CodeOwnerResolverResult globalCodeOwners,
      boolean enableImplicitApprovalFromUploader,
      Account.Id patchSetUploader,
      ImmutableSet<Account.Id> reviewerAccountIds,
      ImmutableSet<Account.Id> approverAccountIds,
      boolean hasOverride,
      boolean isBootstrapping,
      ChangedFile changedFile) {
    logger.atFine().log("computing file status for %s", changedFile);

    // Compute the code owner status for the new path, if there is a new path.
    Optional<PathCodeOwnerStatus> newPathStatus =
        changedFile
            .newPath()
            .map(
                newPath ->
                    getPathCodeOwnerStatus(
                        branch,
                        revision,
                        globalCodeOwners,
                        enableImplicitApprovalFromUploader,
                        patchSetUploader,
                        reviewerAccountIds,
                        approverAccountIds,
                        hasOverride,
                        isBootstrapping,
                        newPath));

    // Compute the code owner status for the old path, if the file was deleted or renamed.
    Optional<PathCodeOwnerStatus> oldPathStatus = Optional.empty();
    if (changedFile.isDeletion() || changedFile.isRename()) {
      checkState(changedFile.oldPath().isPresent(), "old path must be present for deletion/rename");
      logger.atFine().log(
          "file was %s (old path = %s)",
          changedFile.isDeletion() ? "deleted" : "renamed", changedFile.oldPath().get());
      oldPathStatus =
          Optional.of(
              getPathCodeOwnerStatus(
                  branch,
                  revision,
                  globalCodeOwners,
                  enableImplicitApprovalFromUploader,
                  patchSetUploader,
                  reviewerAccountIds,
                  approverAccountIds,
                  hasOverride,
                  isBootstrapping,
                  changedFile.oldPath().get()));
    }

    FileCodeOwnerStatus fileCodeOwnerStatus =
        FileCodeOwnerStatus.create(changedFile, newPathStatus, oldPathStatus);
    logger.atFine().log("fileCodeOwnerStatus = %s", fileCodeOwnerStatus);
    return fileCodeOwnerStatus;
  }

  private PathCodeOwnerStatus getPathCodeOwnerStatus(
      BranchNameKey branch,
      ObjectId revision,
      CodeOwnerResolverResult globalCodeOwners,
      boolean enableImplicitApprovalFromUploader,
      Account.Id patchSetUploader,
      ImmutableSet<Account.Id> reviewerAccountIds,
      ImmutableSet<Account.Id> approverAccountIds,
      boolean hasOverride,
      boolean isBootstrapping,
      Path absolutePath) {
    logger.atFine().log("computing path status for %s", absolutePath);

    if (hasOverride) {
      logger.atFine().log(
          "the status for path %s is %s since an override is present",
          absolutePath, CodeOwnerStatus.APPROVED.name());
      return PathCodeOwnerStatus.create(absolutePath, CodeOwnerStatus.APPROVED);
    }

    return isBootstrapping
        ? getPathCodeOwnerStatusBootstrappingMode(
            branch,
            globalCodeOwners,
            enableImplicitApprovalFromUploader,
            patchSetUploader,
            reviewerAccountIds,
            approverAccountIds,
            absolutePath)
        : getPathCodeOwnerStatusRegularMode(
            branch,
            globalCodeOwners,
            enableImplicitApprovalFromUploader,
            patchSetUploader,
            revision,
            reviewerAccountIds,
            approverAccountIds,
            absolutePath);
  }

  /**
   * Gets the code owner status for the given path when the branch doesn't contain any code owner
   * config file yet (bootstrapping mode).
   *
   * <p>If we are in bootstrapping mode we consider project owners as code owners. This allows
   * bootstrapping the code owner configuration in the branch.
   */
  private PathCodeOwnerStatus getPathCodeOwnerStatusBootstrappingMode(
      BranchNameKey branch,
      CodeOwnerResolverResult globalCodeOwners,
      boolean enableImplicitApprovalFromUploader,
      Account.Id patchSetUploader,
      ImmutableSet<Account.Id> reviewerAccountIds,
      ImmutableSet<Account.Id> approverAccountIds,
      Path absolutePath) {
    logger.atFine().log("computing path status for %s (bootstrapping mode)", absolutePath);

    CodeOwnerStatus codeOwnerStatus = CodeOwnerStatus.INSUFFICIENT_REVIEWERS;
    if (isApprovedBootstrappingMode(
        branch.project(),
        absolutePath,
        globalCodeOwners,
        approverAccountIds,
        enableImplicitApprovalFromUploader,
        patchSetUploader)) {
      codeOwnerStatus = CodeOwnerStatus.APPROVED;
    } else if (isPendingBootstrappingMode(
        branch.project(), absolutePath, globalCodeOwners, reviewerAccountIds)) {
      codeOwnerStatus = CodeOwnerStatus.PENDING;
    }

    PathCodeOwnerStatus pathCodeOwnerStatus =
        PathCodeOwnerStatus.create(absolutePath, codeOwnerStatus);
    logger.atFine().log("pathCodeOwnerStatus = %s", pathCodeOwnerStatus);
    return pathCodeOwnerStatus;
  }

  private boolean isApprovedBootstrappingMode(
      Project.NameKey projectName,
      Path absolutePath,
      CodeOwnerResolverResult globalCodeOwners,
      ImmutableSet<Account.Id> approverAccountIds,
      boolean enableImplicitApprovalFromUploader,
      Account.Id patchSetUploader) {
    return (enableImplicitApprovalFromUploader
            && isImplicitlyApprovedBootstrappingMode(
                projectName, absolutePath, globalCodeOwners, patchSetUploader))
        || isExplicitlyApprovedBootstrappingMode(
            projectName, absolutePath, globalCodeOwners, approverAccountIds);
  }

  private boolean isImplicitlyApprovedBootstrappingMode(
      Project.NameKey projectName,
      Path absolutePath,
      CodeOwnerResolverResult globalCodeOwners,
      Account.Id patchSetUploader) {
    if (isProjectOwner(projectName, patchSetUploader)) {
      // The uploader of the patch set is a project owner and thus a code owner. This means there
      // is an implicit code owner approval from the patch set uploader so that the path is
      // automatically approved.
      logger.atFine().log(
          "%s was implicitly approved by the patch set uploader who is a project owner",
          absolutePath);
      return true;
    }

    if (globalCodeOwners.ownedByAllUsers()
        || globalCodeOwners.codeOwnersAccountIds().contains(patchSetUploader)) {
      // If the uploader of the patch set is a global code owner, there is an implicit code owner
      // approval from the patch set uploader so that the path is automatically approved.
      logger.atFine().log(
          "%s was implicitly approved by the patch set uploader who is a global owner",
          absolutePath);
      return true;
    }

    return false;
  }

  private boolean isExplicitlyApprovedBootstrappingMode(
      Project.NameKey projectName,
      Path absolutePath,
      CodeOwnerResolverResult globalCodeOwners,
      ImmutableSet<Account.Id> approverAccountIds) {
    if (!Collections.disjoint(approverAccountIds, globalCodeOwners.codeOwnersAccountIds())
        || (globalCodeOwners.ownedByAllUsers() && !approverAccountIds.isEmpty())) {
      // At least one of the global code owners approved the change.
      logger.atFine().log("%s was approved by a global code owner", absolutePath);
      return true;
    }

    if (approverAccountIds.stream()
        .anyMatch(approverAccountId -> isProjectOwner(projectName, approverAccountId))) {
      // At least one of the approvers is a project owner and thus a code owner.
      logger.atFine().log("%s was approved by a project owner", absolutePath);
      return true;
    }

    return false;
  }

  private boolean isPendingBootstrappingMode(
      Project.NameKey projectName,
      Path absolutePath,
      CodeOwnerResolverResult globalCodeOwners,
      ImmutableSet<Account.Id> reviewerAccountIds) {
    if (reviewerAccountIds.stream()
        .anyMatch(reviewerAccountId -> isProjectOwner(projectName, reviewerAccountId))) {
      // At least one of the reviewers is a project owner and thus a code owner.
      logger.atFine().log("%s is owned by a reviewer who is project owner", absolutePath);
      return true;
    }

    if (isPending(absolutePath, globalCodeOwners, reviewerAccountIds)) {
      // At least one of the reviewers is a global code owner.
      logger.atFine().log("%s is owned by a reviewer who is a global owner", absolutePath);
      return true;
    }

    return false;
  }

  /**
   * Gets the code owner status for the given path when the branch contains at least one code owner
   * config file (regular mode).
   */
  private PathCodeOwnerStatus getPathCodeOwnerStatusRegularMode(
      BranchNameKey branch,
      CodeOwnerResolverResult globalCodeOwners,
      boolean enableImplicitApprovalFromUploader,
      Account.Id patchSetUploader,
      ObjectId revision,
      ImmutableSet<Account.Id> reviewerAccountIds,
      ImmutableSet<Account.Id> approverAccountIds,
      Path absolutePath) {
    logger.atFine().log("computing path status for %s (regular mode)", absolutePath);

    AtomicReference<CodeOwnerStatus> codeOwnerStatus =
        new AtomicReference<>(CodeOwnerStatus.INSUFFICIENT_REVIEWERS);

    if (isApproved(
        absolutePath,
        globalCodeOwners,
        approverAccountIds,
        enableImplicitApprovalFromUploader,
        patchSetUploader)) {
      logger.atFine().log("%s was approved by a global code owner", absolutePath);
      codeOwnerStatus.set(CodeOwnerStatus.APPROVED);
    } else {
      logger.atFine().log("%s was not approved by a global code owner", absolutePath);

      if (isPending(absolutePath, globalCodeOwners, reviewerAccountIds)) {
        logger.atFine().log("%s is owned by a reviewer who is a global owner", absolutePath);
        codeOwnerStatus.set(CodeOwnerStatus.PENDING);
      }

      codeOwnerConfigHierarchy.visit(
          branch,
          revision,
          absolutePath,
          codeOwnerConfig -> {
            CodeOwnerResolverResult codeOwners = getCodeOwners(codeOwnerConfig, absolutePath);
            logger.atFine().log(
                "code owners = %s (code owner config folder path = %s, file name = %s)",
                codeOwners,
                codeOwnerConfig.key().folderPath(),
                codeOwnerConfig.key().fileName().orElse("<default>"));

            if (isApproved(
                absolutePath,
                codeOwners,
                approverAccountIds,
                enableImplicitApprovalFromUploader,
                patchSetUploader)) {
              codeOwnerStatus.set(CodeOwnerStatus.APPROVED);
              return false;
            } else if (isPending(absolutePath, codeOwners, reviewerAccountIds)) {
              codeOwnerStatus.set(CodeOwnerStatus.PENDING);

              // We need to continue to check if any of the higher-level code owners approved the
              // change.
              return true;
            }

            // We need to continue to check if any of the higher-level code owners approved the
            // change or is a reviewer.
            return true;
          });
    }

    PathCodeOwnerStatus pathCodeOwnerStatus =
        PathCodeOwnerStatus.create(absolutePath, codeOwnerStatus.get());
    logger.atFine().log("pathCodeOwnerStatus = %s", pathCodeOwnerStatus);
    return pathCodeOwnerStatus;
  }

  private boolean isApproved(
      Path absolutePath,
      CodeOwnerResolverResult codeOwners,
      ImmutableSet<Account.Id> approverAccountIds,
      boolean enableImplicitApprovalFromUploader,
      Account.Id patchSetUploader) {
    if (enableImplicitApprovalFromUploader
        && (codeOwners.codeOwnersAccountIds().contains(patchSetUploader)
            || codeOwners.ownedByAllUsers())) {
      // If the uploader of the patch set owns the path, there is an implicit code owner
      // approval from the patch set uploader so that the path is automatically approved.
      logger.atFine().log("%s was implicitly approved by the patch set uploader", absolutePath);
      return true;
    }

    if (!Collections.disjoint(approverAccountIds, codeOwners.codeOwnersAccountIds())
        || (codeOwners.ownedByAllUsers() && !approverAccountIds.isEmpty())) {
      // At least one of the global code owners approved the change.
      logger.atFine().log("%s was explicitly approved by a code owner", absolutePath);
      return true;
    }

    return false;
  }

  private boolean isPending(
      Path absolutePath,
      CodeOwnerResolverResult codeOwners,
      ImmutableSet<Account.Id> reviewerAccountIds) {
    if (!Collections.disjoint(codeOwners.codeOwnersAccountIds(), reviewerAccountIds)
        || (codeOwners.ownedByAllUsers() && !reviewerAccountIds.isEmpty())) {
      logger.atFine().log("%s is owned by a reviewer", absolutePath);
      return true;
    }

    return false;
  }

  /** Whether the given account is a project owner of the given project. */
  private boolean isProjectOwner(Project.NameKey project, Account.Id accountId) {
    try {
      boolean isProjectOwner =
          permissionBackend
              .absentUser(accountId)
              .project(project)
              .test(ProjectPermission.WRITE_CONFIG);
      if (isProjectOwner) {
        logger.atFine().log("Account %d is a project owner", accountId.get());
      }
      return isProjectOwner;
    } catch (PermissionBackendException e) {
      throw new StorageException(
          String.format(
              "failed to check owner permission of project %s for account %d",
              project.get(), accountId.get()),
          e);
    }
  }

  /**
   * Gets the code owners that own the given path according to the given code owner config.
   *
   * @param codeOwnerConfig the code owner config from which the code owners should be retrieved
   * @param absolutePath the path for which the code owners should be retrieved
   */
  private CodeOwnerResolverResult getCodeOwners(
      CodeOwnerConfig codeOwnerConfig, Path absolutePath) {
    return codeOwnerResolver
        .get()
        .enforceVisibility(false)
        .resolvePathCodeOwners(codeOwnerConfig, absolutePath);
  }

  /**
   * Gets the IDs of the accounts that are reviewer on the given change.
   *
   * @param changeNotes the change notes
   */
  private ImmutableSet<Account.Id> getReviewerAccountIds(ChangeNotes changeNotes) {
    return changeNotes.getReviewers().byState(ReviewerStateInternal.REVIEWER);
  }

  /**
   * Gets the IDs of the accounts that posted a patch set approval on the given revisions that
   * counts as code owner approval.
   *
   * @param requiredApproval approval that is required from code owners to approve the files in a
   *     change
   * @param changeNotes the change notes
   */
  private ImmutableSet<Account.Id> getApproverAccountIds(
      RequiredApproval requiredApproval, ChangeNotes changeNotes) {
    return StreamSupport.stream(
            approvalsUtil
                .byPatchSet(
                    changeNotes,
                    changeNotes.getCurrentPatchSet().id(),
                    /** revWalk */
                    null,
                    /** repoConfig */
                    null)
                .spliterator(),
            /** parallel */
            false)
        .filter(requiredApproval::isApprovedBy)
        .map(PatchSetApproval::accountId)
        .collect(toImmutableSet());
  }

  /**
   * Checks whether the given change has an override approval.
   *
   * @param overrideApprovals approvals that count as override for the code owners submit check.
   * @param changeNotes the change notes
   * @return whether the given change has an override approval
   */
  private boolean hasOverride(
      ImmutableSet<RequiredApproval> overrideApprovals, ChangeNotes changeNotes) {
    return changeNotes.getApprovals().get(changeNotes.getCurrentPatchSet().id()).stream()
        .anyMatch(
            patchSetApproval ->
                overrideApprovals.stream()
                    .anyMatch(overrideApproval -> overrideApproval.isApprovedBy(patchSetApproval)));
  }

  /**
   * Gets the current revision of the destination branch of the given change.
   *
   * <p>This is the revision from which the code owner configs should be read when computing code
   * owners for the files that are touched in the change.
   *
   * @throws ResourceConflictException thrown if the destination branch is not found, e.g. when the
   *     branch got deleted after the change was created
   */
  private ObjectId getDestBranchRevision(Change change)
      throws IOException, ResourceConflictException {
    try (Repository repository = repoManager.openRepository(change.getProject());
        RevWalk rw = new RevWalk(repository)) {
      Ref ref = repository.exactRef(change.getDest().branch());
      if (ref == null) {
        throw new ResourceConflictException("destination branch not found");
      }
      return rw.parseCommit(ref.getObjectId());
    }
  }
}