// 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.googlesource.gerrit.plugins.reviewersbyblame;

import com.google.common.collect.Maps;
import com.google.common.collect.Ordering;
import com.google.common.collect.Sets;
import com.google.gerrit.entities.Account;
import com.google.gerrit.entities.Change;
import com.google.gerrit.entities.Patch.ChangeType;
import com.google.gerrit.entities.PatchSet;
import com.google.gerrit.extensions.api.GerritApi;
import com.google.gerrit.extensions.api.changes.ReviewInput;
import com.google.gerrit.extensions.api.changes.ReviewerInput;
import com.google.gerrit.server.account.AccountCache;
import com.google.gerrit.server.account.AccountState;
import com.google.gerrit.server.account.Emails;
import com.google.gerrit.server.patch.DiffNotAvailableException;
import com.google.gerrit.server.patch.DiffOperations;
import com.google.gerrit.server.patch.DiffOptions;
import com.google.gerrit.server.patch.filediff.FileDiffOutput;
import com.google.gerrit.server.patch.filediff.TaggedEdit;
import com.google.inject.Inject;
import com.google.inject.assistedinject.Assisted;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Optional;
import java.util.Set;
import java.util.stream.Collectors;
import org.eclipse.jgit.api.BlameCommand;
import org.eclipse.jgit.api.errors.GitAPIException;
import org.eclipse.jgit.blame.BlameResult;
import org.eclipse.jgit.diff.Edit;
import org.eclipse.jgit.lib.Repository;
import org.eclipse.jgit.revwalk.RevCommit;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class ReviewersByBlame implements Runnable {

  private static final Logger log = LoggerFactory.getLogger(ReviewersByBlame.class);
  private static final int DEFAULT_BASE = 0;

  private final RevCommit commit;
  private final Change change;
  private final PatchSet ps;
  private final Repository repo;
  private final int maxReviewers;
  private final String ignoreFileRegEx;

  private final Emails emails;
  private final AccountCache accountCache;
  private final DiffOperations diffOperations;
  private final GerritApi gApi;

  public interface Factory {
    ReviewersByBlame create(
        RevCommit commit,
        Change change,
        PatchSet ps,
        int maxReviewers,
        Repository repo,
        String ignoreFileRegEx);
  }

  @Inject
  public ReviewersByBlame(
      Emails emails,
      AccountCache accountCache,
      DiffOperations diffOperations,
      GerritApi gApi,
      @Assisted RevCommit commit,
      @Assisted Change change,
      @Assisted PatchSet ps,
      @Assisted int maxReviewers,
      @Assisted Repository repo,
      @Assisted String ignoreFileRegEx) {
    this.emails = emails;
    this.accountCache = accountCache;
    this.diffOperations = diffOperations;
    this.gApi = gApi;
    this.commit = commit;
    this.change = change;
    this.ps = ps;
    this.maxReviewers = maxReviewers;
    this.repo = repo;
    this.ignoreFileRegEx = ignoreFileRegEx;
  }

  @Override
  public void run() {
    Map<Account, Integer> reviewers = Maps.newHashMap();
    Map<String, FileDiffOutput> stringFileDiffOutputMap;
    try {
      stringFileDiffOutputMap =
          diffOperations.listModifiedFilesAgainstParent(
              change.getProject(), ps.commitId(), DEFAULT_BASE, DiffOptions.DEFAULTS);

    } catch (DiffNotAvailableException ex) {
      log.error("Couldn't load patchlist for change {}", change.getKey(), ex);
      return;
    }
    // Ignore merges and initial commit.
    if (commit.getParentCount() != 1) {
      return;
    }
    for (FileDiffOutput entry : stringFileDiffOutputMap.values()) {
      BlameResult blameResult;
      if ((entry.changeType() == ChangeType.MODIFIED || entry.changeType() == ChangeType.DELETED)
          && (ignoreFileRegEx.isEmpty() || !entry.newPath().orElse("").matches(ignoreFileRegEx))
          && (blameResult = computeBlame(entry, commit.getParent(0))) != null) {
        List<Edit> edits =
            entry.edits().stream().map(TaggedEdit::jgitEdit).collect(Collectors.toList());
        reviewers.putAll(getReviewersForPatch(edits, blameResult));
      }
    }
    Set<Account.Id> topReviewers = findTopReviewers(reviewers);
    addReviewers(topReviewers, change);
  }

  /**
   * Append the reviewers to change#{@link Change}
   *
   * @param topReviewers Set of reviewers proposed
   * @param change {@link Change} to add the reviewers to
   */
  private void addReviewers(Set<Account.Id> topReviewers, Change change) {
    try {
      ReviewInput in = new ReviewInput();
      in.reviewers = new ArrayList<>(topReviewers.size());
      for (Account.Id account : topReviewers) {
        ReviewerInput reviewerInput = new ReviewerInput();
        reviewerInput.reviewer = account.toString();
        in.reviewers.add(reviewerInput);
      }
      gApi.changes().id(change.getChangeId()).current().review(in);
    } catch (Exception ex) {
      log.error("Couldn't add reviewers to the change", ex);
    }
  }

  /**
   * Create a set of reviewers based on data collected from line annotations, the reviewers are
   * ordered by their weight and n greatest of the entries are chosen, where n is the maximum number
   * of reviewers
   *
   * @param reviewers A set of reviewers with their weight mapped to their {@link Account}
   * @return Reviewers that are best matches for this change, empty if none, never <code>null</code>
   */
  private Set<Account.Id> findTopReviewers(Map<Account, Integer> reviewers) {
    Set<Account.Id> topReviewers = Sets.newHashSet();
    List<Entry<Account, Integer>> entries =
        Ordering.from(
                new Comparator<Entry<Account, Integer>>() {
                  @Override
                  public int compare(
                      Entry<Account, Integer> first, Entry<Account, Integer> second) {
                    return first.getValue() - second.getValue();
                  }
                })
            .greatestOf(reviewers.entrySet(), this.maxReviewers);
    for (Entry<Account, Integer> entry : entries) {
      topReviewers.add(entry.getKey().id());
    }
    return topReviewers;
  }

  /**
   * Get a map of all the possible reviewers based on the provided blame data
   *
   * @param edits List of edits that were made for this patch
   * @param blameResult Result of blame computation
   * @return a set of all possible reviewers, empty if none, never <code>null</code>
   */
  private Map<Account, Integer> getReviewersForPatch(List<Edit> edits, BlameResult blameResult) {
    Map<Account, Integer> reviewers = Maps.newHashMap();
    for (Edit edit : edits) {
      for (int i = edit.getBeginA(); i < edit.getEndA(); i++) {
        RevCommit commit = blameResult.getSourceCommit(i);
        try {
          Set<Account.Id> ids = emails.getAccountFor(commit.getAuthorIdent().getEmailAddress());
          for (Account.Id id : ids) {
            Optional<Account> accountState = accountCache.get(id).map(AccountState::account);
            if (accountState.isPresent()) {
              Account account = accountState.get();
              if (account.isActive() && !change.getOwner().equals(account.id())) {
                Integer count = reviewers.get(account);
                reviewers.put(account, count == null ? 1 : count.intValue() + 1);
              }
            }
          }
        } catch (IOException e) {
          throw new RuntimeException(
              "Unable to get account with email: " + commit.getAuthorIdent().getEmailAddress(), e);
        }
      }
    }
    return reviewers;
  }

  /**
   * Compute the blame data for the parent, we are not interested in the specific commit but the
   * parent, since we only want to know the last person that edited this specific part of the code.
   *
   * @param entry {@link FileDiffOutput}
   * @param parent Parent {@link RevCommit}
   * @return Result of blame computation, null if the computation fails
   */
  private BlameResult computeBlame(FileDiffOutput entry, RevCommit parent) {
    if (entry.changeType() == ChangeType.ADDED) {
      // This file is not present in the parent commit, so there is no blame
      return null;
    }

    // For all other ChangeType cases this file exists in the old commit and therefore we
    // use the entry.oldPath() which is then guaranteed to be set

    BlameCommand blameCommand = new BlameCommand(repo);
    blameCommand.setStartCommit(parent);
    blameCommand.setFilePath(entry.oldPath().get());
    try {
      BlameResult blameResult = blameCommand.call();
      blameResult.computeAll();
      return blameResult;
    } catch (GitAPIException ex) {
      log.error("Couldn't execute blame for commit {}", parent.getName(), ex);
    } catch (IOException err) {
      log.error("Error while computing blame for commit {}", parent.getName(), err);
    }
    return null;
  }
}