// Copyright (C) 2016 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.change;

import com.google.common.base.Throwables;
import com.google.common.cache.Cache;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.Sets;
import com.google.common.flogger.FluentLogger;
import com.google.common.primitives.Ints;
import com.google.gerrit.entities.Change;
import com.google.gerrit.entities.Project;
import com.google.gerrit.exceptions.StorageException;
import com.google.gerrit.extensions.restapi.Url;
import com.google.gerrit.git.ObjectIds;
import com.google.gerrit.index.IndexConfig;
import com.google.gerrit.metrics.Counter1;
import com.google.gerrit.metrics.Description;
import com.google.gerrit.metrics.Field;
import com.google.gerrit.metrics.MetricMaker;
import com.google.gerrit.server.cache.CacheModule;
import com.google.gerrit.server.logging.Metadata;
import com.google.gerrit.server.notedb.ChangeNotes;
import com.google.gerrit.server.project.NoSuchChangeException;
import com.google.gerrit.server.query.change.ChangeData;
import com.google.gerrit.server.query.change.InternalChangeQuery;
import com.google.inject.Inject;
import com.google.inject.Module;
import com.google.inject.Provider;
import com.google.inject.Singleton;
import com.google.inject.name.Named;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Optional;
import java.util.Set;
import org.eclipse.jgit.errors.RepositoryNotFoundException;

@Singleton
public class ChangeFinder {
  private static final FluentLogger logger = FluentLogger.forEnclosingClass();

  private static final String CACHE_NAME = "changeid_project";

  public static Module module() {
    return new CacheModule() {
      @Override
      protected void configure() {
        cache(CACHE_NAME, Change.Id.class, String.class).maximumWeight(1024);
      }
    };
  }

  public enum ChangeIdType {
    ALL,
    TRIPLET,
    NUMERIC_ID,
    I_HASH,
    PROJECT_NUMERIC_ID,
    COMMIT_HASH
  }

  private final IndexConfig indexConfig;
  private final Cache<Change.Id, String> changeIdProjectCache;
  private final Provider<InternalChangeQuery> queryProvider;
  private final ChangeNotes.Factory changeNotesFactory;
  private final Counter1<ChangeIdType> changeIdCounter;

  @Inject
  ChangeFinder(
      IndexConfig indexConfig,
      @Named(CACHE_NAME) Cache<Change.Id, String> changeIdProjectCache,
      Provider<InternalChangeQuery> queryProvider,
      ChangeNotes.Factory changeNotesFactory,
      MetricMaker metricMaker) {
    this.indexConfig = indexConfig;
    this.changeIdProjectCache = changeIdProjectCache;
    this.queryProvider = queryProvider;
    this.changeNotesFactory = changeNotesFactory;
    this.changeIdCounter =
        metricMaker.newCounter(
            "http/server/rest_api/change_id_type",
            new Description("Total number of API calls per identifier type.")
                .setRate()
                .setUnit("requests"),
            Field.ofEnum(ChangeIdType.class, "change_id_type", Metadata.Builder::changeIdType)
                .build());
  }

  public Optional<ChangeNotes> findOne(String id) {
    // Limit the maximum number of results to just 2 items for saving CPU cycles
    // in reading change-notes.
    List<ChangeNotes> ctls = find(id, 2);
    if (ctls.size() != 1) {
      return Optional.empty();
    }
    return Optional.of(ctls.get(0));
  }

  /**
   * Find changes matching the given identifier.
   *
   * @param id change identifier.
   * @return possibly-empty list of notes for all matching changes; may or may not be visible.
   */
  public List<ChangeNotes> find(String id) {
    return find(id, 0);
  }

  /**
   * Find at most N changes matching the given identifier.
   *
   * @param id change identifier.
   * @param queryLimit maximum number of changes to be returned
   * @return possibly-empty list of notes for all matching changes; may or may not be visible.
   */
  public List<ChangeNotes> find(String id, int queryLimit) {
    if (id.isEmpty()) {
      return Collections.emptyList();
    }

    int z = id.lastIndexOf('~');
    int y = id.lastIndexOf('~', z - 1);
    if (y < 0 && z > 0) {
      // Try project~numericChangeId
      Integer n = Ints.tryParse(id.substring(z + 1));
      if (n != null) {
        changeIdCounter.increment(ChangeIdType.PROJECT_NUMERIC_ID);
        return fromProjectNumber(id.substring(0, z), n.intValue());
      }
    }

    if (y < 0 && z < 0) {
      // Try numeric changeId
      Integer n = Ints.tryParse(id);
      if (n != null) {
        changeIdCounter.increment(ChangeIdType.NUMERIC_ID);
        return find(Change.id(n));
      }
    }

    // Use the index to search for changes, but don't return any stored fields,
    // to force rereading in case the index is stale.
    InternalChangeQuery query = queryProvider.get().noFields();
    if (queryLimit > 0) {
      query.setLimit(queryLimit);
    }

    // Try commit hash
    if (id.matches("^([0-9a-fA-F]{" + ObjectIds.ABBREV_STR_LEN + "," + ObjectIds.STR_LEN + "})$")) {
      changeIdCounter.increment(ChangeIdType.COMMIT_HASH);
      return asChangeNotes(query.byCommit(id));
    }

    if (y > 0 && z > 0) {
      // Try change triplet (project~branch~Ihash...)
      Optional<ChangeTriplet> triplet = ChangeTriplet.parse(id, y, z);
      if (triplet.isPresent()) {
        ChangeTriplet t = triplet.get();
        changeIdCounter.increment(ChangeIdType.TRIPLET);
        return asChangeNotes(query.byBranchKey(t.branch(), t.id()));
      }
    }

    // Try isolated Ihash... format ("Change-Id: Ihash").
    List<ChangeNotes> notes = asChangeNotes(query.byKeyPrefix(id));
    if (!notes.isEmpty()) {
      changeIdCounter.increment(ChangeIdType.I_HASH);
    }
    return notes;
  }

  private List<ChangeNotes> fromProjectNumber(String project, int changeNumber) {
    Change.Id cId = Change.id(changeNumber);
    try {
      return ImmutableList.of(
          changeNotesFactory.createChecked(Project.NameKey.parse(project), cId));
    } catch (NoSuchChangeException e) {
      return Collections.emptyList();
    } catch (StorageException e) {
      // Distinguish between a RepositoryNotFoundException (project argument invalid) and
      // other StorageExceptions (failure in the persistence layer).
      if (Throwables.getRootCause(e) instanceof RepositoryNotFoundException) {
        return Collections.emptyList();
      }
      throw e;
    }
  }

  public Optional<ChangeNotes> findOne(Change.Id id) {
    List<ChangeNotes> notes = find(id);
    if (notes.size() != 1) {
      return Optional.empty();
    }
    return Optional.of(notes.get(0));
  }

  public List<ChangeNotes> find(Change.Id id) {
    String project = changeIdProjectCache.getIfPresent(id);
    if (project != null) {
      return fromProjectNumber(project, id.get());
    }

    // Use the index to search for changes, but don't return any stored fields,
    // to force rereading in case the index is stale.
    InternalChangeQuery query = queryProvider.get().noFields();
    List<ChangeData> r = query.byLegacyChangeId(id);
    if (r.size() == 1) {
      changeIdProjectCache.put(id, Url.encode(r.get(0).project().get()));
    }
    return asChangeNotes(r);
  }

  private List<ChangeNotes> asChangeNotes(List<ChangeData> cds) {
    List<ChangeNotes> notes = new ArrayList<>(cds.size());
    if (!indexConfig.separateChangeSubIndexes()) {
      for (ChangeData cd : cds) {
        try {
          notes.add(cd.notes());
        } catch (NoSuchChangeException e) {
          logger.atWarning().log("Change %s seen in index, but missing in NoteDb", e.getMessage());
        }
      }
      return notes;
    }

    // If an index implementation uses separate non-atomic subindexes, it's possible to temporarily
    // observe a change as present in both subindexes, if this search is concurrent with a write.
    // Dedup to avoid confusing the caller. We can choose an arbitrary ChangeData instance because
    // the index results have no stored fields, so the data is already reloaded. (It's also possible
    // that a change might appear in zero subindexes, but there's nothing we can do here to help
    // this case.)
    Set<Change.Id> seen = Sets.newHashSetWithExpectedSize(cds.size());
    for (ChangeData cd : cds) {
      if (seen.add(cd.getId())) {
        try {
          notes.add(cd.notes());
        } catch (NoSuchChangeException e) {
          logger.atWarning().log("Change %s seen in index, but missing in NoteDb", e.getMessage());
        }
      }
    }
    return notes;
  }
}