// 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.googlesource.gerrit.plugins.task;

import com.google.gerrit.index.FieldDef;
import com.google.gerrit.index.query.AndPredicate;
import com.google.gerrit.index.query.NotPredicate;
import com.google.gerrit.index.query.OrPredicate;
import com.google.gerrit.index.query.Predicate;
import com.google.gerrit.index.query.QueryParseException;
import com.google.gerrit.server.CurrentUser;
import com.google.gerrit.server.index.change.ChangeField;
import com.google.gerrit.server.query.change.ChangeData;
import com.google.gerrit.server.query.change.ChangeIndexPredicate;
import com.google.gerrit.server.query.change.DestinationPredicate;
import com.google.gerrit.server.query.change.RegexProjectPredicate;
import com.google.gerrit.server.query.change.RegexRefPredicate;
import com.google.gerrit.server.query.change.SubmitRequirementChangeQueryBuilder;
import com.google.inject.Inject;
import com.googlesource.gerrit.plugins.task.statistics.HitHashMap;
import com.googlesource.gerrit.plugins.task.statistics.StopWatch;
import com.googlesource.gerrit.plugins.task.util.ThrowingProvider;

public class PredicateCache {
  public static class Statistics {
    protected Object predicatesByQueryCache;
  }

  protected final SubmitRequirementChangeQueryBuilder srcqb;
  protected final TaskPluginConfiguration config;
  protected final CurrentUser user;
  protected final HitHashMap<String, ThrowingProvider<Predicate<ChangeData>, QueryParseException>>
      predicatesByQuery = new HitHashMap<>();

  protected Statistics statistics;

  @Inject
  public PredicateCache(
      TaskPluginConfiguration config, CurrentUser user, SubmitRequirementChangeQueryBuilder srcqb) {
    this.config = config;
    this.user = user;
    this.srcqb = srcqb;
  }

  public void initStatistics(int summaryCount) {
    statistics = new Statistics();
    predicatesByQuery.initStatistics(summaryCount);
  }

  public Object getStatistics() {
    if (statistics != null) {
      statistics.predicatesByQueryCache = predicatesByQuery.getStatistics();
    }
    return statistics;
  }

  @SuppressWarnings("try")
  public Predicate<ChangeData> getPredicate(String query, boolean isVisible)
      throws QueryParseException {
    ThrowingProvider<Predicate<ChangeData>, QueryParseException> predProvider =
        predicatesByQuery.get(query);
    if (predProvider != null) {
      return predProvider.get();
    }
    // never seen 'query' before
    try (StopWatch stopWatch = predicatesByQuery.createLoadingStopWatch(query, isVisible)) {
      Predicate<ChangeData> pred = srcqb.parse(query);
      predicatesByQuery.put(query, new ThrowingProvider.Entry<>(pred));
      return pred;
    } catch (QueryParseException e) {
      predicatesByQuery.put(query, new ThrowingProvider.Thrown<>(e));
      throw e;
    }
  }

  /**
   * Can this query's output be assumed to be constant given any Change destined for the same
   * Branch.NameKey?
   */
  public boolean isCacheableByBranch(String query, boolean isVisible) throws QueryParseException {
    if (query == null
        || "".equals(query)
        || "false".equalsIgnoreCase(query)
        || "true".equalsIgnoreCase(query)) {
      return true;
    }
    return isCacheableByBranch(getPredicate(query, isVisible));
  }

  protected boolean isCacheableByBranch(Predicate<ChangeData> predicate) {
    if (predicate instanceof AndPredicate
        || predicate instanceof NotPredicate
        || predicate instanceof OrPredicate) {
      for (Predicate<ChangeData> subPred : predicate.getChildren()) {
        if (!isCacheableByBranch(subPred)) {
          return false;
        }
      }
      return true;
    }
    if (predicate instanceof DestinationPredicate
        || predicate instanceof RegexProjectPredicate
        || predicate instanceof RegexRefPredicate) {
      return true;
    }
    if (predicate instanceof ChangeIndexPredicate) {
      FieldDef<ChangeData, ?> field = ((ChangeIndexPredicate) predicate).getField();
      if (field.equals(ChangeField.PROJECT) || field.equals(ChangeField.REF)) {
        return true;
      }
    }
    return config
        .getCacheableByBranchPredicateClassNames()
        .contains(predicate.getClass().getName());
  }
}