// 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.gerritforge.gerrit.globalrefdb.validation;

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.logging.PluginMetadata;
import com.google.inject.Inject;
import com.google.inject.Singleton;

/**
 * Creates and registers metrics related to ref-db validations, such as split brains events. Such
 * metrics are exposed by Gerrit and can then be used for monitoring and alerting.
 *
 * <p>This class is a {@link Singleton} to ensure that metrics unique are only registered once.
 */
@Singleton
public class ValidationMetrics {
  private static final String GIT_UPDATE_SPLIT_BRAIN_PREVENTED = "git_update_split_brain_prevented";
  private static final String GIT_UPDATE_SPLIT_BRAIN = "git_update_split_brain";

  private final Counter1<String> splitBrainPreventionCounter;
  private final Counter1<String> splitBrainCounter;

  /**
   * Constructs a new {@code ValidationMetrics}, by passing metricMaker and the global refdb
   * configuration. Both parameters are bound and {@link Inject}ed by Guice.
   *
   * @param metricMaker Factory to create metrics for monitoring
   * @param cfg Configuration of shared ref-database configuration file
   */
  @Inject
  public ValidationMetrics(MetricMaker metricMaker, SharedRefDbConfiguration cfg) {
    this.splitBrainPreventionCounter =
        metricMaker.newCounter(
            String.format("%s/validation/git_update_split_brain_prevented", cfg.pluginName()),
            rateDescription("errors", "Rate of REST API error responses"),
            stringField(
                GIT_UPDATE_SPLIT_BRAIN_PREVENTED,
                "Ref-update operations, split-brain detected and prevented"));

    this.splitBrainCounter =
        metricMaker.newCounter(
            String.format("%s/validation/git_update_split_brain", cfg.pluginName()),
            rateDescription("errors", "Rate of REST API error responses"),
            stringField(
                GIT_UPDATE_SPLIT_BRAIN,
                "Ref-update operation left node in a split-brain scenario"));
  }

  /**
   * Increment the "git_update_split_brain_prevented" metric counter to signal that a split-brain
   * event was prevented by performing validation against the global refdb.
   */
  public void incrementSplitBrainPrevention() {
    splitBrainPreventionCounter.increment(GIT_UPDATE_SPLIT_BRAIN_PREVENTED);
  }

  /**
   * Increment the "git_update_split_brain" metric counter to signal that the current gerrit
   * instance is in split-brain.
   */
  public void incrementSplitBrain() {
    splitBrainCounter.increment(GIT_UPDATE_SPLIT_BRAIN);
  }

  public Field<String> stringField(String metadataKey, String description) {
    return Field.ofString(
            metadataKey,
            (metadataBuilder, fieldValue) ->
                metadataBuilder.addPluginMetadata(PluginMetadata.create(metadataKey, fieldValue)))
        .description(description)
        .build();
  }

  public Description rateDescription(String unit, String description) {
    return new Description(description).setRate().setUnit(unit);
  }
}