common/experiments/src/com/google/idea/common/experiments/ExperimentServiceImpl.java

/*
 * Copyright 2016 The Bazel Authors. All rights reserved.
 *
 * 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.idea.common.experiments;

import static com.google.idea.common.experiments.ExperimentsUtil.hashExperimentName;

import com.google.common.annotations.VisibleForTesting;
import com.google.common.collect.ImmutableList;
import com.intellij.openapi.application.ApplicationManager;
import com.intellij.openapi.components.ApplicationComponent;
import com.intellij.openapi.diagnostic.Logger;
import com.intellij.util.SystemProperties;
import java.io.File;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;
import javax.annotation.Nullable;

/**
 * An experiment service that delegates to {@link ExperimentLoader ExperimentLoaders}, in a specific
 * order.
 *
 * <p>It will check system properties first, then an experiment file in the user's home directory,
 * then finally all files specified by the system property blaze.experiments.file.
 */
public class ExperimentServiceImpl extends ApplicationComponent.Adapter
    implements ExperimentService {
  private static final Logger logger = Logger.getInstance(ExperimentServiceImpl.class);

  private static final String USER_EXPERIMENT_OVERRIDES_FILE =
      SystemProperties.getUserHome() + File.separator + ".intellij-experiments";

  private final List<ExperimentLoader> services;
  private Map<String, String> experiments;
  private int experimentScopeCounter = 0;

  public ExperimentServiceImpl(String pluginName) {
    this(
        new SystemPropertyExperimentLoader(),
        new FileExperimentLoader(USER_EXPERIMENT_OVERRIDES_FILE),
        new WebExperimentLoader(pluginName));
  }

  @VisibleForTesting
  ExperimentServiceImpl(ExperimentLoader... loaders) {
    services = ImmutableList.copyOf(loaders);
  }

  @Override
  public void initComponent() {
    if (!ApplicationManager.getApplication().isUnitTestMode()) {
      services.forEach(ExperimentLoader::initialize);
    }
  }

  @Override
  public boolean getExperiment(String key, boolean defaultValue) {
    String property = getExperiment(key);
    return property != null ? property.equals("1") : defaultValue;
  }

  @Override
  public String getExperimentString(String key, @Nullable String defaultValue) {
    String property = getExperiment(key);
    return property != null ? property : defaultValue;
  }

  @Override
  public int getExperimentInt(String key, int defaultValue) {
    String property = getExperiment(key);
    try {
      return property != null ? Integer.parseInt(property) : defaultValue;
    } catch (NumberFormatException e) {
      logger.warn("Could not parse int for experiment: " + key, e);
      return defaultValue;
    }
  }

  @Override
  public synchronized void startExperimentScope() {
    if (++experimentScopeCounter > 0) {
      experiments = getAllExperiments();
    }
  }

  @Override
  public synchronized void endExperimentScope() {
    if (--experimentScopeCounter <= 0) {
      logger.assertTrue(experimentScopeCounter == 0);
      experiments = null;
    }
  }

  private Map<String, String> getAllExperiments() {
    Map<String, String> experiments = this.experiments;
    if (experiments != null) {
      return experiments;
    } else {
      return services
          .stream()
          .flatMap(service -> service.getExperiments().entrySet().stream())
          .collect(
              Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue, (first, second) -> first));
    }
  }

  private String getExperiment(String key) {
    return getAllExperiments().get(hashExperimentName(key));
  }
}