/*
 * Copyright 2016-present Facebook, Inc.
 *
 * 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.facebook.buck.parser;

import com.facebook.buck.json.ProjectBuildFileParser;
import com.facebook.buck.rules.Cell;
import com.facebook.buck.util.concurrent.ResourcePool;
import com.google.common.base.Function;
import com.google.common.base.Preconditions;
import com.google.common.collect.ImmutableSet;
import com.google.common.util.concurrent.ListenableFuture;
import com.google.common.util.concurrent.ListeningExecutorService;
import java.nio.file.Path;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicLong;
import javax.annotation.concurrent.GuardedBy;

/**
 * Allows multiple concurrently executing futures to share a constrained number of parsers.
 *
 * <p>Parser instances are lazily created up till a fixed maximum. If more than max parser are
 * requested the associated 'requests' are queued up. As soon as a parser is returned it will be
 * used to satisfy the first pending request, otherwise it is "parked".
 */
class ProjectBuildFileParserPool implements AutoCloseable {
  private final int maxParsersPerCell;

  @GuardedBy("this")
  private final Map<Cell, ResourcePool<ProjectBuildFileParser>> parserResourcePools;

  private final Function<Cell, ProjectBuildFileParser> parserFactory;
  private final AtomicBoolean closing;

  /**
   * @param maxParsersPerCell maximum number of parsers to create for a single cell.
   * @param parserFactory function used to create a new parser.
   */
  public ProjectBuildFileParserPool(
      int maxParsersPerCell, Function<Cell, ProjectBuildFileParser> parserFactory) {
    Preconditions.checkArgument(maxParsersPerCell > 0);

    this.maxParsersPerCell = maxParsersPerCell;
    this.parserResourcePools = new HashMap<>();
    this.parserFactory = parserFactory;
    this.closing = new AtomicBoolean(false);
  }

  /**
   * @param cell the cell in which we're parsing
   * @param buildFile the file to parse
   * @param executorService where to perform the parsing.
   * @return a {@link ListenableFuture} containing the result of the parsing. The future will be
   *     cancelled if the {@link ProjectBuildFileParserPool#close()} method is called.
   */
  public ListenableFuture<ImmutableSet<Map<String, Object>>> getAllRulesAndMetaRules(
      final Cell cell,
      final Path buildFile,
      AtomicLong processedBytes,
      final ListeningExecutorService executorService) {
    Preconditions.checkState(!closing.get());

    return getResourcePoolForCell(cell)
        .scheduleOperationWithResource(
            parser ->
                ImmutableSet.copyOf(parser.getAllRulesAndMetaRules(buildFile, processedBytes)),
            executorService);
  }

  private synchronized ResourcePool<ProjectBuildFileParser> getResourcePoolForCell(Cell cell) {
    ResourcePool<ProjectBuildFileParser> pool = parserResourcePools.get(cell);
    if (pool == null) {
      pool =
          new ResourcePool<>(
              maxParsersPerCell,
              // If the Python process garbles the output stream then the bser codec doesn't always
              // recover and subsequent attempts at invoking the parser will fail.
              ResourcePool.ResourceUsageErrorPolicy.RETIRE,
              () -> parserFactory.apply(cell));
      parserResourcePools.put(cell, pool);
    }
    return pool;
  }

  @Override
  public void close() {
    ImmutableSet<ResourcePool<ProjectBuildFileParser>> resourcePools;
    synchronized (this) {
      Preconditions.checkState(!closing.get());
      closing.set(true);
      resourcePools = ImmutableSet.copyOf(parserResourcePools.values());
    }
    resourcePools.forEach(ResourcePool::close);
  }
}