// Copyright 2014 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.devtools.build.skyframe;

import com.google.common.annotations.VisibleForTesting;
import com.google.common.collect.Iterables;
import com.google.common.collect.Maps;
import com.google.devtools.build.lib.collect.compacthashmap.CompactHashMap;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.function.Function;
import javax.annotation.Nullable;

/**
 * An in-memory graph implementation. All operations are thread-safe with ConcurrentMap semantics.
 * Also see {@link NodeEntry}.
 *
 * <p>This class is public only for use in alternative graph implementations.
 */
public class InMemoryGraphImpl implements InMemoryGraph {

  protected final ConcurrentMap<SkyKey, NodeEntry> nodeMap;
  private final boolean keepEdges;

  @VisibleForTesting
  public InMemoryGraphImpl() {
    this(/*keepEdges=*/ true);
  }

  public InMemoryGraphImpl(boolean keepEdges) {
    this(keepEdges, /*initialCapacity=*/ 1 << 10);
  }

  protected InMemoryGraphImpl(boolean keepEdges, int initialCapacity) {
    this.keepEdges = keepEdges;
    this.nodeMap = new ConcurrentHashMap<>(initialCapacity);
  }

  @Override
  public void remove(SkyKey skyKey) {
    nodeMap.remove(skyKey);
  }

  @Override
  public NodeEntry get(@Nullable SkyKey requestor, Reason reason, SkyKey skyKey) {
    return nodeMap.get(skyKey);
  }

  @Override
  public Map<SkyKey, NodeEntry> getBatch(
      SkyKey requestor, Reason reason, Iterable<? extends SkyKey> keys) {
    // Use a HashMap, not an ImmutableMap.Builder, because we have not yet deduplicated these keys
    // and ImmutableMap.Builder does not tolerate duplicates. The map will be thrown away shortly.
    HashMap<SkyKey, NodeEntry> result = new HashMap<>();
    for (SkyKey key : keys) {
      NodeEntry entry = get(null, Reason.OTHER, key);
      if (entry != null) {
        result.put(key, entry);
      }
    }
    return result;
  }

  protected NodeEntry newNodeEntry(SkyKey key) {
    return keepEdges ? new InMemoryNodeEntry() : new EdgelessInMemoryNodeEntry();
  }

  /**
   * This is used to call newNodeEntry() from within computeIfAbsent. Instantiated here to avoid
   * lambda instantiation overhead.
   */
  @SuppressWarnings("UnnecessaryLambda")
  private final Function<SkyKey, NodeEntry> newNodeEntryFunction = k -> newNodeEntry(k);

  @Override
  public Map<SkyKey, NodeEntry> createIfAbsentBatch(
      @Nullable SkyKey requestor, Reason reason, Iterable<SkyKey> keys) {
    Map<SkyKey, NodeEntry> result = CompactHashMap.createWithExpectedSize(Iterables.size(keys));
    for (SkyKey key : keys) {
      result.put(key, nodeMap.computeIfAbsent(key, newNodeEntryFunction));
    }
    return result;
  }

  @Override
  public DepsReport analyzeDepsDoneness(SkyKey parent, Collection<SkyKey> deps) {
    return DepsReport.NO_INFORMATION;
  }

  @Override
  public Map<SkyKey, SkyValue> getValues() {
    return Collections.unmodifiableMap(
        Maps.transformValues(
            nodeMap,
            entry -> {
              try {
                return entry.toValue();
              } catch (InterruptedException e) {
                throw new IllegalStateException(e);
              }
            }));
  }

  @Override
  public Map<SkyKey, NodeEntry> getAllValues() {
    return Collections.unmodifiableMap(nodeMap);
  }

  @Override
  public Map<SkyKey, ? extends NodeEntry> getAllValuesMutable() {
    return nodeMap;
  }
}