// Copyright 2015 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.lib.skyframe;

import com.google.common.collect.ImmutableList;
import com.google.devtools.build.lib.analysis.AspectValue;
import com.google.devtools.build.lib.analysis.ConfiguredTargetValue;
import com.google.devtools.build.lib.packages.AspectDescriptor;
import com.google.devtools.build.lib.skyframe.AspectKeyCreator.AspectKey;
import com.google.devtools.build.lib.skyframe.AspectKeyCreator.TopLevelAspectsKey;
import com.google.devtools.build.lib.skyframe.BuildTopLevelAspectsDetailsFunction.AspectDetails;
import com.google.devtools.build.lib.skyframe.BuildTopLevelAspectsDetailsFunction.BuildTopLevelAspectsDetailsKey;
import com.google.devtools.build.lib.skyframe.BuildTopLevelAspectsDetailsFunction.BuildTopLevelAspectsDetailsValue;
import com.google.devtools.build.skyframe.SkyFunction;
import com.google.devtools.build.skyframe.SkyFunctionException;
import com.google.devtools.build.skyframe.SkyKey;
import com.google.devtools.build.skyframe.SkyValue;
import com.google.devtools.build.skyframe.SkyframeLookupResult;
import java.util.Collection;
import java.util.HashMap;
import java.util.Map;
import java.util.Objects;
import javax.annotation.Nullable;

/**
 * SkyFunction to run the aspects path obtained from top-level aspects on the list of top-level
 * targets.
 *
 * <p>Used for loading top-level aspects. At top level, in {@link
 * com.google.devtools.build.lib.analysis.BuildView}, we cannot invoke two SkyFunctions one after
 * another, so BuildView calls this function to do the work.
 */
final class ToplevelStarlarkAspectFunction implements SkyFunction {
  @Nullable
  @Override
  public SkyValue compute(SkyKey skyKey, Environment env)
      throws TopLevelStarlarkAspectFunctionException, InterruptedException {
    TopLevelAspectsKey topLevelAspectsKey = (TopLevelAspectsKey) skyKey.argument();

    BuildTopLevelAspectsDetailsKey topLevelAspectsDetailsKey =
        BuildTopLevelAspectsDetailsKey.create(
            topLevelAspectsKey.getTopLevelAspectsClasses(),
            topLevelAspectsKey.getTopLevelAspectsParameters());
    ConfiguredTargetKey baseConfiguredTargetKey = topLevelAspectsKey.getBaseConfiguredTargetKey();

    SkyframeLookupResult initialLookupResult =
        env.getValuesAndExceptions(
            ImmutableList.of(topLevelAspectsDetailsKey, baseConfiguredTargetKey));
    var topLevelAspectsDetails =
        (BuildTopLevelAspectsDetailsValue) initialLookupResult.get(topLevelAspectsDetailsKey);
    if (topLevelAspectsDetails == null) {
      return null; // some aspects details are not ready
    }
    var baseConfiguredTargetValue =
        (ConfiguredTargetValue) initialLookupResult.get(baseConfiguredTargetKey);
    if (baseConfiguredTargetValue == null) {
      return null;
    }

    // Keeps AspectKeys canonical by ensuring that they use the real configuration for the base
    // configured target key. The ConfiguredTargetFunction could modify it using a rule transition.
    BuildConfigurationKey realConfiguration =
        baseConfiguredTargetValue.getConfiguredTarget().getConfigurationKey();
    if (!Objects.equals(realConfiguration, baseConfiguredTargetKey.getConfigurationKey())) {
      baseConfiguredTargetKey =
          ConfiguredTargetKey.fromConfiguredTarget(baseConfiguredTargetValue.getConfiguredTarget());
    }

    Collection<AspectKey> aspectsKeys =
        getTopLevelAspectsKeys(topLevelAspectsDetails.getAspectsDetails(), baseConfiguredTargetKey);

    SkyframeLookupResult result = env.getValuesAndExceptions(aspectsKeys);
    if (env.valuesMissing()) {
      return null; // some aspects keys are not evaluated
    }
    ImmutableList.Builder<AspectValue> values =
        ImmutableList.builderWithExpectedSize(aspectsKeys.size());
    for (SkyKey aspectKey : aspectsKeys) {
      AspectValue value = (AspectValue) result.get(aspectKey);
      if (value == null) {
        return null;
      }
      values.add(value);
    }
    return new TopLevelAspectsValue(values.build());
  }

  private static Collection<AspectKey> getTopLevelAspectsKeys(
      ImmutableList<AspectDetails> aspectsDetails, ConfiguredTargetKey topLevelTargetKey) {
    Map<AspectDescriptor, AspectKey> result = new HashMap<>();
    for (AspectDetails aspect : aspectsDetails) {
      buildAspectKey(aspect, result, topLevelTargetKey);
    }
    return result.values();
  }

  private static AspectKey buildAspectKey(
      AspectDetails aspect,
      Map<AspectDescriptor, AspectKey> result,
      ConfiguredTargetKey topLevelTargetKey) {
    if (result.containsKey(aspect.getAspectDescriptor())) {
      return result.get(aspect.getAspectDescriptor());
    }

    ImmutableList.Builder<AspectKey> dependentAspects = ImmutableList.builder();
    for (AspectDetails depAspect : aspect.getUsedAspects()) {
      dependentAspects.add(buildAspectKey(depAspect, result, topLevelTargetKey));
    }

    AspectKey aspectKey =
        AspectKeyCreator.createAspectKey(
            aspect.getAspectDescriptor(),
            dependentAspects.build(),
            topLevelTargetKey);
    result.put(aspectKey.getAspectDescriptor(), aspectKey);
    return aspectKey;
  }

  /** Exceptions thrown from ToplevelStarlarkAspectFunction. */
  public static final class TopLevelStarlarkAspectFunctionException extends SkyFunctionException {
    public TopLevelStarlarkAspectFunctionException(AspectCreationException cause) {
      super(cause, Transience.PERSISTENT);
    }
  }

}