// Copyright 2019 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.analysis.config;

import static com.google.common.collect.ImmutableList.toImmutableList;
import static com.google.devtools.build.lib.packages.DeclaredExecGroup.DEFAULT_EXEC_GROUP_NAME;

import com.github.benmanes.caffeine.cache.Cache;
import com.github.benmanes.caffeine.cache.Caffeine;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Iterables;
import com.google.devtools.build.lib.analysis.PlatformOptions;
import com.google.devtools.build.lib.analysis.config.transitions.ConfigurationTransition;
import com.google.devtools.build.lib.analysis.config.transitions.NoConfigTransition;
import com.google.devtools.build.lib.analysis.config.transitions.PatchTransition;
import com.google.devtools.build.lib.analysis.config.transitions.TransitionFactory;
import com.google.devtools.build.lib.cmdline.Label;
import com.google.devtools.build.lib.events.EventHandler;
import com.google.devtools.build.lib.packages.AttributeTransitionData;
import com.google.devtools.build.lib.rules.config.FeatureFlagValue;
import com.google.devtools.build.lib.starlarkbuildapi.config.StarlarkConfigApi.ExecTransitionFactoryApi;
import com.google.devtools.build.lib.util.Pair;
import java.util.Map;
import javax.annotation.Nullable;

/**
 * {@link TransitionFactory} implementation which creates a {@link PatchTransition} which will
 * transition to a configuration suitable for building dependencies for the execution platform of
 * the depending target.
 *
 * <p>Note that execGroup is not directly consumed by the involved transition but instead stored
 * here. Instead, the rule definition stores it in this factory. Then, toolchain resolution extracts
 * and consumes it to store an execution platform in attrs. Finally, the execution platform is read
 * by the factory to create the transition.
 */
public class ExecutionTransitionFactory
    implements TransitionFactory<AttributeTransitionData>, ExecTransitionFactoryApi {

  /** Returns a new {@link ExecutionTransitionFactory} for the default {@link DeclaredExecGroup}. */
  public static ExecutionTransitionFactory createFactory() {
    return new ExecutionTransitionFactory(DEFAULT_EXEC_GROUP_NAME);
  }

  /** Returns a new {@link ExecutionTransitionFactory} for the given {@link DeclaredExecGroup}. */
  public static ExecutionTransitionFactory createFactory(String execGroup) {
    return new ExecutionTransitionFactory(execGroup);
  }

  /**
   * Guarantees we don't duplicate instances of the same transition.
   *
   * <p>Bazel's Starlark logic also maintains a distinct instance for each Starlark transition.
   * While that makes this cache seem unnecessary, it still has value. The exec transition uniquely
   * takes an extra parameter: the execution platform label. This is provided by toolchain
   * resolution - the transition can't read it from input build options. So we need to cache on
   * {@code label, originalTransition} pairs.
   */
  private static final Cache<Pair<Label, Integer>, PatchTransition> transitionInstanceCache =
      Caffeine.newBuilder().weakValues().build();

  @Override
  public PatchTransition create(AttributeTransitionData dataWithTargetAttributes)
      throws TransitionCreationException {
    // Delete AttributeTransitionData.attributes() so the exec transition doesn't try to read the
    // attributes of the target it's attached to. This is for two reasons:
    //
    //   1) While per-target exec transitions may be interesting, we're not ready to expose that
    //      level of API flexibility
    //   2) No need for StarlarkTransitionCache misses due to different StarlarkTransition instances
    //       bound to different attributes that shouldn't affect output.
    AttributeTransitionData data =
        AttributeTransitionData.builder()
            .analysisData(dataWithTargetAttributes.analysisData())
            .executionPlatform(dataWithTargetAttributes.executionPlatform())
            .build();

    if (data.analysisData() == null) {
      // TODO: https://github.com/bazelbuild/rules_license/issues/148 - This is a temporary hack to
      // prevent the license() rule's license_kinds attribute from failing.
      //
      // license() rules are already configured in NoConfigTransition (see the PR that produced this
      // comment). So when they traverse 'cfg = "exec"' on their license_kind attribute, without
      // this special case they'd throw the below TransitionCreationException.
      //
      // What we really want is to remove 'cfg = "exec"' from license_kind's attribute definition
      // because it's redundant (its purpose was to avoid unnecesary forking from target
      // configurations, not to explicitly use the exec configuration). The problem is that the
      // attribute's definition is in in rules_license Starlark code, but the code that makes its
      // parent license() use NoConfigTransition is in Bazel. We need to wait until that code is
      // in a proper Bazel release before to avoid accidental target forking.
      //
      // So the actionable is: when rules_license() users use a new enough Bazel version, remove
      // 'cfg = exec"' from license()'s license_kinds() attribute, then remove this check.
      if (dataWithTargetAttributes.attributes().has("license_kinds")) {
        return NoConfigTransition.INSTANCE;
      }
      throw new TransitionCreationException(
          "expected a Starlark exec transition definition, but was null");
    }
    @SuppressWarnings("unchecked")
    TransitionFactory<AttributeTransitionData> starlarkExecTransitionProvider =
        (TransitionFactory<AttributeTransitionData>) data.analysisData();

    return transitionInstanceCache.get(
        // A Starlark transition keeps the same instance unless we modify its .bzl file.
        Pair.of(data.executionPlatform(), starlarkExecTransitionProvider.hashCode()),
        (p) ->
            new ExecTransitionFinalizer(
                data.executionPlatform(), starlarkExecTransitionProvider.create(data)));
  }

  private final String execGroup;

  private ExecutionTransitionFactory(String execGroup) {
    this.execGroup = execGroup;
  }

  @Override
  public TransitionType transitionType() {
    return TransitionType.ATTRIBUTE;
  }

  public String getExecGroup() {
    return execGroup;
  }

  @Override
  public boolean isTool() {
    return true;
  }

  /**
   * Complete exec transition.
   *
   * <p>Takes as input the execution platform and the main transition. Calls the main transition,
   * then runs finalizer logic that has to be handled natively.
   */
  private static class ExecTransitionFinalizer implements PatchTransition {
    private static final ImmutableSet<Class<? extends FragmentOptions>> FRAGMENTS =
        ImmutableSet.of(CoreOptions.class, PlatformOptions.class);

    @Nullable private final Label executionPlatform;

    private final ConfigurationTransition mainTransition;

    ExecTransitionFinalizer(
        @Nullable Label executionPlatform, ConfigurationTransition mainTransition) {
      this.executionPlatform = executionPlatform;
      this.mainTransition = mainTransition;
    }

    @Override
    public String getName() {
      return "exec";
    }

    /**
     * Implement {@link ConfigurationTransition#visit}} so {@link
     * com.google.devtools.build.lib.analysis.config.StarlarkTransitionCache} caches application if
     * this is a Starlark transition.
     */
    @Override
    public <E extends Exception> void visit(Visitor<E> visitor) throws E {
      this.mainTransition.visit(visitor);
    }

    @Override
    public ImmutableSet<Class<? extends FragmentOptions>> requiresOptionFragments() {
      // This is technically a lie since the call to underlying().createExecOptions is transitively
      // reading and potentially modifying all fragments. There is currently no way for the
      // transition to actually list all fragments like this and thus only lists the ones that are
      // directly being read here. Note that this transition is exceptional in its implementation.
      return FRAGMENTS;
    }

    @Override
    public BuildOptions patch(BuildOptionsView options, EventHandler eventHandler)
        throws InterruptedException {
      if (executionPlatform == null) {
        // No execution platform is known, so don't change anything.
        return options.underlying();
      }

      Map.Entry<String, BuildOptions> splitOptions =
          Iterables.getOnlyElement(mainTransition.apply(options, eventHandler).entrySet());
      BuildOptions execOptions = splitOptions.getValue();

      // Set the target to the saved execution platform if there is one.
      PlatformOptions platformOptions = execOptions.get(PlatformOptions.class);
      if (platformOptions != null) {
        platformOptions.setPlatforms(ImmutableList.of(executionPlatform));
      }

      // Remove any FeatureFlags that were set.
      ImmutableList<Label> featureFlags =
          execOptions.getStarlarkOptions().entrySet().stream()
              .filter(entry -> entry.getValue() instanceof FeatureFlagValue)
              .map(Map.Entry::getKey)
              .collect(toImmutableList());

      BuildOptions result = execOptions;
      if (!featureFlags.isEmpty()) {
        BuildOptions.Builder resultBuilder = result.toBuilder();
        featureFlags.forEach(resultBuilder::removeStarlarkOption);
        result = resultBuilder.build();
      }

      // The conditional use of a Builder above may have replaced result and underlying options
      // with a clone so must refresh it.
      CoreOptions coreOptions = result.get(CoreOptions.class);
      coreOptions.setCommandLineFlagAliases(
          options.underlying().get(CoreOptions.class).getCommandLineFlagAliases());
      // TODO(blaze-configurability-team): These updates probably requires a bit too much knowledge
      //   of exactly how the immutable state and mutable state of BuildOptions is interacting.
      //   Might be good to have an option to wipeout that state rather than cloning so much.
      coreOptions.setPlatformSuffix("exec");
      coreOptions.setExecutionInfoModifier(
          options.underlying().get(CoreOptions.class).getExecutionInfoModifier());
      coreOptions.setOverridePlatformCpuName(
          options.underlying().get(CoreOptions.class).getOverridePlatformCpuName());
      coreOptions.setDisabledSelectOptions(
          options.underlying().get(CoreOptions.class).getDisabledSelectOptions());
      coreOptions.setIncompatibleTargetCpuFromPlatform(
          options.underlying().get(CoreOptions.class).getIncompatibleTargetCpuFromPlatform());
      return result;
    }
  }
}
