// 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.Lists;
import com.google.common.collect.Multimap;
import com.google.devtools.build.lib.cmdline.Label;
import com.google.devtools.build.lib.events.EventHandler;
import com.google.devtools.build.lib.packages.Attribute;
import com.google.devtools.build.lib.packages.BuildFileContainsErrorsException;
import com.google.devtools.build.lib.packages.DependencyFilter;
import com.google.devtools.build.lib.packages.InputFile;
import com.google.devtools.build.lib.packages.NoSuchPackageException;
import com.google.devtools.build.lib.packages.NoSuchTargetException;
import com.google.devtools.build.lib.packages.OutputFile;
import com.google.devtools.build.lib.packages.Package;
import com.google.devtools.build.lib.packages.PackageGroup;
import com.google.devtools.build.lib.packages.Rule;
import com.google.devtools.build.lib.packages.Target;
import com.google.devtools.build.lib.util.Preconditions;
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.ValueOrException2;

import java.util.Collection;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;

import javax.annotation.Nullable;

/**
 * This class can be extended to define {@link SkyFunction}s that traverse a target and its
 * transitive dependencies and return values based on that traversal.
 *
 * <p>The {@code TProcessedTargets} type parameter represents the result of processing a target and
 * its transitive dependencies.
 *
 * <p>{@code TransitiveBaseTraversalFunction} asks for one to be constructed via {@link
 * #processTarget}, and then asks for it to be updated based on the current target's
 * attributes' dependencies via {@link #processDeps}, and then asks for it to be updated based
 * on the current target' aspects' dependencies via {@link #processDeps}. Finally, it calls
 * {@link #computeSkyValue} with the {#code ProcessedTargets} to get the {@link SkyValue} to
 * return.
 */
abstract class TransitiveBaseTraversalFunction<TProcessedTargets> implements SkyFunction {

  /**
   * Returns a {@link SkyKey} corresponding to the traversal of a target specified by {@code label}
   * and its transitive dependencies.
   *
   * <p>Extenders of this class should implement this function to return a key with their
   * specialized {@link SkyFunction}'s name.
   *
   * <p>{@link TransitiveBaseTraversalFunction} calls this for each dependency of a target, and
   * then gets their values from the environment.
   *
   * <p>The key's {@link SkyFunction} may throw at most {@link NoSuchPackageException} and
   * {@link NoSuchTargetException}. Other exception types are not handled by {@link
   * TransitiveBaseTraversalFunction}.
   */
  abstract SkyKey getKey(Label label);

  abstract TProcessedTargets processTarget(Label label, TargetAndErrorIfAny targetAndErrorIfAny);

  abstract void processDeps(TProcessedTargets processedTargets, EventHandler eventHandler,
      TargetAndErrorIfAny targetAndErrorIfAny,
      Iterable<Entry<SkyKey, ValueOrException2<NoSuchPackageException, NoSuchTargetException>>>
          depEntries);

  /**
   * Returns a {@link SkyValue} based on the target and any errors it has, and the values
   * accumulated across it and a traversal of its transitive dependencies.
   */
  abstract SkyValue computeSkyValue(TargetAndErrorIfAny targetAndErrorIfAny,
      TProcessedTargets processedTargets);

  /**
   * Returns a {@link TargetMarkerValue} corresponding to the {@param targetMarkerKey} or {@code
   * null} if the value isn't ready.
   */
  @Nullable
  abstract TargetMarkerValue getTargetMarkerValue(SkyKey targetMarkerKey, Environment env)
      throws NoSuchTargetException, NoSuchPackageException;

  @Override
  public SkyValue compute(SkyKey key, Environment env)
      throws TransitiveBaseTraversalFunctionException {
    Label label = (Label) key.argument();
    LoadTargetResults loadTargetResults;
    try {
      loadTargetResults = loadTarget(env, label);
    } catch (NoSuchTargetException e) {
      throw new TransitiveBaseTraversalFunctionException(e);
    } catch (NoSuchPackageException e) {
      throw new TransitiveBaseTraversalFunctionException(e);
    }
    LoadTargetResultsType loadTargetResultsType = loadTargetResults.getType();
    if (loadTargetResultsType.equals(LoadTargetResultsType.VALUES_MISSING)) {
      return null;
    }
    Preconditions.checkState(
        loadTargetResultsType.equals(LoadTargetResultsType.TARGET_AND_ERROR_IF_ANY),
        loadTargetResultsType);
    TargetAndErrorIfAny targetAndErrorIfAny = (TargetAndErrorIfAny) loadTargetResults;
    TProcessedTargets processedTargets = processTarget(label, targetAndErrorIfAny);

    // Process deps from attributes.
    Iterable<SkyKey> labelDepKeys = getLabelDepKeys(targetAndErrorIfAny.getTarget());

    Map<SkyKey, ValueOrException2<NoSuchPackageException, NoSuchTargetException>> depMap =
        env.getValuesOrThrow(labelDepKeys, NoSuchPackageException.class,
            NoSuchTargetException.class);
    processDeps(processedTargets, env.getListener(), targetAndErrorIfAny, depMap.entrySet());
    if (env.valuesMissing()) {
      return null;
    }

    // Process deps from aspects.
    Iterable<SkyKey> labelAspectKeys =
        getStrictLabelAspectKeys(targetAndErrorIfAny.getTarget(), depMap, env);
    Set<Entry<SkyKey, ValueOrException2<NoSuchPackageException, NoSuchTargetException>>>
        labelAspectEntries = env.getValuesOrThrow(labelAspectKeys, NoSuchPackageException.class,
        NoSuchTargetException.class).entrySet();
    processDeps(processedTargets, env.getListener(), targetAndErrorIfAny, labelAspectEntries);
    if (env.valuesMissing()) {
      return null;
    }

    return computeSkyValue(targetAndErrorIfAny, processedTargets);
  }

  @Override
  public String extractTag(SkyKey skyKey) {
    return Label.print(((Label) skyKey.argument()));
  }

  /**
   * Return an Iterable of SkyKeys corresponding to the Aspect-related dependencies of target.
   *
   * <p>This method may return a precise set of aspect keys, but may need to request additional
   * dependencies from the env to do so.
   */
  private Iterable<SkyKey> getStrictLabelAspectKeys(Target target,
          Map<SkyKey, ValueOrException2<NoSuchPackageException, NoSuchTargetException>> depMap,
          Environment env) {
    List<SkyKey> depKeys = Lists.newArrayList();
    if (target instanceof Rule) {
      Map<Label, ValueOrException2<NoSuchPackageException, NoSuchTargetException>> labelDepMap =
          new HashMap<>(depMap.size());
      for (Entry<SkyKey, ValueOrException2<NoSuchPackageException, NoSuchTargetException>> entry :
          depMap.entrySet()) {
        labelDepMap.put((Label) entry.getKey().argument(), entry.getValue());
      }

      Multimap<Attribute, Label> transitions =
          ((Rule) target).getTransitions(DependencyFilter.NO_NODEP_ATTRIBUTES);
      for (Entry<Attribute, Label> entry : transitions.entries()) {
        ValueOrException2<NoSuchPackageException, NoSuchTargetException> value =
            labelDepMap.get(entry.getValue());
        for (Label label :
                getAspectLabels((Rule) target, entry.getKey(), entry.getValue(), value, env)) {
          depKeys.add(getKey(label));
        }
      }
    }
    return depKeys;
  }

  /** Get the Aspect-related Label deps for the given edge. */
  protected abstract Collection<Label> getAspectLabels(
      Rule fromRule,
      Attribute attr,
      Label toLabel,
      ValueOrException2<NoSuchPackageException, NoSuchTargetException> toVal,
      Environment env);

  private Iterable<SkyKey> getLabelDepKeys(Target target) {
    List<SkyKey> depKeys = Lists.newArrayList();
    for (Label depLabel : getLabelDeps(target)) {
      depKeys.add(getKey(depLabel));
    }
    return depKeys;
  }

  // TODO(bazel-team): Unify this logic with that in LabelVisitor, and possibly DependencyResolver.
  private static Iterable<Label> getLabelDeps(Target target) {
    final Set<Label> labels = new HashSet<>();
    if (target instanceof OutputFile) {
      Rule rule = ((OutputFile) target).getGeneratingRule();
      labels.add(rule.getLabel());
      visitTargetVisibility(target, labels);
    } else if (target instanceof InputFile) {
      visitTargetVisibility(target, labels);
    } else if (target instanceof Rule) {
      visitTargetVisibility(target, labels);
      visitRule(target, labels);
    } else if (target instanceof PackageGroup) {
      visitPackageGroup((PackageGroup) target, labels);
    }
    return labels;
  }

  private static void visitRule(Target target, Set<Label> labels) {
    labels.addAll(((Rule) target).getTransitions(DependencyFilter.NO_NODEP_ATTRIBUTES).values());
  }

  private static void visitTargetVisibility(Target target, Set<Label> labels) {
    labels.addAll(target.getVisibility().getDependencyLabels());
  }

  private static void visitPackageGroup(PackageGroup packageGroup, Set<Label> labels) {
    labels.addAll(packageGroup.getIncludes());
  }

  enum LoadTargetResultsType {
    VALUES_MISSING,
    TARGET_AND_ERROR_IF_ANY
  }

  interface LoadTargetResults {
    LoadTargetResultsType getType();
  }

  private static class ValuesMissing implements LoadTargetResults {

    private static final ValuesMissing INSTANCE = new ValuesMissing();

    private ValuesMissing() {}

    @Override
    public LoadTargetResultsType getType() {
      return LoadTargetResultsType.VALUES_MISSING;
    }
  }

  interface TargetAndErrorIfAny {

    boolean isPackageLoadedSuccessfully();

    @Nullable NoSuchTargetException getErrorLoadingTarget();

    Target getTarget();
  }

  private static class TargetAndErrorIfAnyImpl implements TargetAndErrorIfAny, LoadTargetResults {

    private final boolean packageLoadedSuccessfully;
    @Nullable private final NoSuchTargetException errorLoadingTarget;
    private final Target target;

    private TargetAndErrorIfAnyImpl(boolean packageLoadedSuccessfully,
        @Nullable NoSuchTargetException errorLoadingTarget, Target target) {
      this.packageLoadedSuccessfully = packageLoadedSuccessfully;
      this.errorLoadingTarget = errorLoadingTarget;
      this.target = target;
    }

    @Override
    public LoadTargetResultsType getType() {
      return LoadTargetResultsType.TARGET_AND_ERROR_IF_ANY;
    }

    @Override
    public boolean isPackageLoadedSuccessfully() {
      return packageLoadedSuccessfully;
    }

    @Override
    @Nullable
    public NoSuchTargetException getErrorLoadingTarget() {
      return errorLoadingTarget;
    }

    @Override
    public Target getTarget() {
      return target;
    }
  }

  private LoadTargetResults loadTarget(Environment env, Label label)
      throws NoSuchTargetException, NoSuchPackageException {
    SkyKey packageKey = PackageValue.key(label.getPackageIdentifier());
    SkyKey targetKey = TargetMarkerValue.key(label);

    boolean packageLoadedSuccessfully;
    Target target;
    NoSuchTargetException errorLoadingTarget = null;
    try {
      TargetMarkerValue targetValue = getTargetMarkerValue(targetKey, env);
      boolean targetValueMissing = targetValue == null;
      Preconditions.checkState(targetValueMissing == env.valuesMissing(), targetKey);
      if (targetValueMissing) {
        return ValuesMissing.INSTANCE;
      }
      PackageValue packageValue = (PackageValue) env.getValueOrThrow(packageKey,
          NoSuchPackageException.class);
      if (packageValue == null) {
        return ValuesMissing.INSTANCE;
      }

      Package pkg = packageValue.getPackage();
      if (pkg.containsErrors()) {
        throw new BuildFileContainsErrorsException(label.getPackageIdentifier());
      }
      packageLoadedSuccessfully = true;
      try {
        target = pkg.getTarget(label.getName());
      } catch (NoSuchTargetException unexpected) {
        // Not expected since the TargetMarkerFunction would have failed earlier if the Target
        // was not present.
        throw new IllegalStateException(unexpected);
      }
    } catch (NoSuchTargetException e) {
      if (!e.hasTarget()) {
        throw e;
      }

      // We know that a Target may be extracted, but we need to get it out of the Package
      // (which is known to be in error).
      PackageValue packageValue =
          (PackageValue) Preconditions.checkNotNull(env.getValue(packageKey), label);
      Package pkg = packageValue.getPackage();
      try {
        target = pkg.getTarget(label.getName());
      } catch (NoSuchTargetException nste) {
        throw new IllegalStateException("Expected target to exist", nste);
      }

      errorLoadingTarget = e;
      packageLoadedSuccessfully = false;
    }
    return new TargetAndErrorIfAnyImpl(packageLoadedSuccessfully, errorLoadingTarget, target);
  }

  /**
   * Used to declare all the exception types that can be wrapped in the exception thrown by
   * {@link TransitiveTraversalFunction#compute}.
   */
  static class TransitiveBaseTraversalFunctionException extends SkyFunctionException {
    /**
     * Used to propagate an error from a direct target dependency to the target that depended on
     * it.
     */
    public TransitiveBaseTraversalFunctionException(NoSuchPackageException e) {
      super(e, Transience.PERSISTENT);
    }

    /**
     * In nokeep_going mode, used to propagate an error from a direct target dependency to the
     * target that depended on it.
     *
     * <p>In keep_going mode, used the same way, but only for targets that could not be loaded at
     * all (we proceed with transitive loading on targets that contain errors).</p>
     */
    public TransitiveBaseTraversalFunctionException(NoSuchTargetException e) {
      super(e, Transience.PERSISTENT);
    }
  }
}