// Copyright 2015 Google Inc. 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.base.Preconditions;
import com.google.common.base.Predicates;
import com.google.devtools.build.lib.cmdline.ResolvedTargets;
import com.google.devtools.build.lib.cmdline.TargetParsingException;
import com.google.devtools.build.lib.events.Event;
import com.google.devtools.build.lib.events.EventHandler;
import com.google.devtools.build.lib.packages.NoSuchPackageException;
import com.google.devtools.build.lib.packages.NoSuchTargetException;
import com.google.devtools.build.lib.packages.Target;
import com.google.devtools.build.lib.pkgcache.ParseFailureListener;
import com.google.devtools.build.lib.skyframe.PrepareDepsOfPatternsValue.TargetPatternSequence;
import com.google.devtools.build.skyframe.SkyFunction;
import com.google.devtools.build.skyframe.SkyKey;
import com.google.devtools.build.skyframe.SkyValue;
import com.google.devtools.build.skyframe.ValueOrException;

import java.util.ArrayList;
import java.util.List;
import java.util.Map;

import javax.annotation.Nullable;

/**
 * PrepareDepsOfPatternsFunction ensures the graph loads targets matching the pattern sequence and
 * their transitive dependencies.
 */
public class PrepareDepsOfPatternsFunction implements SkyFunction {

  /**
   * Given a {@link SkyKey} that contains a sequence of target patterns, when this function returns
   * {@link PrepareDepsOfPatternsValue}, then all targets matching that sequence, and those targets'
   * transitive dependencies, have been loaded.
   */
  @Nullable
  @Override
  public SkyValue compute(SkyKey skyKey, Environment env) throws InterruptedException {
    TargetPatternSequence targetPatternSequence = (TargetPatternSequence) skyKey.argument();
    Iterable<SkyKey> patternSkyKeys = TargetPatternValue.keys(targetPatternSequence.getPatterns(),
        targetPatternSequence.getPolicy(), targetPatternSequence.getOffset());
    Map<SkyKey, ValueOrException<TargetParsingException>> targetPatternValuesByKey =
        env.getValuesOrThrow(patternSkyKeys, TargetParsingException.class);
    if (env.valuesMissing()) {
      return null;
    }

    EventHandler eventHandler = env.getListener();
    boolean handlerIsParseFailureListener = eventHandler instanceof ParseFailureListener;

    ResolvedTargets.Builder<Target> builder = ResolvedTargets.builder();
    for (SkyKey key : patternSkyKeys) {
      try {
        // The only exception type throwable by TargetPatternFunction is TargetParsingException.
        // Therefore all ValueOrException values in the map will either be non-null or throw
        // TargetParsingException when get is called.
        TargetPatternValue resultValue = Preconditions.checkNotNull(
            (TargetPatternValue) targetPatternValuesByKey.get(key).get());
        ResolvedTargets<Target> results = resultValue.getTargets();
        if (((TargetPatternValue.TargetPattern) key.argument()).isNegative()) {
          builder.filter(Predicates.not(Predicates.in(results.getTargets())));
        } else {
          builder.merge(results);
        }
      } catch (TargetParsingException e) {
        // If a target pattern can't be evaluated, notify the user of the problem and keep going.
        handleTargetParsingException(eventHandler, handlerIsParseFailureListener, key, e);
      }
    }
    ResolvedTargets<Target> resolvedTargets = builder.build();

    List<SkyKey> targetKeys = new ArrayList<>();
    for (Target target : resolvedTargets.getTargets()) {
      targetKeys.add(TransitiveTargetValue.key(target.getLabel()));
    }

    // TransitiveTargetFunction can produce exceptions of types NoSuchPackageException and
    // NoSuchTargetException. However, PrepareDepsOfPatternsFunction doesn't care about any errors
    // found during transitive target loading--it just wants the graph to have loaded whatever
    // transitive target values are available.
    env.getValuesOrThrow(targetKeys, NoSuchPackageException.class, NoSuchTargetException.class);
    if (env.valuesMissing()) {
      return null;
    }

    return PrepareDepsOfPatternsValue.INSTANCE;
  }

  private static void handleTargetParsingException(EventHandler eventHandler,
      boolean handlerIsParseFailureListener, SkyKey key, TargetParsingException e) {
    TargetPatternValue.TargetPattern pattern = (TargetPatternValue.TargetPattern) key.argument();
    String rawPattern = pattern.getPattern();
    String errorMessage = e.getMessage();
    eventHandler.handle(Event.error("Skipping '" + rawPattern + "': " + errorMessage));
    if (handlerIsParseFailureListener) {
      ParseFailureListener parseListener = (ParseFailureListener) eventHandler;
      parseListener.parsingError(rawPattern,  errorMessage);
    }
  }

  @Nullable
  @Override
  public String extractTag(SkyKey skyKey) {
    return null;
  }

}