// 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.lib.query2.engine;

import com.google.common.collect.ImmutableList;
import com.google.devtools.build.lib.query2.engine.QueryEnvironment.Argument;
import com.google.devtools.build.lib.query2.engine.QueryEnvironment.ArgumentType;
import com.google.devtools.build.lib.query2.engine.QueryEnvironment.QueryFunction;
import com.google.devtools.build.lib.query2.engine.QueryEnvironment.QueryTaskFuture;
import java.util.ArrayList;
import java.util.List;

/**
 * A label(attr_name, argument) expression, which computes the set of targets whose labels appear in
 * the specified attribute of some rule in 'argument'.
 *
 * <pre>expr ::= LABELS '(' WORD ',' expr ')'</pre>
 *
 * Example:
 *
 * <pre>
 *  labels(srcs, //foo)      The 'srcs' source files to the //foo rule.
 * </pre>
 */
public class LabelsFunction implements QueryFunction {
  LabelsFunction() {
  }

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

  @Override
  public int getMandatoryArguments() {
    return 2;
  }

  @Override
  public List<ArgumentType> getArgumentTypes() {
    return ImmutableList.of(ArgumentType.WORD, ArgumentType.EXPRESSION);
  }

  @Override
  public <T> QueryTaskFuture<Void> eval(
      final QueryEnvironment<T> env,
      QueryExpressionContext<T> context,
      final QueryExpression expression,
      final List<Argument> args,
      final Callback<T> callback) {
    final String attrName = args.get(0).getWord();
    final Uniquifier<T> uniquifier = env.createUniquifier();
    return env.eval(
        args.get(1).getExpression(),
        context,
        new Callback<T>() {
          @Override
          public void process(Iterable<T> partialResult)
              throws QueryException, InterruptedException {
            for (T input : partialResult) {
              if (env.getAccessor().isRule(input)) {
                List<T> targets =
                    uniquifier.unique(
                        env.getAccessor()
                            .getPrerequisites(
                                expression,
                                input,
                                attrName,
                                "in '"
                                    + attrName
                                    + "' of rule "
                                    + env.getAccessor().getLabel(input)
                                    + ": "));
                List<T> result = new ArrayList<>(targets.size());
                for (T target : targets) {
                  result.add(env.getOrCreate(target));
                }
                callback.process(result);
              }
            }
          }
        });
  }
}