// Copyright 2014 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.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 java.util.LinkedHashSet;
import java.util.List;
import java.util.Set;

/**
 * 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>
 */
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> Set<T> eval(QueryEnvironment<T> env, QueryExpression expression, List<Argument> args)
      throws QueryException, InterruptedException {
    Set<T> inputs = args.get(1).getExpression().eval(env);
    Set<T> result = new LinkedHashSet<>();
    String attrName = args.get(0).getWord();
    for (T input : inputs) {
      if (env.getAccessor().isRule(input)) {
        List<T> targets = env.getAccessor().getLabelListAttr(expression, input, attrName,
            "in '" + attrName + "' of rule " + env.getAccessor().getLabel(input) + ": ");
        for (T target : targets) {
          result.add(env.getOrCreate(target));
        }
      }
    }
    return result;
  }
}