// 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.common.collect.Sets;
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.Collection;
import java.util.List;
import java.util.Set;

/**
 * A "deps" query expression, which computes the dependencies of the argument. An optional
 * integer-literal second argument may be specified; its value bounds the search from the arguments.
 *
 * <pre>expr ::= DEPS '(' expr ')'</pre>
 * <pre>       | DEPS '(' expr ',' WORD ')'</pre>
 */
final class DepsFunction implements QueryFunction {
  DepsFunction() {
  }

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

  @Override
  public int getMandatoryArguments() {
    return 1;  // last argument is optional
  }

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

  /**
   * Breadth-first search from the arguments.
   */
  @Override
  public <T> QueryTaskFuture<Void> eval(
      final QueryEnvironment<T> env,
      VariableContext<T> context,
      final QueryExpression expression,
      List<Argument> args,
      final Callback<T> callback) {
    final int depthBound = args.size() > 1 ? args.get(1).getInteger() : Integer.MAX_VALUE;
    final MinDepthUniquifier<T> minDepthUniquifier = env.createMinDepthUniquifier();
    return env.eval(args.get(0).getExpression(), context, new Callback<T>() {
      @Override
      public void process(Iterable<T> partialResult) throws QueryException, InterruptedException {
        Collection<T> current = Sets.newHashSet(partialResult);
        env.buildTransitiveClosure(expression, (Set<T>) current, depthBound);

        // We need to iterate depthBound + 1 times.
        for (int i = 0; i <= depthBound; i++) {
          // Filter already visited nodes: if we see a node in a later round, then we don't need to
          // visit it again, because the depth at which we see it at must be greater than or equal
          // to the last visit.
          ImmutableList<T> toProcess =
              minDepthUniquifier.uniqueAtDepthLessThanOrEqualTo(current, i);
          callback.process(toProcess);
          current = ImmutableList.copyOf(env.getFwdDeps(toProcess));
          if (current.isEmpty()) {
            // Exit when there are no more nodes to visit.
            break;
          }
        }
      }
    });
  }
}