// 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.query2.engine;

import com.google.common.base.Optional;
import com.google.common.base.Predicate;
import com.google.common.base.Predicates;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.Iterables;
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;

/**
 * An "allrdeps" query expression, which computes the reverse dependencies of the argument within
 * the currently known universe. An optional integer-literal second argument may be specified; its
 * value bounds the search from the arguments.
 *
 * <pre>expr ::= ALLRDEPS '(' expr ')'</pre>
 * <pre>       | ALLRDEPS '(' expr ',' WORD ')'</pre>
 */
// Public because SkyQueryEnvironment needs to refer to it directly.
public class AllRdepsFunction implements QueryFunction {

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

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

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

  @Override
  public <T> QueryTaskFuture<Void> eval(
      QueryEnvironment<T> env,
      VariableContext<T> context,
      QueryExpression expression,
      List<Argument> args,
      Callback<T> callback) {
    return eval(env, context, args, callback, Optional.<Predicate<T>>absent());
  }

  protected <T> QueryTaskFuture<Void> eval(
      final QueryEnvironment<T> env,
      VariableContext<T> context,
      final List<Argument> args,
      final Callback<T> callback,
      Optional<Predicate<T>> universeMaybe) {
    final int depth = args.size() > 1 ? args.get(1).getInteger() : Integer.MAX_VALUE;
    final Predicate<T> universe = universeMaybe.isPresent()
        ? universeMaybe.get()
        : Predicates.<T>alwaysTrue();
    if (env instanceof StreamableQueryEnvironment<?>) {
      StreamableQueryEnvironment<T> streamableEnv = ((StreamableQueryEnvironment<T>) env);
      return depth == Integer.MAX_VALUE && !universeMaybe.isPresent()
        ? streamableEnv.getAllRdepsUnboundedParallel(args.get(0).getExpression(), context, callback)
        : streamableEnv.getAllRdeps(
            args.get(0).getExpression(), universe, context, callback, depth);
    } else {
      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 {
              Iterable<T> current = partialResult;
              // We need to iterate depthBound + 1 times.
              for (int i = 0; i <= depth; i++) {
                List<T> next = new ArrayList<>();
                // Restrict to nodes satisfying the universe predicate.
                Iterable<T> currentInUniverse = Iterables.filter(current, universe);
                // 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 must be greater
                // than or equal to the last visit.
                next.addAll(env.getReverseDeps(
                    minDepthUniquifier.uniqueAtDepthLessThanOrEqualTo(currentInUniverse, i)));
                callback.process(currentInUniverse);
                if (next.isEmpty()) {
                  // Exit when there are no more nodes to visit.
                  break;
                }
                current = next;
              }
            }
          });
    }
  }
}