/*
 * 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.facebook.presto.sql.planner.optimizations;

import com.facebook.presto.Session;
import com.facebook.presto.spi.type.Type;
import com.facebook.presto.sql.planner.PlanNodeIdAllocator;
import com.facebook.presto.sql.planner.Symbol;
import com.facebook.presto.sql.planner.SymbolAllocator;
import com.facebook.presto.sql.planner.plan.ApplyNode;
import com.facebook.presto.sql.planner.plan.PlanNode;
import com.facebook.presto.sql.planner.plan.SemiJoinNode;
import com.facebook.presto.sql.planner.plan.SimplePlanRewriter;
import com.facebook.presto.sql.tree.Expression;
import com.facebook.presto.sql.tree.InPredicate;

import java.util.Map;
import java.util.Optional;

import static com.facebook.presto.sql.planner.plan.SimplePlanRewriter.rewriteWith;
import static com.google.common.collect.Iterables.getOnlyElement;
import static java.util.Objects.requireNonNull;

/**
 * This optimizers looks for InPredicate expressions in ApplyNodes and replaces the nodes with SemiJoin nodes.
 * <p/>
 * Plan before optimizer:
 * <pre>
 * Filter(a IN b):
 *   Apply
 *     - correlation: []  // empty
 *     - input: some plan A producing symbol a
 *     - subquery: some plan B producing symbol b
 * </pre>
 * <p/>
 * Plan after optimizer:
 * <pre>
 * Filter(semijoinresult):
 *   SemiJoin
 *     - source: plan A
 *     - filteringSource: symbol a
 *     - sourceJoinSymbol: plan B
 *     - filteringSourceJoinSymbol: symbol b
 *     - semiJoinOutput: semijoinresult
 * </pre>
 */
public class TransformUncorrelatedInPredicateSubqueryToSemiJoin
        implements PlanOptimizer
{
    @Override
    public PlanNode optimize(PlanNode plan, Session session, Map<Symbol, Type> types, SymbolAllocator symbolAllocator, PlanNodeIdAllocator idAllocator)
    {
        return rewriteWith(new InPredicateRewriter(idAllocator), plan, null);
    }

    /**
     * Each ApplyNode which contains InPredicate is replaced by semi join node.
     */
    private static class InPredicateRewriter
            extends SimplePlanRewriter<Void>
    {
        private final PlanNodeIdAllocator idAllocator;

        public InPredicateRewriter(PlanNodeIdAllocator idAllocator)
        {
            this.idAllocator = requireNonNull(idAllocator, "idAllocator is null");
        }

        @Override
        public PlanNode visitApply(ApplyNode node, RewriteContext<Void> context)
        {
            if (!node.getCorrelation().isEmpty()) {
                return context.defaultRewrite(node);
            }

            if (node.getSubqueryAssignments().size() != 1) {
                return context.defaultRewrite(node);
            }

            Expression expression = getOnlyElement(node.getSubqueryAssignments().getExpressions());
            if (!(expression instanceof InPredicate)) {
                return context.defaultRewrite(node);
            }

            PlanNode input = context.rewrite(node.getInput());
            PlanNode subquery = context.rewrite(node.getSubquery());

            InPredicate inPredicate = (InPredicate) expression;
            Symbol semiJoinSymbol = getOnlyElement(node.getSubqueryAssignments().getSymbols());
            return new SemiJoinNode(idAllocator.getNextId(),
                    input,
                    subquery,
                    Symbol.from(inPredicate.getValue()),
                    Symbol.from(inPredicate.getValueList()),
                    semiJoinSymbol,
                    Optional.empty(),
                    Optional.empty(),
                    Optional.empty()
            );
        }
    }
}