/*
 * 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.iterative.rule;

import com.facebook.presto.Session;
import com.facebook.presto.sql.planner.PlanNodeIdAllocator;
import com.facebook.presto.sql.planner.SymbolAllocator;
import com.facebook.presto.sql.planner.iterative.Lookup;
import com.facebook.presto.sql.planner.iterative.Rule;
import com.facebook.presto.sql.planner.plan.DeleteNode;
import com.facebook.presto.sql.planner.plan.ExchangeNode;
import com.facebook.presto.sql.planner.plan.PlanNode;
import com.facebook.presto.sql.planner.plan.TableFinishNode;
import com.facebook.presto.sql.planner.plan.ValuesNode;
import com.facebook.presto.sql.tree.LongLiteral;
import com.google.common.collect.ImmutableList;

import java.util.Optional;

import static com.google.common.collect.Iterables.getOnlyElement;

/**
 * If the predicate for a delete is optimized to false, the target table scan
 * of the delete will be replaced with an empty values node. This type of
 * plan cannot be executed and is meaningless anyway, so we replace the
 * entire thing with a values node.
 * <p>
 * Transforms
 * <pre>
 *  - TableFinish
 *    - Exchange
 *      - Delete
 *        - empty Values
 * </pre>
 * into
 * <pre>
 *  - Values (0)
 * </pre>
 */
public class RemoveEmptyDelete
        implements Rule
{
    @Override
    public Optional<PlanNode> apply(PlanNode node, Lookup lookup, PlanNodeIdAllocator idAllocator, SymbolAllocator symbolAllocator, Session session)
    {
        // TODO split into multiple rules (https://github.com/prestodb/presto/issues/7292)

        if (!(node instanceof TableFinishNode)) {
            return Optional.empty();
        }
        TableFinishNode finish = (TableFinishNode) node;

        PlanNode finishSource = lookup.resolve(finish.getSource());
        if (!(finishSource instanceof ExchangeNode)) {
            return Optional.empty();
        }
        ExchangeNode exchange = (ExchangeNode) finishSource;

        if (exchange.getSources().size() != 1) {
            return Optional.empty();
        }

        PlanNode exchangeSource = lookup.resolve(getOnlyElement(exchange.getSources()));
        if (!(exchangeSource instanceof DeleteNode)) {
            return Optional.empty();
        }
        DeleteNode delete = (DeleteNode) exchangeSource;

        PlanNode deleteSource = lookup.resolve(delete.getSource());
        if (!(deleteSource instanceof ValuesNode)) {
            return Optional.empty();
        }
        ValuesNode values = (ValuesNode) deleteSource;

        if (!values.getRows().isEmpty()) {
            return Optional.empty();
        }

        return Optional.of(
                new ValuesNode(
                        node.getId(),
                        node.getOutputSymbols(),
                        ImmutableList.of(ImmutableList.of(new LongLiteral("0")))));
    }
}