/*
 * 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.DependencyExtractor;
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.iterative.Lookup;
import com.facebook.presto.sql.planner.iterative.Rule;
import com.facebook.presto.sql.planner.plan.PlanNode;
import com.facebook.presto.sql.planner.plan.WindowNode;

import java.util.Iterator;
import java.util.Optional;

import static com.facebook.presto.sql.planner.iterative.rule.Util.transpose;

public class SwapAdjacentWindowsByPartitionsOrder
        implements Rule
{
    @Override
    public Optional<PlanNode> apply(PlanNode node, Lookup lookup, PlanNodeIdAllocator idAllocator, SymbolAllocator symbolAllocator, Session session)
    {
        if (!(node instanceof WindowNode)) {
            return Optional.empty();
        }

        WindowNode parent = (WindowNode) node;

        PlanNode child = lookup.resolve(parent.getSource());
        if (!(child instanceof WindowNode)) {
            return Optional.empty();
        }

        if ((compare(parent, (WindowNode) child) < 0) && (!dependsOn(parent, (WindowNode) child))) {
            return Optional.of(transpose(parent, child));
        }
        else {
            return Optional.empty();
        }
    }

    private static boolean dependsOn(WindowNode parent, WindowNode child)
    {
        return parent.getPartitionBy().stream().anyMatch(child.getCreatedSymbols()::contains)
                || parent.getOrderBy().stream().anyMatch(child.getCreatedSymbols()::contains)
                || parent.getWindowFunctions().values().stream()
                .map(WindowNode.Function::getFunctionCall)
                .map(DependencyExtractor::extractUnique)
                .flatMap(symbols -> symbols.stream())
                .anyMatch(child.getCreatedSymbols()::contains);
    }

    private static int compare(WindowNode o1, WindowNode o2)
    {
        Iterator<Symbol> iterator1 = o1.getPartitionBy().iterator();
        Iterator<Symbol> iterator2 = o2.getPartitionBy().iterator();

        while (iterator1.hasNext() && iterator2.hasNext()) {
            Symbol symbol1 = iterator1.next();
            Symbol symbol2 = iterator2.next();

            int comparison = symbol1.compareTo(symbol2);
            if (comparison != 0) {
                return comparison;
            }
        }

        if (iterator1.hasNext()) {
            return 1;
        }

        if (iterator2.hasNext()) {
            return -1;
        }

        // If both are equal, let's establish an arbitrary order to prevent non-deterministic results of swapping WindowNodes with identical PartitionBy clauses
        return o1.getId().toString().compareTo(o2.getId().toString());
    }
}