/*
 * Copyright 2019-2021 The Polypheny Project
 *
 * 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.
 *
 * This file incorporates code covered by the following terms:
 *
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to you 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,
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package org.polypheny.db.algebra.rules;


import org.polypheny.db.algebra.AlgNode;
import org.polypheny.db.algebra.core.AlgFactories;
import org.polypheny.db.algebra.core.Project;
import org.polypheny.db.plan.AlgOptRule;
import org.polypheny.db.plan.AlgOptRuleCall;
import org.polypheny.db.rex.RexUtil;
import org.polypheny.db.tools.AlgBuilderFactory;


/**
 * Planner rule that, given a {@link Project} node that merely returns its input, converts the node into its child.
 *
 * For example,
 * <code>Project(ArrayReader(a), {$input0})</code>
 * becomes
 * <code>ArrayReader(a)</code>.</p>
 *
 * @see CalcRemoveRule
 * @see ProjectMergeRule
 */
public class ProjectRemoveRule extends AlgOptRule {

    public static final ProjectRemoveRule INSTANCE = new ProjectRemoveRule( AlgFactories.LOGICAL_BUILDER );


    /**
     * Creates a ProjectRemoveRule.
     *
     * @param algBuilderFactory Builder for relational expressions
     */
    public ProjectRemoveRule( AlgBuilderFactory algBuilderFactory ) {
        // Create a specialized operand to detect non-matches early. This keeps the rule queue short.
        super( operandJ( Project.class, null, ProjectRemoveRule::isTrivial, any() ), algBuilderFactory, null );
    }


    @Override
    public void onMatch( AlgOptRuleCall call ) {
        Project project = call.alg( 0 );
        assert isTrivial( project );
        AlgNode stripped = project.getInput();
        if ( stripped instanceof Project ) {
            // Rename columns of child projection if desired field names are given.
            Project childProject = (Project) stripped;
            stripped = childProject.copy(
                    childProject.getTraitSet(),
                    childProject.getInput(),
                    childProject.getProjects(),
                    project.getRowType() );
        }
        AlgNode child = call.getPlanner().register( stripped, project );
        call.transformTo( child );
    }


    /**
     * Returns the child of a project if the project is trivial, otherwise the project itself.
     */
    public static AlgNode strip( Project project ) {
        return isTrivial( project ) ? project.getInput() : project;
    }


    public static boolean isTrivial( Project project ) {
        return RexUtil.isIdentity( project.getProjects(), project.getInput().getRowType() );
    }

}

