content: /*
   * 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, 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 org.apache.asterix.lang.sqlpp.rewrites.visitor;
  
  import static org.apache.asterix.lang.sqlpp.util.SqlppRewriteUtil.substituteExpression;
  
  import java.util.HashMap;
  import java.util.Iterator;
  import java.util.List;
  import java.util.Map;
  
  import org.apache.asterix.common.exceptions.CompilationException;
  import org.apache.asterix.lang.common.base.Expression;
  import org.apache.asterix.lang.common.base.ILangExpression;
  import org.apache.asterix.lang.common.clause.LetClause;
  import org.apache.asterix.lang.common.rewrites.LangRewritingContext;
  import org.apache.asterix.lang.sqlpp.expression.SelectExpression;
  import org.apache.asterix.lang.sqlpp.util.SqlppRewriteUtil;
  import org.apache.asterix.lang.sqlpp.visitor.CheckNonFunctionalExpressionVisitor;
  import org.apache.asterix.lang.sqlpp.visitor.base.AbstractSqlppExpressionScopingVisitor;
  import org.apache.asterix.metadata.declared.MetadataProvider;
  
  public class InlineWithExpressionVisitor extends AbstractSqlppExpressionScopingVisitor {
  
      private final CheckNonFunctionalExpressionVisitor checkNonFunctionalExpressionVisitor;
  
      public InlineWithExpressionVisitor(LangRewritingContext context, MetadataProvider metadataProvider) {
          super(context);
          checkNonFunctionalExpressionVisitor = new CheckNonFunctionalExpressionVisitor(metadataProvider);
      }
  
      @Override
      public Expression visit(SelectExpression selectExpression, ILangExpression arg) throws CompilationException {
          if (selectExpression.hasLetClauses()) {
              // Inlines the leading WITH list.
              Map<Expression, Expression> varExprMap = new HashMap<>();
              List<LetClause> withs = selectExpression.getLetList();
              Iterator<LetClause> with = withs.iterator();
              while (with.hasNext()) {
                  LetClause letClause = with.next();
                  // Replaces the let binding Expr.
                  Expression expr = letClause.getBindingExpr();
                  Expression newBindingExpr = SqlppRewriteUtil.substituteExpression(expr, varExprMap, context);
                  letClause.setBindingExpr(newBindingExpr);
  
                  // Performs the rewriting recursively in the newBindingExpr itself.
                  super.visit(newBindingExpr, arg);
  
                  Expression bindingExpr = letClause.getBindingExpr();
                  Boolean isNonFunctional = bindingExpr.accept(checkNonFunctionalExpressionVisitor, null);
                  if (isNonFunctional != null && isNonFunctional) {
                      continue;
                  }
  
                  // Removes the WITH entry and adds variable-expr mapping into the varExprMap.
                  with.remove();
                  varExprMap.put(letClause.getVarExpr(), bindingExpr);
              }
  
              // Inlines WITH expressions into the select expression.
              SelectExpression newSelectExpression =
                      (SelectExpression) substituteExpression(selectExpression, varExprMap, context);
  
              // Continues to visit the rewritten select expression.
              return super.visit(newSelectExpression, arg);
          } else {
              // Continues to visit inside the select expression.
              return super.visit(selectExpression, arg);
          }
      }
  }
  