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.visitor;
  
  import java.util.Collection;
  import java.util.HashMap;
  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.context.Scope;
  import org.apache.asterix.lang.common.expression.VariableExpr;
  import org.apache.asterix.lang.common.rewrites.LangRewritingContext;
  import org.apache.asterix.lang.sqlpp.util.SqlppRewriteUtil;
  import org.apache.asterix.lang.sqlpp.util.SqlppVariableUtil;
  import org.apache.asterix.lang.sqlpp.visitor.base.AbstractSqlppExpressionScopingVisitor;
  
  /**
   * This visitor is used to substitute expressions in a visiting language structure
   * with an given map.
   */
  public class SqlppSubstituteExpressionVisitor extends AbstractSqlppExpressionScopingVisitor {
  
      private final Map<Expression, Expression> exprMap = new HashMap<>();
  
      public SqlppSubstituteExpressionVisitor(LangRewritingContext context,
              Map<? extends Expression, ? extends Expression> exprMap) {
          super(context);
          this.exprMap.putAll(exprMap);
      }
  
      // Note: we intentionally override preVisit instead of postVisit because we wants larger expressions
      // get substituted first if some of their child expressions are present as keys in the exprMap.
      // An example is:
      // asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/group-by/gby-expr-3/gby-expr-3.3.query.sqlpp
      @Override
      protected Expression preVisit(Expression expr) throws CompilationException {
          return substitute(expr);
      }
  
      protected Expression substitute(Expression expr) throws CompilationException {
          Expression mappedExpr = getMappedExpr(expr);
          // Makes a deep copy before returning to avoid shared references.
          return mappedExpr == null ? expr : (Expression) SqlppRewriteUtil.deepCopy(mappedExpr);
      }
  
      protected Expression getMappedExpr(Expression expr) throws CompilationException {
          Expression mappedExpr = exprMap.get(expr);
          if (mappedExpr == null) {
              return null;
          }
          Collection<VariableExpr> freeVars = SqlppVariableUtil.getFreeVariables(expr);
          for (VariableExpr freeVar : freeVars) {
              Scope currentScope = scopeChecker.getCurrentScope();
              if (currentScope.findSymbol(freeVar.getVar().getValue()) != null) {
                  // If the expression to be substituted uses variables defined in the outer-most expresion
                  // that is being visited, we shouldn't perform the substitution.
                  return null;
              }
          }
          return mappedExpr;
      }
  }
  