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.calcite.sql.util;
  
  import org.apache.calcite.sql.SqlCall;
  import org.apache.calcite.sql.SqlDataTypeSpec;
  import org.apache.calcite.sql.SqlDynamicParam;
  import org.apache.calcite.sql.SqlIdentifier;
  import org.apache.calcite.sql.SqlIntervalQualifier;
  import org.apache.calcite.sql.SqlLiteral;
  import org.apache.calcite.sql.SqlNode;
  import org.apache.calcite.sql.SqlNodeList;
  
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  import java.util.ArrayList;
  import java.util.List;
  
  /**
   * Basic implementation of {@link SqlVisitor} which returns each leaf node
   * unchanged.
   *
   * <p>This class is useful as a base class for classes which implement the
   * {@link SqlVisitor} interface and have {@link SqlNode} as the return type. The
   * derived class can override whichever methods it chooses.
   */
  public class SqlShuttle extends SqlBasicVisitor<@Nullable SqlNode> {
    //~ Methods ----------------------------------------------------------------
  
    @Override public @Nullable SqlNode visit(SqlLiteral literal) {
      return literal;
    }
  
    @Override public @Nullable SqlNode visit(SqlIdentifier id) {
      return id;
    }
  
    @Override public @Nullable SqlNode visit(SqlDataTypeSpec type) {
      return type;
    }
  
    @Override public @Nullable SqlNode visit(SqlDynamicParam param) {
      return param;
    }
  
    @Override public @Nullable SqlNode visit(SqlIntervalQualifier intervalQualifier) {
      return intervalQualifier;
    }
  
    @Override public @Nullable SqlNode visit(final SqlCall call) {
      // Handler creates a new copy of 'call' only if one or more operands
      // change.
      CallCopyingArgHandler argHandler = new CallCopyingArgHandler(call, false);
      call.getOperator().acceptCall(this, call, false, argHandler);
      return argHandler.result();
    }
  
    @Override public @Nullable SqlNode visit(SqlNodeList nodeList) {
      boolean update = false;
      final List<@Nullable SqlNode> newList = new ArrayList<>(nodeList.size());
      for (SqlNode operand : nodeList) {
        SqlNode clonedOperand;
        if (operand == null) {
          clonedOperand = null;
        } else {
          clonedOperand = operand.accept(this);
          if (clonedOperand != operand) {
            update = true;
          }
        }
        newList.add(clonedOperand);
      }
      if (update) {
        return SqlNodeList.of(nodeList.getParserPosition(), newList);
      } else {
        return nodeList;
      }
    }
  
    //~ Inner Classes ----------------------------------------------------------
  
    /**
     * Implementation of
     * {@link org.apache.calcite.sql.util.SqlBasicVisitor.ArgHandler}
     * that deep-copies {@link SqlCall}s and their operands.
     */
    protected class CallCopyingArgHandler implements ArgHandler<@Nullable SqlNode> {
      boolean update;
      final @Nullable SqlNode[] clonedOperands;
      private final SqlCall call;
      private final boolean alwaysCopy;
  
      public CallCopyingArgHandler(SqlCall call, boolean alwaysCopy) {
        this.call = call;
        this.update = false;
        final List<@Nullable SqlNode> operands = (List<@Nullable SqlNode>) call.getOperandList();
        this.clonedOperands = operands.toArray(new SqlNode[0]);
        this.alwaysCopy = alwaysCopy;
      }
  
      @Override public SqlNode result() {
        if (update || alwaysCopy) {
          return call.getOperator().createCall(
              call.getFunctionQuantifier(),
              call.getParserPosition(),
              clonedOperands);
        } else {
          return call;
        }
      }
  
      @Override public @Nullable SqlNode visitChild(
          SqlVisitor<@Nullable SqlNode> visitor,
          SqlNode expr,
          int i,
          @Nullable SqlNode operand) {
        if (operand == null) {
          return null;
        }
        SqlNode newOperand = operand.accept(SqlShuttle.this);
        if (newOperand != operand) {
          update = true;
        }
        clonedOperands[i] = newOperand;
        return newOperand;
      }
    }
  }
  