/*
 * Copyright 2016-2018 shardingsphere.io.
 * <p>
 * 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.
 * </p>
 */

package io.shardingsphere.core.parsing.antlr.extractor.statement.handler;

import java.util.Collection;

import org.antlr.v4.runtime.ParserRuleContext;
import org.antlr.v4.runtime.tree.ParseTree;

import io.shardingsphere.core.parsing.antlr.extractor.statement.handler.result.DropColumnExtractResult;
import io.shardingsphere.core.parsing.antlr.extractor.statement.handler.result.ExtractResult;
import io.shardingsphere.core.parsing.antlr.extractor.statement.util.ASTUtils;
import io.shardingsphere.core.util.SQLUtil;

/**
 * Drop column extract handler.
 *
 * @author duhongjun
 */
public final class DropColumnExtractHandler implements ASTExtractHandler {

    @Override
    public ExtractResult extract(final ParserRuleContext ancestorNode) {
        Collection<ParserRuleContext> result = ASTUtils.getAllDescendantNodes(ancestorNode, RuleName.DROP_COLUMN);
        if (result.isEmpty()) {
            return null;
        }
        DropColumnExtractResult extractResult = new DropColumnExtractResult();
        for (ParserRuleContext each : result) {
            for (ParseTree columnNode : ASTUtils.getAllDescendantNodes(each, RuleName.COLUMN_NAME)) {
                extractResult.getDropColumnNames().add(SQLUtil.getExactlyValue(columnNode.getText()));
            }
        }
        return extractResult;
    }
}

@@ -810,16 +810,57 @@
 eTree;%0A%0A
+import com.google.common.base.Optional;%0A%0A
 import i
@@ -1312,16 +1312,20 @@
 ndler %7B%0A
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@@ -1342,16 +1342,25 @@
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@@ -1356,32 +1356,33 @@
 al%3CExtractResult
+%3E
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@@ -1452,22 +1452,31 @@
 ontext%3E 
-result
+dropColumnNodes
  = ASTUt
@@ -1550,22 +1550,31 @@
     if (
-result
+dropColumnNodes
 .isEmpty
@@ -1602,12 +1602,25 @@
 urn 
-null
+Optional.absent()
 ;%0A  
@@ -1659,24 +1659,17 @@
 tResult 
-extractR
+r
 esult = 
@@ -1737,22 +1737,31 @@
  each : 
-result
+dropColumnNodes
 ) %7B%0A    
@@ -1874,24 +1874,17 @@
         
-extractR
+r
 esult.ge
@@ -1993,17 +1993,27 @@
  return 
-e
+Optional.%3CE
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@@ -2016,16 +2016,27 @@
 ctResult
+%3Eof(result)
 ;%0A    %7D%0A

use optional for checkstyle