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/**
 *  Copyright (c) 1997-2013, www.tinygroup.org ([email protected]).
 *
 *  Licensed under the GPL, Version 3.0 (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.gnu.org/licenses/gpl.html
 *
 *  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.tinygroup.jsqlparser.util;

import org.tinygroup.jsqlparser.expression.Alias;
import org.tinygroup.jsqlparser.expression.BinaryExpression;
import org.tinygroup.jsqlparser.statement.select.*;

import java.util.LinkedList;
import java.util.List;

/**
 * Connect all selected expressions with a binary expression. Out of select a,b
 * from table one gets select a || b as expr from table. The type of binary
 * expression is set by overwriting this class abstract method
 * createBinaryExpression.
 *
 * @author tw
 */
public abstract class ConnectExpressionsVisitor implements SelectVisitor, SelectItemVisitor {

	private String alias = "expr";
	private final List itemsExpr = new LinkedList();

	public ConnectExpressionsVisitor() {
	}

	public ConnectExpressionsVisitor(String alias) {
		this.alias = alias;
	}

	/**
	 * Create instances of this binary expression that connects all selected
	 * expressions.
	 *
	 * @return
	 */
	protected abstract BinaryExpression createBinaryExpression();


	public void visit(PlainSelect plainSelect) {
		for (SelectItem item : plainSelect.getSelectItems()) {
			item.accept(this);
		}

		if (itemsExpr.size() > 1) {
			BinaryExpression binExpr = createBinaryExpression();
			binExpr.setLeftExpression(itemsExpr.get(0).getExpression());
			for (int i = 1; i < itemsExpr.size() - 1; i++) {
				binExpr.setRightExpression(itemsExpr.get(i).getExpression());
				BinaryExpression binExpr2 = createBinaryExpression();
				binExpr2.setLeftExpression(binExpr);
				binExpr = binExpr2;
			}
			binExpr.setRightExpression(itemsExpr.get(itemsExpr.size() - 1).getExpression());

			SelectExpressionItem sei = new SelectExpressionItem();
			sei.setExpression(binExpr);

			plainSelect.getSelectItems().clear();
			plainSelect.getSelectItems().add(sei);
		}

		((SelectExpressionItem) plainSelect.getSelectItems().get(0)).setAlias(new Alias(alias));
	}


	public void visit(SetOperationList setOpList) {
		for (PlainSelect select : setOpList.getPlainSelects()) {
			select.accept(this);
		}
	}


	public void visit(WithItem withItem) {
	}


	public void visit(AllTableColumns allTableColumns) {
		throw new UnsupportedOperationException("Not supported yet.");
	}


	public void visit(AllColumns allColumns) {
		throw new UnsupportedOperationException("Not supported yet.");
	}


	public void visit(SelectExpressionItem selectExpressionItem) {
		itemsExpr.add(selectExpressionItem);
	}
}