Left.java

/*
 * Copyright 1999-2017 Alibaba Group Holding Ltd.
 *
 * 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.
 */
package com.alibaba.druid.sql.visitor.functions;

import static com.alibaba.druid.sql.visitor.SQLEvalVisitor.EVAL_VALUE;

import com.alibaba.druid.sql.ast.SQLExpr;
import com.alibaba.druid.sql.ast.expr.SQLMethodInvokeExpr;
import com.alibaba.druid.sql.visitor.SQLEvalVisitor;
import com.alibaba.druid.sql.visitor.SQLEvalVisitorUtils;

public class Left implements Function {

    public final static Left instance = new Left();

    public Object eval(SQLEvalVisitor visitor, SQLMethodInvokeExpr x) {
        if (x.getParameters().size() != 2) {
            return SQLEvalVisitor.EVAL_ERROR;
        }

        SQLExpr param0 = x.getParameters().get(0);
        SQLExpr param1 = x.getParameters().get(1);
        param0.accept(visitor);
        param1.accept(visitor);

        Object param0Value = param0.getAttributes().get(EVAL_VALUE);
        Object param1Value = param1.getAttributes().get(EVAL_VALUE);
        if (param0Value == null || param1Value == null) {
            return SQLEvalVisitor.EVAL_ERROR;
        }

        String strValue = param0Value.toString();
        int intValue = SQLEvalVisitorUtils.castToInteger(param1Value);
        
        if (intValue > strValue.length()) {
            return SQLEvalVisitor.EVAL_ERROR;
        }

        String result = strValue.substring(0, intValue);

        return result;
    }
}