/*
 * Copyright (C) 2016-2022 ActionTech.
 * License: http://www.gnu.org/licenses/gpl.html GPL version 2 or higher.
 */

package com.actiontech.dble.plan.common.item.function.operator.cmpfunc;

import com.actiontech.dble.plan.common.field.Field;
import com.actiontech.dble.plan.common.item.Item;
import com.actiontech.dble.plan.common.item.function.ItemFunc;
import com.actiontech.dble.plan.common.item.function.primary.ItemBoolFunc;
import com.alibaba.druid.sql.ast.SQLExpr;
import com.alibaba.druid.sql.ast.expr.SQLBinaryOpExpr;
import com.alibaba.druid.sql.ast.expr.SQLBinaryOperator;
import com.alibaba.druid.sql.ast.expr.SQLIdentifierExpr;

import java.math.BigInteger;
import java.util.List;


/*
 * when MySQL's sql_auto_is_null is set to true, and col_nameis auto increment ,
 * select * from table_name where col_name is null retrun last_insert_id
 */
public class ItemFuncIsnull extends ItemBoolFunc {

    public ItemFuncIsnull(Item a, int charsetIndex) {
        super(a, charsetIndex);
        withIsNull = true;
    }

    @Override
    public final String funcName() {
        return "isnull";
    }

    @Override
    public Functype functype() {
        return Functype.ISNULL_FUNC;
    }

    @Override
    public BigInteger valInt() {
        if (args.get(0).isNull()) {
            return BigInteger.ONE;
        } else {
            return BigInteger.ZERO;
        }
    }

    @Override
    public void fixLengthAndDec() {
        decimals = 0;
        maxLength = 1;
        maybeNull = false;
    }

    @Override
    public SQLExpr toExpression() {
        SQLExpr left = args.get(0).toExpression();
        return new SQLBinaryOpExpr(left, SQLBinaryOperator.Is, new SQLIdentifierExpr("UNKNOWN"));
    }

    @Override
    protected Item cloneStruct(boolean forCalculate, List<Item> calArgs, boolean isPushDown, List<Field> fields) {
        List<Item> newArgs = null;
        if (!forCalculate)
            newArgs = cloneStructList(args);
        else
            newArgs = calArgs;
        return new ItemFuncIsnull(newArgs.get(0), charsetIndex);
    }

    @Override
    public ItemFunc nativeConstruct(List<Item> realArgs) {
        return new ItemFuncIsnull(realArgs.get(0), charsetIndex);
    }

}
