// GetColDefaultValue gets default value of the column.
func GetColDefaultValue(ctx context.Context, col *model.ColumnInfo) (interface{}, bool, error) {
	// Check no default value flag.
	if mysql.HasNoDefaultValueFlag(col.Flag) && col.Tp != mysql.TypeEnum {
		return nil, false, errors.Errorf("Field '%s' doesn't have a default value", col.Name)
	}

	// Check and get timestamp/datetime default value.
	if col.Tp == mysql.TypeTimestamp || col.Tp == mysql.TypeDatetime {
		if col.DefaultValue == nil {
			return nil, true, nil
		}

		value, err := expression.GetTimeValue(ctx, col.DefaultValue, col.Tp, col.Decimal)
		if err != nil {
			return nil, true, errors.Errorf("Field '%s' get default value fail - %s", col.Name, errors.Trace(err))
		}

		return value, true, nil
	} else if col.Tp == mysql.TypeEnum {
		// For enum type, if no default value and not null is set,
		// the default value is the first element of the enum list
		if col.DefaultValue == nil && mysql.HasNotNullFlag(col.Flag) {
			return col.FieldType.Elems[0], true, nil
		}
	}

	return col.DefaultValue, true, nil
}

func (t *Table) setOnUpdateData(ctx context.Context, touched []bool, data []interface{}) error {
	ucols := column.FindOnUpdateCols(t.Cols())
	for _, c := range ucols {
		if !touched[c.Offset] {
			v, err := expression.GetTimeValue(ctx, expression.CurrentTimestamp, c.Tp, c.Decimal)
			if err != nil {
				return errors.Trace(err)
			}
			data[c.Offset] = v
			touched[c.Offset] = true
		}
	}
	return nil
}

func getDefaultValue(c *ConstraintOpt, tp byte, fsp int) (interface{}, error) {
	if tp == mysql.TypeTimestamp || tp == mysql.TypeDatetime {
		value, err := expression.GetTimeValue(nil, c.Evalue, tp, fsp)
		if err != nil {
			return nil, errors.Trace(err)
		}

		// Value is nil means `default null`.
		if value == nil {
			return nil, nil
		}

		// If value is mysql.Time, convert it to string.
		if vv, ok := value.(mysql.Time); ok {
			return vv.String(), nil
		}

		return value, nil
	}

	return expression.FastEval(c.Evalue), nil
}

func getDefaultValue(ctx context.Context, c *column.Col) (interface{}, bool, error) {
	// Check no default value flag.
	if mysql.HasNoDefaultValueFlag(c.Flag) {
		return nil, false, errors.Errorf("Field '%s' doesn't have a default value", c.Name)
	}

	// Check and get timestamp/datetime default value.
	if c.Tp == mysql.TypeTimestamp || c.Tp == mysql.TypeDatetime {
		if c.DefaultValue == nil {
			return nil, true, nil
		}

		value, err := expression.GetTimeValue(ctx, c.DefaultValue, c.Tp, c.Decimal)
		if err != nil {
			return nil, true, errors.Errorf("Field '%s' get default value fail - %s", c.Name, errors.Trace(err))
		}

		return value, true, nil
	}

	return c.DefaultValue, true, nil
}