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use crate::backend::Backend;
use crate::expression::{Expression, TypedExpressionType, ValidGrouping};
use crate::query_builder::*;
use crate::result::QueryResult;
use crate::sql_types;

macro_rules! numeric_operation {
    ($name:ident, $op:expr) => {
        #[doc(hidden)]
        #[derive(Debug, Copy, Clone, QueryId, ValidGrouping)]
        pub struct $name<Lhs, Rhs> {
            lhs: Lhs,
            rhs: Rhs,
        }

        impl<Lhs, Rhs> $name<Lhs, Rhs> {
            // This function is used by `operator_allowed!`
            // which is internally used by `table!`
            // for "numeric" columns
            #[doc(hidden)]
            pub fn new(left: Lhs, right: Rhs) -> Self {
                $name {
                    lhs: left,
                    rhs: right,
                }
            }
        }

        impl<Lhs, Rhs> Expression for $name<Lhs, Rhs>
        where
            Lhs: Expression,
            Lhs::SqlType: sql_types::ops::$name,
            Rhs: Expression,
            <Lhs::SqlType as sql_types::ops::$name>::Output: TypedExpressionType,
        {
            type SqlType = <Lhs::SqlType as sql_types::ops::$name>::Output;
        }

        impl<Lhs, Rhs, DB> QueryFragment<DB> for $name<Lhs, Rhs>
        where
            DB: Backend,
            Lhs: QueryFragment<DB>,
            Rhs: QueryFragment<DB>,
        {
            fn walk_ast<'b>(&'b self, mut out: AstPass<'_, 'b, DB>) -> QueryResult<()>
            {
                out.push_sql("(");
                self.lhs.walk_ast(out.reborrow())?;
                out.push_sql($op);
                self.rhs.walk_ast(out.reborrow())?;
                out.push_sql(")");
                Ok(())
            }
        }

        impl_selectable_expression!($name<Lhs, Rhs>);
        generic_numeric_expr!($name, A, B);
    };
}

numeric_operation!(Add, " + ");
numeric_operation!(Sub, " - ");
numeric_operation!(Mul, " * ");
numeric_operation!(Div, " / ");