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use crate::expression::{Expression, ValidGrouping};
use crate::pg::Pg;
use crate::query_builder::*;
use crate::result::QueryResult;
use crate::sql_types::{is_nullable, Date, Nullable, SqlType, Timestamp, Timestamptz, VarChar};

/// Marker trait for types which are valid in `AT TIME ZONE` expressions
pub trait DateTimeLike {}
impl DateTimeLike for Date {}
impl DateTimeLike for Timestamp {}
impl DateTimeLike for Timestamptz {}
impl<T> DateTimeLike for Nullable<T> where T: SqlType<IsNull = is_nullable::NotNull> + DateTimeLike {}
#[derive(Debug, Copy, Clone, QueryId, ValidGrouping)]
pub struct AtTimeZone<Ts, Tz> {
    timestamp: Ts,
    timezone: Tz,
}

impl<Ts, Tz> AtTimeZone<Ts, Tz> {
    pub fn new(timestamp: Ts, timezone: Tz) -> Self {
        AtTimeZone {
            timestamp: timestamp,
            timezone: timezone,
        }
    }
}

impl<Ts, Tz> Expression for AtTimeZone<Ts, Tz>
where
    Ts: Expression,
    Ts::SqlType: DateTimeLike,
    Tz: Expression<SqlType = VarChar>,
{
    type SqlType = Timestamp;
}

impl<Ts, Tz> QueryFragment<Pg> for AtTimeZone<Ts, Tz>
where
    Ts: QueryFragment<Pg>,
    Tz: QueryFragment<Pg>,
{
    fn walk_ast<'b>(&'b self, mut out: AstPass<'_, 'b, Pg>) -> QueryResult<()> {
        self.timestamp.walk_ast(out.reborrow())?;
        out.push_sql(" AT TIME ZONE ");
        self.timezone.walk_ast(out.reborrow())?;
        Ok(())
    }
}

impl_selectable_expression!(AtTimeZone<Ts, Tz>);