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#![allow(missing_docs)]

use std::{ops::DerefMut, pin::Pin, task::Poll};

use futures::Stream;
#[cfg(feature = "sqlx-dep")]
use futures::TryStreamExt;

#[cfg(feature = "sqlx-dep")]
use sqlx::Executor;

use futures::lock::MutexGuard;

use tracing::instrument;

use crate::{DbErr, InnerConnection, QueryResult, Statement};

/// `TransactionStream` cannot be used in a `transaction` closure as it does not impl `Send`.
/// It seems to be a Rust limitation right now, and solution to work around this deemed to be extremely hard.
#[ouroboros::self_referencing]
pub struct TransactionStream<'a> {
    stmt: Statement,
    conn: MutexGuard<'a, InnerConnection>,
    metric_callback: Option<crate::metric::Callback>,
    #[borrows(mut conn, stmt, metric_callback)]
    #[not_covariant]
    stream: Pin<Box<dyn Stream<Item = Result<QueryResult, DbErr>> + 'this + Send>>,
}

impl<'a> std::fmt::Debug for TransactionStream<'a> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "TransactionStream")
    }
}

impl<'a> TransactionStream<'a> {
    #[instrument(level = "trace", skip(metric_callback))]
    pub(crate) fn build(
        conn: MutexGuard<'a, InnerConnection>,
        stmt: Statement,
        metric_callback: Option<crate::metric::Callback>,
    ) -> TransactionStream<'a> {
        TransactionStreamBuilder {
            stmt,
            conn,
            metric_callback,
            stream_builder: |conn, stmt, _metric_callback| match conn.deref_mut() {
                #[cfg(feature = "sqlx-mysql")]
                InnerConnection::MySql(c) => {
                    let query = crate::driver::sqlx_mysql::sqlx_query(stmt);
                    crate::metric::metric_ok!(_metric_callback, stmt, {
                        Box::pin(
                            c.fetch(query)
                                .map_ok(Into::into)
                                .map_err(crate::sqlx_error_to_query_err),
                        )
                            as Pin<Box<dyn Stream<Item = Result<QueryResult, DbErr>> + Send>>
                    })
                }
                #[cfg(feature = "sqlx-postgres")]
                InnerConnection::Postgres(c) => {
                    let query = crate::driver::sqlx_postgres::sqlx_query(stmt);
                    crate::metric::metric_ok!(_metric_callback, stmt, {
                        Box::pin(
                            c.fetch(query)
                                .map_ok(Into::into)
                                .map_err(crate::sqlx_error_to_query_err),
                        )
                            as Pin<Box<dyn Stream<Item = Result<QueryResult, DbErr>> + Send>>
                    })
                }
                #[cfg(feature = "sqlx-sqlite")]
                InnerConnection::Sqlite(c) => {
                    let query = crate::driver::sqlx_sqlite::sqlx_query(stmt);
                    crate::metric::metric_ok!(_metric_callback, stmt, {
                        Box::pin(
                            c.fetch(query)
                                .map_ok(Into::into)
                                .map_err(crate::sqlx_error_to_query_err),
                        )
                            as Pin<Box<dyn Stream<Item = Result<QueryResult, DbErr>> + Send>>
                    })
                }
                #[cfg(feature = "mock")]
                InnerConnection::Mock(c) => c.fetch(stmt),
                #[allow(unreachable_patterns)]
                _ => unreachable!(),
            },
        }
        .build()
    }
}

impl<'a> Stream for TransactionStream<'a> {
    type Item = Result<QueryResult, DbErr>;

    fn poll_next(
        self: Pin<&mut Self>,
        cx: &mut std::task::Context<'_>,
    ) -> Poll<Option<Self::Item>> {
        let this = self.get_mut();
        this.with_stream_mut(|stream| stream.as_mut().poll_next(cx))
    }
}