use std::future;

use axum::extract::State;
use axum_extra::extract::Query;
use futures::stream::{self, StreamExt as _};

use crate::{
    event::Sequenced as _,
    test::fixtures::{self, future::Expect as _},
};

#[tokio::test]
async fn resume() {
    // Set up the environment

    let app = fixtures::scratch_app().await;
    let conversation = fixtures::conversation::create(&app, &fixtures::now()).await;
    let sender = fixtures::user::create(&app, &fixtures::now()).await;
    let resume_point = fixtures::boot::resume_point(&app).await;

    let initial_message =
        fixtures::message::send(&app, &conversation, &sender, &fixtures::now()).await;

    let later_messages = vec![
        fixtures::message::send(&app, &conversation, &sender, &fixtures::now()).await,
        fixtures::message::send(&app, &conversation, &sender, &fixtures::now()).await,
    ];

    // Call the endpoint

    let subscriber = fixtures::identity::create(&app, &fixtures::now()).await;

    let resume_at = {
        // First subscription
        let super::Response(events) = super::handler(
            State(app.clone()),
            subscriber.clone(),
            None,
            Query(super::QueryParams { resume_point }),
        )
        .await
        .expect("subscribe never fails");

        let event = events
            .filter_map(fixtures::event::stream::message)
            .filter_map(fixtures::event::stream::message::sent)
            .filter(|event| future::ready(event.message == initial_message))
            .next()
            .expect_some("delivered event for initial message")
            .await;

        event.sequence()
    };

    // Resume after disconnect
    let super::Response(resumed) = super::handler(
        State(app),
        subscriber,
        Some(resume_at.into()),
        Query(super::QueryParams { resume_point }),
    )
    .await
    .expect("subscribe never fails");

    // Verify final events

    let mut events = resumed
        .filter_map(fixtures::event::stream::message)
        .filter_map(fixtures::event::stream::message::sent)
        .zip(stream::iter(later_messages));

    while let Some((event, message)) = events.next().expect_ready("event ready").await {
        assert_eq!(message, event.message);
    }
}

// This test verifies a real bug I hit developing the vector-of-sequences
// approach to resuming events. A small omission caused the event IDs in a
// resumed stream to _omit_ conversations that were in the original stream
// until those conversations also appeared in the resumed stream.
//
// Clients would see something like
// * In the original stream, Cfoo=5,Cbar=8
// * In the resumed stream, Cfoo=6 (no Cbar sequence number)
//
// Disconnecting and reconnecting a second time, using event IDs from that
// initial period of the first resume attempt, would then cause the second
// resume attempt to restart all other conversations from the beginning, and
// not from where the first disconnection happened.
//
// As we have switched to a single global event sequence number, this scenario
// can no longer arise, but this test is preserved because the actual behaviour
// _is_ a valid way for clients to behave, and should work. We might as well
// keep testing it.
#[tokio::test]
async fn serial_resume() {
    // Set up the environment

    let app = fixtures::scratch_app().await;
    let sender = fixtures::user::create(&app, &fixtures::now()).await;
    let conversation_a = fixtures::conversation::create(&app, &fixtures::now()).await;
    let conversation_b = fixtures::conversation::create(&app, &fixtures::now()).await;
    let resume_point = fixtures::boot::resume_point(&app).await;

    // Call the endpoint

    let subscriber = fixtures::identity::create(&app, &fixtures::now()).await;

    let resume_at = {
        let initial_messages = [
            fixtures::message::send(&app, &conversation_a, &sender, &fixtures::now()).await,
            fixtures::message::send(&app, &conversation_b, &sender, &fixtures::now()).await,
        ];

        // First subscription

        let super::Response(events) = super::handler(
            State(app.clone()),
            subscriber.clone(),
            None,
            Query(super::QueryParams { resume_point }),
        )
        .await
        .expect("subscribe never fails");

        // Check for expected events

        let events = events
            .filter_map(fixtures::event::stream::message)
            .filter_map(fixtures::event::stream::message::sent)
            .zip(stream::iter(initial_messages))
            .collect::<Vec<_>>()
            .expect_ready("zipping a finite list of events is ready immediately")
            .await;

        assert!(
            events
                .iter()
                .all(|(event, message)| message == &event.message)
        );

        let (event, _) = events.last().expect("this vec is non-empty");

        // Take the last one's resume point

        event.sequence()
    };

    // Resume after disconnect
    let resume_at = {
        let resume_messages = [
            // Note that conversation_b does not appear here. The buggy behaviour
            // would be masked if conversation_b happened to send a new message
            // into the resumed event stream.
            fixtures::message::send(&app, &conversation_a, &sender, &fixtures::now()).await,
            fixtures::message::send(&app, &conversation_a, &sender, &fixtures::now()).await,
        ];

        // Second subscription
        let super::Response(events) = super::handler(
            State(app.clone()),
            subscriber.clone(),
            Some(resume_at.into()),
            Query(super::QueryParams { resume_point }),
        )
        .await
        .expect("subscribe never fails");

        // Check for expected events

        let events = events
            .filter_map(fixtures::event::stream::message)
            .filter_map(fixtures::event::stream::message::sent)
            .zip(stream::iter(resume_messages))
            .collect::<Vec<_>>()
            .expect_ready("zipping a finite list of events is ready immediately")
            .await;

        assert!(
            events
                .iter()
                .all(|(event, message)| message == &event.message)
        );

        let (event, _) = events.last().expect("this vec is non-empty");

        // Take the last one's resume point

        event.sequence()
    };

    // Resume after disconnect a second time
    {
        // At this point, we can send on either conversation and demonstrate
        // the problem. The resume point should before both of these messages,
        // but after _all_ prior messages.
        let final_messages = [
            fixtures::message::send(&app, &conversation_a, &sender, &fixtures::now()).await,
            fixtures::message::send(&app, &conversation_b, &sender, &fixtures::now()).await,
        ];

        // Third subscription
        let super::Response(events) = super::handler(
            State(app.clone()),
            subscriber.clone(),
            Some(resume_at.into()),
            Query(super::QueryParams { resume_point }),
        )
        .await
        .expect("subscribe never fails");

        // Check for expected events

        let events = events
            .filter_map(fixtures::event::stream::message)
            .filter_map(fixtures::event::stream::message::sent)
            .zip(stream::iter(final_messages))
            .collect::<Vec<_>>()
            .expect_ready("zipping a finite list of events is ready immediately")
            .await;

        assert!(
            events
                .iter()
                .all(|(event, message)| message == &event.message)
        );
    };
}