use axum::{
    extract::State,
    http::StatusCode,
    response::{
        sse::{self, Sse},
        IntoResponse, Response,
    },
    routing::get,
    Router,
};
use axum_extra::extract::Query;
use chrono::{self, format::SecondsFormat};
use futures::stream::{self, Stream, StreamExt as _, TryStreamExt as _};

use super::repo::broadcast;
use crate::{
    app::App,
    channel::app::EventsError,
    clock::RequestedAt,
    error::InternalError,
    header::LastEventId,
    repo::{channel, login::Login},
};

pub fn router() -> Router<App> {
    Router::new().route("/api/events", get(events))
}

#[derive(serde::Deserialize)]
struct EventsQuery {
    #[serde(default, rename = "channel")]
    channels: Vec<channel::Id>,
}

async fn events(
    State(app): State<App>,
    RequestedAt(now): RequestedAt,
    _: Login, // requires auth, but doesn't actually care who you are
    last_event_id: Option<LastEventId>,
    Query(query): Query<EventsQuery>,
) -> Result<Events<impl Stream<Item = ChannelEvent>>, ErrorResponse> {
    let resume_at = last_event_id.as_deref();

    let streams = stream::iter(query.channels)
        .then(|channel| {
            let app = app.clone();
            async move {
                let events = app
                    .channels()
                    .events(&channel, &now, resume_at)
                    .await?
                    .map(ChannelEvent::wrap(channel));

                Ok::<_, EventsError>(events)
            }
        })
        .try_collect::<Vec<_>>()
        .await
        // impl From would take more code; this is used once.
        .map_err(ErrorResponse)?;

    let stream = stream::select_all(streams);

    Ok(Events(stream))
}

struct Events<S>(S);

impl<S> IntoResponse for Events<S>
where
    S: Stream<Item = ChannelEvent> + Send + 'static,
{
    fn into_response(self) -> Response {
        let Self(stream) = self;
        let stream = stream.map(sse::Event::try_from);
        Sse::new(stream)
            .keep_alive(sse::KeepAlive::default())
            .into_response()
    }
}

struct ErrorResponse(EventsError);

impl IntoResponse for ErrorResponse {
    fn into_response(self) -> Response {
        let Self(error) = self;
        match error {
            not_found @ EventsError::ChannelNotFound(_) => {
                (StatusCode::NOT_FOUND, not_found.to_string()).into_response()
            }
            resume_at @ EventsError::ResumeAtError(_) => {
                (StatusCode::BAD_REQUEST, resume_at.to_string()).into_response()
            }
            other => InternalError::from(other).into_response(),
        }
    }
}

#[derive(serde::Serialize)]
struct ChannelEvent {
    channel: channel::Id,
    #[serde(flatten)]
    message: broadcast::Message,
}

impl ChannelEvent {
    fn wrap(channel: channel::Id) -> impl Fn(broadcast::Message) -> Self {
        move |message| Self {
            channel: channel.clone(),
            message,
        }
    }

    fn event_id(&self) -> String {
        self.message
            .sent_at
            .to_rfc3339_opts(SecondsFormat::AutoSi, /* use_z */ true)
    }
}

impl TryFrom<ChannelEvent> for sse::Event {
    type Error = serde_json::Error;

    fn try_from(value: ChannelEvent) -> Result<Self, Self::Error> {
        let data = serde_json::to_string_pretty(&value)?;
        let event = Self::default().id(value.event_id()).data(&data);

        Ok(event)
    }
}