use crate::http::context::AppContext;
use poem::handler;
use poem::http::StatusCode;
use poem::web::{Data, Path};
use poem::{Body, IntoResponse, Response};
use std::sync::Arc;

/// SSE endpoint: `GET /agents/:story_id/:agent_name/stream`
///
/// Streams `AgentEvent`s as Server-Sent Events. Each event is JSON-encoded
/// with `data:` prefix and double newline terminator per the SSE spec.
#[handler]
pub async fn agent_stream(
    Path((story_id, agent_name)): Path<(String, String)>,
    ctx: Data<&Arc<AppContext>>,
) -> impl IntoResponse {
    let mut rx = match ctx.agents.subscribe(&story_id, &agent_name) {
        Ok(rx) => rx,
        Err(e) => {
            return Response::builder()
                .status(StatusCode::NOT_FOUND)
                .body(Body::from_string(e));
        }
    };

    let stream = async_stream::stream! {
        loop {
            match rx.recv().await {
                Ok(event) => {
                    if let Ok(json) = serde_json::to_string(&event) {
                        yield Ok::<_, std::io::Error>(format!("data: {json}\n\n"));
                    }
                    // Check for terminal events
                    match &event {
                        crate::agents::AgentEvent::Done { .. }
                        | crate::agents::AgentEvent::Error { .. } => break,
                        crate::agents::AgentEvent::Status { status, .. }
                            if status == "stopped" => break,
                        _ => {}
                    }
                }
                Err(tokio::sync::broadcast::error::RecvError::Lagged(n)) => {
                    let msg = format!("{{\"type\":\"warning\",\"message\":\"Skipped {n} events\"}}");
                    yield Ok::<_, std::io::Error>(format!("data: {msg}\n\n"));
                }
                Err(tokio::sync::broadcast::error::RecvError::Closed) => break,
            }
        }
    };

    Response::builder()
        .header("Content-Type", "text/event-stream")
        .header("Cache-Control", "no-cache")
        .header("Connection", "keep-alive")
        .body(Body::from_bytes_stream(
            futures::StreamExt::map(stream, |r| r.map(bytes::Bytes::from)),
        ))
}