use std::path::PathBuf;
use std::sync::Arc;

use anyhow::Context;
use tokio::io::AsyncWriteExt;
use tokio::sync::Mutex;

mod ipc;

use ipc::{AppStateKind, Request, Response};

type Registry = Arc<Mutex<SessionRegistry>>;

#[derive(Default)]
struct SessionRegistry {
    next_id: u64,
    sessions: std::collections::HashMap<u64, AppStateKind>,
}

impl SessionRegistry {
    fn launch(&mut self, _app_id: &str) -> u64 {
        self.next_id += 1;
        let id = self.next_id;
        self.sessions.insert(id, AppStateKind::Starting);
        id
    }

    fn terminate(&mut self, session_id: u64) -> bool {
        self.sessions.remove(&session_id).is_some()
    }

    fn running_ids(&self) -> Vec<u64> {
        self.sessions.keys().copied().collect()
    }

    fn state(&self, session_id: u64) -> AppStateKind {
        self.sessions
            .get(&session_id)
            .cloned()
            .unwrap_or(AppStateKind::NotFound)
    }
}

#[tokio::main]
async fn main() -> anyhow::Result<()> {
    tracing_subscriber::fmt()
        .with_env_filter(
            tracing_subscriber::EnvFilter::try_from_default_env()
                .unwrap_or_else(|_| tracing_subscriber::EnvFilter::new("info")),
        )
        .init();

    run().await
}

async fn run() -> anyhow::Result<()> {
    let socket_path = appd_socket_path()?;

    if let Some(parent) = socket_path.parent() {
        std::fs::create_dir_all(parent).with_context(|| format!("create {}", parent.display()))?;
    }
    let _ = std::fs::remove_file(&socket_path);

    let listener = tokio::net::UnixListener::bind(&socket_path)
        .with_context(|| format!("bind {}", socket_path.display()))?;
    tracing::info!(path = %socket_path.display(), "IPC socket listening");

    let _ = sd_notify::notify(false, &[sd_notify::NotifyState::Ready]);

    let registry: Registry = Arc::new(Mutex::new(SessionRegistry::default()));

    let mut shutdown = std::pin::pin!(tokio::signal::ctrl_c());

    loop {
        tokio::select! {
            result = listener.accept() => {
                let (stream, _) = result.context("accept")?;
                let reg = Arc::clone(&registry);
                tokio::spawn(async move {
                    if let Err(e) = handle_connection(stream, reg).await {
                        tracing::warn!(error = %e, "connection error");
                    }
                });
            }
            _ = &mut shutdown => {
                tracing::info!("shutting down");
                break;
            }
        }
    }

    let _ = std::fs::remove_file(&socket_path);
    Ok(())
}

async fn handle_connection(
    stream: tokio::net::UnixStream,
    registry: Registry,
) -> anyhow::Result<()> {
    let (reader, writer) = tokio::io::split(stream);
    let mut reader = tokio::io::BufReader::new(reader);
    let mut writer = tokio::io::BufWriter::new(writer);

    while let Some(req) = ipc::read_frame(&mut reader).await? {
        tracing::debug!(?req, "request");
        let resp = dispatch(req, &registry).await;
        ipc::write_frame(&mut writer, &resp).await?;
        writer.flush().await?;
    }
    Ok(())
}

async fn dispatch(req: Request, registry: &Registry) -> Response {
    match req {
        Request::LaunchApp {
            app_id,
            surface_id: _,
        } => {
            let session_id = registry.lock().await.launch(&app_id);
            tracing::info!(session_id, %app_id, "launched");
            Response::LaunchAck { session_id }
        }
        Request::TerminateApp { session_id } => {
            let found = registry.lock().await.terminate(session_id);
            if found {
                tracing::info!(session_id, "terminated");
                Response::AppState {
                    session_id,
                    state: AppStateKind::Stopped,
                }
            } else {
                Response::Error {
                    code: 1,
                    message: format!("session {session_id} not found"),
                }
            }
        }
        Request::QueryRunning => {
            let session_ids = registry.lock().await.running_ids();
            Response::RunningApps { session_ids }
        }
        Request::QueryAppState { session_id } => {
            let state = registry.lock().await.state(session_id);
            Response::AppState { session_id, state }
        }
    }
}

fn appd_socket_path() -> anyhow::Result<PathBuf> {
    if let Ok(p) = std::env::var("WEFT_APPD_SOCKET") {
        return Ok(PathBuf::from(p));
    }

    let runtime_dir = std::env::var("XDG_RUNTIME_DIR").context("XDG_RUNTIME_DIR not set")?;

    Ok(PathBuf::from(runtime_dir).join("weft/appd.sock"))
}

#[cfg(test)]
mod tests {
    use super::*;
    use ipc::AppStateKind;

    #[test]
    fn registry_launch_increments_id() {
        let mut reg = SessionRegistry::default();
        let id1 = reg.launch("com.example.a");
        let id2 = reg.launch("com.example.b");
        assert!(id2 > id1);
    }

    #[test]
    fn registry_terminate_known_session() {
        let mut reg = SessionRegistry::default();
        let id = reg.launch("com.example.app");
        assert!(reg.terminate(id));
        assert!(matches!(reg.state(id), AppStateKind::NotFound));
    }

    #[test]
    fn registry_terminate_unknown_returns_false() {
        let mut reg = SessionRegistry::default();
        assert!(!reg.terminate(999));
    }

    #[test]
    fn registry_running_ids_reflects_live_sessions() {
        let mut reg = SessionRegistry::default();
        let id1 = reg.launch("a");
        let id2 = reg.launch("b");
        let mut ids = reg.running_ids();
        ids.sort();
        assert_eq!(ids, vec![id1, id2]);
        reg.terminate(id1);
        assert_eq!(reg.running_ids(), vec![id2]);
    }

    #[test]
    fn registry_state_not_found_for_unknown() {
        let reg = SessionRegistry::default();
        assert!(matches!(reg.state(42), AppStateKind::NotFound));
    }
}