//! Connection auto-detection and mux client helpers.
//!
//! The [`connect`] function tries mux connections first (TCP via env var, then
//! Unix socket), falling back to direct USB serial. This matches the Python
//! client's `connect()` behavior.

use std::time::Duration;

use tracing::debug;

use crate::client::Client;
use crate::discovery;
use crate::transport::{AnyTransport, MuxTransport, SerialTransport};

/// Default read timeout for connections.
const DEFAULT_TIMEOUT: Duration = Duration::from_secs(2);

/// Resolve the mux socket path in priority order.
///
/// 1. `$DONGLORA_MUX` environment variable
/// 2. `$XDG_RUNTIME_DIR/donglora/mux.sock`
/// 3. `/tmp/donglora-mux.sock`
pub fn default_socket_path() -> String {
    if let Ok(env) = std::env::var("DONGLORA_MUX") {
        return env;
    }
    if let Ok(xdg) = std::env::var("XDG_RUNTIME_DIR") {
        return format!("{xdg}/donglora/mux.sock");
    }
    "/tmp/donglora-mux.sock".to_string()
}

/// Find an existing mux socket path, or `None` if no socket file exists.
fn find_mux_socket() -> Option<String> {
    if let Ok(env) = std::env::var("DONGLORA_MUX") {
        if std::path::Path::new(&env).exists() {
            return Some(env);
        }
        return None;
    }
    if let Ok(xdg) = std::env::var("XDG_RUNTIME_DIR") {
        let p = format!("{xdg}/donglora/mux.sock");
        if std::path::Path::new(&p).exists() {
            return Some(p);
        }
    }
    let p = "/tmp/donglora-mux.sock";
    if std::path::Path::new(p).exists() {
        return Some(p.to_string());
    }
    None
}

/// Connect to the mux daemon via Unix domain socket.
#[cfg(unix)]
pub fn mux_connect(
    path: Option<&str>,
    timeout: Duration,
) -> anyhow::Result<Client<MuxTransport>> {
    let path = match path {
        Some(p) => p.to_string(),
        None => find_mux_socket()
            .ok_or_else(|| anyhow::anyhow!("no mux socket found"))?,
    };
    let transport = MuxTransport::unix(&path, timeout)?;
    Ok(Client::new(transport))
}

/// Connect to the mux daemon via TCP.
pub fn mux_tcp_connect(
    host: &str,
    port: u16,
    timeout: Duration,
) -> anyhow::Result<Client<MuxTransport>> {
    let transport = MuxTransport::tcp(host, port, timeout)?;
    Ok(Client::new(transport))
}

/// Auto-detect and connect to a DongLoRa device.
///
/// Priority:
/// 1. `DONGLORA_MUX_TCP` env var → TCP mux connection
/// 2. Unix socket mux (if socket file exists)
/// 3. Direct USB serial (auto-detect by VID:PID, blocks until device appears)
///
/// If `port` is `Some`, skips mux detection and connects directly to that serial port.
pub fn connect(
    port: Option<&str>,
    timeout: Duration,
) -> anyhow::Result<Client<AnyTransport>> {
    // If explicit port given, go direct
    if let Some(port) = port {
        debug!("opening serial port {port}");
        let transport = SerialTransport::open(port, timeout)?;
        return Ok(Client::new(AnyTransport::Serial(transport)));
    }

    // Try TCP mux via environment variable
    if let Ok(tcp) = std::env::var("DONGLORA_MUX_TCP")
        && let Some(transport) = try_tcp_mux(&tcp, timeout)
    {
        debug!("connected to TCP mux at {tcp}");
        return Ok(Client::new(AnyTransport::Mux(transport)));
    }

    // Try Unix socket mux
    #[cfg(unix)]
    if let Some(path) = find_mux_socket() {
        match MuxTransport::unix(&path, timeout) {
            Ok(transport) => {
                debug!("connected to mux socket at {path}");
                return Ok(Client::new(AnyTransport::Mux(transport)));
            }
            Err(_) => {
                // Stale socket or connection refused — fall through
                debug!("mux socket at {path} not reachable, falling back to USB");
            }
        }
    }

    // Direct USB serial — auto-detect or wait
    let port_path = discovery::find_port()
        .unwrap_or_else(discovery::wait_for_device);
    debug!("opening serial port {port_path}");
    let transport = SerialTransport::open(&port_path, timeout)?;
    Ok(Client::new(AnyTransport::Serial(transport)))
}

/// Convenience: connect with default timeout.
pub fn connect_default() -> anyhow::Result<Client<AnyTransport>> {
    connect(None, DEFAULT_TIMEOUT)
}

fn try_tcp_mux(addr: &str, timeout: Duration) -> Option<MuxTransport> {
    let (host, port) = if let Some((h, p)) = addr.rsplit_once(':') {
        let host = if h.is_empty() { "localhost" } else { h };
        let port: u16 = p.parse().ok()?;
        (host.to_string(), port)
    } else {
        let port: u16 = addr.parse().ok()?;
        ("localhost".to_string(), port)
    };
    MuxTransport::tcp(&host, port, timeout).ok()
}