//! [`Config`] and the `serve*` entry points.
//!
//! The listener pool itself lives in [`crate::endpoint`], which is the
//! real API: an endpoint is a supervisable child you place in your own
//! tree. `serve*` is the batteries-included path for a process whose only
//! job is serving HTTP — it owns the runtime and wraps one endpoint in a
//! one-child supervisor.
//!
use crate::conn_actor::ConnLimits;
use crate::plug::Pipeline;

use smarm::supervisor::Shutdown;
use smarm::{ChildSpec, OneForOne, Restart, Strategy};

use std::io::{self, ErrorKind};
use std::net::{SocketAddr, ToSocketAddrs};
use std::time::Duration;

// ---------------------------------------------------------------------------
// Config
// ---------------------------------------------------------------------------

#[derive(Clone, Debug)]
pub struct Config {
    pub addr:               SocketAddr,
    pub listener_pool:      usize,
    pub keep_alive_timeout: Duration,
    pub max_header_count:   usize,
    pub read_buf_size:      usize,
    /// Wall-clock budget for reading the request HEAD (from first byte to
    /// full head parse). Kept short — an incomplete head is the classic
    /// slowloris. See `ConnLimits::head_timeout`.
    pub head_timeout:       Duration,
    /// Absolute wall-clock cap on reading the request BODY (from head-parse
    /// to full body). Sized for slow links, so much larger than
    /// `head_timeout`. See `ConnLimits::body_timeout`.
    pub body_timeout:       Duration,
    /// Burst size that resets the body stall clock. A body dribbling fewer
    /// than this per `body_stall_timeout` window is evicted — the slowloris
    /// / slow-legit discriminator. See `ConnLimits::body_burst_bytes`.
    pub body_burst_bytes:   usize,
    /// Max time since the last qualifying body burst before eviction;
    /// backstopped by `body_timeout`. See `ConnLimits::body_stall_timeout`.
    pub body_stall_timeout: Duration,
    /// Per-write budget for response bytes (the fixed head+body write, and
    /// each streamed chunk). See `ConnLimits::write_timeout`.
    pub write_timeout:      Duration,
    pub max_body_bytes:     usize,
    /// How long a graceful shutdown waits for in-flight requests before
    /// force-stopping the remaining connections. Idle keep-alive
    /// connections are closed immediately on shutdown and do not run the
    /// clock out.
    pub drain_timeout:      Duration,
    /// WebSocket: cap on a single frame's payload (header-checked
    /// before buffering; violation closes 1009).
    pub max_frame_payload:  usize,
    /// WebSocket: cap on a complete reassembled message (spans
    /// fragments; violation closes 1009).
    pub max_message_bytes:  usize,
    /// Registry name for this endpoint's gen_server — how it is addressed
    /// from elsewhere in the app ([`crate::endpoint::whereis`]), and what
    /// must be unique between two endpoints in one process (a public and
    /// an admin port, say). Default `"urus"`.
    pub name:               &'static str,
    /// Stack reserve (RFC 019 `smarm::SpawnOpts::stack_reserve`) given to
    /// each per-connection actor. Request handlers routinely pull in
    /// application code — DB drivers, (de)compression, templating — whose
    /// stack needs comfortably exceed smarm's bare-actor default of 64 KiB
    /// (the exact shape of bug this exists to head off; see smarm RFC 019).
    /// Default: 256 KiB. The reserve is virtual/demand-paged, so raising it
    /// costs address space, not RSS, until a handler actually uses it.
    pub conn_stack_reserve: usize,
}

/// Default per-connection actor stack reserve (see [`Config::conn_stack_reserve`]).
pub const DEFAULT_CONN_STACK_RESERVE: usize = 256 * 1024;

impl Config {
    pub fn new(addr: SocketAddr) -> Self {
        let pool = std::thread::available_parallelism()
            .map(|n| n.get())
            .unwrap_or(2)
            .max(2);
        Self {
            addr,
            listener_pool:      pool,
            keep_alive_timeout: Duration::from_secs(60),
            max_header_count:   64,
            read_buf_size:      8 * 1024,
            head_timeout:       Duration::from_secs(30),
            body_timeout:       Duration::from_secs(300),
            body_burst_bytes:   4 * 1024,
            body_stall_timeout: Duration::from_secs(20),
            write_timeout:      Duration::from_secs(30),
            max_body_bytes:     16 * 1024 * 1024,
            drain_timeout:      Duration::from_secs(30),
            max_frame_payload:  1024 * 1024,
            max_message_bytes:  4 * 1024 * 1024,
            name:               "urus",
            conn_stack_reserve: DEFAULT_CONN_STACK_RESERVE,
        }
    }

    pub(crate) fn to_conn_limits(&self) -> ConnLimits {
        ConnLimits {
            max_headers:        self.max_header_count,
            initial_read_buf:   self.read_buf_size,
            max_head_bytes:     64 * 1024,
            max_body_bytes:     self.max_body_bytes,
            keep_alive_timeout: self.keep_alive_timeout,
            head_timeout:       self.head_timeout,
            body_timeout:       self.body_timeout,
            body_burst_bytes:   self.body_burst_bytes,
            body_stall_timeout: self.body_stall_timeout,
            write_timeout:      self.write_timeout,
            max_frame_payload:  self.max_frame_payload,
            max_message_bytes:  self.max_message_bytes,
        }
    }
}

// ---------------------------------------------------------------------------
// config-file: TOML overlay for tuning knobs
// ---------------------------------------------------------------------------
//
// urus is a library, so it never presumes a config-file path or reads the
// environment — the embedding binary decides where a file lives and hands
// the text here. This overlays a sparse TOML document onto an existing
// `Config` (built with an addr the binary chose): only the keys present are
// applied, everything else keeps the compiled default. Durations are
// integer seconds. Unknown keys are a hard error so a typo is loud, not a
// silent no-op.
//
// Scope for now: the slowloris-tuning knobs only. Migrating the rest of the
// Config surface into the file is a separate, additive job (the loader
// mechanism is general — it just extends `TomlOverrides`).

/// Error from [`Config::with_toml_str`]: the TOML failed to parse or carried
/// an unknown/mistyped key.
#[cfg(feature = "config-file")]
#[derive(Debug)]
pub enum ConfigError {
    Toml(String),
}

#[cfg(feature = "config-file")]
impl std::fmt::Display for ConfigError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            ConfigError::Toml(m) => write!(f, "config TOML error: {m}"),
        }
    }
}

#[cfg(feature = "config-file")]
impl std::error::Error for ConfigError {}

#[cfg(feature = "config-file")]
#[derive(serde::Deserialize)]
#[serde(deny_unknown_fields)]
struct TomlOverrides {
    head_timeout_secs:       Option<u64>,
    body_timeout_secs:       Option<u64>,
    body_burst_bytes:        Option<usize>,
    body_stall_timeout_secs: Option<u64>,
}

#[cfg(feature = "config-file")]
impl Config {
    /// Overlay a TOML document of tuning knobs onto this config (sparse:
    /// only the keys present are applied). Durations are integer seconds.
    ///
    /// Recognized keys: `head_timeout_secs`, `body_timeout_secs`,
    /// `body_burst_bytes`, `body_stall_timeout_secs`. Unknown keys error.
    /// Other `Config` knobs are not yet file-configurable.
    pub fn with_toml_str(mut self, s: &str) -> Result<Self, ConfigError> {
        let o: TomlOverrides =
            toml::from_str(s).map_err(|e| ConfigError::Toml(e.to_string()))?;
        if let Some(v) = o.head_timeout_secs {
            self.head_timeout = Duration::from_secs(v);
        }
        if let Some(v) = o.body_timeout_secs {
            self.body_timeout = Duration::from_secs(v);
        }
        if let Some(v) = o.body_burst_bytes {
            self.body_burst_bytes = v;
        }
        if let Some(v) = o.body_stall_timeout_secs {
            self.body_stall_timeout = Duration::from_secs(v);
        }
        Ok(self)
    }
}

// ---------------------------------------------------------------------------
// Handle / ShutdownSignal — graceful shutdown plumbing for the serve* entries.
// ---------------------------------------------------------------------------

/// A clonable trigger for graceful shutdown, usable from any OS thread
/// (e.g. a signal-handling thread) — the shutdown path for callers who let
/// `serve*` own the runtime and so have no [`smarm::RuntimeHandle`] of
/// their own. If you build the tree yourself with [`crate::endpoint`], use
/// `rt.handle().request_shutdown(root_sup)` instead and ignore this.
#[derive(Clone)]
pub struct Handle {
    tx: smarm::Sender<()>,
}

impl Handle {
    /// Begin graceful shutdown: stop accepting, close idle keep-alive
    /// connections, drain in-flight requests up to `Config.drain_timeout`,
    /// then force-stop stragglers. `serve*` returns once the runtime has
    /// wound down. Idempotent; extra calls are no-ops.
    pub fn shutdown(&self) {
        let _ = self.tx.send(());
    }
}

/// The receiving half consumed by [`serve_with_shutdown`].
pub struct ShutdownSignal {
    rx: smarm::Receiver<()>,
}

/// Create a connected [`Handle`]/[`ShutdownSignal`] pair.
pub fn shutdown_handle() -> (Handle, ShutdownSignal) {
    let (tx, rx) = smarm::channel();
    (Handle { tx }, ShutdownSignal { rx })
}

// ---------------------------------------------------------------------------
// serve* — batteries-included entries for apps whose only job is serving.
// ---------------------------------------------------------------------------
//
// These own the smarm runtime and build a one-child tree around
// `endpoint()`. An app with its own actors should call `endpoint()`
// directly and put it in its own supervision tree — that is the real API;
// everything here is a convenience wrapper over it.

/// Boot a runtime, serve until `signal` fires, then drain and return.
///
/// The tree is `root sup -> [..app_children, endpoint]` on
/// [`Strategy::RestForOne`], with the endpoint on [`Shutdown::Infinity`]
/// so its `drain_timeout` — not a supervisor deadline — bounds the drain.
///
/// `app_children` is your application's actors: a
/// [`PubSub::child`](crate::PubSub::child), a
/// [`ChannelHub::children`](crate::channels::ChannelHub::children), your
/// own state servers. They start **before** the endpoint and, because
/// shutdown is ordered in reverse, stop **after** it has drained — so a
/// request still in flight can still reach the bus. `RestForOne` in that
/// order also means one of them crashing restarts the endpoint behind it,
/// dropping connections whose subscriptions died with it, rather than
/// leaving live sockets addressing a table that no longer knows them.
///
/// The root actor parks on the signal channel; a `Handle::shutdown` from a
/// foreign OS thread wakes it, it shuts the supervisor down and `rt.run`
/// returns when the last actor is gone.
pub fn serve_with_shutdown(
    config: Config,
    rt_config: smarm::Config,
    pipeline: Pipeline,
    app_children: Vec<ChildSpec>,
    signal: ShutdownSignal,
) -> io::Result<()> {
    let addr = config.addr;
    let endpoint = crate::endpoint::endpoint(config, pipeline)?;
    println!("urus: listening on {addr}");

    let rt = smarm::init(rt_config);
    rt.run(move || {
        let sup = smarm::spawn(move || {
            let mut sup = OneForOne::new().strategy(Strategy::RestForOne);
            for child in app_children {
                sup = sup.child(child);
            }
            sup.child(ChildSpec::new(Restart::Permanent, endpoint).shutdown(Shutdown::Infinity))
                .run()
        });

        // Park until told to shut down. If every Handle was dropped the
        // channel closes and no shutdown can ever arrive: serve forever,
        // exactly v1's semantics.
        match signal.rx.recv() {
            Ok(()) => smarm::request_shutdown(sup.pid()),
            Err(_) => {
                // Sender side gone. Park indefinitely; the process is
                // expected to be killed externally.
                loop {
                    smarm::sleep(Duration::from_secs(3600));
                }
            }
        }
        let _ = sup.join();
    });

    Ok(())
}

/// [`serve_with_shutdown`] without a shutdown handle: serves until the
/// process is killed.
pub fn serve_with(
    config: Config,
    rt_config: smarm::Config,
    pipeline: Pipeline,
    app_children: Vec<ChildSpec>,
) -> io::Result<()> {
    // The Handle is dropped immediately: shutdown can never be signalled.
    let (_handle, signal) = shutdown_handle();
    serve_with_shutdown(config, rt_config, pipeline, app_children, signal)
}

/// Defaults all round: default [`Config`], default smarm runtime (one
/// scheduler thread per CPU), no app children, serve until killed.
pub fn serve(addr: impl ToSocketAddrs, pipeline: Pipeline) -> io::Result<()> {
    let addr = addr
        .to_socket_addrs()?
        .next()
        .ok_or_else(|| io::Error::new(ErrorKind::InvalidInput, "no addresses resolved"))?;
    serve_with(Config::new(addr), smarm::Config::default(), pipeline, Vec::new())
}


#[cfg(all(test, feature = "config-file"))]
mod config_file_tests {
    use super::*;

    fn base() -> Config {
        Config::new("127.0.0.1:0".parse().unwrap())
    }

    #[test]
    fn toml_empty_keeps_defaults() {
        let d = base();
        let c = base().with_toml_str("").unwrap();
        assert_eq!(c.head_timeout, d.head_timeout);
        assert_eq!(c.body_timeout, d.body_timeout);
        assert_eq!(c.body_burst_bytes, d.body_burst_bytes);
        assert_eq!(c.body_stall_timeout, d.body_stall_timeout);
    }

    #[test]
    fn toml_partial_overrides_only_named() {
        let d = base();
        let c = base().with_toml_str("head_timeout_secs = 5").unwrap();
        assert_eq!(c.head_timeout, Duration::from_secs(5)); // overridden
        assert_eq!(c.body_timeout, d.body_timeout);         // default kept
        assert_eq!(c.body_burst_bytes, d.body_burst_bytes); // default kept
        assert_eq!(c.body_stall_timeout, d.body_stall_timeout);
    }

    #[test]
    fn toml_full_overrides_all() {
        let c = base()
            .with_toml_str(
                "head_timeout_secs = 10\n\
                 body_timeout_secs = 120\n\
                 body_burst_bytes = 8192\n\
                 body_stall_timeout_secs = 15\n",
            )
            .unwrap();
        assert_eq!(c.head_timeout, Duration::from_secs(10));
        assert_eq!(c.body_timeout, Duration::from_secs(120));
        assert_eq!(c.body_burst_bytes, 8192);
        assert_eq!(c.body_stall_timeout, Duration::from_secs(15));
    }

    #[test]
    fn toml_unknown_key_errors() {
        // A mistyped/unknown key is a hard error, not a silent no-op.
        let e = base().with_toml_str("body_timeout_sec = 120"); // typo: missing 's'
        assert!(e.is_err(), "unknown key should error");
    }

    #[test]
    fn toml_malformed_errors() {
        let e = base().with_toml_str("this is not = valid = toml");
        assert!(e.is_err(), "malformed TOML should error");
    }
}