tachyon-web 0.0.2

//! Axum-compatible Routing and Handler traits.
//!
//! The routing module provides the core mechanism for matching incoming HTTP requests to
//! asynchronous handlers. It embraces an **Axum-like API**, allowing you to build highly
//! readable and modular applications using `Router` and `MethodRouter`.
//!
//! By chaining methods like `.route("/", get(handler))` and `.with_state(state)`, you can
//! effortlessly create scalable web endpoints that automatically extract parameters, state,
//! and payloads with zero-allocation abstractions.

use bytes::Bytes;
use hyper::{Method, Request, Response, StatusCode};
use std::future::Future;
use std::sync::Arc;

pub mod extract;
pub mod handler;
/// Middleware primitives like the `Next` continuation struct.
pub mod middleware;
/// Module for serving static directories with compile-time-like performance.
pub mod static_dir;
/// Optional `tower::Service`/`tower::Layer` interop, gated behind the `tower` feature.
#[cfg(feature = "tower")]
pub mod tower_compat;

use crate::http::response::{Body, IntoResponse};
use crate::routing::extract::PathParams;
pub use handler::{BoxedFuture, BoxedHandler, Handler};

// ─── Method array indices ─────────────────────────────────────────────────────

const IDX_GET: usize = 0;
const IDX_POST: usize = 1;
const IDX_PUT: usize = 2;
const IDX_DELETE: usize = 3;
const IDX_OPTIONS: usize = 4;
const IDX_HEAD: usize = 5;
const IDX_PATCH: usize = 6;
const IDX_TRACE: usize = 7;
const IDX_CONNECT: usize = 8;
const METHOD_COUNT: usize = 9;

const METHOD_NAMES: [&str; METHOD_COUNT] = [
    "GET", "POST", "PUT", "DELETE", "OPTIONS", "HEAD", "PATCH", "TRACE", "CONNECT",
];

#[inline]
const fn method_index(m: &Method) -> Option<usize> {
    match *m {
        Method::GET => Some(IDX_GET),
        Method::POST => Some(IDX_POST),
        Method::PUT => Some(IDX_PUT),
        Method::DELETE => Some(IDX_DELETE),
        Method::OPTIONS => Some(IDX_OPTIONS),
        Method::HEAD => Some(IDX_HEAD),
        Method::PATCH => Some(IDX_PATCH),
        Method::TRACE => Some(IDX_TRACE),
        Method::CONNECT => Some(IDX_CONNECT),
        _ => None,
    }
}

// ─── MethodRouter ─────────────────────────────────────────────────────────────

/// Router that dispatches requests to different handlers based on the HTTP method.
#[derive(Clone)]
pub struct MethodRouter<S> {
    handlers: [Option<middleware::MethodHandler<S>>; METHOD_COUNT],
    /// Path-parameter names for this route, in declaration order, populated by
    /// `Router::compile()`. Cloning an `Arc<str>` per request into `PathParams`
    /// is a refcount bump, avoiding a fresh heap allocation for every param name
    /// on every request (the names are fixed once the route is compiled).
    param_names: Arc<[Arc<str>]>,
    /// The compiled route pattern this handler is registered under (e.g.
    /// `/users/{id}`), populated by `Router::compile()`. Exposed to handlers via
    /// the [`crate::routing::extract::MatchedPath`] extractor, matching Axum.
    matched_path: Arc<str>,
    /// When this route was reached through one or more `Router::nest()` calls,
    /// the accumulated prefix to strip from the request `Uri` before dispatch —
    /// matching Axum's nested-router URI rewriting (see `Router::nest`).
    nest_prefix: Option<Arc<str>>,
}

impl<S> std::fmt::Debug for MethodRouter<S> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        let methods = [
            "GET", "POST", "PUT", "DELETE", "OPTIONS", "HEAD", "PATCH", "TRACE", "CONNECT",
        ];
        let mut dbg = f.debug_struct("MethodRouter");
        for (i, name) in methods.iter().enumerate() {
            let _ = dbg.field(name, &self.handlers[i].is_some());
        }
        let _ = dbg.field("param_names", &self.param_names);
        let _ = dbg.field("matched_path", &self.matched_path);
        let _ = dbg.field("nest_prefix", &self.nest_prefix);
        dbg.finish()
    }
}

impl<S> Default for MethodRouter<S>
where
    S: Clone + Send + Sync + 'static,
{
    fn default() -> Self {
        Self::new()
    }
}

impl<S> MethodRouter<S>
where
    S: Clone + Send + Sync + 'static,
{
    /// Create a new empty `MethodRouter`.
    #[must_use]
    pub fn new() -> Self {
        Self {
            handlers: [None, None, None, None, None, None, None, None, None],
            param_names: Arc::from([]),
            matched_path: Arc::from(""),
            nest_prefix: None,
        }
    }

    fn set<H, T>(mut self, idx: usize, handler: H) -> Self
    where
        H: Handler<T, S>,
        T: 'static,
    {
        self.handlers[idx] = Some(middleware::MethodHandler::new(Arc::new(
            move |req, state| handler.clone().call(req, state),
        )));
        self
    }

    /// Add a handler for HTTP GET requests.
    #[must_use]
    pub fn get<H, T>(self, handler: H) -> Self
    where
        H: Handler<T, S>,
        T: 'static,
    {
        self.set(IDX_GET, handler)
    }
    /// Add a handler for HTTP POST requests.
    #[must_use]
    pub fn post<H, T>(self, handler: H) -> Self
    where
        H: Handler<T, S>,
        T: 'static,
    {
        self.set(IDX_POST, handler)
    }
    /// Add a handler for HTTP PUT requests.
    #[must_use]
    pub fn put<H, T>(self, handler: H) -> Self
    where
        H: Handler<T, S>,
        T: 'static,
    {
        self.set(IDX_PUT, handler)
    }
    /// Add a handler for HTTP DELETE requests.
    #[must_use]
    pub fn delete<H, T>(self, handler: H) -> Self
    where
        H: Handler<T, S>,
        T: 'static,
    {
        self.set(IDX_DELETE, handler)
    }
    /// Add a handler for HTTP OPTIONS requests.
    #[must_use]
    pub fn options<H, T>(self, handler: H) -> Self
    where
        H: Handler<T, S>,
        T: 'static,
    {
        self.set(IDX_OPTIONS, handler)
    }
    /// Add a handler for HTTP HEAD requests.
    #[must_use]
    pub fn head<H, T>(self, handler: H) -> Self
    where
        H: Handler<T, S>,
        T: 'static,
    {
        self.set(IDX_HEAD, handler)
    }
    /// Add a handler for HTTP PATCH requests.
    #[must_use]
    pub fn patch<H, T>(self, handler: H) -> Self
    where
        H: Handler<T, S>,
        T: 'static,
    {
        self.set(IDX_PATCH, handler)
    }
    /// Add a handler for HTTP TRACE requests.
    #[must_use]
    pub fn trace<H, T>(self, handler: H) -> Self
    where
        H: Handler<T, S>,
        T: 'static,
    {
        self.set(IDX_TRACE, handler)
    }
    /// Add a handler for HTTP CONNECT requests.
    #[must_use]
    pub fn connect<H, T>(self, handler: H) -> Self
    where
        H: Handler<T, S>,
        T: 'static,
    {
        self.set(IDX_CONNECT, handler)
    }

    /// Returns the `Allow` header value listing all registered HTTP methods.
    ///
    /// Builds the string with a single pre-sized allocation (sized for the
    /// worst case: all nine methods plus a synthesized `HEAD`) and avoids
    /// an intermediate `Vec` — called only on 405 responses.
    ///
    /// Matches Axum's format: comma-joined with no space, and — since a `GET`
    /// handler transparently answers `HEAD` requests too when no explicit
    /// `HEAD` handler is registered (see `handle_request`'s
    /// `falls_back_to_get` logic) — `HEAD` is listed whenever `GET` is
    /// registered, even without an explicit `HEAD` handler.
    fn allow_header(&self) -> String {
        let mut out = String::with_capacity(56);
        let implicit_head = self.handlers[IDX_GET].is_some() && self.handlers[IDX_HEAD].is_none();
        for (i, name) in METHOD_NAMES.iter().enumerate() {
            if self.handlers[i].is_some() {
                if !out.is_empty() {
                    out.push(',');
                }
                out.push_str(name);
                if i == IDX_GET && implicit_head {
                    out.push_str(",HEAD");
                }
            }
        }
        out
    }

    /// Merges `other`'s method handlers into `self`, matching Axum's
    /// `Router::route` semantics where registering the same path twice with
    /// non-overlapping methods combines into a single route — e.g.
    /// `.route("/x", get(a)).route("/x", post(b))` yields one route that
    /// answers both `GET` and `POST` on `/x`, rather than tachyon-web's
    /// previous behavior of rejecting *any* repeated path outright.
    ///
    /// # Errors
    /// Returns [`RouterError::MethodOverlap`] if `other` defines a method
    /// already present in `self` — matching Axum, which panics with
    /// "Overlapping method route" for the same situation.
    fn merge(mut self, mut other: Self, path: &str) -> Result<Self, RouterError> {
        for (i, (mine, theirs)) in self
            .handlers
            .iter_mut()
            .zip(other.handlers.iter_mut())
            .enumerate()
        {
            if let Some(handler) = theirs.take() {
                if mine.is_some() {
                    return Err(RouterError::MethodOverlap {
                        method: METHOD_NAMES[i],
                        path: path.to_string(),
                    });
                }
                *mine = Some(handler);
            }
        }
        // `nest_prefix` isn't recomputed at `compile()` time (unlike
        // `param_names`/`matched_path`), so a prefix carried by either side
        // must survive the merge — otherwise a route registered via both
        // `.nest()` and a plain `.route()` at the same final path would
        // silently lose its prefix-stripping behavior depending on
        // registration order.
        if self.nest_prefix.is_none() {
            self.nest_prefix = other.nest_prefix;
        }
        Ok(self)
    }

    /// Apply a middleware handler to all endpoints registered in this `MethodRouter`.
    ///
    /// Middleware takes a `Request` and a `Next<S>` continuation.
    #[must_use]
    pub fn hoop<F, Fut, Res>(self, middleware: F) -> Self
    where
        F: Fn(Request<Body>, middleware::Next<S>) -> Fut + Clone + Send + Sync + 'static,
        Fut: Future<Output = Res> + Send + 'static,
        Res: IntoResponse + Send + 'static,
    {
        self.hoop_at(middleware::MiddlewarePosition::First, middleware)
    }

    /// Apply a middleware handler to all endpoints registered in this `MethodRouter` at a specific position (First/Last).
    #[must_use]
    pub fn hoop_at<F, Fut, Res>(
        mut self,
        position: middleware::MiddlewarePosition,
        middleware: F,
    ) -> Self
    where
        F: Fn(Request<Body>, middleware::Next<S>) -> Fut + Clone + Send + Sync + 'static,
        Fut: Future<Output = Res> + Send + 'static,
        Res: IntoResponse + Send + 'static,
    {
        let boxed: middleware::BoxedMiddleware<S> = Arc::new(move |req, next| {
            let fut = middleware(req, next);
            crate::routing::handler::ResponseFuture::Boxed(Box::pin(async move {
                fut.await.into_response()
            }))
        });
        for i in 0..METHOD_COUNT {
            if let Some(handler) = &mut self.handlers[i] {
                match position {
                    middleware::MiddlewarePosition::First => {
                        handler.middlewares.insert(0, boxed.clone());
                    }
                    middleware::MiddlewarePosition::Last => {
                        handler.middlewares.push(boxed.clone());
                    }
                }
                handler.compiled = None;
            }
        }
        self
    }

    /// Compile all handler middleware chains in-place.
    pub fn compile_in_place(&mut self) {
        for i in 0..METHOD_COUNT {
            if let Some(handler) = &mut self.handlers[i] {
                handler.compile_in_place();
            }
        }
    }

    /// Capture a state and transition this method router to another state type.
    #[must_use]
    pub fn with_state<S2>(self, state: &Arc<S>) -> MethodRouter<S2>
    where
        S2: Clone + Send + Sync + 'static,
        S: Clone + Send + Sync + 'static,
    {
        let mut new_handlers: [Option<middleware::MethodHandler<S2>>; METHOD_COUNT] =
            [None, None, None, None, None, None, None, None, None];
        for (i, opt_handler) in self.handlers.iter().enumerate() {
            if let Some(handler) = opt_handler {
                let mut compiled_h = handler.clone();
                compiled_h.compile_in_place();
                let compiled_raw = compiled_h.compiled.unwrap_or(compiled_h.raw);
                let state = state.clone();
                let new_h: BoxedHandler<S2> =
                    Arc::new(move |req, _parent_state| compiled_raw(req, state.clone()));
                new_handlers[i] = Some(middleware::MethodHandler::new(new_h));
            }
        }
        MethodRouter {
            handlers: new_handlers,
            param_names: self.param_names,
            matched_path: self.matched_path,
            nest_prefix: self.nest_prefix,
        }
    }
}

// ─── MethodRouter shortcuts ───────────────────────────────────────────────────

/// Helper to construct a GET-only route.
pub fn get<H, T, S>(handler: H) -> MethodRouter<S>
where
    H: Handler<T, S>,
    T: 'static,
    S: Clone + Send + Sync + 'static,
{
    MethodRouter::new().get(handler)
}

/// Helper to construct a POST-only route.
pub fn post<H, T, S>(handler: H) -> MethodRouter<S>
where
    H: Handler<T, S>,
    T: 'static,
    S: Clone + Send + Sync + 'static,
{
    MethodRouter::new().post(handler)
}

/// Helper to construct a PUT-only route.
pub fn put<H, T, S>(handler: H) -> MethodRouter<S>
where
    H: Handler<T, S>,
    T: 'static,
    S: Clone + Send + Sync + 'static,
{
    MethodRouter::new().put(handler)
}

/// Helper to construct a DELETE-only route.
pub fn delete<H, T, S>(handler: H) -> MethodRouter<S>
where
    H: Handler<T, S>,
    T: 'static,
    S: Clone + Send + Sync + 'static,
{
    MethodRouter::new().delete(handler)
}

/// Helper to construct a PATCH-only route.
pub fn patch<H, T, S>(handler: H) -> MethodRouter<S>
where
    H: Handler<T, S>,
    T: 'static,
    S: Clone + Send + Sync + 'static,
{
    MethodRouter::new().patch(handler)
}

/// Helper to construct an OPTIONS-only route.
pub fn options<H, T, S>(handler: H) -> MethodRouter<S>
where
    H: Handler<T, S>,
    T: 'static,
    S: Clone + Send + Sync + 'static,
{
    MethodRouter::new().options(handler)
}

/// Helper to construct a HEAD-only route.
pub fn head<H, T, S>(handler: H) -> MethodRouter<S>
where
    H: Handler<T, S>,
    T: 'static,
    S: Clone + Send + Sync + 'static,
{
    MethodRouter::new().head(handler)
}

/// Helper to construct a TRACE-only route.
pub fn trace<H, T, S>(handler: H) -> MethodRouter<S>
where
    H: Handler<T, S>,
    T: 'static,
    S: Clone + Send + Sync + 'static,
{
    MethodRouter::new().trace(handler)
}

/// Helper to construct a CONNECT-only route.
pub fn connect<H, T, S>(handler: H) -> MethodRouter<S>
where
    H: Handler<T, S>,
    T: 'static,
    S: Clone + Send + Sync + 'static,
{
    MethodRouter::new().connect(handler)
}

/// Helper to construct a route that dispatches to `handler` for **every** HTTP
/// method (`GET`, `POST`, `PUT`, `DELETE`, `OPTIONS`, `HEAD`, `PATCH`, `TRACE`,
/// `CONNECT`). Matches `axum::routing::any`.
pub fn any<H, T, S>(handler: H) -> MethodRouter<S>
where
    H: Handler<T, S>,
    T: 'static,
    S: Clone + Send + Sync + 'static,
{
    MethodRouter::new()
        .get(handler.clone())
        .post(handler.clone())
        .put(handler.clone())
        .delete(handler.clone())
        .options(handler.clone())
        .head(handler.clone())
        .patch(handler.clone())
        .trace(handler.clone())
        .connect(handler)
}

// ─── Router ──────────────────────────────────────────────────────────────────

/// Axum-like routing table using `matchit` under the hood.
#[derive(Clone)]
pub struct Router<S = ()> {
    routes: Vec<(String, MethodRouter<S>)>,
    fallback: Option<BoxedHandler<S>>,
    method_not_allowed_fallback: Option<BoxedHandler<S>>,
    state: Option<Arc<S>>,
    /// Opt-in trailing-slash normalization (see [`Router::normalize_trailing_slash`]).
    normalize_trailing_slash: bool,
    /// Lazily populated the first time this exact `Router` is driven as a
    /// `tower::Service` (see the `impl Service<...> for Router<S>` below) —
    /// lets `Router` be used as a drop-in `tower::Service`/`.oneshot()`
    /// target exactly like `axum::Router`, with no separate `.compile()`
    /// call the caller has to remember, while still only ever building the
    /// `matchit` tree once rather than per request. Reset to `None` by every
    /// route-table-mutating builder method, so building/serving/mutating
    /// out of order can't silently dispatch against a stale tree.
    #[cfg(feature = "tower")]
    compiled: Option<CompiledRouter<S>>,
}

impl<S> std::fmt::Debug for Router<S> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("Router")
            .field("route_count", &self.routes.len())
            .field("has_fallback", &self.fallback.is_some())
            .field(
                "has_method_not_allowed_fallback",
                &self.method_not_allowed_fallback.is_some(),
            )
            .finish_non_exhaustive()
    }
}

impl<S> Default for Router<S>
where
    S: Clone + Send + Sync + 'static,
{
    fn default() -> Self {
        Self::new()
    }
}

/// Combines two optional per-router handlers (a `fallback` or
/// `method_not_allowed_fallback`) for [`Router::merge`]: `None` if neither side set one,
/// whichever side's if only one did, or a panic with `panic_msg` if both did — matching
/// Axum's "Cannot merge two `Router`s that both have a fallback".
#[allow(clippy::panic)]
fn merge_optional<T>(a: Option<T>, b: Option<T>, panic_msg: &'static str) -> Option<T> {
    match (a, b) {
        (Some(_), Some(_)) => panic!("{panic_msg}"),
        (Some(v), None) | (None, Some(v)) => Some(v),
        (None, None) => None,
    }
}

/// Convert an Axum-style `:param` segment to a `matchit` `{param}` segment,
/// and `*wildcard` to `{*wildcard}`.
///
/// Only converts leading `:` and `*` – pure literal segments are left unchanged.
fn normalize_route_pattern(path: &str) -> String {
    // Fast path: no special characters at all.
    if !path.contains(':') && !path.contains('*') {
        return path.to_string();
    }
    let segments: Vec<String> = path
        .split('/')
        .map(|segment| {
            if segment.starts_with(':') && segment.len() > 1 {
                format!("{{{}}}", &segment[1..])
            } else if segment.starts_with('*') && segment.len() > 1 {
                // matchit wildcard syntax: {*name}
                format!("{{{segment}}}")
            } else {
                segment.to_string()
            }
        })
        .collect();
    segments.join("/")
}

/// Builds a `MethodRouter` that dispatches every HTTP method to the same handler —
/// used to mount raw `tower::Service`s, which (unlike native handlers) typically do
/// their own method matching rather than being registered per-verb.
#[cfg(feature = "tower")]
fn all_methods<H, S>(handler: H) -> MethodRouter<S>
where
    H: Handler<tower_compat::TowerServiceMarker, S>,
    S: Clone + Send + Sync + 'static,
{
    any(handler)
}

impl<S> Router<S>
where
    S: Clone + Send + Sync + 'static,
{
    /// Create a new empty `Router`.
    #[must_use]
    pub fn new() -> Self {
        Self {
            routes: Vec::new(),
            fallback: None,
            method_not_allowed_fallback: None,
            state: None,
            normalize_trailing_slash: false,
            #[cfg(feature = "tower")]
            compiled: None,
        }
    }

    /// Opt in to trailing-slash normalization: strips a single trailing `/`
    /// from the incoming request's path *before* routing, so `/foo` and
    /// `/foo/` reach the same route.
    ///
    /// By default (matching Axum) routing is strict — `/foo` and `/foo/` are
    /// distinct routes, and a mismatch 404s. This opts into the common
    /// convenience behavior natively, without pulling in `tower`/`tower-http`
    /// just for `tower_http::normalize_path::NormalizePathLayer` — this method
    /// mirrors that layer's own semantics exactly (an in-place path
    /// normalization applied once per request, not a redirect), just built in.
    ///
    /// Only meaningful on the outermost `Router` you actually `.compile()` (or
    /// hand to a `Server`) — like `NormalizePathLayer`, it operates on the
    /// whole incoming request before any route matching happens, so setting it
    /// on a router later merged/nested into another has no effect.
    #[must_use]
    pub const fn normalize_trailing_slash(mut self) -> Self {
        self.normalize_trailing_slash = true;
        self
    }

    /// Opt out of search-engine indexing — appropriate default hardening for `.onion`/`.i2p`
    /// deployments, where a crawlable mirror is itself an unintentional discovery/deanonymization
    /// leak (some operators don't realize search engines index onion mirrors at all).
    ///
    /// Adds `X-Robots-Tag: noindex, nofollow` to every response from this router (routes and
    /// fallback alike), and — unless the app already registers its own `/robots.txt` route —
    /// serves a blanket `User-agent: *\nDisallow: /` there too.
    ///
    /// # Example
    /// ```rust
    /// use tachyon_web::{Router, get};
    ///
    /// let router: Router = Router::new()
    ///     .route("/", get(|| async { "hi" }))
    ///     .no_index();
    /// ```
    #[must_use]
    pub fn no_index(mut self) -> Self {
        if !self.routes.iter().any(|(path, _)| path == "/robots.txt") {
            self = self.route(
                "/robots.txt",
                get(|| async { "User-agent: *\nDisallow: /\n" }),
            );
        }
        self.hoop(|req: Request<Body>, next: middleware::Next<S>| async move {
            let mut resp = next.run(req).await;
            let _ = resp.headers_mut().insert(
                hyper::header::HeaderName::from_static("x-robots-tag"),
                hyper::header::HeaderValue::from_static("noindex, nofollow"),
            );
            resp
        })
    }

    /// Set the application state for this router, transitioning it to
    /// another (typically `()`) state type — matching Axum's
    /// `Router<S>::with_state<S2>(self, state: S) -> Router<S2>` signature.
    ///
    /// `S2` is almost always inferred as `()` since a fully-stated router is
    /// normally handed straight to a `Server`, but leaving it generic (rather
    /// than hardcoding `Router<()>`) matches Axum's nested-router pattern,
    /// where an inner router's state is supplied by an outer router before
    /// the two are merged/nested and the outer router still has its own,
    /// different state type to resolve later.
    #[must_use]
    pub fn with_state<S2>(self, state: S) -> Router<S2>
    where
        S2: Clone + Send + Sync + 'static,
    {
        let state_arc = Arc::new(state);

        let new_routes = self
            .routes
            .into_iter()
            .map(|(path, method_router)| (path, method_router.with_state(&state_arc)))
            .collect();

        let rebind = |handler: BoxedHandler<S>| -> BoxedHandler<S2> {
            let state_arc = state_arc.clone();
            Arc::new(move |req, _parent_state| handler(req, state_arc.clone()))
        };
        let new_fallback = self.fallback.map(rebind);
        let new_method_not_allowed_fallback = self.method_not_allowed_fallback.map(rebind);

        Router {
            routes: new_routes,
            fallback: new_fallback,
            method_not_allowed_fallback: new_method_not_allowed_fallback,
            state: None,
            normalize_trailing_slash: self.normalize_trailing_slash,
            #[cfg(feature = "tower")]
            compiled: None,
        }
    }

    /// Inserts `method_router` at `path`, merging it into an already-registered
    /// `MethodRouter` for the same path (combining non-overlapping methods
    /// into one route) rather than always appending a new entry.
    ///
    /// # Panics
    /// Panics if `method_router` defines an HTTP method already registered
    /// for `path` — matching Axum's `Router::route`, which panics with
    /// "Overlapping method route" in the same situation. This is a
    /// deliberate, direct port of that panic-on-programmer-error behavior
    /// (a route conflict is a build-time bug, not a runtime condition to
    /// recover from), not an oversight.
    #[allow(clippy::panic)]
    fn push_or_merge_route(&mut self, path: String, method_router: MethodRouter<S>) {
        #[cfg(feature = "tower")]
        {
            self.compiled = None;
        }
        if let Some(pos) = self.routes.iter().position(|(p, _)| *p == path) {
            let (_, existing) = self.routes.remove(pos);
            let merged = existing
                .merge(method_router, &path)
                .unwrap_or_else(|e| panic!("{e}"));
            self.routes.insert(pos, (path, merged));
        } else {
            self.routes.push((path, method_router));
        }
    }

    /// Add a route to the router.
    ///
    /// Registering the same path more than once merges the method routers —
    /// e.g. `.route("/x", get(a)).route("/x", post(b))` yields one route that
    /// answers both `GET` and `POST` — matching Axum. Registering the *same*
    /// method for the same path twice panics, also matching Axum.
    #[must_use]
    pub fn route(mut self, path: &str, method_router: MethodRouter<S>) -> Self {
        let normalized = normalize_route_pattern(path);
        self.push_or_merge_route(normalized, method_router);
        self
    }

    /// A dummy/compatibility method that returns the router itself, matching Axum's API
    /// when preparing a router to be run with a server listener.
    #[must_use]
    pub const fn into_make_service(self) -> Self {
        self
    }

    /// Serve an entire directory as static files — the simplest, Nginx-like API.
    ///
    /// Serves directly from disk on every request; it does not call
    /// [`static_dir::ServeDir::preload`], so `CacheConfig::enabled`'s default of
    /// `true` has no effect here. Use [`serve_dir`](Self::serve_dir) with a
    /// manually-preloaded `ServeDir` if you want the in-memory RAM cache.
    ///
    /// Do not point `dir_path` at a directory that can ever contain files an
    /// untrusted user chose the bytes of (e.g. an upload folder mixed into the
    /// served tree) — see [`static_dir::ServeDir`]'s docs for why (in short: a
    /// user-supplied `.svg` served this way can carry an executable
    /// `<script>`).
    ///
    /// # Example
    /// ```rust,no_run
    /// use tachyon_web::Router;
    ///
    /// // Serve ./public/ at /, with index.html as the default.
    /// let router = Router::new()
    ///     .serve_static("./public");
    /// # let _ = router.with_state::<()>(());
    /// ```
    #[must_use]
    pub fn serve_static(self, dir_path: impl AsRef<std::path::Path>) -> Self {
        let sd = static_dir::ServeDir::new(&dir_path).index("index.html");
        self.serve_dir("/", sd)
    }

    /// Serve an entire static directory under a URL prefix with full configuration control.
    ///
    /// Registers both an exact route (`prefix`) and a wildcard route (`prefix/*path`).
    /// Use `serve_static()` for the common case of serving a dir at `/`. See
    /// [`static_dir::ServeDir`]'s docs for the upload-safety warning before
    /// serving a directory that can contain user-supplied files.
    #[must_use]
    pub fn serve_dir(mut self, prefix: &str, serve_dir: static_dir::ServeDir) -> Self {
        let prefix = prefix.trim_end_matches('/');
        let exact_route = if prefix.is_empty() { "/" } else { prefix };
        let wildcard_route = format!("{prefix}/*path");

        self = self.route(exact_route, serve_dir.clone().into_method_router());
        self = self.route(&wildcard_route, serve_dir.into_method_router());
        self
    }

    /// Natively serve a specific file on a specific route.
    ///
    /// The file is read **once at startup** into a `Bytes` buffer. Every subsequent
    /// request is served from that buffer with **zero I/O and zero allocations**,
    /// rivalling `include_bytes!` without inflating the binary.
    ///
    /// # Errors
    /// Returns an `Err` if the file cannot be read at startup.
    pub fn serve_file(self, path: &str, file_path: &str) -> Result<Self, std::io::Error> {
        let content = std::fs::read(file_path)?;
        let content_bytes = Bytes::from(content);
        let mime_type = static_dir::guess_mime_type(std::path::Path::new(file_path));

        Ok(self.route(
            path,
            get(move |_req: Request<Body>| {
                let body_content = content_bytes.clone();
                async move {
                    let mut resp = Response::new(Body::full(body_content));
                    let mime_val = hyper::header::HeaderValue::from_static(mime_type);
                    let _ = resp
                        .headers_mut()
                        .insert(hyper::header::CONTENT_TYPE, mime_val);
                    resp
                }
            }),
        ))
    }

    /// Natively serve a specific file on a specific route dynamically.
    ///
    /// The file is read from disk on every request. Ideal for large files that
    /// change frequently where startup preloading is undesirable.
    #[must_use]
    pub fn serve_file_dynamic(self, path: &str, file_path: &str) -> Self {
        let file_path_str = file_path.to_string();
        let mime_type = static_dir::guess_mime_type(std::path::Path::new(file_path));

        self.route(
            path,
            get(move |_req: Request<Body>| {
                let fp = file_path_str.clone();
                async move {
                    let Ok(content) = tokio::fs::read(&fp).await else {
                        let mut resp = Response::new(Body::empty());
                        *resp.status_mut() = StatusCode::NOT_FOUND;
                        return resp;
                    };
                    let mut resp = Response::new(Body::full(Bytes::from(content)));
                    let mime_val = hyper::header::HeaderValue::from_static(mime_type);
                    let _ = resp
                        .headers_mut()
                        .insert(hyper::header::CONTENT_TYPE, mime_val);
                    resp
                }
            }),
        )
    }

    /// Nest another router under a given path prefix.
    ///
    /// Seamlessly merges all routes from the sub-router into this router.
    ///
    /// Matches Axum: handlers inside the nested router see a request `Uri` with
    /// `prefix` stripped (e.g. a request to `/api/users/1` nested under `/api`
    /// sees `/users/1`), while [`crate::routing::extract::OriginalUri`] recovers
    /// the pre-strip, full path. Nesting is resolved once at `compile()` time —
    /// there's no per-request recursive dispatch — so this is exactly as fast as
    /// a flat route table; only the one matched route's prefix is ever stripped.
    ///
    /// # Deviation from Axum: the inner router's own `fallback` is not carried over
    ///
    /// In real Axum, nesting mounts the whole inner `Router` as a recursive sub-service, so a
    /// request under `prefix` that the inner router's own routes don't match still reaches the
    /// *inner* router's `fallback` before ever falling through to the outer one. Because this
    /// implementation flattens the inner router's routes into the same top-level route table
    /// (the design that keeps nesting as fast as a flat lookup — see above), there is no
    /// separate inner dispatch step left for a per-nest fallback to hook into: any path under
    /// `prefix` that isn't one of the inner router's own registered routes simply falls through
    /// to whatever `Router::fallback` (or the default `404`) is configured on the *outermost*
    /// router — the inner router's own `.fallback(...)`, if it set one, is never called. Use
    /// [`Router::fallback`] on the outer router (or register an explicit catch-all route under
    /// `prefix`) if you need a per-module 404 handler.
    #[must_use]
    pub fn nest(mut self, prefix: &str, mut router: Self) -> Self {
        let prefix = prefix.trim_end_matches('/');
        for (path, mut method_router) in router.routes.drain(..) {
            let nested_path = if path == "/" || path.is_empty() {
                prefix.to_string()
            } else {
                format!("{prefix}{path}")
            };
            let final_path = if nested_path.is_empty() {
                "/".to_string()
            } else {
                nested_path
            };
            // Accumulate the strip prefix across multiple levels of nesting
            // (e.g. `.nest("/api", Router::new().nest("/v1", inner))` strips
            // `/api/v1`, not just `/v1`).
            let accumulated = method_router.nest_prefix.as_ref().map_or_else(
                || prefix.to_string(),
                |existing| format!("{prefix}{existing}"),
            );
            method_router.nest_prefix = Some(Arc::from(accumulated));
            self.push_or_merge_route(final_path, method_router);
        }
        self
    }

    /// Merge another router's routes into this router.
    ///
    /// If exactly one of the two routers has a [`fallback`](Self::fallback) (or a
    /// [`method_not_allowed_fallback`](Self::method_not_allowed_fallback)) configured, the
    /// merged router adopts it — matching Axum, which does the same for `Router::fallback`.
    /// Unlike [`nest`](Self::nest) (where the inner router's fallback is deliberately never
    /// reachable — it would only ever fire for a request the outer router's own routing
    /// already decided was unmatched, which the outer fallback already handles), `merge`
    /// treats both routers as peers, so silently dropping one side's fallback would silently
    /// change which handler answers unmatched requests.
    ///
    /// # Panics
    /// Panics if `other` defines a method for a path already registered in `self`, or if
    /// both routers already have a `fallback`/`method_not_allowed_fallback` configured —
    /// matching Axum's `Router::merge`.
    #[must_use]
    pub fn merge(mut self, mut other: Self) -> Self {
        #[cfg(feature = "tower")]
        {
            self.compiled = None;
        }
        for (path, method_router) in other.routes.drain(..) {
            self.push_or_merge_route(path, method_router);
        }
        self.fallback = merge_optional(
            self.fallback.take(),
            other.fallback.take(),
            "Cannot merge two `Router`s that both have a fallback",
        );
        self.method_not_allowed_fallback = merge_optional(
            self.method_not_allowed_fallback.take(),
            other.method_not_allowed_fallback.take(),
            "Cannot merge two `Router`s that both have a method_not_allowed_fallback",
        );
        self
    }

    /// Mount a raw `tower::Service` at `path`, handling every HTTP method.
    ///
    /// Requires the `tower` feature. Prefer `.route(path, get(handler))` with a native
    /// handler where possible — this exists to bridge in pre-built Tower/tower-http
    /// services (e.g. `tower_http::services::ServeFile`) without a rewrite.
    #[cfg(feature = "tower")]
    #[must_use]
    pub fn route_service<Svc, RespBody>(self, path: &str, service: Svc) -> Self
    where
        Svc: tower::Service<Request<Bytes>, Response = Response<RespBody>>
            + Clone
            + Send
            + Sync
            + 'static,
        Svc::Future: Send + 'static,
        Svc::Error: Into<crate::http::error::Error> + Send,
        RespBody: hyper::body::Body<Data = Bytes> + Send + 'static,
        RespBody::Error: Into<crate::http::error::Error>,
    {
        let handler = tower_compat::ServiceHandler {
            service,
            strip_prefix: None,
        };
        self.route(path, all_methods(handler))
    }

    /// Nest a raw `tower::Service` under `prefix`, with the mounted path rewritten
    /// relative to `prefix` before the service sees it (matching Axum's `nest_service`).
    ///
    /// Requires the `tower` feature.
    #[must_use]
    #[cfg(feature = "tower")]
    pub fn nest_service<Svc, RespBody>(self, prefix: &str, service: Svc) -> Self
    where
        Svc: tower::Service<Request<Bytes>, Response = Response<RespBody>>
            + Clone
            + Send
            + Sync
            + 'static,
        Svc::Future: Send + 'static,
        Svc::Error: Into<crate::http::error::Error> + Send,
        RespBody: hyper::body::Body<Data = Bytes> + Send + 'static,
        RespBody::Error: Into<crate::http::error::Error>,
    {
        let prefix = prefix.trim_end_matches('/');
        let exact = if prefix.is_empty() { "/" } else { prefix };
        let wildcard = format!("{prefix}/*__tachyon_nest_rest");
        let handler = tower_compat::ServiceHandler {
            service,
            strip_prefix: Some(Arc::from(prefix)),
        };
        self.route(exact, all_methods(handler.clone()))
            .route(&wildcard, all_methods(handler))
    }

    /// Set a raw `tower::Service` as the fallback for unmatched paths.
    ///
    /// Requires the `tower` feature.
    #[must_use]
    #[cfg(feature = "tower")]
    pub fn fallback_service<Svc, RespBody>(mut self, service: Svc) -> Self
    where
        Svc: tower::Service<Request<Bytes>, Response = Response<RespBody>>
            + Clone
            + Send
            + Sync
            + 'static,
        Svc::Future: Send + 'static,
        Svc::Error: Into<crate::http::error::Error> + Send,
        RespBody: hyper::body::Body<Data = Bytes> + Send + 'static,
        RespBody::Error: Into<crate::http::error::Error>,
    {
        let handler = tower_compat::ServiceHandler {
            service,
            strip_prefix: None,
        };
        self.fallback = Some(Arc::new(move |req, state| handler.clone().call(req, state)));
        self.compiled = None;
        self
    }

    /// Apply a `tower::Layer` to every route **and** the fallback in this router.
    ///
    /// Requires the `tower` feature. Prefer `.hoop()`/`.hoop_at()` for new code — this
    /// exists to bridge in existing Tower/tower-http layers (tracing, compression,
    /// timeouts) without rewriting them as native middleware.
    #[must_use]
    #[cfg(feature = "tower")]
    pub fn layer<L, RespBody>(self, layer: L) -> Self
    where
        L: tower::Layer<tower_compat::NextService<S>> + Clone + Send + Sync + 'static,
        L::Service: tower::Service<Request<Bytes>, Response = Response<RespBody>> + Send + 'static,
        <L::Service as tower::Service<Request<Bytes>>>::Future: Send + 'static,
        <L::Service as tower::Service<Request<Bytes>>>::Error:
            Into<crate::http::error::Error> + Send,
        RespBody: hyper::body::Body<Data = Bytes> + Send + 'static,
        RespBody::Error: Into<crate::http::error::Error>,
    {
        self.hoop_at(
            middleware::MiddlewarePosition::First,
            tower_compat::from_tower_layer(layer),
        )
    }

    /// Apply a `tower::Layer` to every registered route, but *not* the fallback —
    /// matching Axum's distinction between `.layer()` and `.route_layer()`.
    ///
    /// Requires the `tower` feature.
    #[must_use]
    #[cfg(feature = "tower")]
    pub fn route_layer<L, RespBody>(mut self, layer: L) -> Self
    where
        L: tower::Layer<tower_compat::NextService<S>> + Clone + Send + Sync + 'static,
        L::Service: tower::Service<Request<Bytes>, Response = Response<RespBody>> + Send + 'static,
        <L::Service as tower::Service<Request<Bytes>>>::Future: Send + 'static,
        <L::Service as tower::Service<Request<Bytes>>>::Error:
            Into<crate::http::error::Error> + Send,
        RespBody: hyper::body::Body<Data = Bytes> + Send + 'static,
        RespBody::Error: Into<crate::http::error::Error>,
    {
        let mw = tower_compat::from_tower_layer(layer);
        for (_path, method_router) in &mut self.routes {
            let m = mw.clone();
            let old_mr = std::mem::take(method_router);
            *method_router = old_mr.hoop_at(middleware::MiddlewarePosition::Last, m);
        }
        self.compiled = None;
        self
    }

    /// Set a custom fallback handler for requests that don't match any route.
    #[must_use]
    pub fn fallback<H, T>(mut self, handler: H) -> Self
    where
        H: Handler<T, S>,
        T: 'static,
    {
        self.fallback = Some(Arc::new(move |req, state| {
            let handler = handler.clone();
            handler.call(req, state)
        }));
        #[cfg(feature = "tower")]
        {
            self.compiled = None;
        }
        self
    }

    /// Set a custom fallback handler for requests whose path matches a route but
    /// whose method has no registered handler (the default is a bare `405 Method
    /// Not Allowed` with an `Allow` header).
    #[must_use]
    pub fn method_not_allowed_fallback<H, T>(mut self, handler: H) -> Self
    where
        H: Handler<T, S>,
        T: 'static,
    {
        self.method_not_allowed_fallback = Some(Arc::new(move |req, state| {
            let handler = handler.clone();
            handler.call(req, state)
        }));
        #[cfg(feature = "tower")]
        {
            self.compiled = None;
        }
        self
    }

    /// Apply a middleware handler to ALL routes and the fallback registered in this `Router`.
    #[must_use]
    pub fn hoop<F, Fut, Res>(self, middleware: F) -> Self
    where
        F: Fn(Request<Body>, middleware::Next<S>) -> Fut + Clone + Send + Sync + 'static,
        Fut: Future<Output = Res> + Send + 'static,
        Res: IntoResponse + Send + 'static,
    {
        self.hoop_at(middleware::MiddlewarePosition::First, middleware)
    }

    /// Apply a middleware handler at a specific position (First/Last) to ALL routes and the fallback.
    #[must_use]
    pub fn hoop_at<F, Fut, Res>(
        mut self,
        position: middleware::MiddlewarePosition,
        middleware: F,
    ) -> Self
    where
        F: Fn(Request<Body>, middleware::Next<S>) -> Fut + Clone + Send + Sync + 'static,
        Fut: Future<Output = Res> + Send + 'static,
        Res: IntoResponse + Send + 'static,
    {
        #[cfg(feature = "tower")]
        {
            self.compiled = None;
        }
        for (_path, method_router) in &mut self.routes {
            let mw = middleware.clone();
            let old_mr = std::mem::take(method_router);
            *method_router = old_mr.hoop_at(position, mw);
        }

        if let Some(fallback) = self.fallback.take() {
            let mw = middleware.clone();
            self.fallback = Some(Arc::new(move |req, state| {
                let next = middleware::Next {
                    handler: fallback.clone(),
                    state,
                };
                let fut = mw(req, next);
                crate::routing::handler::ResponseFuture::Boxed(Box::pin(async move {
                    fut.await.into_response()
                }))
            }));
        }

        if let Some(handler) = self.method_not_allowed_fallback.take() {
            let mw = middleware;
            self.method_not_allowed_fallback = Some(Arc::new(move |req, state| {
                let next = middleware::Next {
                    handler: handler.clone(),
                    state,
                };
                let fut = mw(req, next);
                crate::routing::handler::ResponseFuture::Boxed(Box::pin(async move {
                    fut.await.into_response()
                }))
            }));
        }

        self
    }

    /// Route an incoming request directly, compiling the router on the fly.
    /// Primarily useful for testing.
    ///
    /// # Panics
    /// Panics if router compilation fails (e.g. a duplicate route was registered).
    #[allow(clippy::expect_used)]
    pub async fn handle_request(&self, req: Request<Body>) -> Response<Body>
    where
        S: Default,
    {
        let compiled = self.clone().compile().expect("Router compilation failed");
        compiled.handle_request(req).await
    }

    /// Build and compile the routing tree, returning a `CompiledRouter`.
    ///
    /// # Errors
    /// Returns `RouterError::DuplicateRoute` if the same literal path somehow
    /// reaches `compile()` twice. In practice this can't happen through the
    /// public API — `route()`/`nest()`/`merge()` all merge same-path entries
    /// (panicking on overlapping methods, matching Axum) — this is an
    /// internal invariant check, not a condition callers need to handle.
    pub fn compile(self) -> Result<CompiledRouter<S>, RouterError>
    where
        S: Default,
    {
        let mut matcher: matchit::Router<MethodRouter<S>> = matchit::Router::new();

        let mut seen = std::collections::HashSet::new();
        for (path, mut method_router) in self.routes {
            if !seen.insert(path.clone()) {
                return Err(RouterError::DuplicateRoute(path));
            }
            method_router.compile_in_place();
            method_router.param_names = extract_param_names(&path);
            method_router.matched_path = Arc::from(path.as_str());
            matcher.insert(path, method_router)?;
        }

        let state = self.state.unwrap_or_else(|| Arc::new(S::default()));

        Ok(CompiledRouter {
            matcher,
            fallback: self.fallback,
            method_not_allowed_fallback: self.method_not_allowed_fallback,
            state,
            normalize_trailing_slash: self.normalize_trailing_slash,
        })
    }
}

/// Errors that can occur during router construction or compilation.
#[derive(Debug)]
pub enum RouterError {
    /// Duplicate route registered.
    DuplicateRoute(String),
    /// The same path was registered with the same HTTP method more than
    /// once (via separate `.route()` calls) — matching Axum's "Overlapping
    /// method route" panic. Registering the same path with *different*
    /// methods across multiple `.route()` calls is fine and merges into one
    /// route, exactly like Axum.
    MethodOverlap {
        /// The HTTP method that was registered twice.
        method: &'static str,
        /// The path it was registered twice for.
        path: String,
    },
    /// matchit insert error.
    Insert(matchit::InsertError),
}

impl std::fmt::Display for RouterError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            Self::DuplicateRoute(path) => write!(f, "Duplicate route path registered: '{path}'"),
            Self::MethodOverlap { method, path } => {
                write!(
                    f,
                    "Overlapping method route: {method} {path} already exists"
                )
            }
            Self::Insert(e) => write!(f, "Router insert error: {e}"),
        }
    }
}

impl std::error::Error for RouterError {}

impl From<matchit::InsertError> for RouterError {
    fn from(e: matchit::InsertError) -> Self {
        Self::Insert(e)
    }
}

// ─── CompiledRouter ───────────────────────────────────────────────────────────

/// A compiled routing table ready to serve requests.
#[derive(Clone)]
pub struct CompiledRouter<S> {
    matcher: matchit::Router<MethodRouter<S>>,
    fallback: Option<BoxedHandler<S>>,
    method_not_allowed_fallback: Option<BoxedHandler<S>>,
    state: Arc<S>,
    normalize_trailing_slash: bool,
}

impl<S> std::fmt::Debug for CompiledRouter<S> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("CompiledRouter")
            .field("has_fallback", &self.fallback.is_some())
            .field(
                "has_method_not_allowed_fallback",
                &self.method_not_allowed_fallback.is_some(),
            )
            .finish_non_exhaustive()
    }
}

/// Parses the `{name}` / `{*name}` placeholders out of a compiled route
/// pattern, in declaration order, matching the order `matchit` yields them
/// in `Match::params`. Computed once per route at `compile()` time so the
/// hot path (`resolve()`) never has to allocate a `String` for a param key.
fn extract_param_names(path: &str) -> Arc<[Arc<str>]> {
    let mut names = Vec::new();
    let bytes = path.as_bytes();
    let mut i = 0;
    while i < bytes.len() {
        if bytes[i] == b'{'
            && let Some(end) = path[i + 1..].find('}')
        {
            let inner = &path[i + 1..i + 1 + end];
            let name = inner.strip_prefix('*').unwrap_or(inner);
            names.push(Arc::from(name));
            i += 1 + end + 1;
        } else {
            i += 1;
        }
    }
    Arc::from(names)
}

/// Zero-allocation percent-decoding helper for path parameters.
///
/// Returns `None` if the input contains invalid percent encoding.
pub(crate) fn percent_decode(s: &str) -> Option<std::borrow::Cow<'_, str>> {
    let bytes = s.as_bytes();
    if !bytes.contains(&b'%') {
        return Some(std::borrow::Cow::Borrowed(s));
    }
    let mut decoded = Vec::with_capacity(bytes.len());
    let mut i = 0;
    while i < bytes.len() {
        if bytes[i] == b'%' {
            if i + 2 < bytes.len() {
                let hex = &bytes[i + 1..i + 3];
                if let Ok(hex_str) = std::str::from_utf8(hex)
                    && let Ok(val) = u8::from_str_radix(hex_str, 16)
                {
                    decoded.push(val);
                    i += 3;
                    continue;
                }
            }
            return None; // invalid percent encoding
        }
        decoded.push(bytes[i]);
        i += 1;
    }
    let s = String::from_utf8(decoded).ok()?;
    Some(std::borrow::Cow::Owned(s))
}

/// Strips `prefix` from `req`'s `Uri` path in place, used by nested routers
/// (native [`Router::nest`] and [`tower_compat::ServiceHandler`]'s
/// `nest_service`) to match Axum's nested-router URI rewriting.
///
/// The prefix is stripped directly from the request's raw (still
/// percent-encoded) `path()` string, and the original query string is carried
/// over untouched — this deliberately avoids reconstructing the URI from a
/// percent-*decoded* path segment, which would let a client smuggle a `?`/`#`
/// past routing by percent-encoding it (e.g. `/api/foo%3Fadmin=1` decoding into
/// a synthesized `?admin=1` query the router never evaluated as one).
pub(crate) fn strip_uri_prefix(req: &mut Request<Body>, prefix: &str) {
    let path = req.uri().path();
    let stripped = path.strip_prefix(prefix).unwrap_or(path);
    let new_path = if stripped.starts_with('/') {
        stripped.to_string()
    } else {
        format!("/{stripped}")
    };
    let path_and_query = match req.uri().query() {
        Some(q) if !q.is_empty() => format!("{new_path}?{q}"),
        _ => new_path,
    };
    let mut parts = req.uri().clone().into_parts();
    if let Ok(pq) = path_and_query.parse() {
        parts.path_and_query = Some(pq);
    }
    if let Ok(new_uri) = hyper::Uri::from_parts(parts) {
        *req.uri_mut() = new_uri;
    }
}

/// Strips a single trailing `/` from `req`'s `Uri` path in place (used by
/// [`Router::normalize_trailing_slash`]), preserving the query string and
/// never stripping the root `/` itself. Mirrors
/// `tower_http::normalize_path::NormalizePathLayer`'s own behavior: an
/// in-place normalization applied before routing, not a redirect.
fn strip_trailing_slash(req: &mut Request<Body>) {
    let path = req.uri().path();
    if path.len() <= 1 || !path.ends_with('/') {
        return;
    }
    let new_path = &path[..path.len() - 1];
    let path_and_query = match req.uri().query() {
        Some(q) if !q.is_empty() => format!("{new_path}?{q}"),
        _ => new_path.to_string(),
    };
    let mut parts = req.uri().clone().into_parts();
    if let Ok(pq) = path_and_query.parse() {
        parts.path_and_query = Some(pq);
    }
    if let Ok(new_uri) = hyper::Uri::from_parts(parts) {
        *req.uri_mut() = new_uri;
    }
}

impl<S> CompiledRouter<S>
where
    S: Clone + Send + Sync + 'static,
{
    /// Route an incoming request, returning the resulting HTTP response.
    ///
    /// # Trailing-slash handling
    ///
    /// Tachyon follows the same semantics as Axum: routes are matched **exactly**.
    /// `/foo` and `/foo/` are distinct routes — a request for one does **not**
    /// fall back to a route registered under the other, unless the router opted
    /// into [`Router::normalize_trailing_slash`], in which case a trailing `/`
    /// is stripped from the request path before matching (in-place, not a
    /// redirect — the same behavior as `tower_http`'s `NormalizePathLayer`). We
    /// also do **not** perform case-folding, which would silently obscure bugs
    /// and change observable behavior.
    ///
    /// This is the hot path: the `matchit` radix-tree lookup is `O(path_len)`,
    /// challenge interception is a single prefix check, and method dispatch
    /// is an array index — all zero-allocation on the happy path.
    #[inline]
    pub async fn handle_request(&self, req: Request<Body>) -> Response<Body> {
        let mut req = req;

        if self.normalize_trailing_slash {
            strip_trailing_slash(&mut req);
        }

        let path = req.uri().path();

        #[cfg(feature = "lets-encrypt")]
        if path.starts_with("/.well-known/acme-challenge/") {
            use hyper::StatusCode;
            let token = path
                .strip_prefix("/.well-known/acme-challenge/")
                .unwrap_or("");
            if let Some(key_auth) = crate::tls::acme::get_challenge(token) {
                return Response::builder()
                    .status(StatusCode::OK)
                    .header(hyper::header::CONTENT_TYPE, "text/plain")
                    .body(Body::full(Bytes::copy_from_slice(key_auth.as_bytes())))
                    .unwrap_or_else(|_| Response::new(Body::empty()));
            }
        }

        let (method_router, params): RouteResolution<'_, S> = match self.resolve(path) {
            Some(r) => r,
            None => {
                return if let Some(fb) = &self.fallback {
                    fb(req, self.state.clone()).await
                } else {
                    Response::builder()
                        .status(StatusCode::NOT_FOUND)
                        .body(Body::full(Bytes::from_static(b"Not Found")))
                        .unwrap_or_else(|_| Response::new(Body::empty()))
                };
            }
        };

        // Insert path params into extensions before handing off to the handler.
        // Skip the extension insert entirely on parameterless routes (common case).
        if !params.is_empty() {
            let _ = req.extensions_mut().insert(PathParams(params));
        }

        #[cfg(feature = "matched-path")]
        {
            let _ = req
                .extensions_mut()
                .insert(crate::routing::extract::MatchedPath(
                    method_router.matched_path.clone(),
                ));
        }

        // If this route was reached through `Router::nest()`, strip the
        // accumulated prefix from the `Uri` the handler sees, preserving the
        // pre-strip path via `OriginalUri` — matching Axum's nested-router
        // semantics (see `Router::nest`'s docs).
        if let Some(prefix) = &method_router.nest_prefix {
            #[cfg(feature = "original-uri")]
            {
                let original_uri = req.uri().clone();
                let _ = req
                    .extensions_mut()
                    .insert(crate::routing::extract::OriginalUri(original_uri));
            }
            strip_uri_prefix(&mut req, prefix);
        }

        let method = req.method();
        let idx = method_index(method);

        // HEAD uses an explicit HEAD handler when registered; otherwise it
        // falls back to the GET handler, with the body discarded afterwards.
        let is_head = *method == Method::HEAD;
        let falls_back_to_get =
            is_head && method_router.handlers[IDX_HEAD].is_none() && idx == Some(IDX_HEAD);
        let effective_idx = if falls_back_to_get {
            Some(IDX_GET)
        } else {
            idx
        };

        let handler = effective_idx.and_then(|i| method_router.handlers[i].as_ref());

        if let Some(h) = handler {
            let mut resp = h.call(req, self.state.clone()).await;
            // Per HTTP semantics, a HEAD response must never carry a body,
            // regardless of whether it came from an explicit HEAD handler or
            // the implicit GET fallback.
            if is_head {
                *resp.body_mut() = Body::empty();
            }
            resp
        } else if let Some(fb) = &self.method_not_allowed_fallback {
            // Route exists but this method has no handler, and a custom fallback
            // was configured for that case via `Router::method_not_allowed_fallback`.
            fb(req, self.state.clone()).await
        } else {
            // Route exists but this method has no handler → 405 with Allow header.
            let allow = method_router.allow_header();
            Response::builder()
                .status(StatusCode::METHOD_NOT_ALLOWED)
                .header(hyper::header::ALLOW, &allow)
                .body(Body::full(Bytes::from_static(b"Method Not Allowed")))
                .unwrap_or_else(|_| Response::new(Body::empty()))
        }
    }

    /// Internal: attempt to match `path`, returning `RouteResolution`.
    #[inline]
    fn resolve(&self, path: &str) -> Option<RouteResolution<'_, S>> {
        let m = self.matcher.at(path).ok()?;
        let params = if m.params.is_empty() {
            Vec::new()
        } else {
            // Param names are precomputed once at `compile()` time and cloning an
            // `Arc<str>` is a refcount bump, not a heap allocation — only the
            // decoded value needs to be freshly allocated per request.
            let names = &m.value.param_names;
            let mut p = Vec::with_capacity(m.params.len());
            for (name, (_, v)) in names.iter().zip(m.params.iter()) {
                let decoded =
                    percent_decode(v).map_or_else(|| v.to_string(), std::borrow::Cow::into_owned);
                p.push((name.clone(), decoded));
            }
            p
        };
        Some((m.value, params))
    }
}

/// Type alias for matched route results to keep signatures clean.
pub type RouteResolution<'a, S> = (&'a MethodRouter<S>, Vec<(Arc<str>, String)>);

// ─── Unit tests ───────────────────────────────────────────────────────────────

#[cfg(test)]
mod tests {
    #![allow(clippy::unwrap_used)]
    use super::*;
    use crate::routing::extract::Path;
    use serde::Deserialize;

    #[derive(Debug, Deserialize)]
    struct IdParam {
        id: u32,
    }

    async fn handle_root() -> &'static str {
        "root"
    }
    async fn handle_id(Path(p): Path<IdParam>) -> String {
        format!("id:{}", p.id)
    }
    async fn handle_post() -> &'static str {
        "post"
    }
    async fn handle_delete() -> &'static str {
        "deleted"
    }

    fn make_req(method: &str, uri: &str) -> Request<Body> {
        Request::builder()
            .method(method)
            .uri(uri)
            .body(Body::empty())
            .expect("valid request")
    }

    fn compile_app() -> CompiledRouter<()> {
        Router::new()
            .route("/", get(handle_root))
            .route(
                "/user/:id",
                get(handle_id).post(handle_post).delete(handle_delete),
            )
            .with_state::<()>(())
            .compile()
            .expect("compile router")
    }

    // ── routing correctness ──────────────────────────────────────────────────

    #[tokio::test]
    async fn test_root_route() {
        let router = compile_app();
        let resp = router.handle_request(make_req("GET", "/")).await;
        assert_eq!(resp.status(), StatusCode::OK);
    }

    #[tokio::test]
    async fn test_path_param_extraction() {
        use http_body_util::BodyExt;
        let router = compile_app();
        let resp = router.handle_request(make_req("GET", "/user/42")).await;
        assert_eq!(resp.status(), StatusCode::OK);
        let body = resp.into_body().collect().await.unwrap().to_bytes();
        assert_eq!(body.as_ref(), b"id:42");
    }

    #[tokio::test]
    async fn test_not_found() {
        let router = compile_app();
        let resp = router.handle_request(make_req("GET", "/nonexistent")).await;
        assert_eq!(resp.status(), StatusCode::NOT_FOUND);
    }

    #[tokio::test]
    async fn test_method_not_allowed_has_allow_header() {
        let router = compile_app();
        // /user/:id has GET, POST, DELETE — PATCH is not registered
        let resp = router.handle_request(make_req("PATCH", "/user/1")).await;
        assert_eq!(resp.status(), StatusCode::METHOD_NOT_ALLOWED);
        let allow = resp
            .headers()
            .get(hyper::header::ALLOW)
            .expect("Allow header must be present");
        let allow_str = allow.to_str().expect("valid utf8");
        assert!(allow_str.contains("GET"), "Allow: {allow_str}");
        assert!(allow_str.contains("POST"), "Allow: {allow_str}");
        assert!(allow_str.contains("DELETE"), "Allow: {allow_str}");
        assert!(!allow_str.contains("PATCH"), "Allow: {allow_str}");
    }

    // ── trailing slash strictness (matches Axum: /foo and /foo/ are distinct) ──

    #[tokio::test]
    async fn test_trailing_slash_not_stripped() {
        let router = compile_app();
        // "/user/5/" must NOT match "/user/:id" — Axum treats these as distinct routes.
        let resp = router.handle_request(make_req("GET", "/user/5/")).await;
        assert_eq!(resp.status(), StatusCode::NOT_FOUND);
    }

    #[tokio::test]
    async fn test_trailing_slash_not_added() {
        // register route with trailing slash, request without — must NOT match.
        let router = Router::new()
            .route("/about/", get(handle_root))
            .with_state::<()>(())
            .compile()
            .expect("compile");
        let resp = router.handle_request(make_req("GET", "/about")).await;
        assert_eq!(resp.status(), StatusCode::NOT_FOUND);
    }

    // ── case sensitivity ──────────────────────────────────────────────────────

    #[tokio::test]
    async fn test_case_sensitive_routing() {
        // Paths must match exactly — no silent case-folding.
        let router = compile_app();
        let resp = router.handle_request(make_req("GET", "/User/1")).await;
        assert_eq!(resp.status(), StatusCode::NOT_FOUND);
    }

    // ── fallback ──────────────────────────────────────────────────────────────

    #[tokio::test]
    async fn test_custom_fallback() {
        let router = Router::new()
            .route("/", get(handle_root))
            .fallback(|_req: Request<Body>| async { (StatusCode::FOUND, "redirected") })
            .with_state::<()>(())
            .compile()
            .expect("compile");
        let resp = router.handle_request(make_req("GET", "/missing")).await;
        assert_eq!(resp.status(), StatusCode::FOUND);
    }

    // ── route deduplication ───────────────────────────────────────────────────

    #[tokio::test]
    async fn test_overlapping_method_route_panics() {
        async fn v1() -> &'static str {
            "v1"
        }
        async fn v2() -> &'static str {
            "v2"
        }

        // Registering the same method for the same path twice panics,
        // matching Axum's "Overlapping method route" panic.
        let result = std::panic::catch_unwind(|| {
            Router::<()>::new()
                .route("/dup", get(v1))
                .route("/dup", get(v2))
        });
        assert!(result.is_err());
    }

    #[tokio::test]
    async fn test_non_overlapping_methods_on_same_path_merge() {
        async fn handle_get() -> &'static str {
            "got"
        }
        async fn handle_post() -> &'static str {
            "posted"
        }

        // Registering different methods for the same path across separate
        // `.route()` calls merges into a single route answering both —
        // matching Axum, not tachyon-web's previous "any repeat path errors"
        // behavior.
        let app = Router::new()
            .route("/x", get(handle_get))
            .route("/x", post(handle_post))
            .with_state::<()>(())
            .compile()
            .expect("compile");

        let get_resp = app.handle_request(make_req("GET", "/x")).await;
        assert_eq!(get_resp.status(), StatusCode::OK);
        let get_body = http_body_util::BodyExt::collect(get_resp.into_body())
            .await
            .unwrap()
            .to_bytes();
        assert_eq!(&get_body[..], b"got");

        let post_resp = app.handle_request(make_req("POST", "/x")).await;
        assert_eq!(post_resp.status(), StatusCode::OK);
        let post_body = http_body_util::BodyExt::collect(post_resp.into_body())
            .await
            .unwrap()
            .to_bytes();
        assert_eq!(&post_body[..], b"posted");
    }

    // ── normalize_route_pattern ───────────────────────────────────────────────

    #[test]
    fn test_normalize_no_change() {
        assert_eq!(normalize_route_pattern("/static/path"), "/static/path");
    }

    #[test]
    fn test_normalize_colon_param() {
        assert_eq!(normalize_route_pattern("/user/:id"), "/user/{id}");
    }

    #[test]
    fn test_normalize_wildcard() {
        assert_eq!(normalize_route_pattern("/files/*path"), "/files/{*path}");
    }

    #[test]
    fn test_normalize_mixed() {
        assert_eq!(
            normalize_route_pattern("/api/:version/files/*rest"),
            "/api/{version}/files/{*rest}"
        );
    }

    // ── nested routers ────────────────────────────────────────────────────────

    #[tokio::test]
    async fn test_nested_router() {
        let api = Router::new().route("/status", get(handle_root));
        let app = Router::new()
            .nest("/api/v1", api)
            .with_state::<()>(())
            .compile()
            .expect("compile");

        let resp = app.handle_request(make_req("GET", "/api/v1/status")).await;
        assert_eq!(resp.status(), StatusCode::OK);
    }

    #[tokio::test]
    async fn test_nested_router_root() {
        let api = Router::new().route("/", get(handle_root));
        let app = Router::new()
            .nest("/api", api)
            .with_state::<()>(())
            .compile()
            .expect("compile");

        let resp = app.handle_request(make_req("GET", "/api")).await;
        assert_eq!(resp.status(), StatusCode::OK);
    }

    // ── nest() URI stripping (Axum parity) ───────────────────────────────────

    #[tokio::test]
    async fn test_nest_strips_prefix_from_uri() {
        use hyper::Uri;

        async fn echo_uri(uri: Uri) -> String {
            uri.path().to_string()
        }

        let api = Router::new().route("/users/{id}", get(echo_uri));
        let app = Router::new()
            .nest("/api", api)
            .with_state::<()>(())
            .compile()
            .expect("compile");

        let resp = app.handle_request(make_req("GET", "/api/users/42")).await;
        assert_eq!(resp.status(), StatusCode::OK);
        let body = http_body_util::BodyExt::collect(resp.into_body())
            .await
            .unwrap()
            .to_bytes();
        // Matches Axum: the nested handler sees the prefix-stripped path.
        assert_eq!(&body[..], b"/users/42");
    }

    #[cfg(feature = "original-uri")]
    #[tokio::test]
    async fn test_nest_original_uri_preserves_full_path() {
        use crate::routing::extract::OriginalUri;

        async fn echo_original(OriginalUri(uri): OriginalUri) -> String {
            uri.path().to_string()
        }

        let api = Router::new().route("/users/{id}", get(echo_original));
        let app = Router::new()
            .nest("/api", api)
            .with_state::<()>(())
            .compile()
            .expect("compile");

        let resp = app.handle_request(make_req("GET", "/api/users/42")).await;
        assert_eq!(resp.status(), StatusCode::OK);
        let body = http_body_util::BodyExt::collect(resp.into_body())
            .await
            .unwrap()
            .to_bytes();
        // OriginalUri recovers the full, pre-strip path.
        assert_eq!(&body[..], b"/api/users/42");
    }

    #[tokio::test]
    async fn test_nest_two_levels_accumulates_prefix() {
        async fn echo_uri(uri: hyper::Uri) -> String {
            uri.path().to_string()
        }

        let innermost = Router::new().route("/users", get(echo_uri));
        let v1 = Router::new().nest("/v1", innermost);
        let app = Router::new()
            .nest("/api", v1)
            .with_state::<()>(())
            .compile()
            .expect("compile");

        let resp = app.handle_request(make_req("GET", "/api/v1/users")).await;
        assert_eq!(resp.status(), StatusCode::OK);
        let body = http_body_util::BodyExt::collect(resp.into_body())
            .await
            .unwrap()
            .to_bytes();
        assert_eq!(&body[..], b"/users");
    }

    #[tokio::test]
    async fn test_non_nested_route_uri_unaffected() {
        // A route registered directly (no `.nest()`) must see its Uri untouched.
        async fn echo_uri(uri: hyper::Uri) -> String {
            uri.path().to_string()
        }
        let app = Router::new()
            .route("/users/{id}", get(echo_uri))
            .with_state::<()>(())
            .compile()
            .expect("compile");

        let resp = app.handle_request(make_req("GET", "/users/7")).await;
        let body = http_body_util::BodyExt::collect(resp.into_body())
            .await
            .unwrap()
            .to_bytes();
        assert_eq!(&body[..], b"/users/7");
    }

    // ── MatchedPath ───────────────────────────────────────────────────────────

    #[cfg(feature = "matched-path")]
    #[tokio::test]
    async fn test_matched_path_returns_route_pattern() {
        use crate::routing::extract::MatchedPath;

        async fn handler(path: MatchedPath) -> String {
            path.as_str().to_string()
        }

        let app = Router::new()
            .route("/users/{id}", get(handler))
            .with_state::<()>(())
            .compile()
            .expect("compile");

        let resp = app.handle_request(make_req("GET", "/users/99")).await;
        assert_eq!(resp.status(), StatusCode::OK);
        let body = http_body_util::BodyExt::collect(resp.into_body())
            .await
            .unwrap()
            .to_bytes();
        assert_eq!(&body[..], b"/users/{id}");
    }

    #[cfg(feature = "matched-path")]
    #[tokio::test]
    async fn test_matched_path_missing_returns_500() {
        use crate::routing::extract::{FromRequestParts, MatchedPath};
        // Directly exercising the extractor without going through the router at
        // all (no `MatchedPath` extension present) must reject with 500.
        let mut parts = Request::builder().uri("/").body(()).unwrap().into_parts().0;
        let res = MatchedPath::from_request_parts(&mut parts, &());
        assert!(res.is_err());
    }

    // ── any() / CONNECT ───────────────────────────────────────────────────────

    #[tokio::test]
    async fn test_any_dispatches_every_method() {
        async fn handler() -> &'static str {
            "any"
        }
        let app = Router::new()
            .route("/x", any(handler))
            .with_state::<()>(())
            .compile()
            .expect("compile");

        for method in [
            "GET", "POST", "PUT", "DELETE", "OPTIONS", "HEAD", "PATCH", "TRACE",
        ] {
            let resp = app.handle_request(make_req(method, "/x")).await;
            assert_eq!(resp.status(), StatusCode::OK, "method: {method}");
        }
    }

    #[tokio::test]
    async fn test_connect_route() {
        async fn handler() -> &'static str {
            "connected"
        }
        let app = Router::new()
            .route("/tunnel", connect(handler))
            .with_state::<()>(())
            .compile()
            .expect("compile");

        let resp = app.handle_request(make_req("CONNECT", "/tunnel")).await;
        assert_eq!(resp.status(), StatusCode::OK);
    }

    #[tokio::test]
    async fn test_extra_routing_features() {
        async fn dummy() -> &'static str {
            "ok"
        }

        // 1. method_index with other methods
        assert_eq!(method_index(&Method::OPTIONS), Some(4));
        assert_eq!(method_index(&Method::HEAD), Some(5));
        assert_eq!(method_index(&Method::TRACE), Some(7));
        assert_eq!(method_index(&Method::CONNECT), Some(8));
        assert_eq!(method_index(&Method::PATCH), Some(6));

        // 2. MethodRouter debug and default
        let mr = MethodRouter::<()>::default();
        let dbg = format!("{mr:?}");
        assert!(dbg.contains("MethodRouter"));

        // 3. MethodRouter shortcuts & helpers
        let _mr2 = MethodRouter::<()>::new()
            .options(dummy)
            .head(dummy)
            .trace(dummy)
            .put(dummy)
            .delete(dummy)
            .patch(dummy);

        let _mr3 = put::<_, _, ()>(dummy);
        let _mr4 = delete::<_, _, ()>(dummy);
        let _mr5 = patch::<_, _, ()>(dummy);

        // 4. Router debug, default, and RouterError display/from
        let r = Router::<()>::default();
        let r_dbg = format!("{r:?}");
        assert!(r_dbg.contains("Router"));

        let compiled = r.compile().unwrap();
        let cr_dbg = format!("{compiled:?}");
        assert!(cr_dbg.contains("CompiledRouter"));

        let dup_err = RouterError::DuplicateRoute("foo".to_string());
        assert!(dup_err.to_string().contains("Duplicate route"));

        // Trigger matchit InsertError
        let bad_router = Router::new()
            .route("/user/:id", get(dummy))
            .route("/user/*path", get(dummy))
            .with_state::<()>(())
            .compile();
        assert!(bad_router.is_err());
        let insert_err = bad_router.unwrap_err();
        assert!(insert_err.to_string().contains("Router insert error"));

        // 5. serve_static
        let dir = tempfile::tempdir().unwrap();
        std::fs::write(dir.path().join("index.html"), "hello static").unwrap();
        let app_static = Router::new()
            .serve_static(dir.path())
            .with_state::<()>(())
            .compile()
            .unwrap();
        let resp = app_static.handle_request(make_req("GET", "/")).await;
        assert_eq!(resp.status(), StatusCode::OK);

        // 6. serve_file_dynamic
        let file_path = dir.path().join("dynamic.txt");
        std::fs::write(&file_path, "hello dynamic").unwrap();
        let app_dynamic = Router::new()
            .serve_file_dynamic("/dyn", file_path.to_str().unwrap())
            .with_state::<()>(())
            .compile()
            .unwrap();

        let resp_dyn = app_dynamic.handle_request(make_req("GET", "/dyn")).await;
        assert_eq!(resp_dyn.status(), StatusCode::OK);

        // serve_file_dynamic error path
        let app_dyn_err = Router::new()
            .serve_file_dynamic("/dyn_err", "/nonexistent/file")
            .with_state::<()>(())
            .compile()
            .unwrap();
        let resp_dyn_err = app_dyn_err
            .handle_request(make_req("GET", "/dyn_err"))
            .await;
        assert_eq!(resp_dyn_err.status(), StatusCode::NOT_FOUND);

        // 7. Nest empty nested_path
        let sub = Router::new().route("/", get(dummy));
        let nested_empty = Router::new()
            .nest("", sub)
            .with_state::<()>(())
            .compile()
            .unwrap();
        let resp_nested = nested_empty.handle_request(make_req("GET", "/")).await;
        assert_eq!(resp_nested.status(), StatusCode::OK);

        // 8. Router merge
        let r1 = Router::new().route("/r1", get(dummy));
        let r2 = Router::new().route("/r2", get(dummy));
        let merged = r1.merge(r2).with_state::<()>(()).compile().unwrap();
        assert_eq!(
            merged.handle_request(make_req("GET", "/r1")).await.status(),
            StatusCode::OK
        );
        assert_eq!(
            merged.handle_request(make_req("GET", "/r2")).await.status(),
            StatusCode::OK
        );
    }

    #[tokio::test]
    async fn test_merge_adopts_the_one_fallback_present() {
        async fn h() -> &'static str {
            "h"
        }
        async fn fb() -> &'static str {
            "merged-fallback"
        }

        let r1 = Router::new().route("/r1", get(h));
        let r2 = Router::new().route("/r2", get(h)).fallback(fb);
        let merged = r1.merge(r2).with_state::<()>(()).compile().unwrap();

        let resp = merged.handle_request(make_req("GET", "/missing")).await;
        assert_eq!(resp.status(), StatusCode::OK);
        let body = http_body_util::BodyExt::collect(resp.into_body())
            .await
            .unwrap()
            .to_bytes();
        assert_eq!(&body[..], b"merged-fallback");
    }

    #[test]
    fn test_merge_two_fallbacks_panics() {
        async fn fb1() -> &'static str {
            "fb1"
        }
        async fn fb2() -> &'static str {
            "fb2"
        }

        let result = std::panic::catch_unwind(|| {
            let r1 = Router::<()>::new().fallback(fb1);
            let r2 = Router::<()>::new().fallback(fb2);
            r1.merge(r2)
        });
        assert!(result.is_err());
    }

    // ── MethodRouter::hoop() (single-middleware shorthand) ──────────────────────

    #[tokio::test]
    async fn test_method_router_hoop_installs_middleware() {
        async fn handler() -> &'static str {
            "hi"
        }
        async fn tag_response(req: Request<Body>, next: middleware::Next<()>) -> Response<Body> {
            let mut resp = next.run(req).await;
            let _ = resp.headers_mut().insert(
                hyper::header::HeaderName::from_static("x-mr-hoop"),
                hyper::header::HeaderValue::from_static("yes"),
            );
            resp
        }

        // `.hoop()` on a bare `MethodRouter` — distinct from `Router::hoop`,
        // which never calls through to `MethodRouter::hoop`; it calls
        // `MethodRouter::hoop_at` directly on every registered route instead.
        let mr = get(handler).hoop(tag_response);
        let app = Router::new()
            .route("/x", mr)
            .with_state::<()>(())
            .compile()
            .expect("compile");

        let resp = app.handle_request(make_req("GET", "/x")).await;
        assert_eq!(resp.status(), StatusCode::OK);
        assert_eq!(resp.headers().get("x-mr-hoop").expect("header set"), "yes");
    }

    // ── options()/head()/trace() free functions ──────────────────────────────────

    #[tokio::test]
    async fn test_options_head_trace_free_functions() {
        async fn handle_options() -> &'static str {
            "opts"
        }
        async fn handle_trace() -> &'static str {
            "trace"
        }
        async fn handle_head() -> Response<Body> {
            Response::builder()
                .header("x-handler", "head")
                .body(Body::full(Bytes::from_static(b"head-only")))
                .unwrap_or_else(|_| Response::new(Body::empty()))
        }
        async fn handle_get_for_head() -> Response<Body> {
            Response::builder()
                .header("x-handler", "get")
                .body(Body::full(Bytes::from_static(b"get-for-head")))
                .unwrap_or_else(|_| Response::new(Body::empty()))
        }
        async fn handle_get_only() -> &'static str {
            "get-only"
        }

        let app = Router::new()
            .route("/opts", options(handle_options))
            .route("/tracer", trace(handle_trace))
            // An explicit HEAD handler must take priority over the implicit
            // GET fallback (see `CompiledRouter::handle_request`'s
            // `falls_back_to_get` logic).
            .route("/headroute", head(handle_head).get(handle_get_for_head))
            // No explicit HEAD handler here, so HEAD must still fall back to GET.
            .route("/getonly", get(handle_get_only))
            .with_state::<()>(())
            .compile()
            .expect("compile");

        let resp = app.handle_request(make_req("OPTIONS", "/opts")).await;
        assert_eq!(resp.status(), StatusCode::OK);
        let body = http_body_util::BodyExt::collect(resp.into_body())
            .await
            .unwrap()
            .to_bytes();
        assert_eq!(&body[..], b"opts");

        let resp = app.handle_request(make_req("TRACE", "/tracer")).await;
        assert_eq!(resp.status(), StatusCode::OK);
        let body = http_body_util::BodyExt::collect(resp.into_body())
            .await
            .unwrap()
            .to_bytes();
        assert_eq!(&body[..], b"trace");

        // The explicit HEAD handler must be the one that actually runs.
        let resp = app.handle_request(make_req("HEAD", "/headroute")).await;
        assert_eq!(resp.status(), StatusCode::OK);
        assert_eq!(
            resp.headers()
                .get("x-handler")
                .map(hyper::header::HeaderValue::as_bytes),
            Some(&b"head"[..])
        );
        let body = http_body_util::BodyExt::collect(resp.into_body())
            .await
            .unwrap()
            .to_bytes();
        assert!(body.is_empty(), "HEAD responses must have an empty body");

        // GET on the same route still goes to the GET handler.
        let get_resp = app.handle_request(make_req("GET", "/headroute")).await;
        assert_eq!(
            get_resp
                .headers()
                .get("x-handler")
                .map(hyper::header::HeaderValue::as_bytes),
            Some(&b"get"[..])
        );
        let get_body = http_body_util::BodyExt::collect(get_resp.into_body())
            .await
            .unwrap()
            .to_bytes();
        assert_eq!(&get_body[..], b"get-for-head");

        // No HEAD handler registered: HEAD must fall back to the GET handler.
        let resp = app.handle_request(make_req("HEAD", "/getonly")).await;
        assert_eq!(resp.status(), StatusCode::OK);
        let body = http_body_util::BodyExt::collect(resp.into_body())
            .await
            .unwrap()
            .to_bytes();
        assert!(body.is_empty(), "HEAD responses must have an empty body");
    }

    // ── into_make_service() (Axum API-parity no-op) ──────────────────────────────

    #[tokio::test]
    async fn test_into_make_service_returns_usable_router() {
        async fn handler() -> &'static str {
            "ims"
        }

        let app = Router::new()
            .route("/x", get(handler))
            .into_make_service()
            .with_state::<()>(())
            .compile()
            .expect("compile");

        let resp = app.handle_request(make_req("GET", "/x")).await;
        assert_eq!(resp.status(), StatusCode::OK);
    }

    // ── method_not_allowed_fallback ──────────────────────────────────────────────

    #[tokio::test]
    async fn test_method_not_allowed_fallback_overrides_default_405() {
        async fn get_handler() -> &'static str {
            "got"
        }
        async fn custom_405() -> (StatusCode, &'static str) {
            (StatusCode::IM_A_TEAPOT, "custom-405")
        }

        let app = Router::new()
            .route("/x", get(get_handler))
            .method_not_allowed_fallback(custom_405)
            .with_state::<()>(())
            .compile()
            .expect("compile");

        // /x exists but has no POST handler — the custom fallback answers
        // instead of the default bare 405.
        let resp = app.handle_request(make_req("POST", "/x")).await;
        assert_eq!(resp.status(), StatusCode::IM_A_TEAPOT);
        let body = http_body_util::BodyExt::collect(resp.into_body())
            .await
            .unwrap()
            .to_bytes();
        assert_eq!(&body[..], b"custom-405");
    }

    // ── hoop()/hoop_at() wrapping the fallback & method_not_allowed_fallback ────

    #[tokio::test]
    async fn test_hoop_wraps_fallback_and_method_not_allowed_fallback() {
        async fn get_handler() -> &'static str {
            "got"
        }
        async fn custom_fallback() -> &'static str {
            "custom-fallback"
        }
        async fn custom_405() -> &'static str {
            "custom-405"
        }
        async fn tag_response(req: Request<Body>, next: middleware::Next<()>) -> Response<Body> {
            let mut resp = next.run(req).await;
            let _ = resp.headers_mut().insert(
                hyper::header::HeaderName::from_static("x-hoop"),
                hyper::header::HeaderValue::from_static("wrapped"),
            );
            resp
        }

        // `.fallback()`/`.method_not_allowed_fallback()` must be set *before*
        // `.hoop()`, since `Router::hoop_at` only wraps whichever of the two
        // is already installed at the time it runs.
        let app = Router::new()
            .route("/x", get(get_handler))
            .fallback(custom_fallback)
            .method_not_allowed_fallback(custom_405)
            .hoop(tag_response)
            .with_state::<()>(())
            .compile()
            .expect("compile");

        // Middleware still runs around a normally-matched route.
        let resp = app.handle_request(make_req("GET", "/x")).await;
        assert_eq!(resp.status(), StatusCode::OK);
        assert_eq!(
            resp.headers().get("x-hoop").expect("wraps route"),
            "wrapped"
        );

        // Middleware still runs around the custom fallback (unmatched path).
        let resp = app.handle_request(make_req("GET", "/missing")).await;
        assert_eq!(resp.status(), StatusCode::OK);
        assert_eq!(
            resp.headers().get("x-hoop").expect("wraps fallback"),
            "wrapped"
        );
        let body = http_body_util::BodyExt::collect(resp.into_body())
            .await
            .unwrap()
            .to_bytes();
        assert_eq!(&body[..], b"custom-fallback");

        // Middleware still runs around the method-not-allowed fallback too.
        let resp = app.handle_request(make_req("POST", "/x")).await;
        assert_eq!(resp.status(), StatusCode::OK);
        assert_eq!(
            resp.headers().get("x-hoop").expect("wraps 405 fallback"),
            "wrapped"
        );
        let body = http_body_util::BodyExt::collect(resp.into_body())
            .await
            .unwrap()
            .to_bytes();
        assert_eq!(&body[..], b"custom-405");
    }

    // ── RouterError::DuplicateRoute ───────────────────────────────────────────────

    #[test]
    fn test_compile_returns_duplicate_route_err() {
        async fn handler() -> &'static str {
            "dup"
        }

        // `Router::route`/`.nest()`/`.merge()` all merge same-path entries via
        // `push_or_merge_route`, so two *identical* path strings can never
        // reach `compile()`'s `routes` `Vec` through the public builder API —
        // see the doc comment on `RouterError::DuplicateRoute`. Constructing
        // the `Router` directly is the only way to exercise this internal
        // invariant check; this test lives inside the `routing` module tree,
        // so it can see the otherwise-private `routes` field to do that.
        let router = Router::<()> {
            routes: vec![
                ("/dup".to_string(), get(handler)),
                ("/dup".to_string(), get(handler)),
            ],
            fallback: None,
            method_not_allowed_fallback: None,
            state: None,
            normalize_trailing_slash: false,
            #[cfg(feature = "tower")]
            compiled: None,
        };

        let result = router.compile();
        assert!(matches!(result, Err(RouterError::DuplicateRoute(ref p)) if p == "/dup"));
    }

    // ── nest() query-string preservation ──────────────────────────────────────────

    #[tokio::test]
    async fn test_nest_strips_prefix_preserves_query_string() {
        async fn echo_full(uri: hyper::Uri) -> String {
            uri.query()
                .map_or_else(|| uri.path().to_string(), |q| format!("{}?{q}", uri.path()))
        }

        let api = Router::new().route("/users/{id}", get(echo_full));
        let app = Router::new()
            .nest("/api", api)
            .with_state::<()>(())
            .compile()
            .expect("compile");

        let resp = app
            .handle_request(make_req("GET", "/api/users/42?active=true"))
            .await;
        assert_eq!(resp.status(), StatusCode::OK);
        let body = http_body_util::BodyExt::collect(resp.into_body())
            .await
            .unwrap()
            .to_bytes();
        assert_eq!(&body[..], b"/users/42?active=true");
    }

    // ── normalize_trailing_slash ────────────────────────────────────────────────

    #[tokio::test]
    async fn test_normalize_trailing_slash_preserves_query_string() {
        async fn echo_full(uri: hyper::Uri) -> String {
            uri.query()
                .map_or_else(|| uri.path().to_string(), |q| format!("{}?{q}", uri.path()))
        }

        let app = Router::new()
            .route("/about", get(echo_full))
            .normalize_trailing_slash()
            .with_state::<()>(())
            .compile()
            .expect("compile");

        let resp = app.handle_request(make_req("GET", "/about/?x=1")).await;
        assert_eq!(resp.status(), StatusCode::OK);
        let body = http_body_util::BodyExt::collect(resp.into_body())
            .await
            .unwrap()
            .to_bytes();
        assert_eq!(&body[..], b"/about?x=1");
    }

    #[tokio::test]
    async fn test_normalize_trailing_slash_no_trailing_slash_is_untouched() {
        async fn handler() -> &'static str {
            "no-trailing"
        }

        let app = Router::new()
            .route("/about", get(handler))
            .normalize_trailing_slash()
            .with_state::<()>(())
            .compile()
            .expect("compile");

        // Already has no trailing slash → `strip_trailing_slash`'s
        // early-return branch.
        let resp = app.handle_request(make_req("GET", "/about")).await;
        assert_eq!(resp.status(), StatusCode::OK);

        // Root `/` is length 1 → also hits the early-return branch, so it's
        // never stripped down to an empty (invalid) path.
        let root_app = Router::new()
            .route("/", get(handler))
            .normalize_trailing_slash()
            .with_state::<()>(())
            .compile()
            .expect("compile");
        let resp = root_app.handle_request(make_req("GET", "/")).await;
        assert_eq!(resp.status(), StatusCode::OK);
    }
}