//! The router — itself a plug.
//!
//! v1: linear scan over a Vec of compiled route patterns. The spec calls for
//! a radix trie eventually; for "good enough to build a CRUD app" with
//! typical route counts (<50), the linear scan is dominant noise next to
//! everything else on the request path. Replace with a trie when there's
//! evidence it matters.
//!
//! Pattern syntax:
//!   - `/users`              — literal
//!   - `/users/:id`          — `id` param
//!   - `/users/:id/posts/:n` — multiple params
//!
//! No wildcards in v1. They are not needed for CRUD.

use crate::conn::{Conn, Method, Params};
use crate::plug::{Next, Plug};
use std::sync::Arc;

// ---------------------------------------------------------------------------
// Pattern
// ---------------------------------------------------------------------------

/// A compiled URL pattern: a list of segments, each either a literal or a
/// named parameter. Segment compilation happens at `Router::get(...)` time;
/// matching at request time is a single-pass loop.
#[derive(Debug, Clone)]
struct Pattern {
    segments: Vec<Segment>,
}

#[derive(Debug, Clone)]
enum Segment {
    Literal(String),
    Param(String),
}

impl Pattern {
    fn compile(path: &str) -> Self {
        // Treat empty path the same as "/" — single empty segment.
        let trimmed = path.trim_start_matches('/');
        if trimmed.is_empty() {
            return Pattern { segments: Vec::new() };
        }
        let segments = trimmed
            .split('/')
            .map(|s| {
                if let Some(name) = s.strip_prefix(':') {
                    Segment::Param(name.to_string())
                } else {
                    Segment::Literal(s.to_string())
                }
            })
            .collect();
        Pattern { segments }
    }

    /// Match `path` against this pattern. Returns extracted params on
    /// success, `None` on miss. Strict path equality — trailing slashes
    /// matter; that's standard HTTP behaviour and we don't paper over it.
    fn match_path(&self, path: &str) -> Option<Params> {
        let trimmed = path.trim_start_matches('/');
        if trimmed.is_empty() {
            return if self.segments.is_empty() { Some(Params::new()) } else { None };
        }
        let parts: Vec<&str> = trimmed.split('/').collect();
        if parts.len() != self.segments.len() {
            return None;
        }
        let mut params = Params::new();
        for (seg, part) in self.segments.iter().zip(parts.iter()) {
            match seg {
                Segment::Literal(lit) => {
                    if lit != part {
                        return None;
                    }
                }
                Segment::Param(name) => {
                    params.put(name.clone(), (*part).to_string());
                }
            }
        }
        Some(params)
    }
}

// ---------------------------------------------------------------------------
// Route
// ---------------------------------------------------------------------------

struct Route {
    method:  Method,
    pattern: Pattern,
    handler: Arc<dyn Plug>,
}

// ---------------------------------------------------------------------------
// Router
// ---------------------------------------------------------------------------

pub struct Router {
    routes: Vec<Route>,
}

impl Router {
    pub fn new() -> Self {
        Self { routes: Vec::new() }
    }

    fn add(mut self, method: Method, path: &str, plug: impl Plug) -> Self {
        self.routes.push(Route {
            method,
            pattern: Pattern::compile(path),
            handler: Arc::new(plug),
        });
        self
    }

    pub fn get(self,     path: &str, plug: impl Plug) -> Self { self.add(Method::Get,    path, plug) }
    pub fn post(self,    path: &str, plug: impl Plug) -> Self { self.add(Method::Post,   path, plug) }
    pub fn put(self,     path: &str, plug: impl Plug) -> Self { self.add(Method::Put,    path, plug) }
    pub fn delete(self,  path: &str, plug: impl Plug) -> Self { self.add(Method::Delete, path, plug) }
    pub fn patch(self,   path: &str, plug: impl Plug) -> Self { self.add(Method::Patch,  path, plug) }
    pub fn head(self,    path: &str, plug: impl Plug) -> Self { self.add(Method::Head,   path, plug) }
    pub fn options(self, path: &str, plug: impl Plug) -> Self { self.add(Method::Options, path, plug) }
}

impl Default for Router {
    fn default() -> Self { Self::new() }
}

impl Plug for Router {
    fn call(&self, conn: Conn, next: Next) -> Conn {
        // Two-pass dispatch: first match on method+path; if no method-and-
        // path matches but a same-path-different-method does, return 405.
        // Otherwise pass through to `next` so outer pipelines can layer a
        // 404 handler (or skip and let the connection actor emit a default).
        //
        // Matching runs under the `router` causal site (RFC 007); the
        // winning handler and the `next` fall-through run outside it, so
        // the site measures dispatch, not what it dispatches to.
        let mut path_seen = false;
        let mut hit = None;
        {
            #[cfg(feature = "smarm-causal")]
            let _g = smarm::causal_site!("router");
            for (i, route) in self.routes.iter().enumerate() {
                if let Some(params) = route.pattern.match_path(&conn.path) {
                    if route.method == conn.method {
                        hit = Some((i, params));
                        break;
                    }
                    path_seen = true;
                }
            }
        }
        if let Some((i, params)) = hit {
            let conn = conn.put_params(params);
            return self.routes[i].handler.call(conn, next);
        }
        if path_seen {
            // Path is known, method isn't — RFC 7231 §6.5.5.
            conn.put_status(405)
                .put_header("content-length", "0")
                .halt()
        } else {
            // No route matched at all; let outer plugs / default handler
            // deal with it.
            next.run(conn)
        }
    }
}

// ---------------------------------------------------------------------------
// Tests
// ---------------------------------------------------------------------------

#[cfg(test)]
mod tests {
    use super::*;
    use crate::plug::Pipeline;

    fn ok_handler(_label: &'static str) -> impl Plug {
        move |conn: Conn, _next: Next| conn.put_status(200).put_body(_label)
    }

    #[test]
    fn literal_match() {
        let r = Router::new().get("/ping", ok_handler("pong"));
        let mut c = Conn::new();
        c.method = Method::Get;
        c.path   = "/ping".into();
        let out = Pipeline::new().plug(r).run(c);
        assert_eq!(out.status, Some(200));
    }

    #[test]
    fn param_match() {
        let r = Router::new().get("/users/:id", |conn: Conn, _n: Next| {
            let id = conn.params.get("id").unwrap_or("").to_string();
            conn.put_status(200).put_body(id)
        });
        let mut c = Conn::new();
        c.method = Method::Get;
        c.path   = "/users/42".into();
        let out = Pipeline::new().plug(r).run(c);
        assert_eq!(out.status, Some(200));
        match &out.resp_body {
            crate::conn::RespBody::Bytes(b) => assert_eq!(b, b"42"),
            _ => panic!("expected bytes"),
        }
    }

    #[test]
    fn method_mismatch_yields_405() {
        let r = Router::new().get("/users", ok_handler("list"));
        let mut c = Conn::new();
        c.method = Method::Post;
        c.path   = "/users".into();
        let out = Pipeline::new().plug(r).run(c);
        assert_eq!(out.status, Some(405));
    }

    #[test]
    fn no_route_falls_through() {
        // Router returns conn unchanged; next plug (a 404 default) handles it.
        let r = Router::new().get("/users", ok_handler("list"));
        let default_404 = |conn: Conn, _n: Next|
            conn.put_status(404).put_body("not found");
        let mut c = Conn::new();
        c.method = Method::Get;
        c.path   = "/nowhere".into();
        let out = Pipeline::new().plug(r).plug(default_404).run(c);
        assert_eq!(out.status, Some(404));
    }
}