clay-borg/tools/cb-play/src/hotseat.rs

//! Hot-seat play in a browser (ADR-0007, INTENT stage 1).
//!
//! One loopback listener, one tab, seats taking turns. The server blocks
//! inside [`Policy::choose`] until the page reports a pointer fact that
//! resolves to a legal command — so the game loop is the same
//! `games_ground::bot::play` loop the CLI and the bots run through, and a
//! browser seat is indistinguishable from a CLI seat to the driver.
//!
//! Every control in ADR-0007 §Decision 5 lives in `cb-render-html`; this
//! module is the socket and the turn-taking. It deliberately holds no
//! game logic beyond "which seat is being asked" — [`cb_render_html`]
//! decides what a drag means, and the aggregate decides whether the
//! result is legal.

use std::cell::RefCell;
use std::io::{Read, Write};
use std::net::{TcpListener, TcpStream};
use std::rc::Rc;

use cb_game_runtime::{Project, Viewer};
use cb_kernel::PlayerId;
use cb_render_html::{document, resolve, Guard, PointerFact, Request};
use games_ground::bot::{Choice, Policy};
use games_ground::{GroundCommand, GroundState};

/// The shared listener. One per process; every human seat borrows it.
pub struct Server {
    listener: TcpListener,
    guard: Guard,
    log: RefCell<Vec<String>>,
}

impl Server {
    pub fn bind(port: u16) -> Result<Self, String> {
        let listener = cb_render_html::serve::bind(port).map_err(|e| format!("bind: {e}"))?;
        let port = listener
            .local_addr()
            .map_err(|e| format!("local_addr: {e}"))?
            .port();
        Ok(Self {
            listener,
            guard: Guard::mint(port),
            log: RefCell::new(Vec::new()),
        })
    }

    /// The URL to open, token and all. Printed once at start; the page
    /// cannot mint one for itself.
    pub fn url(&self) -> String {
        self.guard.page_url()
    }

    /// What was refused, for the evidence a session leaves behind.
    pub fn refusals(&self) -> Vec<String> {
        self.log.borrow().clone()
    }

    /// Serve until the page reports something that resolves to a move.
    ///
    /// Requests that fail a control are answered and the loop continues —
    /// a refused request must not end someone's game, and must not be
    /// silently indistinguishable from one that did nothing.
    pub fn next_choice(
        &self,
        state: &GroundState,
        seat: PlayerId,
        legal: &[GroundCommand],
        may_pass: bool,
    ) -> Result<Choice, String> {
        let view = state.project(Viewer::Player(seat));
        loop {
            let (mut stream, _) = self.listener.accept().map_err(|e| format!("accept: {e}"))?;
            let raw = match read_request(&mut stream) {
                Ok(r) => r,
                Err(e) => {
                    respond(&mut stream, 400, "text/plain", &e);
                    continue;
                }
            };
            let req = match Request::parse(&raw) {
                Ok(r) => r,
                Err(refusal) => {
                    self.log.borrow_mut().push(refusal.to_string());
                    respond(&mut stream, 400, "text/plain", &refusal.to_string());
                    continue;
                }
            };
            if let Err(refusal) = self.guard.admit(&req) {
                self.log.borrow_mut().push(refusal.to_string());
                respond(&mut stream, 403, "text/plain", &refusal.to_string());
                continue;
            }

            match (req.method.as_str(), req.path.as_str()) {
                ("GET", "/") => {
                    let page = document(&view, legal, &self.guard.endpoint(), Some(seat), may_pass);
                    respond(&mut stream, 200, "text/html; charset=utf-8", &page);
                }
                ("POST", "/command") => {
                    let fact = match PointerFact::parse(&req.body) {
                        Ok(f) => f,
                        Err(e) => {
                            respond(&mut stream, 400, "text/plain", &e);
                            continue;
                        }
                    };
                    if may_pass && fact.down == "pass" && fact.up == "pass" {
                        respond(&mut stream, 200, "text/plain", "ok: passed");
                        return Ok(Choice::Pass);
                    }
                    match resolve(&fact, legal, seat) {
                        Ok(i) => {
                            respond(&mut stream, 200, "text/plain", "ok");
                            return Ok(Choice::Command(i));
                        }
                        // Not an error: the player dragged somewhere that
                        // means nothing. Say so and keep the turn.
                        Err(why) => respond(&mut stream, 200, "text/plain", &why),
                    }
                }
                _ => respond(&mut stream, 404, "text/plain", "no such thing here"),
            }
        }
    }
}

/// One seat's view of the shared server.
pub struct SeatPolicy {
    server: Rc<Server>,
    failure: Rc<RefCell<Option<String>>>,
}

impl SeatPolicy {
    pub fn new(server: Rc<Server>, failure: Rc<RefCell<Option<String>>>) -> Self {
        Self { server, failure }
    }
}

impl Policy for SeatPolicy {
    fn name(&self) -> &'static str {
        "browser"
    }

    fn choose(
        &mut self,
        state: &GroundState,
        seat: PlayerId,
        legal: &[GroundCommand],
        may_pass: bool,
    ) -> Choice {
        match self.server.next_choice(state, seat, legal, may_pass) {
            Ok(c) => c,
            Err(e) => {
                // Same shape as the CLI's out-of-input path: record the
                // real reason and return something the driver will
                // reject, rather than inventing a move.
                *self.failure.borrow_mut() = Some(e);
                Choice::Command(usize::MAX)
            }
        }
    }
}

fn read_request(stream: &mut TcpStream) -> Result<String, String> {
    let mut buf = Vec::new();
    let mut chunk = [0u8; 1024];
    loop {
        let n = stream.read(&mut chunk).map_err(|e| format!("read: {e}"))?;
        if n == 0 {
            break;
        }
        buf.extend_from_slice(&chunk[..n]);
        // Once the head is in, read exactly the declared body and stop —
        // otherwise a keep-alive connection blocks here forever.
        if let Some(head_end) = find(&buf, b"\r\n\r\n") {
            let head = String::from_utf8_lossy(&buf[..head_end]).to_string();
            let want: usize = head
                .split("\r\n")
                .find_map(|l| {
                    let (k, v) = l.split_once(':')?;
                    k.eq_ignore_ascii_case("content-length")
                        .then(|| v.trim().parse().ok())?
                })
                .unwrap_or(0);
            if buf.len() >= head_end + 4 + want {
                break;
            }
        }
        if buf.len() > 64 * 1024 {
            return Err("request too large".to_string());
        }
    }
    String::from_utf8(buf).map_err(|_| "request is not UTF-8".to_string())
}

fn find(haystack: &[u8], needle: &[u8]) -> Option<usize> {
    haystack.windows(needle.len()).position(|w| w == needle)
}

fn respond(stream: &mut TcpStream, status: u16, content_type: &str, body: &str) {
    let reason = match status {
        200 => "OK",
        400 => "Bad Request",
        403 => "Forbidden",
        _ => "Not Found",
    };
    let head = format!(
        "HTTP/1.1 {status} {reason}\r\nContent-Type: {content_type}\r\n\
         Content-Length: {}\r\nConnection: close\r\n\
         X-Content-Type-Options: nosniff\r\n\r\n",
        body.len()
    );
    let _ = stream.write_all(head.as_bytes());
    let _ = stream.write_all(body.as_bytes());
    let _ = stream.flush();
}

#[cfg(test)]
mod tests {
    use super::*;
    use games_ground::Action;

    /// One client thread issuing requests **in order**, each on its own
    /// `Connection: close` socket and each fully read before the next is
    /// sent. Two concurrent clients would race the server's `accept`, and
    /// a test whose outcome depends on which socket wins is worse than no
    /// test.
    fn converse(port: u16, requests: Vec<String>) -> std::thread::JoinHandle<Vec<String>> {
        std::thread::spawn(move || {
            requests
                .into_iter()
                .map(|raw| {
                    let mut s = TcpStream::connect(("127.0.0.1", port)).expect("connect");
                    s.write_all(raw.as_bytes()).expect("write");
                    let mut out = String::new();
                    let _ = s.read_to_string(&mut out);
                    out
                })
                .collect()
        })
    }

    fn get(token: &str) -> String {
        format!(
            "GET /?t={token} HTTP/1.1\r\nHost: 127.0.0.1\r\n\
             Sec-Fetch-Site: same-origin\r\n\r\n"
        )
    }

    fn post(token: &str, body: &str) -> String {
        format!(
            "POST /command?t={token} HTTP/1.1\r\nHost: 127.0.0.1\r\n\
             Sec-Fetch-Site: same-origin\r\nContent-Length: {}\r\n\r\n{body}",
            body.len()
        )
    }

    fn ground_only() -> Vec<GroundCommand> {
        vec![GroundCommand::SelectAction {
            action: Action::Ground,
            target: None,
            problem: None,
        }]
    }

    fn state() -> GroundState {
        <GroundState as cb_game_runtime::ScenarioGame>::setup(
            &cb_game_runtime::Setup {
                players: 3,
                preset: "standard-3p".to_string(),
                patch: Default::default(),
            },
            7,
        )
        .expect("setup")
    }

    /// The whole loop, with a real socket and no browser: the page is
    /// served, a pointer fact is posted, and the seat's choice comes back.
    #[test]
    fn a_drag_posted_over_the_socket_becomes_a_choice() {
        let server = Server::bind(0).expect("bind");
        let port = server.listener.local_addr().unwrap().port();
        let token = server.url().rsplit("t=").next().unwrap().to_string();
        let client = converse(
            port,
            vec![get(&token), post(&token, "down=action-ground&up=table")],
        );

        let choice = server
            .next_choice(&state(), PlayerId(0), &ground_only(), false)
            .expect("a choice");
        assert_eq!(choice, Choice::Command(0));

        let replies = client.join().expect("client thread");
        assert!(replies[0].contains("200 OK"), "{}", replies[0]);
        assert!(replies[0].contains("GROUND"), "the page was not the table");
        assert!(
            replies[0].contains("id=\"action-ground\""),
            "the offered action was not on the page"
        );
        assert!(replies[1].contains("200 OK"));
        assert!(server.refusals().is_empty());
    }

    /// ADR-0007 control 1, end to end rather than in the unit: a page
    /// without the token gets nothing, and the seat keeps its turn.
    ///
    /// M-D1-MUT: make `admit` return `Ok(())` unconditionally and this
    /// goes red — the token-less request is served the table. Run
    /// 2026-08-02.
    #[test]
    fn a_token_less_request_over_the_socket_is_refused_and_the_turn_continues() {
        let server = Server::bind(0).expect("bind");
        let port = server.listener.local_addr().unwrap().port();
        let token = server.url().rsplit("t=").next().unwrap().to_string();
        let client = converse(
            port,
            vec![
                "GET / HTTP/1.1\r\nHost: 127.0.0.1\r\nSec-Fetch-Site: same-origin\r\n\r\n"
                    .to_string(),
                post(&token, "down=action-ground&up=table"),
            ],
        );

        // The turn survives the refusal and is decided by the good request.
        let choice = server
            .next_choice(&state(), PlayerId(0), &ground_only(), false)
            .expect("a choice");
        assert_eq!(choice, Choice::Command(0));

        let replies = client.join().expect("client thread");
        assert!(replies[0].contains("403 Forbidden"), "{}", replies[0]);
        assert!(
            !replies[0].contains("GROUND"),
            "the table leaked to a token-less request"
        );
        assert!(replies[1].contains("200 OK"));
        assert_eq!(
            server.refusals(),
            vec!["refused: no session token".to_string()]
        );
    }

    /// A drag that means nothing must not end the turn, and must say so.
    #[test]
    fn a_meaningless_drag_keeps_the_turn() {
        let server = Server::bind(0).expect("bind");
        let port = server.listener.local_addr().unwrap().port();
        let token = server.url().rsplit("t=").next().unwrap().to_string();
        let client = converse(
            port,
            vec![
                post(&token, "down=seat-1&up=seat-2"),
                post(&token, "down=action-ground&up=table"),
            ],
        );

        let choice = server
            .next_choice(&state(), PlayerId(0), &ground_only(), false)
            .expect("a choice");
        assert_eq!(choice, Choice::Command(0));

        let replies = client.join().expect("client thread");
        assert!(replies[0].contains("200 OK"));
        assert!(
            replies[0].contains("not a legal move"),
            "a meaningless drag must be told it meant nothing: {}",
            replies[0]
        );
        assert!(replies[1].contains("200 OK"));
    }
}