clay-borg/crates/cb-game-runtime/src/lib.rs

//! cb-game-runtime — round/phase machinery, commit windows, projections,
//! and the scenario runner (GameKernel §2.5, §3). Game-agnostic.

#[cfg(feature = "scenarios")]
pub mod scenario;

/// K10 replay bundles. Dev-only: a shipped game runtime writes no bundles.
#[cfg(feature = "scenarios")]
pub mod replay;

#[cfg(feature = "scenarios")]
pub use scenario::{parse_actor, run, CommandStep, RunOutcome, ScenarioFile, ScenarioGame, Setup};

use cb_kernel::PlayerId;
use serde::{Deserialize, Serialize};
use std::collections::BTreeMap;

/// A simultaneous commit window (GameKernel K12): the runtime opens it
/// naming who must submit; submissions are commitment events hidden from
/// projections until reveal.
///
/// **PROVISIONAL — zero non-test users as of 2026-08-01 (K14, GameKernel
/// §2.5a).** GROUND implements the same contract inline in its own
/// aggregate. This type is the *extracted* form, kept because it
/// documents the seam stage 3 and stage 4 will need — but INTENT says a
/// concept becomes canonical only *"after surviving a second concrete
/// use"*, and this has survived none.
///
/// **Delete it if no second game uses it by 2026-12-31.** A primitive
/// with one hypothetical user and a test that exercises only itself is
/// the AM-11 shape, and this project has paid for that shape twice.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct CommitWindow<C> {
    /// Players who must submit, and their commitment once received.
    pending: BTreeMap<PlayerId, Option<C>>,
}

impl<C> CommitWindow<C> {
    pub fn open(players: impl IntoIterator<Item = PlayerId>) -> Self {
        Self {
            pending: players.into_iter().map(|p| (p, None)).collect(),
        }
    }

    /// Record a commitment. Errors on players outside the window or on a
    /// duplicate submission (GameKernel K12).
    pub fn submit(&mut self, player: PlayerId, commitment: C) -> Result<(), CommitError> {
        match self.pending.get_mut(&player) {
            None => Err(CommitError::NotInWindow(player)),
            Some(slot @ None) => {
                *slot = Some(commitment);
                Ok(())
            }
            Some(Some(_)) => Err(CommitError::AlreadyCommitted(player)),
        }
    }

    pub fn is_complete(&self) -> bool {
        self.pending.values().all(Option::is_some)
    }

    /// Consume the window at reveal, yielding commitments in PlayerId
    /// order (deterministic iteration, GameKernel K6).
    pub fn reveal(self) -> Result<Vec<(PlayerId, C)>, CommitError> {
        if !self.is_complete() {
            return Err(CommitError::Incomplete);
        }
        Ok(self
            .pending
            .into_iter()
            .map(|(p, c)| (p, c.expect("checked complete")))
            .collect())
    }
}

#[derive(Debug, PartialEq, Eq)]
pub enum CommitError {
    NotInWindow(PlayerId),
    AlreadyCommitted(PlayerId),
    Incomplete,
}

impl core::fmt::Display for CommitError {
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        match self {
            CommitError::NotInWindow(p) => write!(f, "player {p} is not in this window"),
            CommitError::AlreadyCommitted(p) => write!(f, "player {p} already committed"),
            CommitError::Incomplete => write!(f, "window is not complete"),
        }
    }
}

/// Per-player projection (GameKernel K13): a total function from state to
/// what one seat may see. Implemented by game packages; the runtime only
/// fixes the shape so projections can never feed back into validation.
pub trait Project {
    type View: Serialize;
    fn project(&self, viewer: Viewer) -> Self::View;
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum Viewer {
    Player(PlayerId),
    Spectator,
}

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

    #[test]
    fn commit_window_gates_and_reveals_in_order() {
        let mut w: CommitWindow<u8> = CommitWindow::open([PlayerId(0), PlayerId(1)]);
        assert_eq!(
            w.submit(PlayerId(2), 9),
            Err(CommitError::NotInWindow(PlayerId(2)))
        );
        w.submit(PlayerId(1), 7).unwrap();
        assert_eq!(
            w.submit(PlayerId(1), 8),
            Err(CommitError::AlreadyCommitted(PlayerId(1)))
        );
        assert!(!w.is_complete());
        w.submit(PlayerId(0), 5).unwrap();
        assert!(w.is_complete());
        assert_eq!(
            w.reveal().unwrap(),
            vec![(PlayerId(0), 5), (PlayerId(1), 7)]
        );
    }
}