use crate::factor::VarStore;

/// Reusable scratch buffers for `Game::likelihoods`.
///
/// A `Batch` owns one arena; all events in the slice share it across
/// the convergence iterations.
#[derive(Debug, Default)]
pub struct ScratchArena {
    pub(crate) vars: VarStore,
    pub(crate) sort_buf: Vec<usize>,
}

impl ScratchArena {
    pub fn new() -> Self {
        Self::default()
    }

    #[inline]
    pub(crate) fn reset(&mut self) {
        self.vars.clear();
        self.sort_buf.clear();
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::{N_INF, gaussian::Gaussian};

    #[test]
    fn reset_keeps_capacity() {
        let mut arena = ScratchArena::new();
        arena.vars.alloc(N_INF);
        arena.sort_buf.push(42);
        let var_cap = arena.vars.marginals.capacity();
        let sort_cap = arena.sort_buf.capacity();
        arena.reset();
        assert_eq!(arena.vars.len(), 0);
        assert_eq!(arena.sort_buf.len(), 0);
        assert_eq!(arena.vars.marginals.capacity(), var_cap);
        assert_eq!(arena.sort_buf.capacity(), sort_cap);
    }
}