ncpig 0.6.1

Non-Cooperative Perfect Information Games, and algorithms to play them.
Documentation 
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//! A search strategy which chooses the next [`Action`] at random.

use std::cell::RefCell;

use rand::rngs::ThreadRng;
use rand::seq::IteratorRandom;

use super::SearchError;
#[cfg(doc)]
use crate::game::Action;
use crate::game::{Game, GameError};
use crate::search::SearchChoose;

/// Errors related to the [`Random`] [`SearchChoose`].
#[derive(Debug, thiserror::Error)]
pub enum RandomError<const N: usize, G: Game<N>> {
    /// Error if the random number generator cannot be borrowed mutably.
    #[error(transparent)]
    RngBorrowError(#[from] std::cell::BorrowMutError),

    /// An error occured within the game.
    #[error(transparent)]
    GameError(G::Error),
}

impl<const N: usize, G: Game<N>> SearchError for RandomError<N, G> {}

impl<const N: usize, G: Game<N, Error = E>, E: GameError> From<E> for RandomError<N, G> {
    fn from(value: G::Error) -> Self {
        Self::GameError(value)
    }
}

/// A "search" strategy which chooses randomly from the [`Game::available_actions`].
#[derive(Debug, Clone, Default)]
pub struct Random {
    rng: RefCell<ThreadRng>,
}

impl Random {
    /// Initialize a random searcher.
    pub fn new() -> Self {
        Random {
            rng: RefCell::new(ThreadRng::default()),
        }
    }
}

impl<const N: usize, G: Game<N>> SearchChoose<N, G> for Random
where
    G::Action: Clone,
{
    type Error = RandomError<N, G>;

    fn choose_action(
        &self,
        game: &G,
        state: &<G as Game<N>>::State,
    ) -> Result<Option<<G as Game<N>>::Action>, RandomError<N, G>> {
        let actions = game.available_actions(state)?;
        let mut rng = self.rng.try_borrow_mut()?;
        Ok(actions.iter().choose(&mut *rng).cloned())
    }
}