// Simulation RNG system
// Injectable ChaCha RNG resource for deterministic replay (D-030)
// Ensures same seed produces same outcomes

use bevy_ecs::prelude::*;
use rand::SeedableRng;
use rand_chacha::ChaCha20Rng;

/// Simulation RNG resource
/// ChaCha20 RNG with stored seed for deterministic replay
#[derive(Resource)]
pub struct SimRng {
    pub rng: ChaCha20Rng,
    seed: u64,
}

impl SimRng {
    /// Create a new SimRng with the given seed
    pub fn new(seed: u64) -> Self {
        Self {
            rng: ChaCha20Rng::seed_from_u64(seed),
            seed,
        }
    }

    /// Get the seed used to initialize this RNG
    pub fn seed(&self) -> u64 {
        self.seed
    }
}

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

    #[test]
    fn same_seed_same_sequence() {
        let mut rng1 = SimRng::new(42);
        let mut rng2 = SimRng::new(42);
        let vals1: Vec<u32> = (0..100).map(|_| rng1.rng.random()).collect();
        let vals2: Vec<u32> = (0..100).map(|_| rng2.rng.random()).collect();
        assert_eq!(vals1, vals2);
    }

    #[test]
    fn different_seed_different_sequence() {
        let mut rng1 = SimRng::new(42);
        let mut rng2 = SimRng::new(43);
        let val1: u32 = rng1.rng.random();
        let val2: u32 = rng2.rng.random();
        assert_ne!(val1, val2);
    }
}