From 2cd07d0e8977e4a1d41877af5c60f85f5f11f9e3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Gon=C3=A7alo=20Rica=20Pais=20da=20Silva?=
 <bluefinger@gmail.com>
Date: Fri, 5 Jul 2024 15:39:24 +0200
Subject: [PATCH] feat: Add set_seed method to GlobalRngSeed

---
 Cargo.toml           |  2 +-
 src/seed.rs          |  5 ++++
 tests/determinism.rs | 67 ++++++++++++++++++++++++++++++++++++++++++--
 3 files changed, 71 insertions(+), 3 deletions(-)

diff --git a/Cargo.toml b/Cargo.toml
index 78b3bc1..fa69698 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -7,7 +7,7 @@ authors = ["Gonçalo Rica Pais da Silva <bluefinger@gmail.com>"]
 edition = "2021"
 repository = "https://github.com/Bluefinger/bevy_rand"
 license = "MIT OR Apache-2.0"
-version = "0.7.0"
+version = "0.7.1"
 rust-version = "1.76.0"
 
 [workspace.dependencies]
diff --git a/src/seed.rs b/src/seed.rs
index aa5131a..f04b1a2 100644
--- a/src/seed.rs
+++ b/src/seed.rs
@@ -61,6 +61,11 @@ where
         self.seed.clone()
     }
 
+    /// Set the global seed to a new value
+    pub fn set_seed(&mut self, seed: R::Seed) {
+        self.seed = seed;
+    }
+
     /// Initializes an instance of [`GlobalRngSeed`] with a randomised seed
     /// value, drawn from thread-local or OS sources.
     #[inline]
diff --git a/tests/determinism.rs b/tests/determinism.rs
index cb4584a..9742ab2 100644
--- a/tests/determinism.rs
+++ b/tests/determinism.rs
@@ -1,11 +1,11 @@
 #![allow(clippy::type_complexity)]
 
 use bevy::prelude::*;
-use bevy_prng::{ChaCha12Rng, ChaCha8Rng, WyRand};
+use bevy_prng::{ChaCha12Rng, ChaCha8Rng, SeedableEntropySource, WyRand};
 use bevy_rand::prelude::{
     EntropyComponent, EntropyPlugin, ForkableAsRng, ForkableRng, GlobalEntropy, GlobalRngSeed,
 };
-use rand::prelude::Rng;
+use rand::prelude::{Rng, SeedableRng};
 
 use rand_core::RngCore;
 #[cfg(target_arch = "wasm32")]
@@ -132,3 +132,66 @@ fn test_parallel_determinism() {
         )
         .run();
 }
+
+#[test]
+#[cfg_attr(target_arch = "wasm32", wasm_bindgen_test)]
+fn test_global_reseeding() {
+    /// Basic Reseeding mechanism by change detection against GlobalRngSeed
+    fn reseed_global_rng<R: SeedableEntropySource>(
+        seed: Res<GlobalRngSeed<R>>,
+        mut rng: ResMut<GlobalEntropy<R>>,
+    ) where
+        R::Seed: Sync + Send + Clone,
+    {
+        if seed.is_changed() && !seed.is_added() {
+            rng.reseed(seed.get_seed());
+        }
+    }
+
+    let mut app = App::new();
+
+    let seed = [2; 32];
+
+    let rng_eq = GlobalEntropy::<ChaCha8Rng>::from_seed(seed);
+
+    app.add_plugins(EntropyPlugin::<ChaCha8Rng>::with_seed(seed))
+        .add_systems(PreUpdate, reseed_global_rng::<ChaCha8Rng>);
+
+    {
+        let global_rng = app.world().resource_ref::<GlobalEntropy<ChaCha8Rng>>();
+        let global_seed = app.world().resource_ref::<GlobalRngSeed<ChaCha8Rng>>();
+
+        // Our RNGs should be the same as each other as they were initialised with the same seed
+        assert_eq!(global_rng.as_ref(), &rng_eq);
+
+        // The condition here should mean our reseeding system will NOT run
+        assert!(global_seed.is_changed() && global_seed.is_added());
+    }
+
+    app.update();
+
+    {
+        let global_rng = app.world().resource_ref::<GlobalEntropy<ChaCha8Rng>>();
+
+        // Our RNGs should remain the same as each other as we have not run the update
+        assert_eq!(global_rng.as_ref(), &rng_eq);
+    }
+
+    {
+        let mut global_seed = app.world_mut().resource_mut::<GlobalRngSeed<ChaCha8Rng>>();
+
+        global_seed.set_seed([3; 32]);
+
+        // The condition here should mean our reseeding system WILL run
+        assert!(global_seed.is_changed() && !global_seed.is_added());
+    }
+
+    app.update();
+
+    {
+        let global_rng = app.world().resource_ref::<GlobalEntropy<ChaCha8Rng>>();
+
+        // Now our RNG will not be the same, even though we did not use it directly
+        assert_ne!(global_rng.as_ref(), &rng_eq);
+    }
+}