From 53837d469bd96b5e0827e469893b7b167ac1f334 Mon Sep 17 00:00:00 2001
From: SeanOMik <seanomik@gmail.com>
Date: Wed, 24 Apr 2024 00:28:01 -0400
Subject: [PATCH] ecs: fix BatchedSystem, implement ways for `Criteria`s to
 modify the world before and after execution

---
 lyra-ecs/src/system/batched.rs  | 48 +++++++++++++++++++++++++++------
 lyra-ecs/src/system/criteria.rs | 20 ++++++++------
 2 files changed, 52 insertions(+), 16 deletions(-)

diff --git a/lyra-ecs/src/system/batched.rs b/lyra-ecs/src/system/batched.rs
index 00de666..d8f4d64 100644
--- a/lyra-ecs/src/system/batched.rs
+++ b/lyra-ecs/src/system/batched.rs
@@ -1,9 +1,9 @@
 use lyra_ecs::World;
-use tracing::debug_span;
+use tracing::{debug_span, instrument};
 
 use crate::Access;
 
-use super::{System, Criteria, IntoSystem};
+use super::{Criteria, GraphExecutorError, IntoSystem, System};
 
 /// A system that executes a batch of systems in order that they were given.
 /// You can optionally add criteria that must pass before the systems are
@@ -13,6 +13,7 @@ pub struct BatchedSystem {
     systems: Vec<Box<dyn System>>,
     criteria: Vec<Box<dyn Criteria>>,
     criteria_checks: u32,
+    did_run: bool,
 }
 
 impl BatchedSystem {
@@ -47,6 +48,7 @@ impl System for BatchedSystem {
         }
     }
 
+    #[instrument(skip(self, world))]
     fn execute(&mut self, world: std::ptr::NonNull<World>) -> anyhow::Result<()> {
         let mut can_run = true;
         let mut check_again = false;
@@ -69,13 +71,26 @@ impl System for BatchedSystem {
         }
 
         if can_run {
+            for criteria in self.criteria.iter_mut() {
+                criteria.modify_world(world);
+            }
+
             for (idx, system) in self.systems.iter_mut().enumerate() {
-                let sys_span = debug_span!("batch", system=tracing::field::Empty);
-                sys_span.record("system", idx);
-                let _e = sys_span.enter();
+                let span = debug_span!("batch", system=idx);
+                let _e = span.enter();
 
                 system.execute(world)?;
+
+                /* let deferred_span = debug_span!("deferred_exec");
+                let _e = deferred_span.enter();
+
+                if let Err(e) = system.execute_deferred(world)
+                        .map_err(|e| GraphExecutorError::Command(e)) {
+                    return Err(e.into());
+                } */
             }
+
+            self.did_run = true;
         }
 
         if check_again {
@@ -87,9 +102,26 @@ impl System for BatchedSystem {
 
         Ok(())
     }
-    
-    fn execute_deferred(&mut self, _: std::ptr::NonNull<World>) -> anyhow::Result<()> {
-        todo!()
+
+    #[instrument(skip(self, world))]
+    fn execute_deferred(&mut self, world: std::ptr::NonNull<World>) -> anyhow::Result<()> {
+        if self.did_run {
+            for (idx, system) in self.systems.iter_mut().enumerate() {
+                let span = debug_span!("batch", system=idx);
+                let _e = span.enter();
+                
+                system.execute_deferred(world)
+                    .map_err(|e| GraphExecutorError::Command(e))?;
+            }
+
+            for criteria in self.criteria.iter_mut() {
+                criteria.undo_world_modifications(world);
+            }
+        }
+
+        self.did_run = false;
+
+        Ok(())
     }
 }
 
diff --git a/lyra-ecs/src/system/criteria.rs b/lyra-ecs/src/system/criteria.rs
index d0a2868..95e4699 100644
--- a/lyra-ecs/src/system/criteria.rs
+++ b/lyra-ecs/src/system/criteria.rs
@@ -26,13 +26,17 @@ pub trait Criteria {
     /// * `world` - The ecs world.
     /// * `check_count` - The amount of times the Criteria has been checked this tick.
     fn can_run(&mut self, world: NonNull<World>, check_count: u32) -> CriteriaSchedule;
-}
 
-impl<F> Criteria for F
-    where F: FnMut(&mut World, u32) -> CriteriaSchedule
-{
-    fn can_run(&mut self, mut world: NonNull<World>, check_count: u32) -> CriteriaSchedule {
-        let world_mut = unsafe { world.as_mut() };
-        self(world_mut, check_count)
-    }
+    /// Modify the world after the [`Criteria`] in the system batch allows the systems to run.
+    /// 
+    /// This can be great if this Criteria limits the execution of systems based off of resources.
+    /// A `FixedTimestep` criteria would use this to replace the [`DeltaTime`] resource in the
+    /// world to match the timestep time.
+    fn modify_world(&mut self, world: NonNull<World>);
+
+    /// Undo modifications to the world after the systems in the batch have been executed.
+    /// 
+    /// The `FixedTimestep` criteria (see docs for [`Criteria::modify_world`]) uses this
+    /// to replace the [`DeltaTime`] resource with its original value before it was replaced.
+    fn undo_world_modifications(&mut self, world: NonNull<World>);
 }
\ No newline at end of file