From 268f1b4ff8b63a6245ef3a5b5b45b4ad222f4ff6 Mon Sep 17 00:00:00 2001
From: lifning <>
Date: Sun, 17 Oct 2021 21:46:12 -0700
Subject: [PATCH] add scary-looking-but-safe dynamic downcast for a
 component_mut accessor

---
 ferretro_components/src/base/mod.rs | 36 +++++++++++++++++++++++------
 ferretro_components/src/lib.rs      |  2 +-
 2 files changed, 30 insertions(+), 8 deletions(-)

diff --git a/ferretro_components/src/base/mod.rs b/ferretro_components/src/base/mod.rs
index 9d68197..f464c2c 100644
--- a/ferretro_components/src/base/mod.rs
+++ b/ferretro_components/src/base/mod.rs
@@ -1,5 +1,6 @@
 use crate::prelude::*;
 use ferretro_base::retro::ffi::*;
+use std::any::{Any, TypeId};
 use std::os::raw::c_uint;
 use std::path::{PathBuf, Path};
 use std::pin::Pin;
@@ -9,7 +10,8 @@ pub struct RetroComponentBase {
     retro: LibretroWrapper,
     libretro_path: PathBuf,
     // TODO: control when things get added to this with lifetime constraints defined by implementers
-    components: Vec<Box<dyn RetroComponent>>,
+    components: Vec<Pin<Box<dyn RetroComponent>>>,
+    component_ptrs: Vec<(TypeId, *mut ())>,
 
     // replaying env calls for late-added components
     cached_rom_path: Option<PathBuf>,
@@ -25,6 +27,9 @@ pub struct RetroComponentBase {
     cached_geometry: Option<GameGeometry>,
 }
 
+#[derive(Copy, Clone, Debug)]
+pub struct RetroComponentId(usize);
+
 // TODO: replace with std::ops::ControlFlow when it becomes stable
 pub enum ControlFlow {
     Continue,
@@ -35,7 +40,7 @@ pub type Result<T> = std::result::Result<T, Box<dyn std::error::Error>>;
 
 #[rustfmt::skip]
 #[allow(unused_variables)]
-pub trait RetroComponent: RetroCallbacks {
+pub trait RetroComponent: RetroCallbacks + Any {
     fn pre_init(&mut self, retro: &mut LibretroWrapper) -> Result<()> { Ok(()) }
     fn post_init(&mut self, retro: &mut LibretroWrapper) -> Result<()> { Ok(()) }
     fn pre_load_game(&mut self, retro: &mut LibretroWrapper, rom: &Path) -> Result<()> { Ok(()) }
@@ -55,6 +60,7 @@ impl RetroComponentBase {
             retro,
             libretro_path: core_path.as_ref().to_path_buf(),
             components: Vec::new(),
+            component_ptrs: Vec::new(),
             cached_rom_path: None,
             cached_pixel_format: None,
             cached_input_descriptors: None,
@@ -87,11 +93,13 @@ impl RetroComponentBase {
         Ok(())
     }
 
-    pub fn register_component<T>(&mut self, comp: T) -> Option<()> // TODO: Result
-        where T: RetroComponent
+    pub fn register_component<T>(&mut self, comp: T) -> Result<RetroComponentId>
+        where T: RetroComponent + Any
     {
         // TODO: match comp.schedule { BeforeInit, BeforeLoad, BeforeFirstRun, Anytime }
-        let mut comp = Box::new(comp);
+        let comp_type = comp.type_id();
+        let mut comp = Box::pin(comp);
+        let comp_ptr = comp.as_mut().get_mut() as *mut T;
         if let Some(cached) = &self.cached_pixel_format {
             if let Some(false) = comp.set_pixel_format(*cached) {
                 // TODO: error, and propagate this pattern downward
@@ -126,12 +134,26 @@ impl RetroComponentBase {
         }
 
         if let Some(cached) = &self.cached_rom_path {
-            comp.post_load_game(&mut self.retro, &cached);
+            comp.post_load_game(&mut self.retro, &cached)?;
         }
 
         self.components.push(comp);
+        self.component_ptrs.push((comp_type, comp_ptr as *mut ()));
 
-        Some(())
+        Ok(RetroComponentId(self.components.len() - 1))
+    }
+
+    pub fn component_mut<T: RetroComponent>(&mut self, id: RetroComponentId) -> Result<&mut T> {
+        let (comp_type, comp_ptr) = self.component_ptrs.get(id.0)
+            .ok_or_else(|| format!("Invalid ID given to component_mut: {:?}", id))?;
+        if *comp_type == TypeId::of::<T>() {
+            Ok(unsafe { &mut *(*comp_ptr as *mut T) })
+        } else {
+            Err(format!(
+                "Invalid downcast for {:?}: {:?} != {:?}",
+                id, comp_type, TypeId::of::<T>()
+            ).into())
+        }
     }
 
     pub fn load_game(&mut self, rom: impl AsRef<Path>) -> Result<()> {
diff --git a/ferretro_components/src/lib.rs b/ferretro_components/src/lib.rs
index 87754d8..170ce1d 100644
--- a/ferretro_components/src/lib.rs
+++ b/ferretro_components/src/lib.rs
@@ -2,7 +2,7 @@ pub mod provided;
 pub mod base;
 
 pub mod prelude {
-    pub use crate::base::{RetroComponent, RetroComponentBase};
+    pub use crate::base::{RetroComponent, RetroComponentBase, RetroComponentId};
     pub use ferretro_base::retro::constants::*;
     pub use ferretro_base::retro::wrapped_types::*;
     pub use ferretro_base::retro::wrapper::{RetroCallbacks, LibretroWrapper, LibretroWrapperAccess};