Refactor services into layers

crates/fj-core/src/algorithms/approx/curve.rs

@@ -192,7 +192,7 @@ mod tests {
         let (surface_path, boundary) =
             SurfacePath::line_from_points([[1., 1.], [2., 1.]]);
         let boundary = CurveBoundary::from(boundary);
-        let surface = core.services.objects.surfaces.xz_plane();
+        let surface = core.layers.objects.surfaces.xz_plane();
 
         let tolerance = 1.;
         let approx =
@@ -263,7 +263,7 @@ mod tests {
         let surface_path =
             SurfacePath::circle_from_center_and_radius([0., 0.], 1.);
         let boundary = CurveBoundary::from([[0.], [TAU]]);
-        let surface = core.services.objects.surfaces.xz_plane();
+        let surface = core.layers.objects.surfaces.xz_plane();
 
         let tolerance = 1.;
         let approx =

crates/fj-core/src/algorithms/intersect/curve_face.rs

@@ -186,7 +186,7 @@ mod tests {
         ];
 
         let face =
-            Face::unbound(core.services.objects.surfaces.xy_plane(), &mut core)
+            Face::unbound(core.layers.objects.surfaces.xy_plane(), &mut core)
                 .update_region(
                     |region, core| {
                         region

crates/fj-core/src/algorithms/intersect/face_face.rs

@@ -85,8 +85,8 @@ mod tests {
             [1., 2.],
         ];
         let [a, b] = [
-            core.services.objects.surfaces.xy_plane(),
-            core.services.objects.surfaces.xz_plane(),
+            core.layers.objects.surfaces.xy_plane(),
+            core.layers.objects.surfaces.xz_plane(),
         ]
         .map(|surface| {
             Face::unbound(surface, &mut core).update_region(
@@ -116,8 +116,8 @@ mod tests {
             [-1.,  1.],
         ];
         let surfaces = [
-            core.services.objects.surfaces.xy_plane(),
-            core.services.objects.surfaces.xz_plane(),
+            core.layers.objects.surfaces.xy_plane(),
+            core.layers.objects.surfaces.xz_plane(),
         ];
         let [a, b] = surfaces.clone().map(|surface| {
             Face::unbound(surface, &mut core).update_region(

crates/fj-core/src/algorithms/intersect/face_point.rs

@@ -148,7 +148,7 @@ mod tests {
         let mut core = Instance::new();
 
         let face =
-            Face::unbound(core.services.objects.surfaces.xy_plane(), &mut core)
+            Face::unbound(core.layers.objects.surfaces.xy_plane(), &mut core)
                 .update_region(
                     |region, core| {
                         region.update_exterior(
@@ -174,7 +174,7 @@ mod tests {
         let mut core = Instance::new();
 
         let face =
-            Face::unbound(core.services.objects.surfaces.xy_plane(), &mut core)
+            Face::unbound(core.layers.objects.surfaces.xy_plane(), &mut core)
                 .update_region(
                     |region, core| {
                         region.update_exterior(
@@ -203,7 +203,7 @@ mod tests {
         let mut core = Instance::new();
 
         let face =
-            Face::unbound(core.services.objects.surfaces.xy_plane(), &mut core)
+            Face::unbound(core.layers.objects.surfaces.xy_plane(), &mut core)
                 .update_region(
                     |region, core| {
                         region.update_exterior(
@@ -232,7 +232,7 @@ mod tests {
         let mut core = Instance::new();
 
         let face =
-            Face::unbound(core.services.objects.surfaces.xy_plane(), &mut core)
+            Face::unbound(core.layers.objects.surfaces.xy_plane(), &mut core)
                 .update_region(
                     |region, core| {
                         region.update_exterior(
@@ -261,7 +261,7 @@ mod tests {
         let mut core = Instance::new();
 
         let face =
-            Face::unbound(core.services.objects.surfaces.xy_plane(), &mut core)
+            Face::unbound(core.layers.objects.surfaces.xy_plane(), &mut core)
                 .update_region(
                     |region, core| {
                         region.update_exterior(
@@ -290,7 +290,7 @@ mod tests {
         let mut core = Instance::new();
 
         let face =
-            Face::unbound(core.services.objects.surfaces.xy_plane(), &mut core)
+            Face::unbound(core.layers.objects.surfaces.xy_plane(), &mut core)
                 .update_region(
                     |region, core| {
                         region.update_exterior(
@@ -325,7 +325,7 @@ mod tests {
         let mut core = Instance::new();
 
         let face =
-            Face::unbound(core.services.objects.surfaces.xy_plane(), &mut core)
+            Face::unbound(core.layers.objects.surfaces.xy_plane(), &mut core)
                 .update_region(
                     |region, core| {
                         region.update_exterior(
@@ -362,7 +362,7 @@ mod tests {
         let mut core = Instance::new();
 
         let face =
-            Face::unbound(core.services.objects.surfaces.xy_plane(), &mut core)
+            Face::unbound(core.layers.objects.surfaces.xy_plane(), &mut core)
                 .update_region(
                     |region, core| {
                         region.update_exterior(

crates/fj-core/src/algorithms/intersect/ray_face.rs

@@ -164,7 +164,7 @@ mod tests {
         let ray = HorizontalRayToTheRight::from([0., 0., 0.]);
 
         let face =
-            Face::unbound(core.services.objects.surfaces.yz_plane(), &mut core)
+            Face::unbound(core.layers.objects.surfaces.yz_plane(), &mut core)
                 .update_region(
                     |region, core| {
                         region.update_exterior(
@@ -196,7 +196,7 @@ mod tests {
         let ray = HorizontalRayToTheRight::from([0., 0., 0.]);
 
         let face =
-            Face::unbound(core.services.objects.surfaces.yz_plane(), &mut core)
+            Face::unbound(core.layers.objects.surfaces.yz_plane(), &mut core)
                 .update_region(
                     |region, core| {
                         region.update_exterior(
@@ -231,7 +231,7 @@ mod tests {
         let ray = HorizontalRayToTheRight::from([0., 0., 0.]);
 
         let face =
-            Face::unbound(core.services.objects.surfaces.yz_plane(), &mut core)
+            Face::unbound(core.layers.objects.surfaces.yz_plane(), &mut core)
                 .update_region(
                     |region, core| {
                         region.update_exterior(
@@ -263,7 +263,7 @@ mod tests {
         let ray = HorizontalRayToTheRight::from([0., 0., 0.]);
 
         let face =
-            Face::unbound(core.services.objects.surfaces.yz_plane(), &mut core)
+            Face::unbound(core.layers.objects.surfaces.yz_plane(), &mut core)
                 .update_region(
                     |region, core| {
                         region.update_exterior(
@@ -305,7 +305,7 @@ mod tests {
         let ray = HorizontalRayToTheRight::from([0., 0., 0.]);
 
         let face =
-            Face::unbound(core.services.objects.surfaces.yz_plane(), &mut core)
+            Face::unbound(core.layers.objects.surfaces.yz_plane(), &mut core)
                 .update_region(
                     |region, core| {
                         region.update_exterior(
@@ -348,7 +348,7 @@ mod tests {
         let ray = HorizontalRayToTheRight::from([0., 0., 0.]);
 
         let face =
-            Face::unbound(core.services.objects.surfaces.xy_plane(), &mut core)
+            Face::unbound(core.layers.objects.surfaces.xy_plane(), &mut core)
                 .update_region(
                     |region, core| {
                         region.update_exterior(
@@ -382,7 +382,7 @@ mod tests {
         let ray = HorizontalRayToTheRight::from([0., 0., 0.]);
 
         let face =
-            Face::unbound(core.services.objects.surfaces.xy_plane(), &mut core)
+            Face::unbound(core.layers.objects.surfaces.xy_plane(), &mut core)
                 .update_region(
                     |region, core| {
                         region.update_exterior(

crates/fj-core/src/algorithms/intersect/surface_surface.rs

@@ -85,8 +85,8 @@ mod tests {
     fn plane_plane() {
         let mut core = Instance::new();
 
-        let xy = core.services.objects.surfaces.xy_plane();
-        let xz = core.services.objects.surfaces.xz_plane();
+        let xy = core.layers.objects.surfaces.xy_plane();
+        let xz = core.layers.objects.surfaces.xz_plane();
 
         // Coincident and parallel planes don't have an intersection curve.
         assert_eq!(

crates/fj-core/src/algorithms/triangulate/mod.rs

@@ -99,7 +99,7 @@ mod tests {
         let d = [0., 1.];
 
         let face =
-            Face::unbound(core.services.objects.surfaces.xy_plane(), &mut core)
+            Face::unbound(core.layers.objects.surfaces.xy_plane(), &mut core)
                 .update_region(
                     |region, core| {
                         region.update_exterior(
@@ -139,7 +139,7 @@ mod tests {
         let g = [3., 3.];
         let h = [3., 1.];
 
-        let surface = core.services.objects.surfaces.xy_plane();
+        let surface = core.layers.objects.surfaces.xy_plane();
 
         let face = Face::unbound(surface.clone(), &mut core).update_region(
             |region, core| {
@@ -204,7 +204,7 @@ mod tests {
         let d = [1., 1.];
         let e = [0., 9.];
 
-        let surface = core.services.objects.surfaces.xy_plane();
+        let surface = core.layers.objects.surfaces.xy_plane();
 
         let face = Face::unbound(surface.clone(), &mut core).update_region(
             |region, core| {

crates/fj-core/src/instance.rs

@@ -2,27 +2,27 @@
 //!
 //! See [`Instance`].
 
-use crate::{services::Services, validate::ValidationConfig};
+use crate::{layers::Layers, validate::ValidationConfig};
 
 /// An instance of the Fornjot core
 ///
 /// This is the main entry point to `fj-core`'s API.
 pub struct Instance {
-    /// Event-sourced background services
-    pub services: Services,
+    /// The layers of data that make up the state of a core instance
+    pub layers: Layers,
 }
 
 impl Instance {
     /// Construct an instance of `Instance`
     pub fn new() -> Self {
-        let services = Services::new();
-        Self { services }
+        let layers = Layers::new();
+        Self { layers }
     }
 
     /// Construct an instance of `Instance`, using the provided configuration
     pub fn with_validation_config(config: ValidationConfig) -> Self {
-        let services = Services::with_validation_config(config);
-        Self { services }
+        let layers = Layers::with_validation_config(config);
+        Self { layers }
     }
 }
 

crates/fj-core/src/services/service.rs → crates/fj-core/src/layers/layer.rs

@@ -1,38 +1,35 @@
 use std::ops::Deref;
 
-/// A service that controls access to some state
+/// A generic layer, which controls access to layer state
 ///
-/// `Service` is a generic wrapper around some state, as well as code that knows
-/// how to operate on that state. It processes commands, changes the state based
-/// on those command, and produces events that capture these changes. These
-/// events are stored, providing a log of all changes to the state, and can be
-/// replayed later to re-create the state at any point in time.
+/// `Layer` is a generic wrapper around some state and controls access to it. It
+/// [`Deref`]s to the state it wraps, for easy read access, but prevents any
+/// direct write access.
 ///
-/// The wrapped state must implement [`State`], which defines the type of
-/// command that this service processes, and the type of event that captures
-/// state changes. It also defines methods that operate on the state, commands,
-/// and events.
+/// Instead, each write access to state is reified as a command, which are
+/// processed by [`Layer::process`]. Processing a command can result in any
+/// number of events, which can then be used as commands for other layers.
 ///
-/// Implementations of [`State`] might also define an extension trait for a
-/// specific `Service<MyState>`, to provide a convenient API to callers.
+/// All of this is mediated through [`State`], which the wrapped state must
+/// implement.
 ///
 /// This design takes inspiration from, and uses the nomenclature of, this
 /// article:
 /// <https://thinkbeforecoding.com/post/2021/12/17/functional-event-sourcing-decider>
-pub struct Service<S: State> {
+pub struct Layer<S: State> {
     state: S,
 }
 
-impl<S: State> Service<S> {
-    /// Create an instance of `Service`
+impl<S: State> Layer<S> {
+    /// Create an instance of `Layer`
     pub fn new(state: S) -> Self {
         Self { state }
     }
 
-    /// Execute a command
+    /// Process a command
     ///
-    /// The command is executed synchronously. When this method returns, the
-    /// state has been updated and any events have been logged.
+    /// The command is processed synchronously. When this method returns, the
+    /// state has been updated.
     pub fn process(&mut self, command: S::Command, events: &mut Vec<S::Event>) {
         self.state.decide(command, events);
 
@@ -47,15 +44,15 @@ impl<S: State> Service<S> {
     }
 }
 
-impl<S: State> Deref for Service<S> {
+impl<S: State> Deref for Layer<S> {
     type Target = S;
 
     fn deref(&self) -> &Self::Target {
         &self.state
     }
 }
 
-impl<S: State> Default for Service<S>
+impl<S: State> Default for Layer<S>
 where
     S: Default,
 {
@@ -64,16 +61,19 @@ where
     }
 }
 
-/// Implemented for state that can be wrapped by a [`Service`]
+/// The state of a specific layer
 ///
-/// See [`Service`] for a detailed explanation.
+/// Implementations of this trait are wrapped by the generic [`Layer`], which is
+/// the consumer of this trait's API.
+///
+/// See [`Layer`] for a more detailed explanation.
 pub trait State {
-    /// A command that relates to the state
+    /// A command that encodes a request to update the state
     ///
     /// Commands are processed by [`State::decide`].
     type Command;
 
-    /// An event that captures modifications to this state
+    /// An event that encodes a change to the state
     ///
     /// Events are produced by [`State::decide`] and processed by
     /// [`State::evolve`].
@@ -87,8 +87,8 @@ pub trait State {
 
     /// Evolve the state according to the provided event
     ///
-    /// This is the only method gets mutable access to the state, making sure
-    /// that all changes to the state are captured as events.
+    /// This is the only method that gets mutable access to the state, making
+    /// sure that all changes to the state are captured as events.
     ///
     /// Implementations of this method are supposed to be relatively dumb. Any
     /// decisions that go into updating the state should be made in