feat(nav): Gen3 Navigation policies and factory (#3760)

Terminology:

- "Navigation delegate": the function that is registered with a tracking volume. In principle, this can be anything
- "Navigation policy": the object that is registered with the tracking volume. It contains a method that is connected to the "navigation delegate". It has extra methods
- "Navigation policy factory": To delay construction of the actual policy object **until after** the volume is fully sized and has all of its internal structure registered, the blueprint tree only contains *navigation policy factories*. This is configurable. During construction, the factory is applied to volumes, and produces a policy that is registered with the volume. This is called "navigation policy factory" from a conceptual point of view.
- "MultiNavigationPolicy": chains together multiple policies in a sort of composition. You can have one policy that only deals with portals, one for sensitive and one for passive surfaces, for example.
- To make this less annoying to construct, as you would have to manage the factory, I'm adding a concrete class `NavigationPolicyFactory`. Its job is to make defining a factory that produces a "MultiNavigationPolicy" easy, like:
  ```cpp
  using namespace Acts;
  using SurfaceArrayNavigationPolicy::LayerType;
  SurfaceArrayNavigationPolicy::Config config{
    .layerType = LayerType::Cylinder,
    .bins = {10, 10}
  };
  auto factory = NavigationPolicyFactory::make()
    .add<TryAllPortalNavigationPolicy>()
    .add<SurfaceArrayNavigationPolicy>(config);
  ```
  or in python:
  ```python
  policy = (
    acts.NavigationPolicyFactory.make()
      .add(acts.TryAllPortalNavigationPolicy)
      .add(acts.TryAllSurfaceNavigationPolicy)
      .add(
        acts.SurfaceArrayNavigationPolicy,
        acts.SurfaceArrayNavigationPolicy.Config(
            layerType=acts.SurfaceArrayNavigationPolicy.LayerType.Plane,
            bins=(10, 10),
        ),
      )
  )
  ```

Part of #3502

Core/include/Acts/Geometry/NavigationPolicyFactory.hpp

@@ -0,0 +1,220 @@
+// This file is part of the ACTS project.
+//
+// Copyright (C) 2016 CERN for the benefit of the ACTS project
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at https://mozilla.org/MPL/2.0/.
+
+#pragma once
+
+#include "Acts/Navigation/INavigationPolicy.hpp"
+#include "Acts/Navigation/MultiNavigationPolicy.hpp"
+
+#include <concepts>
+#include <memory>
+namespace Acts {
+
+class TrackingVolume;
+class GeometryContext;
+class Logger;
+class INavigationPolicy;
+
+namespace detail {
+template <typename... Factories>
+class NavigationPolicyFactoryImpl;
+}
+
+/// Base class for navigation policy factories. The factory can be assembled
+/// iteratively by using `make` followed by a number of calls to the `add`
+/// function of the helper type. Example:
+///
+/// ```cpp
+/// auto factory = NavigationPolicyFactory::make()
+///  .add<NavigationPolicy1>(arg1, arg2)
+///  .add<NavigationPolicy2>(/*no args*/)
+///  .asUniquePtr();
+/// ```
+class NavigationPolicyFactory {
+ public:
+  virtual ~NavigationPolicyFactory() = default;
+
+  // This needs to be listed here, but the return type cannot be spelled out
+  // yet.
+  static auto make();
+
+  // This will potentially get serialization interface and deserialization
+  // functionality
+
+  virtual std::unique_ptr<INavigationPolicy> build(
+      const GeometryContext& gctx, const TrackingVolume& volume,
+      const Logger& logger) const = 0;
+};
+
+namespace detail {
+
+template <typename F, typename... Args>
+concept NavigationPolicyIsolatedFactoryConcept = requires(F f) {
+  {
+    f(std::declval<const GeometryContext&>(),
+      std::declval<const TrackingVolume&>(), std::declval<const Logger&>(),
+      std::declval<Args>()...)
+  } -> std::derived_from<INavigationPolicy>;
+
+  requires NavigationPolicyConcept<decltype(f(
+      std::declval<const GeometryContext&>(),
+      std::declval<const TrackingVolume&>(), std::declval<const Logger&>(),
+      std::declval<Args>()...))>;
+
+  requires(std::is_copy_constructible_v<Args> && ...);
+};
+
+template <>
+class NavigationPolicyFactoryImpl<> {
+ public:
+  template <typename...>
+  friend class NavigationPolicyFactoryImpl;
+  NavigationPolicyFactoryImpl() = default;
+
+  /// Create a factory with the specified policy added
+  /// @tparam P The policy type to add
+  /// @param args The arguments to pass to the policy constructor
+  /// @note Arguments need to be copy constructible because the factory must be
+  ///       able to execute multiple times.
+  /// @return A new policy factory including the @c P policy.
+  template <NavigationPolicyConcept P, typename... Args>
+    requires(std::is_constructible_v<P, const GeometryContext&,
+                                     const TrackingVolume&, const Logger&,
+                                     Args...> &&
+             (std::is_copy_constructible_v<Args> && ...))
+  constexpr auto add(Args&&... args) && {
+    auto factory = [=](const GeometryContext& gctx,
+                       const TrackingVolume& volume, const Logger& logger) {
+      return P{gctx, volume, logger, args...};
+    };
+
+    return NavigationPolicyFactoryImpl<decltype(factory)>{
+        std::make_tuple(std::move(factory))};
+  }
+
+  /// Create a factory with a policy returned by a factory function
+  /// @tparam Fn The type of the function to construct the policy
+  /// @param args The arguments to pass to the policy factory
+  /// @note Arguments need to be copy constructible because the factory must be
+  ///       able to execute multiple times.
+  /// @return A new policy factory including the function
+  template <typename Fn, typename... Args>
+    requires(NavigationPolicyIsolatedFactoryConcept<Fn, Args...>)
+  constexpr auto add(Fn&& fn, Args&&... args) {
+    auto factory = [=](const GeometryContext& gctx,
+                       const TrackingVolume& volume, const Logger& logger) {
+      return fn(gctx, volume, logger, args...);
+    };
+
+    return NavigationPolicyFactoryImpl<decltype(factory)>{
+        std::make_tuple(std::move(factory))};
+  }
+};
+
+template <typename F, typename... Fs>
+class NavigationPolicyFactoryImpl<F, Fs...> : public NavigationPolicyFactory {
+ public:
+  /// Create a factory with the specified policy added
+  /// @tparam P The policy type to add
+  /// @param args The arguments to pass to the policy constructor
+  /// @note Arguments need to be copy constructible because the factory must be
+  ///       able to execute multiple times.
+  /// @return A new policy factory including the @c P policy.
+  template <NavigationPolicyConcept P, typename... Args>
+    requires(std::is_constructible_v<P, const GeometryContext&,
+                                     const TrackingVolume&, const Logger&,
+                                     Args...> &&
+             (std::is_copy_constructible_v<Args> && ...))
+  constexpr auto add(Args&&... args) && {
+    auto factory = [=](const GeometryContext& gctx,
+                       const TrackingVolume& volume, const Logger& logger) {
+      return P{gctx, volume, logger, args...};
+    };
+
+    return NavigationPolicyFactoryImpl<F, Fs..., decltype(factory)>{
+        std::tuple_cat(std::move(m_factories),
+                       std::make_tuple(std::move(factory)))};
+  }
+
+  /// Create a factory with a policy returned by a factory function
+  /// @tparam Fn The type of the function to construct the policy
+  /// @param args The arguments to pass to the policy factory
+  /// @note Arguments need to be copy constructible because the factory must be
+  ///       able to execute multiple times.
+  /// @return A new policy factory including the function
+  template <typename Fn, typename... Args>
+    requires(NavigationPolicyIsolatedFactoryConcept<Fn, Args...>)
+  constexpr auto add(Fn&& fn, Args&&... args) && {
+    auto factory = [=](const GeometryContext& gctx,
+                       const TrackingVolume& volume, const Logger& logger) {
+      return fn(gctx, volume, logger, args...);
+    };
+
+    return NavigationPolicyFactoryImpl<F, Fs..., decltype(factory)>{
+        std::tuple_cat(std::move(m_factories),
+                       std::make_tuple(std::move(factory)))};
+  }
+
+  /// Move the factory into a unique pointer
+  /// @note Only callable on rvalue references
+  /// @return A unique pointer to the factory
+  constexpr std::unique_ptr<NavigationPolicyFactoryImpl<F, Fs...>>
+  asUniquePtr() && {
+    return std::make_unique<NavigationPolicyFactoryImpl<F, Fs...>>(
+        std::move(*this));
+  }
+
+  /// Construct a navigation policy using the factories
+  /// @param gctx The geometry context
+  /// @param volume The tracking volume
+  /// @param logger The logger
+  auto operator()(const GeometryContext& gctx, const TrackingVolume& volume,
+                  const Logger& logger) const {
+    return std::apply(
+        [&](auto&&... factories) {
+          // Deduce policy type explicitly here...
+          using policy_type = decltype(MultiNavigationPolicy{
+              std::invoke(factories, std::declval<const GeometryContext&>(),
+                          std::declval<const TrackingVolume&>(),
+                          std::declval<const Logger&>())...});
+
+          // ... so we can create a unique_ptr of the concrete type here rather
+          // than the base. (`make_unique` can't do type deduction)
+          return std::make_unique<policy_type>(
+              std::invoke(factories, gctx, volume, logger)...);
+        },
+        m_factories);
+  }
+
+  /// Construct a navigation policy using the factories
+  /// @param gctx The geometry context
+  /// @param volume The tracking volume
+  /// @param logger The logger
+  std::unique_ptr<INavigationPolicy> build(
+      const GeometryContext& gctx, const TrackingVolume& volume,
+      const Logger& logger) const override {
+    return operator()(gctx, volume, logger);
+  }
+
+ private:
+  template <typename...>
+  friend class NavigationPolicyFactoryImpl;
+
+  NavigationPolicyFactoryImpl(std::tuple<F, Fs...>&& factories)
+      : m_factories(std::move(factories)) {}
+
+  std::tuple<F, Fs...> m_factories;
+};
+
+}  // namespace detail
+
+inline auto NavigationPolicyFactory::make() {
+  return detail::NavigationPolicyFactoryImpl<>{};
+}
+
+}  // namespace Acts

Core/include/Acts/Geometry/TrackingVolume.hpp

@@ -13,13 +13,13 @@
 #include "Acts/Geometry/BoundarySurfaceT.hpp"
 #include "Acts/Geometry/GeometryContext.hpp"
 #include "Acts/Geometry/GeometryIdentifier.hpp"
-#include "Acts/Geometry/GlueVolumesDescriptor.hpp"
 #include "Acts/Geometry/Layer.hpp"
 #include "Acts/Geometry/Portal.hpp"
 #include "Acts/Geometry/TrackingVolumeVisitorConcept.hpp"
 #include "Acts/Geometry/Volume.hpp"
 #include "Acts/Material/IVolumeMaterial.hpp"
-#include "Acts/Surfaces/BoundaryTolerance.hpp"
+#include "Acts/Navigation/NavigationDelegate.hpp"
+#include "Acts/Navigation/NavigationStream.hpp"
 #include "Acts/Surfaces/Surface.hpp"
 #include "Acts/Surfaces/SurfaceArray.hpp"
 #include "Acts/Surfaces/SurfaceVisitorConcept.hpp"
@@ -35,22 +35,22 @@
 #include <utility>
 #include <vector>
 
-#include <boost/container/small_vector.hpp>
+#include <boost/container/container_fwd.hpp>
 
 namespace Acts {
 
 class GlueVolumesDescriptor;
 class VolumeBounds;
 template <typename object_t>
 struct NavigationOptions;
-class GeometryIdentifier;
 class IMaterialDecorator;
 class ISurfaceMaterial;
 class IVolumeMaterial;
 class Surface;
 class TrackingVolume;
 struct GeometryIdentifierHook;
 class Portal;
+class INavigationPolicy;
 
 /// Interface types of the Gen1 geometry model
 /// @note This interface is being replaced, and is subject to removal
@@ -117,8 +117,8 @@ class TrackingVolume : public Volume {
   ~TrackingVolume() override;
   TrackingVolume(const TrackingVolume&) = delete;
   TrackingVolume& operator=(const TrackingVolume&) = delete;
-  TrackingVolume(TrackingVolume&&) = default;
-  TrackingVolume& operator=(TrackingVolume&&) = default;
+  TrackingVolume(TrackingVolume&&);
+  TrackingVolume& operator=(TrackingVolume&&);
 
   /// Constructor for a container Volume
   /// - vacuum filled volume either as a for other tracking volumes
@@ -155,7 +155,6 @@ class TrackingVolume : public Volume {
   /// @param volumeName is a string identifier
   TrackingVolume(Volume& volume, const std::string& volumeName = "undefined");
 
-  // @TODO: This needs to be refactored to include Gen3 volumes
   /// Return the associated sub Volume, returns THIS if no subVolume exists
   /// @param gctx The current geometry context object, e.g. alignment
   /// @param position is the global position associated with that search
@@ -498,6 +497,21 @@ class TrackingVolume : public Volume {
                  const ViewConfig& portalViewConfig,
                  const ViewConfig& sensitiveViewConfig) const;
 
+  /// Register a navigation policy with this volume. The argument can not be
+  /// nullptr.
+  /// @param policy is the navigation policy to be registered
+  void setNavigationPolicy(std::unique_ptr<INavigationPolicy> policy);
+
+  /// Populate the navigation stream with navigation candidates from this
+  /// volume. Internally, this consults the registered navigation policy, where
+  /// the default is a noop.
+  /// @param args are the navigation arguments
+  /// @param stream is the navigation stream to be updated
+  /// @param logger is the logger
+  void initializeNavigationCandidates(const NavigationArguments& args,
+                                      AppendOnlyNavigationStream& stream,
+                                      const Logger& logger) const;
+
  private:
   void connectDenseBoundarySurfaces(
       MutableTrackingVolumeVector& confinedDenseVolumes);
@@ -561,6 +575,10 @@ class TrackingVolume : public Volume {
   std::vector<std::unique_ptr<TrackingVolume>> m_volumes;
   std::vector<std::shared_ptr<Portal>> m_portals;
   std::vector<std::shared_ptr<Surface>> m_surfaces;
+
+  std::unique_ptr<INavigationPolicy> m_navigationPolicy;
+
+  NavigationDelegate m_navigationDelegate{};
 };
 
 }  // namespace Acts

Core/include/Acts/Navigation/INavigationPolicy.hpp

@@ -0,0 +1,73 @@
+// This file is part of the ACTS project.
+//
+// Copyright (C) 2016 CERN for the benefit of the ACTS project
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at https://mozilla.org/MPL/2.0/.
+
+#pragma once
+
+#include "Acts/Navigation/NavigationDelegate.hpp"
+#include "Acts/Navigation/NavigationStream.hpp"
+#include "Acts/Utilities/DelegateChainBuilder.hpp"
+
+#include <type_traits>
+
+namespace Acts {
+
+class TrackingVolume;
+class INavigationPolicy;
+
+/// Concept for a navigation policy
+/// This exists so `updateState` can be a non-virtual method and we still have a
+/// way to enforce it exists.
+template <typename T>
+concept NavigationPolicyConcept = requires {
+  requires std::is_base_of_v<INavigationPolicy, T>;
+  // Has a conforming update method
+  requires requires(T policy, const NavigationArguments& args) {
+    policy.initializeCandidates(args,
+                                std::declval<AppendOnlyNavigationStream&>(),
+                                std::declval<const Logger&>());
+  };
+};
+
+/// Base class for all navigation policies. The policy needs to be *connected*
+/// to a delegate via a virtual method for it to become active. The update
+/// method is not part of the class interface. The conventional `updateState`
+/// method is only required for use with the navigation policy factory,
+/// otherwise `connect` is free to connect any function.
+class INavigationPolicy {
+ public:
+  /// Noop update function that is suitable as a default for default navigation
+  /// delegates.
+  static void noopInitializeCandidates(const NavigationArguments& /*unused*/,
+                                       AppendOnlyNavigationStream& /*unused*/,
+                                       const Logger& /*unused*/) {}
+
+  /// Virtual destructor so policies can be held through this base class.
+  virtual ~INavigationPolicy() = default;
+
+  /// Connect a policy with a delegate (usually a member of a volume).
+  /// This method exists to allow a policy to ensure a non-virtual function is
+  /// registered with the delegate.
+  /// @param delegate The delegate to connect to
+  virtual void connect(NavigationDelegate& delegate) const = 0;
+
+ protected:
+  /// Internal helper function for derived classes that conform to the concept
+  /// and have a conventional `updateState` method. Mainly used to save some
+  /// boilerplate.
+  /// @tparam T The type of the navigation policy
+  /// @param delegate The delegate to connect to
+  template <NavigationPolicyConcept T>
+  void connectDefault(NavigationDelegate& delegate) const {
+    // This cannot be a concept because we use it in CRTP below
+    const auto* self = static_cast<const T*>(this);
+    DelegateChainBuilder{delegate}.add<&T::initializeCandidates>(self).store(
+        delegate);
+  }
+};
+
+}  // namespace Acts