Config: renaming & add change subscriptions

include/dusk/config.hpp

@@ -1,9 +1,11 @@
 #ifndef DUSK_CONFIG_HPP
 #define DUSK_CONFIG_HPP
 
+#include <concepts>
 #include <functional>
+#include <nlohmann/json.hpp>
 #include <stdexcept>
-#include "nlohmann/json.hpp"
+
 #include "config_var.hpp"
 
 namespace dusk::config {
@@ -40,7 +42,7 @@ public:
     [[nodiscard]] virtual nlohmann::json dumpToJson(const ConfigVarBase& cVar) const = 0;
 };
 
-template<ConfigValue T>
+template <ConfigValue T>
 class ConfigImpl : public ConfigImplBase {
     // Just downcasting the references...
     void loadFromJson(ConfigVarBase& cVar, const nlohmann::json& jsonValue) const final {
@@ -90,20 +92,28 @@ public:
 void Register(ConfigVarBase& configVar);
 
 /**
- * \brief Indicate that all registrations have happened and everything should lock in.
+ * \brief Unregister a CVar, detaching it from the config system.
+ *
+ * If the CVar carries a user-set value (Value or Speedrun layer), it is stashed as an
+ * unregistered key: Save() keeps writing it, and a later Register() of the same name restores
+ * it through the normal back-fill path. The CVar may be destroyed after this returns.
  */
-void FinishRegistration();
+void unregister(ConfigVarBase& configVar);
 
 /**
  * \brief Load config from the standard user preferences location.
  */
-void LoadFromUserPreferences();
-void LoadFromFileName(const char* path);
+void load_from_user_preferences();
+void load_from_file_name(const char* path);
+
+void load_arg_override(std::string_view name, std::string_view value);
+
+void shutdown();
 
 /**
  * \brief Save the config to file.
  */
-void Save();
+void save();
 
 /**
  * \brief Get a registered CVar by name.
@@ -124,6 +134,59 @@ void ClearAllActionBindings(int port);
  */
 void EnumerateRegistered(std::function<void(ConfigVarBase&)> callback);
 
+/**
+ * \brief Type-erased change callback. previousValue points at the value before the mutation
+ * (a `const T*` for a `ConfigVar<T>`) and is valid only for the duration of the call.
+ */
+using ChangeCallback = std::function<void(ConfigVarBase& cVar, const void* previousValue)>;
+
+/**
+ * \brief Token identifying a change subscription. 0 is never a valid token.
+ */
+using Subscription = u64;
+
+/**
+ * \brief Subscribe to changes of the named CVar (registered or not yet registered).
+ *
+ * Fired synchronously on the mutating thread (in practice the game thread) whenever the CVar's
+ * effective value changes at runtime: setValue, override/speedrun setters and clears. Values
+ * applied by config load or launch arguments do *not* notify: loads happen during startup
+ * before the subsystems callbacks push values into are initialized, and each subsystem reads
+ * its initial value itself at its own init. Callbacks may mutate other CVars; a nested
+ * mutation of the same CVar applies but does not re-notify.
+ */
+Subscription subscribe(std::string_view name, ChangeCallback callback);
+
+/**
+ * \brief Typed convenience overload: the callback receives the current and previous values.
+ */
+template <ConfigValue T, typename Callback>
+requires std::invocable<Callback, const T&, const T&> Subscription subscribe(
+    ConfigVar<T>& cVar, Callback&& callback) {
+    return subscribe(cVar.getName(),
+        [&cVar, cb = std::forward<Callback>(callback)](ConfigVarBase&, const void* previousValue) {
+            cb(cVar.getValue(), *static_cast<const T*>(previousValue));
+        });
+}
+
+void unsubscribe(Subscription token);
+
+/**
+ * \brief Register a CVar and attach a change callback in one step.
+ *
+ * Useful for pushing settings into external systems (e.g. aurora) from one place instead of
+ * every UI setter. The callback fires only for runtime changes (see subscribe); the value
+ * loaded from config or launch arguments does not fire it — the external system reads its
+ * initial value itself at its own initialization.
+ */
+template <ConfigValue T, typename Callback>
+requires std::invocable<Callback, const T&, const T&> Subscription Register(
+    ConfigVar<T>& cVar, Callback&& onChange) {
+    auto subscription = subscribe(cVar, std::forward<Callback>(onChange));
+    Register(static_cast<ConfigVarBase&>(cVar));
+    return subscription;
+}
+
 template <ConfigValue T>
 const ConfigImplBase* GetConfigImpl() {
     static ConfigImpl<T> config;

include/dusk/config_var.hpp

@@ -2,10 +2,12 @@
 #define DUSK_CONFIG_VAR_HPP
 
 #include "dolphin/types.h"
-#include <type_traits>
+#include <concepts>
 #include <cstdlib>
 #include <limits>
+#include <optional>
 #include <string>
+#include <type_traits>
 
 /**
  * The configuration system.
@@ -69,7 +71,7 @@ protected:
     /**
      * The name of this CVar, used in the configuration file.
      */
-    const char* name;
+    std::string name;
 
     /**
      * Whether this CVar has been registered with the global managing logic.
@@ -87,8 +89,8 @@ protected:
      */
     const ConfigImplBase* impl;
 
-    ConfigVarBase(const char* name, const ConfigImplBase* impl);
-    virtual ~ConfigVarBase() = default;
+    ConfigVarBase(const ConfigVarBase&) = delete;
+    ConfigVarBase(std::string name, const ConfigImplBase* impl);
 
     /**
      * Check that the CVar is registered, aborting if this is not the case.
@@ -98,7 +100,22 @@ protected:
             abort();
     }
 
+    /**
+     * Whether any change subscriber (see config::subscribe) is attached to this CVar's name.
+     */
+    [[nodiscard]] bool has_subscribers() const;
+
+    /**
+     * Notify change subscribers (see config::subscribe) that the effective value of this CVar
+     * changed. Called by mutators after the change has been applied; previousValue points at
+     * the old value (a `const T*` for a `ConfigVar<T>`), valid only for the duration of the
+     * call.
+     */
+    void notify_changed(const void* previousValue);
+
 public:
+    virtual ~ConfigVarBase();
+
     /**
      * Get the name of this CVar, used in the configuration file.
      */
@@ -121,6 +138,7 @@ public:
      * This is necessary to make it legal to access.
      */
     void markRegistered();
+    void unmarkRegistered();
 
     /**
      * Clear a speedrun-mode override if one is active on this CVar.
@@ -155,6 +173,7 @@ template <typename T>
 concept ConfigValue =
     !std::is_const_v<T>
     && !std::is_volatile_v<T>
+    && std::equality_comparable<T>
     && (std::is_same_v<T, bool>
         || ConfigValueInteger<T>
         || std::is_same_v<T, f32>
@@ -166,6 +185,9 @@ concept ConfigValue =
 template <ConfigValue T>
 const ConfigImplBase* GetConfigImpl();
 
+template <ConfigValue T>
+class ConfigImpl;
+
 template <typename T>
 struct ConfigEnumRange {
     static constexpr auto min = std::numeric_limits<std::underlying_type_t<T>>::min();
@@ -192,10 +214,12 @@ public:
      * @param arg Arguments to forward to construct the default value.
      */
     template <typename... Args>
-    ConfigVar(const char* name, Args&&... arg)
-        : ConfigVarBase(name, GetConfigImpl<T>()), defaultValue(std::forward<Args>(arg)...),
+    ConfigVar(std::string name, Args&&... arg)
+        : ConfigVarBase(std::move(name), GetConfigImpl<T>()), defaultValue(std::forward<Args>(arg)...),
         value(), overrideValue() {}
 
+    ConfigVar(ConfigVar const&) = delete;
+
     /**
      * \brief Get the current value of the CVar.
      *
@@ -234,6 +258,7 @@ public:
      */
     void setValue(T newValue, bool replaceOverride = true) {
         checkRegistered();
+        const auto previous = previous_for_notify();
         value = std::move(newValue);
 
         if (replaceOverride) {
@@ -242,6 +267,7 @@ public:
         } else if (layer != ConfigVarLayer::Override) {
             layer = ConfigVarLayer::Value;
         }
+        notify_if_changed(previous);
     }
 
     operator const T&() {
@@ -258,8 +284,10 @@ public:
      */
     void setOverrideValue(T newValue) {
         checkRegistered();
+        const auto previous = previous_for_notify();
         overrideValue = std::move(newValue);
         layer = ConfigVarLayer::Override;
+        notify_if_changed(previous);
     }
 
     /**
@@ -273,25 +301,31 @@ public:
     void setSpeedrunValue(T newValue) {
         checkRegistered();
         if (layer != ConfigVarLayer::Override) {
+            const auto previous = previous_for_notify();
             priorLayer = layer;
             overrideValue = std::move(newValue);
             layer = ConfigVarLayer::Speedrun;
+            notify_if_changed(previous);
         }
     }
 
     void clearOverride() {
         checkRegistered();
         if (layer == ConfigVarLayer::Override) {
+            const auto previous = previous_for_notify();
             overrideValue = {};
             layer = ConfigVarLayer::Value;
+            notify_if_changed(previous);
         }
     }
 
     void clearSpeedrunOverride() override {
         checkRegistered();
         if (layer == ConfigVarLayer::Speedrun) {
+            const auto previous = previous_for_notify();
             overrideValue = {};
             layer = priorLayer;
+            notify_if_changed(previous);
         }
     }
 
@@ -305,6 +339,48 @@ public:
         const ConfigVarLayer effectiveLayer = (layer == ConfigVarLayer::Speedrun) ? priorLayer : layer;
         return effectiveLayer == ConfigVarLayer::Default ? defaultValue : value;
     }
+
+private:
+    // The config loader applies values through the silent load_* methods below.
+    friend class ConfigImpl<T>;
+
+    /**
+     * Copy of the effective value before a mutation, taken only when someone is subscribed.
+     */
+    [[nodiscard]] std::optional<T> previous_for_notify() const {
+        return has_subscribers() ? std::optional<T>{getValue()} : std::nullopt;
+    }
+
+    /**
+     * Notify subscribers if the effective value actually changed across a mutation.
+     */
+    void notify_if_changed(const std::optional<T>& previous) {
+        if (previous.has_value() && !(getValue() == *previous)) {
+            notify_changed(&*previous);
+        }
+    }
+
+    /**
+     * setValue(newValue, false) without notifying change subscribers. Used when loading config:
+     * loads happen during startup before the subsystems change callbacks push values into are
+     * initialized, and each subsystem applies the loaded value itself at its own init.
+     */
+    void load_value(T newValue) {
+        checkRegistered();
+        value = std::move(newValue);
+        if (layer != ConfigVarLayer::Override) {
+            layer = ConfigVarLayer::Value;
+        }
+    }
+
+    /**
+     * setOverrideValue without notifying change subscribers (see load_value).
+     */
+    void load_override_value(T newValue) {
+        checkRegistered();
+        overrideValue = std::move(newValue);
+        layer = ConfigVarLayer::Override;
+    }
 };
 
 using ActionBindConfigVar = ConfigVar<int>;

include/dusk/settings.h

@@ -7,7 +7,8 @@
 
 namespace dusk {
 
-using namespace config;
+using config::ConfigVar;
+using config::ActionBindConfigVar;
 
 enum class BloomMode : int {
     Off = 0,