ftb/hooks.hpp

#pragma once
#include "./arraylist.hpp"

// For std::decay
#include <type_traits>

template<typename>
struct Lambda; // intentionally not defined

template<typename R, typename ...Args>
struct Lambda<R(Args...)>
{
    using Dispatcher = R(*)(void*, Args...);

    Dispatcher m_Dispatcher; // A pointer to the static function that will call the
    // wrapped invokable object
    void* m_Target;          // A pointer to the invokable object

    // Dispatch() is instantiated by the Lambda constructor,
    // which will store a pointer to the function in m_Dispatcher.
    template<typename S>
    static R Dispatch(void* target, Args... args)
    {
        return (*(S*)target)(args...);
    }

    template<typename T>
    Lambda(T&& target)
        : m_Dispatcher(&Dispatch<typename std::decay<T>::type>)
        , m_Target(&target)
    {
    }

    // Specialize for reference-to-function, to ensure that a valid pointer is
    // stored.
    using TargetFunctionRef = R(Args...);
    Lambda(TargetFunctionRef target)
        : m_Dispatcher(Dispatch<TargetFunctionRef>)
    {
        static_assert(sizeof(void*) == sizeof target,
                      "It will not be possible to pass functions by reference on this platform. "
                      "Please use explicit function pointers i.e. foo(target) -> foo(&target)");
        m_Target = (void*)target;
    }

    R operator()(Args... args) const
    {
        return m_Dispatcher(m_Target, args...);
    }
};

struct Hook {
    Array_List<Lambda<void()>> lambdas;
    Hook() {
        lambdas.alloc();
    }
    ~Hook () {
        lambdas.dealloc();
    }
    void operator<<(Lambda<void()>&& f) {
        lambdas.append(f);
    }
    void operator()() {
        for (auto l : lambdas) {
            l();
        }
        lambdas.clear();
    }
};

// struct __System_Shutdown_Hook : Hook {
//     void operator()() = delete;
//     ~__System_Shutdown_Hook() {
//         Hook::operator()();
//         lambdas.dealloc();
//     }
// } system_shutdown_hook;