StateMachine.hpp

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#ifndef GALAXY_STATE_STATEMACHINE_HPP_
#define GALAXY_STATE_STATEMACHINE_HPP_
 
#include <ankerl/unordered_dense.h>
 
#include "galaxy/math/FNV1a.hpp"
#include "galaxy/state/State.hpp"
#include "galaxy/logging/Log.hpp"
 
namespace galaxy
{
    template<std::derived_from<State> Stored>
    class StateMachine
    {
        using Stack = std::vector<std::shared_ptr<Stored>>;
 
        using Map = ankerl::unordered_dense::map<std::uint64_t, std::shared_ptr<Stored>>;
 
    public:
        StateMachine() noexcept;
 
        StateMachine(StateMachine<Stored>&&);
 
        StateMachine<Stored>& operator=(StateMachine<Stored>&&);
 
        virtual ~StateMachine();
 
        template<typename Child = Stored, typename... Args>
        [[maybe_unused]]
        std::shared_ptr<Stored> add(const std::string& key, Args&&... args);
 
        [[nodiscard]]
        std::shared_ptr<Stored> get(const std::string& key) noexcept;
 
        [[nodiscard]]
        bool has(const std::string& key) noexcept;
 
        void remove(const std::string& key);
 
        void push(const std::string& key) noexcept;
 
        void pop() noexcept;
 
        void pop_all() noexcept;
 
        [[nodiscard]]
        std::shared_ptr<Stored> top() const noexcept;
 
        [[nodiscard]]
        Stack& stack() noexcept;
 
        [[nodiscard]]
        Map& storage() noexcept;
 
    protected:
        Stack m_stack;
 
        Map m_storage;
 
    private:
        StateMachine(const StateMachine<Stored>&) = delete;
 
        StateMachine<Stored>& operator=(const StateMachine<Stored>&) = delete;
    };
 
    template<std::derived_from<State> Stored>
    StateMachine<Stored>::StateMachine() noexcept
    {
    }
 
    template<std::derived_from<State> Stored>
    inline StateMachine<Stored>::StateMachine(StateMachine<Stored>&& sm)
    {
        this->m_stack   = std::move(sm.m_stack);
        this->m_storage = std::move(sm.m_storage);
    }
 
    template<std::derived_from<State> Stored>
    inline StateMachine<Stored>& StateMachine<Stored>::operator=(StateMachine<Stored>&& sm)
    {
        if (this != &sm)
        {
            this->m_stack   = std::move(sm.m_stack);
            this->m_storage = std::move(sm.m_storage);
        }
 
        return *this;
    }
 
    template<std::derived_from<State> Stored>
    inline StateMachine<Stored>::~StateMachine()
    {
        pop_all();
 
        m_stack.clear();
        m_storage.clear();
    }
 
    template<std::derived_from<State> Stored>
    template<typename Child, typename... Args>
    inline std::shared_ptr<Stored> StateMachine<Stored>::add(const std::string& key, Args&&... args)
    {
        const auto hash = math::fnv1a(key.c_str());
 
        if (!m_storage.contains(hash))
        {
            m_storage[hash] = std::make_shared<Child>(key, std::forward<Args>(args)...);
            return m_storage[hash];
        }
        else
        {
            GALAXY_LOG(GALAXY_WARN, "Tried to create a scene with a duplicate key of '{0}'.", key);
            return nullptr;
        }
    }
 
    template<std::derived_from<State> Stored>
    inline std::shared_ptr<Stored> StateMachine<Stored>::get(const std::string& key) noexcept
    {
        const auto hash = math::fnv1a(key.c_str());
 
        if (m_storage.contains(hash))
        {
            return m_storage[hash];
        }
        else
        {
            GALAXY_LOG(GALAXY_WARN, "State '{0}' does not exist.", key);
            return nullptr;
        }
    }
 
    template<std::derived_from<State> Stored>
    inline bool StateMachine<Stored>::has(const std::string& key) noexcept
    {
        const auto hash = math::fnv1a(key.c_str());
        return m_storage.contains(hash);
    }
 
    template<std::derived_from<State> Stored>
    inline void StateMachine<Stored>::remove(const std::string& key)
    {
        for (auto&& state : m_stack)
        {
            if (state->name() == key)
            {
                GALAXY_LOG(GALAXY_WARN, "Cant remove an active state.");
                return;
            }
        }
 
        const auto hash = math::fnv1a(key.c_str());
        m_storage.erase(hash);
    }
 
    template<std::derived_from<State> Stored>
    inline void StateMachine<Stored>::push(const std::string& key) noexcept
    {
        if (auto state = get(key))
        {
            m_stack.push_back(state);
            m_stack.back()->on_push();
        }
        else
        {
            GALAXY_LOG(GALAXY_WARN, "Tried to push non-existent scene '{0}'.", key);
        }
    }
 
    template<std::derived_from<State> Stored>
    inline void StateMachine<Stored>::pop() noexcept
    {
        if (auto state = top())
        {
            state->on_pop();
            m_stack.pop_back();
        }
 
        if (m_stack.size() > 0)
        {
            m_stack.back()->on_pop();
        }
    }
 
    template<std::derived_from<State> Stored>
    inline void StateMachine<Stored>::pop_all() noexcept
    {
        while (!m_stack.empty())
        {
            pop();
        }
    }
 
    template<std::derived_from<State> Stored>
    inline std::shared_ptr<Stored> StateMachine<Stored>::top() const noexcept
    {
        if (!m_stack.empty())
        {
            return m_stack.back();
        }
 
        return nullptr;
    }
 
    template<std::derived_from<State> Stored>
    inline StateMachine<Stored>::Stack& StateMachine<Stored>::stack() noexcept
    {
        return m_stack;
    }
 
    template<std::derived_from<State> Stored>
    inline StateMachine<Stored>::Map& StateMachine<Stored>::storage() noexcept
    {
        return m_storage;
    }
} // namespace galaxy
 
#endif