zecsy/zecsy.hpp

#pragma once
#include <cstdint>
#include <bitset>
#include <format>
#include <stdexcept>

#ifndef MAX_ZECSY_ENTITIES
    #define MAX_ZECSY_ENTITIES 65536
#endif // !MAX_ZECSY_ENTITIES


namespace zecsy 
{
    using entity_id = uint64_t;

    class entity final
    {
    public:
        entity(class world* w, entity_id id);

        entity() = default;
        entity(const entity &) = default;
        entity(entity &&) = default;
        entity &operator=(const entity &) = default;
        entity &operator=(entity &&) = default;
        operator entity_id() const;

        bool is_alive() const;
    private:
        entity_id id = 0;
        class world* w = nullptr;
    };

    class world final
    {
    public:
        world() = default;
        world(const world &) = default;
        world(world &&) = default;
        world &operator=(const world &) = default;
        world &operator=(world &&) = default;
   
        entity make_entity();
        void destroy_entity(entity_id e);
        bool is_alive(entity_id e) const; 
    private:
        std::bitset<MAX_ZECSY_ENTITIES + 1> entities_bitset;
        entity_id entity_counter = 0;
    };

    inline entity::entity(class world* w, entity_id id): w(w), id(id)
    {

    }

    inline entity::operator entity_id() const 
    {
        return id;
    }

    inline bool entity::is_alive() const
    {
        return w && w->is_alive(id);
    }

    inline entity world::make_entity()
    {
        auto id = ++entity_counter;
        
        if(id > MAX_ZECSY_ENTITIES)
        {
            throw std::runtime_error(std::format("Entity id {} exceeds " 
                        "MAX_ZECSY_ENTITIES ({})", id, MAX_ZECSY_ENTITIES));
        }

        entities_bitset.set(id);
        return entity(this, id);
    }

    inline void world::destroy_entity(entity_id e)
    {
        entities_bitset.reset(e);
    }

    inline bool world::is_alive(entity_id e) const
    {
        return entities_bitset.test(e);
    }
};