From 21c7e416ecaceb511d4fc275762219b1a0ec7262 Mon Sep 17 00:00:00 2001
From: NukeBird <nukebird.dev@gmail.com>
Date: Fri, 14 Feb 2025 23:42:01 +0300
Subject: [PATCH] Attach simple components to an entity

---
 tests/zecsy.cpp |  46 ++++++++++++++++-
 zecsy.hpp       | 131 +++++++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 174 insertions(+), 3 deletions(-)

diff --git a/tests/zecsy.cpp b/tests/zecsy.cpp
index 0174c37..2659208 100644
--- a/tests/zecsy.cpp
+++ b/tests/zecsy.cpp
@@ -2,7 +2,7 @@
 #define CATCH_CONFIG_MAIN
 #include <catch2/catch_all.hpp>
 
-#define MAX_ZECSY_ENTITIES 4
+//#define MAX_ZECSY_ENTITIES 4
 #include "../zecsy.hpp"
 
 using namespace zecsy;
@@ -45,8 +45,50 @@ TEST_CASE("World should throw on id overflow")
 
     for(int i = 0; i < MAX_ZECSY_ENTITIES; ++i)
     {
-        REQUIRE_NOTHROW(w.make_entity());
+        w.make_entity();
     }
 
     REQUIRE_THROWS(w.make_entity());
 }
+
+struct ChoosenOne
+{
+
+};
+
+TEST_CASE("Entity shouldn't have a component that wasn't attached to it")
+{
+    world w;
+
+    auto e = w.make_entity();
+
+    REQUIRE_FALSE(w.has<ChoosenOne>(e));
+    REQUIRE_FALSE(e.has<ChoosenOne>());
+}
+
+TEST_CASE("Attempt of getting non-owned component should throw")
+{
+    world w;
+
+    auto e = w.make_entity();
+
+    REQUIRE_THROWS(w.get<ChoosenOne>(e));
+    REQUIRE_THROWS(e.get<ChoosenOne>());
+}
+
+TEST_CASE("Attach a simple component to an entity and verify it is correctly associated")
+{
+    world w;
+
+    auto e1 = w.make_entity();
+    e1.set(ChoosenOne{});
+
+    REQUIRE(e1.has<ChoosenOne>());
+    REQUIRE(w.has<ChoosenOne>(e1));
+
+    auto e2 = w.make_entity();
+    w.set(e2, ChoosenOne{});
+
+    REQUIRE(e2.has<ChoosenOne>());
+    REQUIRE(w.has<ChoosenOne>(e2));
+}
diff --git a/zecsy.hpp b/zecsy.hpp
index 3ff0be3..7b5fe27 100644
--- a/zecsy.hpp
+++ b/zecsy.hpp
@@ -3,6 +3,9 @@
 #include <bitset>
 #include <format>
 #include <stdexcept>
+#include <typeindex>
+#include <unordered_map>
+#include <new>
 
 #ifndef MAX_ZECSY_ENTITIES
     #define MAX_ZECSY_ENTITIES 65536
@@ -26,11 +29,49 @@ namespace zecsy
         operator entity_id() const;
 
         bool is_alive() const;
+
+        template<typename T>
+        bool has() const;
+
+        template<typename T>
+        T& get();
+
+        template<typename T>
+        void set(const T& comp = T{});
     private:
         entity_id id = 0;
         class world* w = nullptr;
     };
 
+    using zecsy_bits = std::bitset<MAX_ZECSY_ENTITIES + 1>;
+
+    class component_storage
+    {
+    public:
+        template<typename T>
+        bool has(entity_id e) const;
+
+        template<typename T>
+        T& get(entity_id e);
+
+        template<typename T>
+        void set(entity_id e, const T& comp = T{});
+    private:
+        using comp_index = std::type_index;
+        using comp_to_bitset = std::unordered_map<comp_index, zecsy_bits>;
+        using entity_to_index = std::unordered_map<entity_id, size_t>;
+
+        using comp_to_entity_dict = std::unordered_map<comp_index, 
+              entity_to_index>;
+        
+        using comp_to_storage = std::unordered_map<comp_index, 
+              std::vector<uint8_t>>;
+
+        comp_to_bitset bitset_dict;
+        comp_to_entity_dict entity_dict; 
+        comp_to_storage storage_dict;
+    };
+
     class world final
     {
     public:
@@ -43,9 +84,19 @@ namespace zecsy
         entity make_entity();
         void destroy_entity(entity_id e);
         bool is_alive(entity_id e) const; 
+
+        template<typename T>
+        bool has(entity_id e) const;
+
+        template<typename T>
+        T& get(entity_id e);
+
+        template<typename T>
+        void set(entity_id e, const T& comp = T{});
     private:
-        std::bitset<MAX_ZECSY_ENTITIES + 1> entities_bitset;
+        zecsy_bits entities_bitset;
         entity_id entity_counter = 0;
+        component_storage storage;
     };
 
     inline entity::entity(class world* w, entity_id id): w(w), id(id)
@@ -86,4 +137,82 @@ namespace zecsy
     {
         return entities_bitset.test(e);
     }
+
+    template<typename T>
+    inline bool world::has(entity_id e) const
+    {
+        return storage.has<T>(e);
+    }
+
+    template<typename T>
+    inline bool component_storage::has(entity_id e) const
+    {
+        if(bitset_dict.contains(typeid(T)))
+        {
+            return bitset_dict.at(typeid(T)).test(e);
+        }
+        return false;
+    }
+
+    template<typename T>
+    inline T& component_storage::get(entity_id e)
+    {
+        if(!has<T>(e))
+        {
+            throw std::runtime_error(std::format("Entity #{} doesn't have {}",
+                        e, typeid(T).name()));
+        }
+
+        auto index = entity_dict[typeid(T)].at(e);
+        
+        auto* ptr = reinterpret_cast<T*>(&storage_dict[typeid(T)][0]);
+        ptr += index;
+
+        return *ptr;
+    }
+
+    template<typename T>
+    inline bool entity::has() const
+    {
+        return w->has<T>(id);    
+    }
+
+    template<typename T>
+    inline T& world::get(entity_id e)
+    {
+        return storage.get<T>(e);
+    }
+
+    template<typename T>
+    inline T& entity::get()
+    {
+        return w->get<T>(id);
+    }
+
+    template<typename T>
+    inline void component_storage::set(entity_id id, const T& comp)
+    {
+        bitset_dict[typeid(T)].set(id);
+
+        auto& storage = storage_dict[typeid(T)];
+
+        size_t T_size = sizeof(T);
+        size_t old_size = storage.size();
+
+        storage.resize(old_size + T_size);
+        void* ptr = &storage[0] + old_size;
+        new(ptr) T(comp);
+    }
+
+    template<typename T>
+    inline void world::set(entity_id e, const T& comp)
+    {
+        storage.set(e, comp);
+    }
+
+    template<typename T>
+    inline void entity::set(const T& comp)
+    {
+        w->set(id, comp);
+    }
 };