From 6bd041342aa4b0a769dc85e793002420dce4aa62 Mon Sep 17 00:00:00 2001
From: NukeBird <nukebird.dev@gmail.com>
Date: Thu, 20 Feb 2025 01:42:06 +0300
Subject: [PATCH] =?UTF-8?q?=F0=9F=93=A6Archetypes=F0=9F=93=A6?=
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---
 zecsy.hpp | 128 +++++++++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 113 insertions(+), 15 deletions(-)

diff --git a/zecsy.hpp b/zecsy.hpp
index 9f583e0..e7ec72b 100644
--- a/zecsy.hpp
+++ b/zecsy.hpp
@@ -1,4 +1,5 @@
 #pragma once
+#include <algorithm>
 #include <concepts>
 #include <cstdint>
 #include <cstdlib>
@@ -74,30 +75,60 @@ namespace zecsy
         struct component_pool
         {
             std::vector<uint8_t> data;
-            std::vector<size_t> free_list; // Reusable indices
+            std::vector<size_t> free_list;
             std::unordered_map<entity_id, size_t> entity_to_index;
             std::unordered_map<size_t, entity_id> index_to_entity;
         };
 
         std::unordered_map<comp_id, component_pool> pools;
 
-        template<typename T>
-        static comp_id get_component_id()
+        using archetype_signature = std::vector<comp_id>;
+        using entity_group = std::vector<entity_id>;
+
+        struct archetype_hash
         {
-            static comp_id id = next_component_id++;
-            return id;
-        }
+            size_t operator()(const archetype_signature& vec) const;
+        };
+
+        std::unordered_map<archetype_signature, entity_group, archetype_hash>
+            archetypes;
+
+        template<Component T>
+        static comp_id get_component_id();
 
         static comp_id next_component_id;
     };
 
+    inline size_t world::archetype_hash::operator()(
+        const world::archetype_signature& vec) const
+    {
+        size_t seed = vec.size();
+        for(const auto& id: vec)
+        {
+            seed ^= id + 0x9e3779b9 + (seed << 6) + (seed >> 2);
+        }
+        return seed;
+    }
+
+    template<Component T>
+    inline world::comp_id world::get_component_id()
+    {
+        static comp_id id = next_component_id++;
+        return id;
+    }
+
     inline world::comp_id world::next_component_id = 0;
 
     inline entity_id world::make_entity()
     {
         auto id = ++entity_counter;
         alive_entities.emplace(id);
-        // entity_to_comps[id] = {};
+        entity_to_comps[id] = {};
+
+        std::vector<comp_id> key;
+        auto& group = archetypes[key];
+        group.emplace_back(id);
+
         return id;
     }
 
@@ -105,7 +136,18 @@ namespace zecsy
     {
         alive_entities.erase(e);
 
-        for(comp_id id: entity_to_comps[e])
+        auto& comp_set = entity_to_comps[e];
+        std::vector<comp_id> key(comp_set.begin(), comp_set.end());
+
+        auto& group = archetypes[key];
+        group.erase(std::remove(group.begin(), group.end(), e), group.end());
+
+        if(archetypes[key].empty())
+        {
+            archetypes.erase(key);
+        }
+
+        for(comp_id id: comp_set)
         {
             auto& pool = pools[id];
             auto index = pool.entity_to_index[e];
@@ -169,7 +211,26 @@ namespace zecsy
         pool.entity_to_index[e] = index;
         pool.index_to_entity[index] = e;
 
-        entity_to_comps[e].emplace(id);
+        auto& comp_set = entity_to_comps[e];
+        std::set<comp_id> old_set = comp_set;
+        auto [it, inserted] = comp_set.insert(id);
+
+        if(inserted)
+        {
+            std::vector<comp_id> old_key(old_set.begin(), old_set.end());
+
+            auto& group = archetypes[old_key];
+            group.erase(std::remove(group.begin(), group.end(), e),
+                        group.end());
+
+            if(archetypes[old_key].empty())
+            {
+                archetypes.erase(old_key);
+            }
+
+            std::vector<comp_id> new_key(comp_set.begin(), comp_set.end());
+            archetypes[new_key].emplace_back(e);
+        }
     }
 
     template<Component T>
@@ -182,18 +243,38 @@ namespace zecsy
     inline void world::remove(entity_id e)
     {
         auto id = get_component_id<T>();
-        if(!has<T>(e))
+        auto& comp_set = entity_to_comps[e];
+
+        if(!comp_set.contains(id))
         {
             return;
         }
 
+        std::set<comp_id> old_set = comp_set;
+        size_t removed = comp_set.erase(id);
+
+        if(removed > 0)
+        {
+            std::vector<comp_id> old_key(old_set.begin(), old_set.end());
+
+            auto& group = archetypes[old_key];
+            group.erase(std::remove(group.begin(), group.end(), e),
+                        group.end());
+
+            if(archetypes[old_key].empty())
+            {
+                archetypes.erase(old_key);
+            }
+
+            std::vector<comp_id> new_key(comp_set.begin(), comp_set.end());
+            archetypes[new_key].emplace_back(e);
+        }
+
         auto& pool = pools[id];
         auto index = pool.entity_to_index[e];
-
         pool.free_list.push_back(index);
         pool.entity_to_index.erase(e);
         pool.index_to_entity.erase(index);
-        entity_to_comps[e].erase(id);
     }
 
     template<Component First, Component Second, Component... Rest>
@@ -230,11 +311,28 @@ namespace zecsy
     template<Component... T>
     inline void world::query(std::invocable<entity_id, T&...> auto&& system)
     {
-        for(auto e: alive_entities)
+        std::vector<comp_id> required = {get_component_id<T>()...};
+        std::sort(required.begin(), required.end());
+
+        for(const auto& [archetype_key, entities]: archetypes)
         {
-            if((has<T...>(e)))
+            bool match = true;
+            for(comp_id req_id: required)
             {
-                system(e, get<T>(e)...);
+                if(!std::binary_search(archetype_key.begin(),
+                                       archetype_key.end(), req_id))
+                {
+                    match = false;
+                    break;
+                }
+            }
+
+            if(match)
+            {
+                for(entity_id e: entities)
+                {
+                    system(e, get<T>(e)...);
+                }
             }
         }
     }