From 7d026497c7af244d4999380b749edaeb302e9f0f Mon Sep 17 00:00:00 2001
From: Steven Le Rouzic <steven.lerouzic@gmail.com>
Date: Tue, 17 Jun 2025 00:23:38 +0200
Subject: WIP: Add IndexPool

---
 asl/handle_pool/index_pool.hpp       | 111 ++++++++++++++++++++++++++++++++++-
 asl/handle_pool/index_pool_tests.cpp |   7 +++
 2 files changed, 117 insertions(+), 1 deletion(-)

diff --git a/asl/handle_pool/index_pool.hpp b/asl/handle_pool/index_pool.hpp
index 1d359d5..ece61c3 100644
--- a/asl/handle_pool/index_pool.hpp
+++ b/asl/handle_pool/index_pool.hpp
@@ -11,6 +11,7 @@ namespace asl
 {
 
 // @Todo Uniquely represented for the handle?
+// @Todo niche for handles
 
 template<
     int kIndexBits_,
@@ -27,6 +28,7 @@ struct index_pool_config
     using PrimitiveUserType = smallest_unsigned_integer_type_for_width<size_of<UserType> * 8>;
 
     static_assert(trivially_copy_constructible<UserType>);
+    static_assert(trivially_destructible<UserType>);
     static_assert(size_of<UserType> == size_of<PrimitiveUserType>, "UserType should be of size 1, 2 or 4");
 
     static constexpr int kUserBits = []() static -> int {
@@ -60,9 +62,10 @@ template<
 >
 class index_pool_handle
 {
-    // using config = index_pool_config<5, 5>;
+public:
     using config = index_pool_config<kIndexBits_, kGenBits_, UserType_, kUserBits_>;
 
+private:
     config::HandleType m_handle{};
 
 public:
@@ -116,5 +119,111 @@ public:
     constexpr bool operator==(this index_pool_handle self, index_pool_handle other) = default;
 };
 
+template<
+    int kIndexBits_,
+    int kGenBits_,
+    typename UserType_ = empty,
+    int kUserBits_ = 0,
+    typename Payload = empty,
+    allocator Allocator = DefaultAllocator
+>
+class IndexPool
+{
+public:
+    using handle = index_pool_handle<kIndexBits_, kGenBits_, UserType_, kUserBits_>;
+    
+private:
+    using config = handle::config;
+    
+    static constexpr bool kHasPayload = !same_as<Payload, empty>;
+
+    // @Todo Remove need for default constructible & trivially destructible for payload
+    // Use union in slot to store the variants
+
+    // @Todo Use dummy user type with inactive handle type -> no need to set user data when allocating handle
+
+    static_assert(default_constructible<Payload>);
+    static_assert(copy_constructible<Payload>);
+    static_assert(trivially_destructible<Payload>);
+
+    struct Slot
+    {
+        bool is_end_of_list : 1;
+        bool is_active      : 1;
+
+        handle handle;
+
+        ASL_NO_UNIQUE_ADDRESS Payload payload;
+    };
+
+    chunked_buffer<Slot, 256, Allocator> m_slots;
+
+    // We only use the index, this is essentially the head of the linked
+    // list to the first available slot.
+    // Then the index of each slot points to the next available one.
+    handle m_first_available;
+
+    static constexpr handle make_handle(uint64_t index, uint64_t gen, [[maybe_unused]] config::UserType user_data)
+    {
+        if constexpr (config::kHasUser)
+        {
+            return handle(index, gen, user_data);
+        }
+        else
+        {
+            return handle(index, gen);
+        }
+    };
+
+    void allocate_new_slot(config::UserType user)
+    {
+        // @Todo Check that we don't go past capacity.
+
+        const auto new_index = static_cast<uint64_t>(m_slots.size());
+        const handle new_handle = make_handle(new_index, 0, user);
+        
+        m_slots.push(Slot{
+            .is_end_of_list = true,
+            .is_active      = false,
+            .handle         = new_handle,
+            .payload        = Payload{}
+        });
+
+        m_first_available = new_handle;
+    }
+
+    handle acquire_handle(const Payload& payload, config::UserType user)
+    {
+        if (!m_first_available.is_valid())
+        {
+            allocate_new_slot(user);
+        }
+
+        ASL_ASSERT(m_first_available.is_valid());
+
+        auto index = static_cast<isize_t>(m_first_available.index());
+        
+        Slot& slot = m_slots[index];
+        ASL_ASSERT(!slot.is_active);
+
+        m_first_available = slot.is_end_of_line ? handle{} : slot.handle;
+
+        slot.is_active = true;
+        slot.payload   = payload;
+
+        return make_handle(index, slot.handle.gen(), user);
+    }
+
+public:
+    IndexPool() requires default_constructible<Allocator> = default;
+
+    explicit IndexPool(Allocator allocator) : m_slots{std::move(allocator)} {}
+
+    handle acquire(const Payload& payload)
+    {
+        return acquire_handle(payload);
+    }
+};
+
 } // namespace asl
 
diff --git a/asl/handle_pool/index_pool_tests.cpp b/asl/handle_pool/index_pool_tests.cpp
index 3156320..d690878 100644
--- a/asl/handle_pool/index_pool_tests.cpp
+++ b/asl/handle_pool/index_pool_tests.cpp
@@ -108,3 +108,10 @@ ASL_TEST(compare) // NOLINT
 
     ASL_TEST_EXPECT(idx4 != idx5);
 }
+
+ASL_TEST(pool)
+{
+    using Pool = asl::IndexPool<8, 8>;
+    Pool pool;
+    auto a = pool.acquire({});
+}
-- 
cgit