entity per world

Game/Entity/Entity.cpp

@@ -21,6 +21,48 @@ internal void serialize(Archive& ar, uint16 /*version*/, Entity& entity)
     SERIALIZE(ar, position, entity.position);
 }
 
+String format_entity_id(NonNullPtr<Arena> arena, EntityID entity_id)
+{
+    // Format:
+    // U = UserID
+    // LC = Local Entity Counter
+    // UU_LCLCLCLCLCLCLC
+    uint8  user_id = get_user_id(entity_id);
+    uint64 counter = get_local_counter(entity_id);
+
+    constexpr size_t kBufferSize = 18;
+    char*            buffer      = ArenaPushArray<char>(arena, kBufferSize);
+    Assert(buffer);
+
+    juliet_snprintf(buffer, kBufferSize, "%02X_%014llX", (unsigned int)user_id, counter);
+    return { buffer, kBufferSize - 1 };
+}
+
+bool parse_entity_id(String str, EntityID& out_id)
+{
+    bool result = false;
+    out_id      = kInvalid_entity_id;
+
+    if (!(str.Size != 17 || str.Str == nullptr || str.Str[2] != '_'))
+    {
+        char  user_hex[3]{ str.Str[0], str.Str[1], '\0' };
+        char* end     = user_hex;
+        uint8 user_id = strtoul(user_hex, &end, 16);
+        if (end != user_hex && user_id != kInvalid_user_id)
+        {
+            char* counter_hex = str.Str + 3;
+            end               = counter_hex;
+            uint64 counter    = strtoull(counter_hex, &end, 16);
+            if (end != counter_hex && counter < kEntityID_user_id_mask)
+            {
+                out_id = make_entity_id(user_id, counter);
+                result = true;
+            }
+        }
+    }
+    return result;
+}
+
 const Class* resolve_entity_class(uint8 kind, uint32 crc)
 {
     Assert(kind <= ENTITY(Count));

Game/Entity/Entity.h

@@ -30,6 +30,32 @@ concept EntityConcept = requires(EntityType entity) {
     requires std::same_as<decltype(entity.base), Entity*>;
 };
 
+inline constexpr EntityID make_entity_id(uint8 user_id, uint64 local_counter)
+{
+    Assert(user_id != kInvalid_user_id);
+    Assert((local_counter & kEntityID_user_id_mask) == kInvalid_entity_id);
+
+    EntityID result = kInvalid_user_id;
+    result          = ((EntityID)user_id << kEntityID_user_id_shift) | (local_counter & kEntityID_user_id_mask);
+    return result;
+}
+
+inline constexpr uint8 get_user_id(EntityID entity_id)
+{
+    return (((uint8)entity_id & kEntityID_user_id_mask) << kEntityID_user_id_shift);
+}
+
+inline constexpr uint64 get_local_counter(EntityID entity_id)
+{
+    return (uint64)entity_id & kEntityID_user_id_mask;
+}
+
+inline constexpr bool is_entity_id_valid(EntityID entity_id)
+{
+    bool result = entity_id != kInvalid_entity_id;
+    return result;
+}
+
 template <typename EntityType>
     requires EntityConcept<EntityType>
 [[nodiscard]] bool IsA(const Entity* entity)
@@ -66,6 +92,12 @@ template <typename EntityType>
 
 void serialize(Archive& ar, NonNullPtr<Entity> entity);
 
+JULIET_API uint8 get_local_user_id();
+
+JULIET_API String format_entity_id(NonNullPtr<Arena> arena, EntityID id);
+
+JULIET_API bool parse_entity_id(String str, EntityID& outId);
+
 [[nodiscard]] const Class* find_class_by_name(String name);
 
 [[nodiscard]] const Class* resolve_entity_class(uint8 kind, uint32 crc);

Game/Entity/EntityManager.cpp

@@ -7,6 +7,7 @@
 #include <Entity/entity_types.h>
 #include <game.h>
 #include <Graphics/MeshRenderer.h>
+#include "Engine/user.h"
 
 EntityID EntityManager::ID = 0;
 
@@ -45,6 +46,17 @@ EntityManager& GetEntityManager()
     return *entityManager;
 }
 
+EntityID generate_next_entity_id(EntityManager& manager)
+{
+    UserID user = get_local_user_id();
+    Assert(user != kInvalid_user_id);
+    Assert(manager.next_local_counter != kEntityID_user_id_mask);
+
+    EntityID new_id = make_entity_id(user, manager.next_local_counter);
+    manager.next_local_counter += 1ULL;
+    return new_id;
+}
+
 EntityTemplate* RegisterEntity(EntityManager& manager, Entity* base, DerivedType entity)
 {
     base->ID      = EntityManager::ID++;
@@ -143,3 +155,16 @@ Entity* deserialize_entity(Archive& ar, EntityManager& manager)
 
     return entity_base;
 }
+
+void update_local_counter(EntityManager& manager, EntityID entity_id)
+{
+    uint8 user_id = get_local_user_id();
+    if (get_user_id(entity_id) == user_id)
+    {
+        uint64 counter = get_local_counter(entity_id);
+        if (counter >= manager.next_local_counter)
+        {
+            manager.next_local_counter = counter + 1ULL;
+        }
+    }
+}

Game/Entity/EntityManager.h

@@ -18,6 +18,7 @@ struct typed_entity_array
 struct EntityManager
 {
     static EntityID ID;
+    uint64          next_local_counter = 1ULL;
 
     // TODO: Should be a pool
     VectorArena<Entity, 100'000> Entities;
@@ -31,4 +32,5 @@ EntityManager&        GetEntityManager();
 EntityTemplate*       RegisterEntity(EntityManager& manager, Entity* base, DerivedType entity);
 [[nodiscard]] Entity* allocate_entity(EntityManager& manager, NonNullPtr<const Class> derived_type_class);
 void                  UpdateEntityManager(EntityManager& manager);
-[[nodisacrd]] Entity* deserialize_entity(Archive& archive, EntityManager& manager);
+[[nodiscard]] Entity* deserialize_entity(Archive& archive, EntityManager& manager);
+void                  update_local_counter(EntityManager& manager, EntityID entity_id);

Game/Entity/entity_common.h

@@ -7,6 +7,12 @@ struct Class;
 using DerivedType = void*;
 using EntityID    = uint64_t;
 
+constexpr uint8 kInvalid_user_id = 0U;
+constexpr EntityID kInvalid_entity_id = 0ULL;
+
+constexpr EntityID kEntityID_user_id_shift = 56ULL;
+constexpr EntityID kEntityID_user_id_mask = 0xFF00'0000'0000'0000ULL;
+
 // clang-format off
 #define ENTITY_TYPE_LIST(X) X(Inert),
 

Juliet/include/Core/HAL/Filesystem/Filesystem.h

@@ -1,4 +1,4 @@
-#pragma once
+#pragma once
 
 #include <Core/Common/String.h>
 
@@ -33,3 +33,10 @@ JULIET_API Path fs_create_clean_path(NonNullPtr<Arena> arena, String path);
 JULIET_API bool fs_create_directory(String path, bool recursive);
 
 JULIET_API bool fs_path_exists(String path);
+
+JULIET_API bool fs_move_file(Path old_path, Path new_path);
+
+JULIET_API bool fs_delete_file(String path);
+
+using fs_iterate_director_callback = void (*)(Path path, bool is_director, void* user_payload);
+JULIET_API void fs_iterate_directory(Path directory_path, String extension, void* user_payload, fs_iterate_director_callback callback);

Juliet/include/Core/HAL/IO/IOStream.h

@@ -3,6 +3,7 @@
 #include <Core/Common/NonNullPtr.h>
 #include <Core/Common/String.h>
 #include <Juliet.h>
+#include "Core/HAL/Filesystem/Filesystem.h"
 
 // Opaque type
 struct IOStream;
@@ -52,15 +53,17 @@ extern JULIET_API IOStream* IOFromInterface(NonNullPtr<Arena> arena, NonNullPtr<
                                             NonNullPtr<IOStreamDataPayload> payload);
 
 // Write formatted string into the stream.
-extern JULIET_API size_t IOPrintf(NonNullPtr<IOStream> stream, _Printf_format_string_ const char* format, ...);
-extern JULIET_API size_t IOWrite(NonNullPtr<IOStream> stream, ByteBuffer inBuffer);
+JULIET_API size_t IOPrintf(NonNullPtr<IOStream> stream, _Printf_format_string_ const char* format, ...);
+JULIET_API size_t IOWrite(NonNullPtr<IOStream> stream, ByteBuffer inBuffer);
 
-extern JULIET_API size_t IORead(NonNullPtr<IOStream> stream, void* ptr, size_t size);
-extern JULIET_API int64  IOSeek(NonNullPtr<IOStream> stream, int64 offset, IOStreamSeekPivot pivot);
+JULIET_API size_t IORead(NonNullPtr<IOStream> stream, void* ptr, size_t size);
+JULIET_API int64  IOSeek(NonNullPtr<IOStream> stream, int64 offset, IOStreamSeekPivot pivot);
 
-extern JULIET_API int64 IOSize(NonNullPtr<IOStream> stream);
+JULIET_API int64 IOSize(NonNullPtr<IOStream> stream);
 
-extern JULIET_API ByteBuffer LoadFile(NonNullPtr<Arena> arena, String filename);
-extern JULIET_API ByteBuffer LoadFile(NonNullPtr<Arena> arena, NonNullPtr<IOStream> stream, bool closeStreamWhenDone);
+JULIET_API ByteBuffer LoadFile(NonNullPtr<Arena> arena, String filename);
+JULIET_API ByteBuffer LoadFile(NonNullPtr<Arena> arena, NonNullPtr<IOStream> stream, bool closeStreamWhenDone);
 
-extern JULIET_API bool IOClose(NonNullPtr<IOStream> stream);
+JULIET_API size_t IO_atomic_file_write(Path filepath, ByteBuffer file_content);
+
+JULIET_API bool IOClose(NonNullPtr<IOStream> stream);

Juliet/include/Engine/user.h

@@ -5,4 +5,4 @@ using UserID = uint8;
 void initialize_user_system();
 void shutdown_user_system();
 
-uint8 get_local_user_id();
+JULIET_API uint8 get_local_user_id();

Juliet/src/Core/HAL/Filesystem/Filesystem.cpp

@@ -1,4 +1,4 @@
-#include <Core/Common/CoreUtils.h>
+#include <Core/Common/CoreUtils.h>
 #include <Core/Common/String.h>
 #include <Core/HAL/Filesystem/Filesystem.h>
 #include <Core/HAL/Filesystem/Filesystem_Platform.h>
@@ -106,6 +106,27 @@ bool fs_path_exists(String path)
     return Platform::fs_path_exists(path);
 }
 
+bool fs_move_file(Path old_path, Path new_path)
+{
+    return Platform::fs_move_file(old_path, new_path);
+}
+
+bool fs_delete_file(String path)
+{
+    Assert(IsValid(path));
+    return Platform::fs_delete_file(path);
+}
+
+void fs_iterate_directory(Path directory_path, String extension, void* user_payload, fs_iterate_director_callback callback)
+{
+    Assert(IsValid(directory_path));
+    Assert(callback);
+
+    TempArena scratch = scratch_begin(nullptr, 0);
+
+    scratch_end(scratch);
+}
+
 void InitFilesystem(NonNullPtr<Arena> arena)
 {
     CachedBasePath = Platform::GetBasePath(arena);

Juliet/src/Core/HAL/Filesystem/Filesystem_Platform.h

@@ -1,4 +1,4 @@
-#pragma once
+#pragma once
 
 #include <Core/HAL/Filesystem/Filesystem.h>
 
@@ -9,4 +9,6 @@ namespace Platform
     Path fs_create_clean_path(NonNullPtr<Arena> arena, String path);
     bool fs_create_directory(String path, bool recursive);
     bool fs_path_exists(String path);
+    bool fs_move_file(Path old_path, Path new_path);
+    bool fs_delete_file(String path);
 } // namespace Platform

Juliet/src/Core/HAL/Filesystem/Win32/Win32Filesystem.cpp

@@ -1,4 +1,4 @@
-#include <Core/Common/String.h>
+#include <Core/Common/String.h>
 #include <Core/HAL/Filesystem/Filesystem_Platform.h>
 #include <Core/HAL/Win32.h>
 #include <Core/Logging/LogManager.h>
@@ -167,10 +167,9 @@ namespace Platform
             if (!create_result)
             {
                 const DWORD error = GetLastError();
-                if (error != ERROR_ALREADY_EXISTS)
+                if (error == ERROR_ALREADY_EXISTS)
                 {
                     LogDebug(LogCategory::Core, "Folder already exists");
-                    result = false;
                 }
                 else
                 {
@@ -191,4 +190,20 @@ namespace Platform
         const bool  result  = (attribs != INVALID_FILE_ATTRIBUTES);
         return result;
     }
+
+    bool fs_move_file(Path old_path, Path new_path)
+    {
+        bool result = MoveFileExA(CStr(old_path.FullPath), CStr(new_path.FullPath), MOVEFILE_REPLACE_EXISTING | MOVEFILE_WRITE_THROUGH);
+        return result;
+    }
+
+    bool fs_delete_file(String path)
+    {
+        if (!DeleteFileA(CStr(path)))
+        {
+            LogError(LogCategory::Core, "Failed to delete file %s. Error: %lu", CStr(path), GetLastError());
+            return false;
+        }
+        return true;
+    }
 } // namespace Platform

Juliet/src/Core/HAL/IO/IOStream.cpp

@@ -5,6 +5,7 @@
 #include <Core/Logging/LogManager.h>
 #include <Core/Logging/LogTypes.h>
 #include <Core/Thread/Thread.h>
+#include "Core/Thread/ThreadContext.h"
 
 IOStream* IOFromFile(NonNullPtr<Arena> arena, String filename, String mode)
 {
@@ -212,6 +213,51 @@ ByteBuffer LoadFile(NonNullPtr<Arena> arena, NonNullPtr<IOStream> stream, bool c
     return resultBuffer;
 }
 
+size_t IO_atomic_file_write(Path filepath, ByteBuffer file_content)
+{
+    size_t written_size = 0;
+
+    TempArena temp_arena = scratch_begin(nullptr, 0);
+
+    size_t temp_size = filepath.FullPath.Size + sizeof(".tmp");
+    char*  tmp_str   = (char*)ArenaPushSize(temp_arena.Arena, temp_size, 8, true JULIET_DEBUG_PARAM("Temp path"));
+    juliet_snprintf(tmp_str, temp_size, "%s.tmp", CStr(filepath.FullPath));
+    Path temp_path = fs_create_clean_path(temp_arena.Arena, WrapString(tmp_str));
+
+    if (IOStream* temp_stream = IOFromFile(temp_arena.Arena, temp_path.FullPath, ConstString("w+")))
+    {
+        written_size = IOWrite(temp_stream, file_content);
+        bool closed  = IOClose(temp_stream);
+        if (closed && written_size == file_content.Size)
+        {
+            if (!fs_move_file(temp_path, filepath))
+            {
+                LogError(LogCategory::Core, "IO_atomic_file_write [%s] failed to move from temp to final file. Aborting",
+                         CStr(filepath.FullPath));
+                written_size = 0;
+            }
+        }
+        else
+        {
+            LogError(LogCategory::Core, "IO_atomic_file_write [%s] failed to write into temporary file. Aborting",
+                     CStr(filepath.FullPath));
+        }
+
+        if (written_size == 0)
+        {
+            fs_delete_file(temp_path.FullPath);
+        }
+    }
+    else
+    {
+        LogError(LogCategory::Core, "IO_atomic_file_write [%s] failed creating temporary file. Aborting", CStr(filepath.FullPath));
+    }
+
+    scratch_end(temp_arena);
+
+    return written_size;
+}
+
 bool IOClose(NonNullPtr<IOStream> stream)
 {
     bool result = true;

Juliet/src/Engine/Engine.cpp

@@ -1,4 +1,4 @@
-#include <Engine/Engine.h>
+#include <Engine/Engine.h>
 
 #include <Core/Common/CoreUtils.h>
 #include <Core/HAL/Event/SystemEvent.h>
@@ -154,12 +154,12 @@ void InitializeEngine(JulietInit_Flags flags)
 
     InitializeLogManager();
 
+    InitFilesystem(EngineInstance.PlatformArena);
+
 #if JULIET_DEBUG
     UnitTest::RunUnitTests();
 #endif
 
-    InitFilesystem(EngineInstance.PlatformArena);
-
     initialize_user_system();
 
     JulietInit(flags);

Juliet/src/UnitTest/RunUnitTests.cpp

@@ -12,6 +12,7 @@ namespace UnitTest
     void TestMemoryArena();
     void SerializationUnitTest();
     void os_unit_test();
+    void iostream_unit_test();
 
     void RunUnitTests()
     {
@@ -21,6 +22,7 @@ namespace UnitTest
         TestMemoryArena();
         VectorUnitTest();
         SerializationUnitTest();
+        iostream_unit_test();
 
         LogMessage(LogCategory::Core, "Unit Tests Completed Successfully.");
     }

Juliet/src/UnitTest/iostream_test.cpp

@@ -0,0 +1,472 @@
+#if JULIET_DEBUG
+
+#include <Core/Common/CoreUtils.h>
+#include <Core/Common/String.h>
+#include <Core/HAL/Filesystem/Filesystem.h>
+#include <Core/HAL/IO/IOStream.h>
+#include <Core/Logging/LogManager.h>
+#include <Core/Logging/LogTypes.h>
+#include <Core/Memory/MemoryArena.h>
+#include <Core/Memory/Utils.h>
+#include <Core/Thread/ThreadContext.h>
+
+namespace UnitTest
+{
+    struct IOStreamTestMemoryPayload : IOStreamDataPayload
+    {
+        Byte*  data;
+        size_t capacity;
+        size_t size;
+        size_t position;
+        bool   is_closed;
+    };
+
+    internal IOStreamTestMemoryPayload* iostream_test_get_payload(NonNullPtr<IOStreamDataPayload> payload)
+    {
+        return static_cast<IOStreamTestMemoryPayload*>(payload.Get());
+    }
+
+    internal int64 iostream_test_mem_size(NonNullPtr<IOStreamDataPayload> payload)
+    {
+        return static_cast<int64>(iostream_test_get_payload(payload)->size);
+    }
+
+    internal int64 iostream_test_mem_seek(NonNullPtr<IOStreamDataPayload> payload, int64 offset, IOStreamSeekPivot pivot)
+    {
+        auto* memory = iostream_test_get_payload(payload);
+
+        int64 base = 0;
+        switch (pivot)
+        {
+            case IOStreamSeekPivot::Begin: base = 0; break;
+            case IOStreamSeekPivot::Current: base = static_cast<int64>(memory->position); break;
+            case IOStreamSeekPivot::End: base = static_cast<int64>(memory->size); break;
+            case IOStreamSeekPivot::Count: return -1;
+        }
+
+        int64 new_position = base + offset;
+        if ((new_position < 0) || (new_position > static_cast<int64>(memory->size)))
+        {
+            return -1;
+        }
+
+        memory->position = static_cast<size_t>(new_position);
+        return new_position;
+    }
+
+    internal size_t iostream_test_mem_read(NonNullPtr<IOStreamDataPayload> payload, void* out_buffer, size_t size,
+                                           NonNullPtr<IOStreamStatus> /*status*/)
+    {
+        Assert(out_buffer != nullptr);
+
+        auto*  memory     = iostream_test_get_payload(payload);
+        size_t bytes_left = memory->size - memory->position;
+        size_t to_read    = Min(size, bytes_left);
+        MemCopy(out_buffer, memory->data + memory->position, to_read);
+        memory->position += to_read;
+        return to_read;
+    }
+
+    internal size_t iostream_test_mem_write(NonNullPtr<IOStreamDataPayload> payload, ByteBuffer in_buffer,
+                                            NonNullPtr<IOStreamStatus> /*status*/)
+    {
+        Assert(IsValid(in_buffer));
+
+        auto*  memory     = iostream_test_get_payload(payload);
+        size_t space_left = memory->capacity - memory->position;
+        size_t to_write   = Min(in_buffer.Size, space_left);
+        MemCopy(memory->data + memory->position, in_buffer.Data, to_write);
+        memory->position += to_write;
+        memory->size = Max(memory->size, memory->position);
+        return to_write;
+    }
+
+    internal bool iostream_test_mem_flush(NonNullPtr<IOStreamDataPayload> /*payload*/, NonNullPtr<IOStreamStatus> /*status*/)
+    {
+        return true;
+    }
+
+    internal bool iostream_test_mem_close(NonNullPtr<IOStreamDataPayload> payload)
+    {
+        iostream_test_get_payload(payload)->is_closed = true;
+        return true;
+    }
+
+    internal IOStreamInterface iostream_test_make_full_interface()
+    {
+        IOStreamInterface stream_interface = {};
+        stream_interface.Version           = sizeof(IOStreamInterface);
+        stream_interface.Size              = iostream_test_mem_size;
+        stream_interface.Seek              = iostream_test_mem_seek;
+        stream_interface.Read              = iostream_test_mem_read;
+        stream_interface.Write             = iostream_test_mem_write;
+        stream_interface.Flush             = iostream_test_mem_flush;
+        stream_interface.Close             = iostream_test_mem_close;
+        return stream_interface;
+    }
+
+    internal IOStreamTestMemoryPayload iostream_test_make_payload(NonNullPtr<Arena> arena, size_t capacity)
+    {
+        Assert(capacity > 0);
+
+        IOStreamTestMemoryPayload payload = {};
+        payload.data                      = ArenaPushArray<Byte>(arena, capacity);
+        payload.capacity                  = capacity;
+        Assert(payload.data != nullptr);
+        return payload;
+    }
+
+    internal ByteBuffer iostream_test_buffer_from_string(String str)
+    {
+        Assert(IsValid(str));
+        return { .Data = reinterpret_cast<Byte*>(str.Str), .Size = str.Size };
+    }
+
+    internal bool iostream_test_buffer_equals(ByteBuffer buffer, String expected)
+    {
+        return (buffer.Size == expected.Size) && (MemCompare(buffer.Data, expected.Str, expected.Size) == 0);
+    }
+
+    internal String iostream_test_append_suffix(NonNullPtr<Arena> arena, String str, String suffix)
+    {
+        Assert(IsValid(str));
+        Assert(IsValid(suffix));
+
+        size_t total_size = str.Size + suffix.Size;
+        char*  buffer     = ArenaPushArray<char>(arena, total_size + 1);
+        Assert(buffer != nullptr);
+
+        MemCopy(buffer, str.Str, str.Size);
+        MemCopy(buffer + str.Size, suffix.Str, suffix.Size);
+        buffer[total_size] = '\0';
+        return { buffer, total_size };
+    }
+
+    internal void iostream_test_delete_file(String filename)
+    {
+        Assert(IsValid(filename));
+        if (fs_path_exists(filename))
+        {
+            Assert(fs_delete_file(filename));
+        }
+        Assert(!fs_path_exists(filename));
+    }
+
+    // Test files live in <repo>/Intermediate/UnitTest/ (exe is in <repo>/bin/x64-<Config>/)
+    internal Path iostream_test_make_path(NonNullPtr<Arena> arena, String filename)
+    {
+        Assert(IsValid(filename));
+
+        Path   base_path      = GetBasePath();
+        String raw_directory  = iostream_test_append_suffix(arena, base_path.Directories,
+                                                            ConstString("..\\..\\Intermediate\\UnitTest\\"));
+        Path   test_directory = fs_create_clean_path(arena, raw_directory);
+        Assert(IsValid(test_directory));
+
+        if (!fs_path_exists(test_directory.FullPath))
+        {
+            Assert(fs_create_directory(test_directory.FullPath, true));
+        }
+
+        Path file_path = fs_create_clean_path(arena, iostream_test_append_suffix(arena, test_directory.FullPath, filename));
+        Assert(IsValid(file_path));
+        return file_path;
+    }
+
+    internal void iostream_test_write_file(String filename, String mode, String content)
+    {
+        TempArena scratch = scratch_begin(nullptr, 0);
+
+        IOStream* stream = IOFromFile(scratch.Arena, filename, mode);
+        Assert(stream != nullptr);
+        Assert(IOWrite(stream, iostream_test_buffer_from_string(content)) == content.Size);
+        Assert(IOClose(stream));
+
+        scratch_end(scratch);
+    }
+
+    // IOFromInterface + IOWrite / IOPrintf / IOSize / IOSeek / IORead / IOClose on a full interface
+    internal void iostream_test_memory_stream()
+    {
+        TempArena scratch = scratch_begin(nullptr, 0);
+
+        IOStreamInterface         stream_interface = iostream_test_make_full_interface();
+        IOStreamTestMemoryPayload payload          = iostream_test_make_payload(scratch.Arena, 256);
+
+        IOStream* stream = IOFromInterface(scratch.Arena, &stream_interface, &payload);
+        Assert(stream != nullptr);
+
+        String hello = ConstString("Hello");
+        Assert(IOWrite(stream, iostream_test_buffer_from_string(hello)) == hello.Size);
+        Assert(IOWrite(stream, {}) == 0);
+        Assert(IOPrintf(stream, " %s %d", "World", 42) == 9);
+
+        String expected = ConstString("Hello World 42");
+        Assert(IOSize(stream) == static_cast<int64>(expected.Size));
+
+        Assert(IOSeek(stream, 0, IOStreamSeekPivot::Begin) == 0);
+        char read_buffer[64] = {};
+        Assert(IORead(stream, read_buffer, expected.Size) == expected.Size);
+        Assert(MemCompare(read_buffer, expected.Str, expected.Size) == 0);
+
+        Assert(IORead(stream, read_buffer, sizeof(read_buffer)) == 0);
+        Assert(IORead(stream, read_buffer, 0) == 0);
+
+        Assert(IOSeek(stream, -2, IOStreamSeekPivot::End) == static_cast<int64>(expected.Size - 2));
+        Assert(IORead(stream, read_buffer, 2) == 2);
+        Assert(MemCompare(read_buffer, "42", 2) == 0);
+
+        Assert(IOSeek(stream, -8, IOStreamSeekPivot::Current) == 6);
+        Assert(IORead(stream, read_buffer, 5) == 5);
+        Assert(MemCompare(read_buffer, "World", 5) == 0);
+
+        Assert(!payload.is_closed);
+        Assert(IOClose(stream));
+        Assert(payload.is_closed);
+
+        scratch_end(scratch);
+        LogMessage(LogCategory::Core, "iostream_test_memory_stream passed.");
+    }
+
+    // Behavior when the interface is missing some functions
+    internal void iostream_test_capability_fallbacks()
+    {
+        TempArena scratch = scratch_begin(nullptr, 0);
+
+        String content = ConstString("Hello World 42");
+
+        // Read only, no seek, no size, no close
+        {
+            IOStreamInterface read_only_interface = {};
+            read_only_interface.Version           = sizeof(IOStreamInterface);
+            read_only_interface.Read              = iostream_test_mem_read;
+
+            IOStreamTestMemoryPayload payload = iostream_test_make_payload(scratch.Arena, 64);
+            MemCopy(payload.data, content.Str, content.Size);
+            payload.size = content.Size;
+
+            IOStream* stream = IOFromInterface(scratch.Arena, &read_only_interface, &payload);
+            Assert(stream != nullptr);
+
+            Assert(IOWrite(stream, iostream_test_buffer_from_string(content)) == 0);
+            Assert(IOSeek(stream, 0, IOStreamSeekPivot::Begin) == -1);
+            Assert(IOSize(stream) == -1);
+
+            char read_buffer[64] = {};
+            Assert(IORead(stream, read_buffer, content.Size) == content.Size);
+            Assert(MemCompare(read_buffer, content.Str, content.Size) == 0);
+
+            Assert(IOClose(stream));
+            Assert(!payload.is_closed);
+        }
+
+        // Write only
+        {
+            IOStreamInterface write_only_interface = {};
+            write_only_interface.Version           = sizeof(IOStreamInterface);
+            write_only_interface.Write             = iostream_test_mem_write;
+
+            IOStreamTestMemoryPayload payload = iostream_test_make_payload(scratch.Arena, 64);
+
+            IOStream* stream = IOFromInterface(scratch.Arena, &write_only_interface, &payload);
+            Assert(stream != nullptr);
+
+            Assert(IOWrite(stream, iostream_test_buffer_from_string(content)) == content.Size);
+
+            char read_buffer[64] = {};
+            Assert(IORead(stream, read_buffer, content.Size) == 0);
+            Assert(IOClose(stream));
+        }
+
+        // No Size function: IOSize falls back on Seek and restores the position
+        {
+            IOStreamInterface seek_interface = iostream_test_make_full_interface();
+            seek_interface.Size              = nullptr;
+
+            IOStreamTestMemoryPayload payload = iostream_test_make_payload(scratch.Arena, 64);
+            MemCopy(payload.data, content.Str, content.Size);
+            payload.size = content.Size;
+
+            IOStream* stream = IOFromInterface(scratch.Arena, &seek_interface, &payload);
+            Assert(stream != nullptr);
+
+            Assert(IOSeek(stream, 3, IOStreamSeekPivot::Begin) == 3);
+            Assert(IOSize(stream) == static_cast<int64>(content.Size));
+            Assert(IOSeek(stream, 0, IOStreamSeekPivot::Current) == 3);
+            Assert(IOClose(stream));
+        }
+
+        scratch_end(scratch);
+        LogMessage(LogCategory::Core, "iostream_test_capability_fallbacks passed.");
+    }
+
+    // LoadFile(arena, stream, closeStreamWhenDone) with known size and chunked fallback
+    internal void iostream_test_load_file_from_stream()
+    {
+        TempArena scratch = scratch_begin(nullptr, 0);
+
+        String content = ConstString("Juliet LoadFile content");
+
+        // Known size, stream closed when done
+        {
+            IOStreamInterface         stream_interface = iostream_test_make_full_interface();
+            IOStreamTestMemoryPayload payload          = iostream_test_make_payload(scratch.Arena, 64);
+            MemCopy(payload.data, content.Str, content.Size);
+            payload.size = content.Size;
+
+            IOStream* stream = IOFromInterface(scratch.Arena, &stream_interface, &payload);
+            Assert(stream != nullptr);
+
+            ByteBuffer loaded = LoadFile(scratch.Arena, stream, true);
+            Assert(iostream_test_buffer_equals(loaded, content));
+            Assert(loaded.Data[loaded.Size] == Byte{ 0 });
+            Assert(payload.is_closed);
+        }
+
+        // Known size, stream kept open
+        {
+            IOStreamInterface         stream_interface = iostream_test_make_full_interface();
+            IOStreamTestMemoryPayload payload          = iostream_test_make_payload(scratch.Arena, 64);
+            MemCopy(payload.data, content.Str, content.Size);
+            payload.size = content.Size;
+
+            IOStream* stream = IOFromInterface(scratch.Arena, &stream_interface, &payload);
+            Assert(stream != nullptr);
+
+            ByteBuffer loaded = LoadFile(scratch.Arena, stream, false);
+            Assert(iostream_test_buffer_equals(loaded, content));
+            Assert(!payload.is_closed);
+            Assert(IOClose(stream));
+        }
+
+        // Unknown size (no Size / Seek): loaded chunk by chunk, bigger than one chunk
+        {
+            constexpr size_t k_big_content_size = 3000;
+
+            IOStreamInterface stream_interface = iostream_test_make_full_interface();
+            stream_interface.Size              = nullptr;
+            stream_interface.Seek              = nullptr;
+
+            IOStreamTestMemoryPayload payload = iostream_test_make_payload(scratch.Arena, k_big_content_size);
+            for (size_t index = 0; index < k_big_content_size; ++index)
+            {
+                payload.data[index] = static_cast<Byte>('a' + (index % 26));
+            }
+            payload.size = k_big_content_size;
+
+            IOStream* stream = IOFromInterface(scratch.Arena, &stream_interface, &payload);
+            Assert(stream != nullptr);
+
+            ByteBuffer loaded = LoadFile(scratch.Arena, stream, true);
+            Assert(loaded.Size == k_big_content_size);
+            Assert(MemCompare(loaded.Data, payload.data, k_big_content_size) == 0);
+            Assert(loaded.Data[loaded.Size] == Byte{ 0 });
+            Assert(payload.is_closed);
+        }
+
+        scratch_end(scratch);
+        LogMessage(LogCategory::Core, "iostream_test_load_file_from_stream passed.");
+    }
+
+    // IOFromFile + LoadFile(arena, filename) on a real file
+    internal void iostream_test_file_stream()
+    {
+        TempArena scratch = scratch_begin(nullptr, 0);
+
+        Path file_path = iostream_test_make_path(scratch.Arena, ConstString("juliet_iostream_unit_test.bin"));
+        Assert(IsValid(file_path));
+        iostream_test_delete_file(file_path.FullPath);
+
+        Assert(IOFromFile(scratch.Arena, {}, ConstString("rb")) == nullptr);
+        Assert(IOFromFile(scratch.Arena, file_path.FullPath, {}) == nullptr);
+        Assert(IOFromFile(scratch.Arena, file_path.FullPath, ConstString("rb")) == nullptr);
+
+        String first_part  = ConstString("First part.");
+        String second_part = ConstString(" Second part.");
+        String full        = ConstString("First part. Second part.");
+
+        iostream_test_write_file(file_path.FullPath, ConstString("wb"), first_part);
+        Assert(fs_path_exists(file_path.FullPath));
+        Assert(iostream_test_buffer_equals(LoadFile(scratch.Arena, file_path.FullPath), first_part));
+
+        iostream_test_write_file(file_path.FullPath, ConstString("ab"), second_part);
+        Assert(iostream_test_buffer_equals(LoadFile(scratch.Arena, file_path.FullPath), full));
+
+        // Seek / Size / partial read on a file stream
+        {
+            IOStream* stream = IOFromFile(scratch.Arena, file_path.FullPath, ConstString("rb"));
+            Assert(stream != nullptr);
+            Assert(IOSize(stream) == static_cast<int64>(full.Size));
+            Assert(IOSeek(stream, static_cast<int64>(first_part.Size), IOStreamSeekPivot::Begin) ==
+                   static_cast<int64>(first_part.Size));
+
+            char read_buffer[64] = {};
+            Assert(IORead(stream, read_buffer, second_part.Size) == second_part.Size);
+            Assert(MemCompare(read_buffer, second_part.Str, second_part.Size) == 0);
+            Assert(IORead(stream, read_buffer, sizeof(read_buffer)) == 0);
+            Assert(IOWrite(stream, iostream_test_buffer_from_string(first_part)) == 0);
+            Assert(IOClose(stream));
+        }
+
+        // "w" truncates
+        iostream_test_write_file(file_path.FullPath, ConstString("wb"), second_part);
+        Assert(iostream_test_buffer_equals(LoadFile(scratch.Arena, file_path.FullPath), second_part));
+
+        iostream_test_delete_file(file_path.FullPath);
+
+        scratch_end(scratch);
+        LogMessage(LogCategory::Core, "iostream_test_file_stream passed.");
+    }
+
+    // IO_atomic_file_write: writes to <file>.tmp then moves it to <file>
+    internal void iostream_test_atomic_file_write()
+    {
+        TempArena scratch = scratch_begin(nullptr, 0);
+
+        Path file_path = iostream_test_make_path(scratch.Arena, ConstString("juliet_iostream_atomic_unit_test.bin"));
+        Assert(IsValid(file_path));
+        String temp_filename = iostream_test_append_suffix(scratch.Arena, file_path.FullPath, ConstString(".tmp"));
+
+        iostream_test_delete_file(file_path.FullPath);
+        iostream_test_delete_file(temp_filename);
+
+        // Create a new file
+        String first_content = ConstString("Atomic content that is long enough");
+        Assert(IO_atomic_file_write(file_path, iostream_test_buffer_from_string(first_content)) == first_content.Size);
+        Assert(fs_path_exists(file_path.FullPath));
+        Assert(!fs_path_exists(temp_filename));
+        Assert(iostream_test_buffer_equals(LoadFile(scratch.Arena, file_path.FullPath), first_content));
+
+        // Replace an existing file with shorter content
+        String second_content = ConstString("Shorter");
+        Assert(IO_atomic_file_write(file_path, iostream_test_buffer_from_string(second_content)) == second_content.Size);
+        Assert(!fs_path_exists(temp_filename));
+        Assert(iostream_test_buffer_equals(LoadFile(scratch.Arena, file_path.FullPath), second_content));
+
+        // A leftover temp file from a previous crash must not break the write
+        iostream_test_write_file(temp_filename, ConstString("wb"), ConstString("Stale temp data"));
+        Assert(IO_atomic_file_write(file_path, iostream_test_buffer_from_string(first_content)) == first_content.Size);
+        Assert(!fs_path_exists(temp_filename));
+        Assert(iostream_test_buffer_equals(LoadFile(scratch.Arena, file_path.FullPath), first_content));
+
+        iostream_test_delete_file(file_path.FullPath);
+
+        scratch_end(scratch);
+        LogMessage(LogCategory::Core, "iostream_test_atomic_file_write passed.");
+    }
+
+    void iostream_unit_test()
+    {
+        LogMessage(LogCategory::Core, "=== Running IOStream Unit Tests ===");
+
+        iostream_test_memory_stream();
+        iostream_test_capability_fallbacks();
+        iostream_test_load_file_from_stream();
+        iostream_test_file_stream();
+        iostream_test_atomic_file_write();
+
+        LogMessage(LogCategory::Core, "=== All IOStream Unit Tests Passed Successfully ===");
+    }
+} // namespace UnitTest
+
+#endif