// Copyright 2014 Citra Emulator Project
// Licensed under GPLv2 or any later version
// Refer to the license.txt file included.

#include <utility>
#include "common/assert.h"
#include "common/logging/log.h"
#include "core/core.h"
#include "core/hle/kernel/errors.h"
#include "core/hle/kernel/handle_table.h"
#include "core/hle/kernel/process.h"
#include "core/hle/kernel/thread.h"

namespace Kernel {
namespace {
constexpr u16 GetSlot(Handle handle) {
    return static_cast<u16>(handle >> 15);
}

constexpr u16 GetGeneration(Handle handle) {
    return static_cast<u16>(handle & 0x7FFF);
}
} // Anonymous namespace

HandleTable::HandleTable() {
    next_generation = 1;
    Clear();
}

HandleTable::~HandleTable() = default;

ResultVal<Handle> HandleTable::Create(SharedPtr<Object> obj) {
    DEBUG_ASSERT(obj != nullptr);

    u16 slot = next_free_slot;
    if (slot >= generations.size()) {
        LOG_ERROR(Kernel, "Unable to allocate Handle, too many slots in use.");
        return ERR_HANDLE_TABLE_FULL;
    }
    next_free_slot = generations[slot];

    u16 generation = next_generation++;

    // Overflow count so it fits in the 15 bits dedicated to the generation in the handle.
    // Horizon OS uses zero to represent an invalid handle, so skip to 1.
    if (next_generation >= (1 << 15)) {
        next_generation = 1;
    }

    generations[slot] = generation;
    objects[slot] = std::move(obj);

    Handle handle = generation | (slot << 15);
    return MakeResult<Handle>(handle);
}

ResultVal<Handle> HandleTable::Duplicate(Handle handle) {
    SharedPtr<Object> object = GetGeneric(handle);
    if (object == nullptr) {
        LOG_ERROR(Kernel, "Tried to duplicate invalid handle: {:08X}", handle);
        return ERR_INVALID_HANDLE;
    }
    return Create(std::move(object));
}

ResultCode HandleTable::Close(Handle handle) {
    if (!IsValid(handle))
        return ERR_INVALID_HANDLE;

    u16 slot = GetSlot(handle);

    objects[slot] = nullptr;

    generations[slot] = next_free_slot;
    next_free_slot = slot;
    return RESULT_SUCCESS;
}

bool HandleTable::IsValid(Handle handle) const {
    std::size_t slot = GetSlot(handle);
    u16 generation = GetGeneration(handle);

    return slot < MAX_COUNT && objects[slot] != nullptr && generations[slot] == generation;
}

SharedPtr<Object> HandleTable::GetGeneric(Handle handle) const {
    if (handle == CurrentThread) {
        return GetCurrentThread();
    } else if (handle == CurrentProcess) {
        return Core::CurrentProcess();
    }

    if (!IsValid(handle)) {
        return nullptr;
    }
    return objects[GetSlot(handle)];
}

void HandleTable::Clear() {
    for (u16 i = 0; i < MAX_COUNT; ++i) {
        generations[i] = i + 1;
        objects[i] = nullptr;
    }
    next_free_slot = 0;
}

} // namespace Kernel