#include <XCEngine/Core/Asset/AsyncLoader.h>
#include <XCEngine/Core/Asset/ResourceManager.h>
#include <XCEngine/Core/Asset/ResourceTypes.h>
#include <XCEngine/Debug/Logger.h>

namespace XCEngine {
namespace Resources {

namespace {

std::string ToStdString(const Containers::String& value) {
    return std::string(value.CStr());
}

bool ShouldTraceAsyncPath(const Containers::String& path) {
    const std::string text = ToStdString(path);
    return text.rfind("builtin://", 0) == 0 ||
           text.find("backpack") != std::string::npos ||
           text.find("New Material.mat") != std::string::npos;
}

void TraceAsyncLoad(const Containers::String& message) {
    Debug::Logger::Get().Info(Debug::LogCategory::FileSystem, message);
}

} // namespace

Core::uint64 LoadRequest::GenerateRequestId() {
    static std::atomic<Core::uint64> s_requestId{0};
    return ++s_requestId;
}

AsyncLoader& AsyncLoader::Get() {
    static AsyncLoader instance;
    return instance;
}

void AsyncLoader::Initialize(Core::uint32 workerThreadCount) {
    if (m_running.exchange(true)) {
        return;
    }

    if (workerThreadCount == 0) {
        workerThreadCount = 1;
    }

    m_workerThreads.reserve(workerThreadCount);
    for (Core::uint32 index = 0; index < workerThreadCount; ++index) {
        m_workerThreads.emplace_back(&AsyncLoader::WorkerThread, this);
    }
}

void AsyncLoader::Shutdown() {
    {
        std::lock_guard<std::mutex> lock(m_queueMutex);
        m_running = false;
        m_pendingQueue.clear();
        m_pendingCount = 0;
    }
    m_pendingCondition.notify_all();

    for (std::thread& workerThread : m_workerThreads) {
        if (workerThread.joinable()) {
            workerThread.join();
        }
    }
    m_workerThreads.clear();

    {
        std::lock_guard<std::mutex> lock(m_completedMutex);
        m_completedQueue.clear();
    }

    m_completedCount = 0;
    m_totalRequested = 0;
}

void AsyncLoader::Submit(const Containers::String& path, ResourceType type,
                        std::function<void(LoadResult)> callback) {
    Submit(path, type, nullptr, std::move(callback));
}

void AsyncLoader::Submit(const Containers::String& path, ResourceType type, ImportSettings* settings,
                        std::function<void(LoadResult)> callback) {
    LoadRequest request(path, type, std::move(callback), settings);
    SubmitInternal(std::move(request));
}

void AsyncLoader::SubmitInternal(LoadRequest request) {
    IResourceLoader* loader = FindLoader(request.type);

    if (!loader) {
        if (request.callback) {
            LoadResult result(Containers::String("No loader for type: ") + 
                           GetResourceTypeName(request.type));
            request.callback(result);
        }
        return;
    }

    {
        std::lock_guard<std::mutex> lock(m_queueMutex);
        if (!m_running) {
            if (request.callback) {
                request.callback(LoadResult("Async loader is not initialized"));
            }
            return;
        }

        m_pendingQueue.emplace_back(std::move(request));
        ++m_pendingCount;
        ++m_totalRequested;

        const LoadRequest& queuedRequest = m_pendingQueue.back();
        if (ShouldTraceAsyncPath(queuedRequest.path)) {
            TraceAsyncLoad(
                Containers::String("[AsyncLoader] submit id=") +
                Containers::String(std::to_string(queuedRequest.requestId).c_str()) +
                " type=" +
                GetResourceTypeName(queuedRequest.type) +
                " path=" +
                queuedRequest.path +
                " pending=" +
                Containers::String(std::to_string(m_pendingCount.load()).c_str()));
        }
    }

    m_pendingCondition.notify_one();
}

void AsyncLoader::Update() {
    std::deque<CompletedLoadRequest> completed;

    {
        std::lock_guard<std::mutex> lock(m_completedMutex);
        completed.swap(m_completedQueue);
    }

    for (CompletedLoadRequest& entry : completed) {
        if (m_pendingCount > 0) {
            --m_pendingCount;
        }
        ++m_completedCount;

        if (ShouldTraceAsyncPath(entry.request.path)) {
            TraceAsyncLoad(
                Containers::String("[AsyncLoader] dispatch id=") +
                Containers::String(std::to_string(entry.request.requestId).c_str()) +
                " type=" +
                GetResourceTypeName(entry.request.type) +
                " path=" +
                entry.request.path +
                " success=" +
                Containers::String(entry.result && entry.result.resource != nullptr ? "1" : "0") +
                " pending=" +
                Containers::String(std::to_string(m_pendingCount.load()).c_str()) +
                (entry.result.errorMessage.Empty()
                    ? Containers::String()
                    : Containers::String(" error=") + entry.result.errorMessage));
        }

        if (entry.request.callback) {
            entry.request.callback(std::move(entry.result));
        }
    }
}

float AsyncLoader::GetProgress() const {
    const Core::uint64 totalRequested = m_totalRequested.load();
    if (totalRequested == 0) {
        return 1.0f;
    }

    return static_cast<float>(totalRequested - m_pendingCount.load()) /
           static_cast<float>(totalRequested);
}

void AsyncLoader::CancelAll() {
    std::lock_guard<std::mutex> lock(m_queueMutex);
    if (!m_pendingQueue.empty()) {
        const Core::uint32 queuedCount = static_cast<Core::uint32>(m_pendingQueue.size());
        m_pendingQueue.clear();
        if (m_pendingCount >= queuedCount) {
            m_pendingCount -= queuedCount;
        } else {
            m_pendingCount = 0;
        }
    }
}

void AsyncLoader::Cancel(Core::uint64 requestId) {
    std::lock_guard<std::mutex> lock(m_queueMutex);
    for (auto it = m_pendingQueue.begin(); it != m_pendingQueue.end(); ++it) {
        if (it->requestId == requestId) {
            m_pendingQueue.erase(it);
            if (m_pendingCount > 0) {
                --m_pendingCount;
            }
            return;
        }
    }
}

IResourceLoader* AsyncLoader::FindLoader(ResourceType type) const {
    return ResourceManager::Get().GetLoader(type);
}

void AsyncLoader::WorkerThread() {
    for (;;) {
        LoadRequest request;
        {
            std::unique_lock<std::mutex> lock(m_queueMutex);
            m_pendingCondition.wait(lock, [this]() {
                return !m_running || !m_pendingQueue.empty();
            });

            if (!m_running && m_pendingQueue.empty()) {
                return;
            }

            if (m_pendingQueue.empty()) {
                continue;
            }

            request = std::move(m_pendingQueue.front());
            m_pendingQueue.pop_front();
        }

        if (ShouldTraceAsyncPath(request.path)) {
            TraceAsyncLoad(
                Containers::String("[AsyncLoader] worker-begin id=") +
                Containers::String(std::to_string(request.requestId).c_str()) +
                " type=" +
                GetResourceTypeName(request.type) +
                " path=" +
                request.path);
        }

        LoadResult result;
        try {
            result = ResourceManager::Get().LoadResource(request.path, request.type, request.settings);
        } catch (const std::exception& exception) {
            Debug::Logger::Get().Error(
                Debug::LogCategory::FileSystem,
                Containers::String("Async load threw exception for resource: ") +
                request.path +
                " - " +
                exception.what());
            result = LoadResult(
                Containers::String("Async load threw exception: ") + exception.what());
        } catch (...) {
            Debug::Logger::Get().Error(
                Debug::LogCategory::FileSystem,
                Containers::String("Async load threw unknown exception for resource: ") +
                request.path);
            result = LoadResult("Async load threw unknown exception");
        }

        if (ShouldTraceAsyncPath(request.path)) {
            TraceAsyncLoad(
                Containers::String("[AsyncLoader] worker-end id=") +
                Containers::String(std::to_string(request.requestId).c_str()) +
                " type=" +
                GetResourceTypeName(request.type) +
                " path=" +
                request.path +
                " success=" +
                Containers::String(result && result.resource != nullptr ? "1" : "0") +
                (result.errorMessage.Empty()
                    ? Containers::String()
                    : Containers::String(" error=") + result.errorMessage));
        }

        QueueCompleted(std::move(request), std::move(result));
    }
}

void AsyncLoader::QueueCompleted(LoadRequest request, LoadResult result) {
    std::lock_guard<std::mutex> lock(m_completedMutex);
    m_completedQueue.emplace_back(std::move(request), std::move(result));
}

} // namespace Resources
} // namespace XCEngine