// SPDX-FileCopyrightText: Copyright 2020 yuzu Emulator Project
// SPDX-License-Identifier: GPL-2.0-or-later

#include <condition_variable>
#include <functional>
#include <mutex>
#include <thread>
#include <vector>
#include <queue>

#include "common/scope_exit.h"
#include "common/thread.h"
#include "core/hle/kernel/k_session.h"
#include "core/hle/kernel/k_thread.h"
#include "core/hle/kernel/kernel.h"
#include "core/hle/kernel/service_thread.h"

namespace Kernel {

class ServiceThread::Impl final {
public:
    explicit Impl(KernelCore& kernel, std::size_t num_threads, const std::string& name);
    ~Impl();

    void QueueSyncRequest(KSession& session, std::shared_ptr<HLERequestContext>&& context);

private:
    std::vector<std::jthread> threads;
    std::queue<std::function<void()>> requests;
    std::mutex queue_mutex;
    std::condition_variable_any condition;
    const std::string service_name;
};

ServiceThread::Impl::Impl(KernelCore& kernel, std::size_t num_threads, const std::string& name)
    : service_name{name} {
    for (std::size_t i = 0; i < num_threads; ++i) {
        threads.emplace_back([this, &kernel](std::stop_token stop_token) {
            Common::SetCurrentThreadName(std::string{service_name}.c_str());

            // Wait for first request before trying to acquire a render context
            {
                std::unique_lock lock{queue_mutex};
                condition.wait(lock, stop_token, [this] { return !requests.empty(); });
            }

            if (stop_token.stop_requested()) {
                return;
            }

            // Allocate a dummy guest thread for this host thread.
            kernel.RegisterHostThread();

            while (true) {
                std::function<void()> task;

                {
                    std::unique_lock lock{queue_mutex};
                    condition.wait(lock, stop_token, [this] { return !requests.empty(); });

                    if (stop_token.stop_requested()) {
                        return;
                    }

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

                    task = std::move(requests.front());
                    requests.pop();
                }

                task();
            }
        });
    }
}

void ServiceThread::Impl::QueueSyncRequest(KSession& session,
                                           std::shared_ptr<HLERequestContext>&& context) {
    {
        std::unique_lock lock{queue_mutex};

        auto* server_session{&session.GetServerSession()};

        // Open a reference to the session to ensure it is not closes while the service request
        // completes asynchronously.
        server_session->Open();

        requests.emplace([server_session, context{std::move(context)}]() {
            // Close the reference.
            SCOPE_EXIT({ server_session->Close(); });

            // Complete the service request.
            server_session->CompleteSyncRequest(*context);
        });
    }
    condition.notify_one();
}

ServiceThread::Impl::~Impl() {
    condition.notify_all();
    for (auto& thread : threads) {
        thread.request_stop();
        thread.join();
    }
}

ServiceThread::ServiceThread(KernelCore& kernel, std::size_t num_threads, const std::string& name)
    : impl{std::make_unique<Impl>(kernel, num_threads, name)} {}

ServiceThread::~ServiceThread() = default;

void ServiceThread::QueueSyncRequest(KSession& session,
                                     std::shared_ptr<HLERequestContext>&& context) {
    impl->QueueSyncRequest(session, std::move(context));
}

} // namespace Kernel
