#include "common.hh"

#include "io.hh"
#include "timer_state.hh"
#include "unique_fd.hh"

#include <errno.h>
#include <fcntl.h>
#include <functional>
#include <iostream>
#include <sdbus-c++/sdbus-c++.h>
#include <string.h>
#include <sys/file.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
#include <thread>

namespace {

const sdbus::ServiceName kServiceName{"org.the_jk.timer"};
const sdbus::ObjectPath kObjectPath{"/org/the_jk/timer/state"};
const sdbus::InterfaceName kInterfaceName{"org.the_jk.timer.State"};

class TimerStateImpl {
public:
  virtual ~TimerStateImpl() = default;

  virtual void start() = 0;
  virtual void stop() = 0;
  virtual void reset() = 0;

  virtual void enterLoop() {
    conn_->enterEventLoop();
  }

  virtual void leaveLoop() {
    conn_->leaveEventLoop();
  }

protected:
  TimerStateImpl(std::shared_ptr<sdbus::IConnection> conn,
                 TimerState::Delegate* delegate)
    : conn_(std::move(conn)), delegate_(delegate) {
  }

  std::shared_ptr<sdbus::IConnection> conn_;
  TimerState::Delegate* const delegate_;
};

class TimerStateClient : public TimerStateImpl {
public:
  TimerStateClient(std::shared_ptr<sdbus::IConnection> conn,
                   TimerState::Delegate* delegate)
    : TimerStateImpl(std::move(conn), delegate) {}

  void start() override {
    try {
      proxy_->callMethod("start").onInterface(kInterfaceName).dontExpectReply();
    } catch (sdbus::Error const& err) {
      std::cerr << "Failed to call start: " << err.what() << std::endl;
    }
  }

  void stop() override {
    try {
      proxy_->callMethod("stop").onInterface(kInterfaceName).dontExpectReply();
    } catch (sdbus::Error const& err) {
      std::cerr << "Failed to call stop: " << err.what() << std::endl;
    }
  }

  void reset() override {
    try {
      proxy_->callMethod("reset").onInterface(kInterfaceName).dontExpectReply();
    } catch (sdbus::Error const& err) {
      std::cerr << "Failed to call reset: " << err.what() << std::endl;
    }
  }

  bool init() {
    try {
      proxy_ = sdbus::createProxy(*conn_.get(), kServiceName, kObjectPath);
      proxy_->uponSignal("started").onInterface(kInterfaceName)
        .call([this](uint32_t total, int64_t epoch){
          signal_started(std::chrono::minutes(total),
                         std::chrono::system_clock::from_time_t(epoch));
        });
      proxy_->uponSignal("stopped").onInterface(kInterfaceName)
        .call([this](uint32_t total){
          signal_stopped(std::chrono::minutes(total));
        });
      proxy_->uponSignal("reset").onInterface(kInterfaceName)
        .call([this](){ signal_reset(); });

      dbus_proxy_ = sdbus::createProxy(*conn_.get(), sdbus::ServiceName{"org.freedesktop.DBus"},
                                       sdbus::ObjectPath{"/org/freedesktop/DBus"});
      dbus_proxy_->uponSignal("NameOwnerChanged")
        .onInterface("org.freedesktop.DBus")
        .call([this](const std::string& name,
                     const std::string& /* old_owner */,
                     const std::string& new_owner) {
          if (name == kServiceName && new_owner.empty()) {
            signal_restart();
          }
        });

      sync_state();
    } catch (sdbus::Error const& err) {
      std::cerr << "Failed to init client: " << err.what() << std::endl;
      return false;
    }

    return true;
  }

private:
  void signal_started(
      std::chrono::minutes total,
      std::chrono::time_point<std::chrono::system_clock> epoch) {
    delegate_->start(total, epoch);
  }

  void signal_stopped(std::chrono::minutes total) {
    delegate_->stop(total);
  }

  void signal_reset() {
    delegate_->reset();
  }

  void signal_restart() {
    delegate_->restart();
  }

  void sync_state() {
    auto method = proxy_->createMethodCall(kInterfaceName, sdbus::MethodName{"get_state"});
    auto reply = proxy_->callMethod(std::move(method));
    bool active;
    uint32_t total;
    int64_t epoch;
    reply >> active;
    reply >> total;
    reply >> epoch;
    if (active) {
      delegate_->start(std::chrono::minutes(total),
                       std::chrono::system_clock::from_time_t(epoch));
    } else {
      delegate_->stop(std::chrono::minutes(total));
    }
  }

  std::unique_ptr<sdbus::IProxy> proxy_;
  std::unique_ptr<sdbus::IProxy> dbus_proxy_;
};

class TimerStateServer : public TimerStateImpl {
public:
  TimerStateServer(std::shared_ptr<sdbus::IConnection> conn,
                   TimerState::Delegate* delegate)
    : TimerStateImpl(std::move(conn), delegate) {}

  void start() override {
    if (active_) return;
    active_ = true;
    start_ = std::chrono::system_clock::now();
    write_state();

    try {
      object_->emitSignal("started").onInterface(kInterfaceName).withArguments(
          static_cast<uint32_t>(total_.count()),
          static_cast<int64_t>(std::chrono::system_clock::to_time_t(start_)));
    } catch (sdbus::Error const& err) {
      std::cerr << "Failed to emit started: " << err.what() << std::endl;
    }
    delegate_->start(total_, start_);
  }

  void stop() override {
    if (!active_) return;
    active_ = false;
    total_ +=
      std::chrono::duration_cast<std::chrono::minutes>(
          std::chrono::system_clock::now() - start_);
    write_state();

    try {
      object_->emitSignal("stopped").onInterface(kInterfaceName).withArguments(
          static_cast<uint32_t>(total_.count()));
    } catch (sdbus::Error const& err) {
      std::cerr << "Failed to emit started: " << err.what() << std::endl;
    }
    delegate_->stop(total_);
  }

  void reset() override {
    if (active_) return;
    total_ = std::chrono::minutes::zero();
    write_state();

    try {
      object_->emitSignal("reset").onInterface(kInterfaceName);
    } catch (sdbus::Error const& err) {
      std::cerr << "Failed to emit reset: " << err.what() << std::endl;
    }
    delegate_->reset();
  }

  bool init(std::filesystem::path state_file) {
    if (!load_state(state_file))
      return false;

    try {
      auto object = sdbus::createObject(*conn_.get(), kObjectPath);
      auto start = [this]() { this->start(); };
      auto stop = [this]() { this->stop(); };
      auto reset = [this]() { this->reset(); };
      auto get_state = std::bind(&TimerStateServer::get_state, this, std::placeholders::_1);
      object->addVTable(
          sdbus::registerMethod("start").implementedAs(std::move(start)).withNoReply(),
          sdbus::registerMethod("stop").implementedAs(std::move(stop)).withNoReply(),
          sdbus::registerMethod("reset").implementedAs(std::move(reset)).withNoReply(),
          sdbus::MethodVTableItem{
            sdbus::MethodName{"get_state"}, sdbus::Signature{""}, {}, sdbus::Signature{"bux"}, {}, get_state, {}
          },
          sdbus::registerSignal("started").withParameters<uint32_t, int64_t>(),
          sdbus::registerSignal("stopped").withParameters<uint32_t>(),
          sdbus::registerSignal("reset")
      ).forInterface(kInterfaceName);

      object_ = std::move(object);
    } catch (sdbus::Error const& err) {
      std::cerr << "Failed to init server: " << err.what() << std::endl;
      return false;
    }

    if (active_) {
      delegate_->start(total_, start_);
    } else {
      delegate_->stop(total_);
    }

    return true;
  }

private:
  void get_state(sdbus::MethodCall call) {
    try {
      auto reply = call.createReply();
      reply << active_;
      reply << static_cast<uint32_t>(total_.count());
      if (active_) {
        reply << static_cast<int64_t>(
            std::chrono::system_clock::to_time_t(start_));
      } else {
        reply << static_cast<int64_t>(0);
      }
      reply.send();
    } catch (sdbus::Error const& err) {
      std::cerr << "Failed to reply to get_state: " << err.what() << std::endl;
    }
  }

  bool load_state(std::filesystem::path state_file) {
    fd_.reset(open(state_file.c_str(), O_RDWR | O_CREAT, S_IRWXU));
    if (!fd_) {
      std::cerr << "Unable to open or create " << state_file
                << " for reading and writing." << std::endl;
      return false;
    }
    if (flock(fd_.get(), LOCK_EX | LOCK_NB)) {
      std::cerr << "Unable to get exclusive lock on " << state_file
                << ": " << strerror(errno) << std::endl;
      return false;
    }
    std::string data;
    if (!io::read_all(fd_.get(), &data)) {
      std::cerr << "Error reading " << state_file
                << ": " << strerror(errno) << std::endl;
      return false;
    }
    if (data.empty()) {
      // Newly created file.
      active_ = false;
      total_ = std::chrono::minutes::zero();
    } else {
      if (!parse_state(std::move(data))) {
        std::cerr << "Invalid data in state " << state_file
                  << "." << std::endl;
        return false;
      }
    }
    return true;
  }

  bool parse_state(std::string data) {
    try {
      size_t end;
      auto active = std::stol(data, &end);
      if (end == data.size() || data[end] != '|')
        return false;
      data = data.substr(end + 1);
      auto total = std::stoul(data, &end);
      if (end == data.size() || data[end] != '|')
        return false;
      struct tm tm;
      auto* endp = strptime(
          data.substr(end + 1).c_str(), "%Y-%m-%d %H:%M:%S", &tm);
      if (!endp || (*endp != '\0' && *endp != '\n'))
        return false;

      active_ = active == 1;
      total_ = std::chrono::minutes(total);
      start_ = std::chrono::system_clock::from_time_t(timegm(&tm));

      return true;
    } catch (std::exception const& e) {
      return false;
    }
  }

  bool write_state() {
    std::string data =
      std::to_string(active_ ? 1L : -1L) + '|' + std::to_string(
          std::chrono::duration_cast<std::chrono::minutes>(total_).count())
      + '|';
    char tmp[50];
    auto time = std::chrono::system_clock::to_time_t(start_);
    auto len = strftime(tmp, sizeof(tmp), "%Y-%m-%d %H:%M:%S", gmtime(&time));
    if (len == 0 || len == sizeof(tmp)) {
      std::cerr << "Failed to store state: invalid time." << std::endl;
      return false;
    }
    data.append(tmp, len);
    data.push_back('\n');
    if (lseek(fd_.get(), 0, SEEK_SET) ||
        !io::write_all(fd_.get(), data) ||
        ftruncate(fd_.get(), data.size())) {
      std::cerr << "Failed to store state: " << strerror(errno) << std::endl;
      return false;
    }
    return true;
  }

  bool active_{false};
  std::chrono::minutes total_{0};
  std::chrono::time_point<std::chrono::system_clock> start_;
  std::unique_ptr<sdbus::IObject> object_;
  unique_fd fd_;
};

class TimerStateWrapper : public TimerState {
public:
  explicit TimerStateWrapper(Delegate* delegate)
    : delegate_(delegate) {}

  ~TimerStateWrapper() override {
    if (impl_) impl_->leaveLoop();
    thread_.join();
  }

  bool init(std::filesystem::path state_file) {
    try {
      std::shared_ptr<sdbus::IConnection> conn(
          sdbus::createSessionBusConnection());

      try {
        conn->requestName(kServiceName);

        auto server = std::make_unique<TimerStateServer>(conn, delegate_);
        if (server->init(std::move(state_file))) {
          impl_ = std::move(server);
          return post_init();
        }
        // If server fails to init in any way, try client as backup.
      } catch (sdbus::Error const& e) {
        // This is here to catch requestName call, if requestName fails there
        // is a server running.
      }

      auto client = std::make_unique<TimerStateClient>(conn, delegate_);
      if (client->init()) {
        impl_ = std::move(client);
        return post_init();
      }
    } catch (sdbus::Error const& e) {
    }
    return false;
  }

  void start() override {
    impl_->start();
  }

  void stop() override {
    impl_->stop();
  }

  void reset() override {
    impl_->reset();
  }

private:
  bool post_init() {
    thread_ = std::thread(&TimerStateWrapper::run_impl, this);
    return true;
  }

  void run_impl() {
    impl_->enterLoop();
  }

  Delegate* const delegate_;
  std::unique_ptr<TimerStateImpl> impl_;
  std::thread thread_;
};

}  // namespace

std::unique_ptr<TimerState> TimerState::create(std::filesystem::path state_file,
                                               Delegate* delegate) {
  auto state = std::make_unique<TimerStateWrapper>(delegate);
  return state->init(std::move(state_file)) ? std::move(state) : nullptr;
}