mpd: revamped to event-driven, single-threaded

Fix MPD connection issues by converting/rewriting module into a
state-machine driven system. It is fully single-threaded and uses
events for transitioning between states. It supports all features
and functionality of the previous MPD module.

Signed-off-by: Joseph Benden <joe@benden.us>

include/factory.hpp

@@ -37,7 +37,7 @@
 #include "modules/pulseaudio.hpp"
 #endif
 #ifdef HAVE_LIBMPDCLIENT
-#include "modules/mpd.hpp"
+#include "modules/mpd/mpd.hpp"
 #endif
 #ifdef HAVE_LIBSNDIO
 #include "modules/sndio.hpp"

include/modules/mpd.hpp

@@ -1,74 +0,0 @@
-#pragma once
-
-#include <fmt/format.h>
-#include <mpd/client.h>
-#include <condition_variable>
-#include <thread>
-#include "ALabel.hpp"
-
-namespace waybar::modules {
-
-class MPD : public ALabel {
- public:
-  MPD(const std::string&, const Json::Value&);
-  auto update() -> void;
-
- private:
-  std::thread periodic_updater();
-  std::string getTag(mpd_tag_type type, unsigned idx = 0);
-  void        setLabel();
-  std::string getStateIcon();
-  std::string getOptionIcon(std::string optionName, bool activated);
-
-  std::thread event_listener();
-
-  // Assumes `connection_lock_` is locked
-  void tryConnect();
-  // If checking errors on the main connection, make sure to lock it using
-  // `connection_lock_` before calling checkErrors
-  void checkErrors(mpd_connection* conn);
-
-  // Assumes `connection_lock_` is locked
-  void fetchState();
-  void waitForEvent();
-
-  bool handlePlayPause(GdkEventButton* const&);
-
-  bool stopped();
-  bool playing();
-  bool paused();
-
-  const std::string module_name_;
-
-  using unique_connection = std::unique_ptr<mpd_connection, decltype(&mpd_connection_free)>;
-  using unique_status = std::unique_ptr<mpd_status, decltype(&mpd_status_free)>;
-  using unique_song = std::unique_ptr<mpd_song, decltype(&mpd_song_free)>;
-
-  // Not using unique_ptr since we don't manage the pointer
-  // (It's either nullptr, or from the config)
-  const char*    server_;
-  const unsigned port_;
-
-  unsigned timeout_;
-
-  // We need a mutex here because we can trigger updates from multiple thread:
-  // the event based updates, the periodic updates needed for the elapsed time,
-  // and the click play/pause feature
-  std::mutex        connection_lock_;
-  unique_connection connection_;
-  // The alternate connection will be used to wait for events: since it will
-  // be blocking (idle) we can't send commands via this connection
-  //
-  // No lock since only used in the event listener thread
-  unique_connection alternate_connection_;
-
-  // Protect them using the `connection_lock_`
-  unique_status status_;
-  mpd_state     state_;
-  unique_song   song_;
-
-  // To make sure the previous periodic_updater stops before creating a new one
-  std::mutex periodic_lock_;
-};
-
-}  // namespace waybar::modules

include/modules/mpd/mpd.hpp

@@ -0,0 +1,66 @@
+#pragma once
+
+#include <mpd/client.h>
+#include <fmt/format.h>
+#include <spdlog/spdlog.h>
+
+#include <condition_variable>
+#include <thread>
+
+#include "ALabel.hpp"
+#include "modules/mpd/state.hpp"
+
+namespace waybar::modules {
+
+class MPD : public ALabel {
+  friend class detail::Context;
+
+  // State machine
+  detail::Context context_{this};
+
+  const std::string module_name_;
+
+  // Not using unique_ptr since we don't manage the pointer
+  // (It's either nullptr, or from the config)
+  const char*    server_;
+  const unsigned port_;
+
+  unsigned timeout_;
+
+  detail::unique_connection connection_;
+
+  detail::unique_status status_;
+  mpd_state             state_;
+  detail::unique_song   song_;
+
+ public:
+  MPD(const std::string&, const Json::Value&);
+  virtual ~MPD() noexcept = default;
+  auto update() -> void;
+
+ private:
+  std::string getTag(mpd_tag_type type, unsigned idx = 0) const;
+  void        setLabel();
+  std::string getStateIcon() const;
+  std::string getOptionIcon(std::string optionName, bool activated) const;
+
+  // GUI-side methods
+  bool handlePlayPause(GdkEventButton* const&);
+  void emit() { dp.emit(); }
+
+  // MPD-side, Non-GUI methods.
+  void tryConnect();
+  void checkErrors(mpd_connection* conn);
+  void fetchState();
+  void queryMPD();
+
+  inline bool stopped() const { return connection_ && state_ == MPD_STATE_STOP; }
+  inline bool playing() const { return connection_ && state_ == MPD_STATE_PLAY; }
+  inline bool paused() const { return connection_ && state_ == MPD_STATE_PAUSE; }
+};
+
+#if !defined(MPD_NOINLINE)
+#include "modules/mpd/state.inl.hpp"
+#endif
+
+}  // namespace waybar::modules

include/modules/mpd/state.hpp

@@ -0,0 +1,217 @@
+#pragma once
+
+#include <mpd/client.h>
+#include <fmt/format.h>
+#include <spdlog/spdlog.h>
+
+#include <condition_variable>
+#include <thread>
+
+#include "ALabel.hpp"
+
+namespace waybar::modules {
+class MPD;
+}  // namespace waybar::modules
+
+namespace waybar::modules::detail {
+
+using unique_connection = std::unique_ptr<mpd_connection, decltype(&mpd_connection_free)>;
+using unique_status = std::unique_ptr<mpd_status, decltype(&mpd_status_free)>;
+using unique_song = std::unique_ptr<mpd_song, decltype(&mpd_song_free)>;
+
+class Context;
+
+/// This state machine loosely follows a non-hierarchical, statechart
+/// pattern, and includes ENTRY and EXIT actions.
+///
+/// The State class is the base class for all other states. The
+/// entry and exit methods are automatically called when entering
+/// into a new state and exiting from the current state. This
+/// includes initially entering (Disconnected class) and exiting
+/// Waybar.
+///
+/// The following nested "top-level" states are represented:
+/// 1. Idle - await notification of MPD activity.
+/// 2. All Non-Idle states:
+///    1. Playing - An active song is producing audio output.
+///    2. Paused - The current song is paused.
+///    3. Stopped - No song is actively playing.
+/// 3. Disconnected - periodically attempt MPD (re-)connection.
+///
+/// NOTE: Since this statechart is non-hierarchical, the above
+/// states are flattened into a set.
+
+class State {
+ public:
+  virtual ~State() noexcept = default;
+
+  virtual void entry() noexcept { spdlog::debug("mpd: ignore entry action"); }
+  virtual void exit() noexcept { spdlog::debug("mpd: ignore exit action"); }
+
+  virtual void play() { spdlog::debug("mpd: ignore play state transition"); }
+  virtual void stop() { spdlog::debug("mpd: ignore stop state transition"); }
+  virtual void pause() { spdlog::debug("mpd: ignore pause state transition"); }
+
+  /// Request state update the GUI.
+  virtual void update() noexcept { spdlog::debug("mpd: ignoring update method request"); }
+};
+
+class Idle : public State {
+  Context* const   ctx_;
+  sigc::connection idle_connection_;
+
+ public:
+  Idle(Context* const ctx) : ctx_{ctx} {}
+  virtual ~Idle() noexcept { this->exit(); };
+
+  void entry() noexcept override;
+  void exit() noexcept override;
+
+  void play() override;
+  void stop() override;
+  void pause() override;
+  void update() noexcept override;
+
+ private:
+  Idle(const Idle&) = delete;
+  Idle& operator=(const Idle&) = delete;
+
+  bool on_io(Glib::IOCondition const&);
+};
+
+class Playing : public State {
+  Context* const   ctx_;
+  sigc::connection timer_connection_;
+
+ public:
+  Playing(Context* const ctx) : ctx_{ctx} {}
+  virtual ~Playing() noexcept { this->exit(); }
+
+  void entry() noexcept override;
+  void exit() noexcept override;
+
+  void pause() override;
+  void stop() override;
+  void update() noexcept override;
+
+ private:
+  Playing(Playing const&) = delete;
+  Playing& operator=(Playing const&) = delete;
+
+  bool on_timer();
+};
+
+class Paused : public State {
+  Context* const   ctx_;
+  sigc::connection timer_connection_;
+
+ public:
+  Paused(Context* const ctx) : ctx_{ctx} {}
+  virtual ~Paused() noexcept { this->exit(); }
+
+  void entry() noexcept override;
+  void exit() noexcept override;
+
+  void play() override;
+  void stop() override;
+  void update() noexcept override;
+
+ private:
+  Paused(Paused const&) = delete;
+  Paused& operator=(Paused const&) = delete;
+
+  bool on_timer();
+};
+
+class Stopped : public State {
+  Context* const   ctx_;
+  sigc::connection timer_connection_;
+
+ public:
+  Stopped(Context* const ctx) : ctx_{ctx} {}
+  virtual ~Stopped() noexcept { this->exit(); }
+
+  void entry() noexcept override;
+  void exit() noexcept override;
+
+  void play() override;
+  void pause() override;
+  void update() noexcept override;
+
+ private:
+  Stopped(Stopped const&) = delete;
+  Stopped& operator=(Stopped const&) = delete;
+
+  bool on_timer();
+};
+
+class Disconnected : public State {
+  Context* const   ctx_;
+  sigc::connection timer_connection_;
+
+ public:
+  Disconnected(Context* const ctx) : ctx_{ctx} {}
+  virtual ~Disconnected() noexcept { this->exit(); }
+
+  void entry() noexcept override;
+  void exit() noexcept override;
+
+  void update() noexcept override;
+
+ private:
+  Disconnected(Disconnected const&) = delete;
+  Disconnected& operator=(Disconnected const&) = delete;
+
+  void arm_timer(int interval) noexcept;
+  void disarm_timer() noexcept;
+
+  bool on_timer();
+};
+
+class Context {
+  std::unique_ptr<State> state_;
+  waybar::modules::MPD*  mpd_module_;
+
+  friend class State;
+  friend class Playing;
+  friend class Paused;
+  friend class Stopped;
+  friend class Disconnected;
+  friend class Idle;
+
+ protected:
+  void setState(std::unique_ptr<State>&& new_state) noexcept {
+    if (state_.get() != nullptr) {
+      state_->exit();
+    }
+    state_ = std::move(new_state);
+    state_->entry();
+  }
+
+  bool                             is_connected() const;
+  bool                             is_playing() const;
+  bool                             is_paused() const;
+  bool                             is_stopped() const;
+  constexpr std::size_t            interval() const;
+  void                             tryConnect() const;
+  void                             checkErrors(mpd_connection*) const;
+  void                             do_update();
+  void                             queryMPD() const;
+  void                             fetchState() const;
+  constexpr mpd_state              state() const;
+  void                             emit() const;
+  [[nodiscard]] unique_connection& connection();
+
+ public:
+  explicit Context(waybar::modules::MPD* const mpd_module)
+      : state_{std::make_unique<Disconnected>(this)}, mpd_module_{mpd_module} {
+    state_->entry();
+  }
+
+  void play() { state_->play(); }
+  void stop() { state_->stop(); }
+  void pause() { state_->pause(); }
+  void update() noexcept { state_->update(); }
+};
+
+}  // namespace waybar::modules::detail

include/modules/mpd/state.inl.hpp

@@ -0,0 +1,24 @@
+#pragma once
+
+namespace detail {
+
+inline bool Context::is_connected() const { return mpd_module_->connection_ != nullptr; }
+inline bool Context::is_playing() const { return mpd_module_->playing(); }
+inline bool Context::is_paused() const { return mpd_module_->paused(); }
+inline bool Context::is_stopped() const { return mpd_module_->stopped(); }
+
+constexpr inline std::size_t Context::interval() const { return mpd_module_->interval_.count(); }
+inline void                  Context::tryConnect() const { mpd_module_->tryConnect(); }
+inline unique_connection&    Context::connection() { return mpd_module_->connection_; }
+constexpr inline mpd_state   Context::state() const { return mpd_module_->state_; }
+
+inline void Context::do_update() {
+  mpd_module_->setLabel();
+}
+
+inline void Context::checkErrors(mpd_connection* conn) const { mpd_module_->checkErrors(conn); }
+inline void Context::queryMPD() const { mpd_module_->queryMPD(); }
+inline void Context::fetchState() const { mpd_module_->fetchState(); }
+inline void Context::emit() const { mpd_module_->emit(); }
+
+}  // namespace detail

meson.build

@@ -213,7 +213,8 @@ endif
 
 if libmpdclient.found()
     add_project_arguments('-DHAVE_LIBMPDCLIENT', language: 'cpp')
-    src_files += 'src/modules/mpd.cpp'
+    src_files += 'src/modules/mpd/mpd.cpp'
+    src_files += 'src/modules/mpd/state.cpp'
 endif
 
 if gtk_layer_shell.found()

src/modules/mpd/mpd.cpp

@@ -1,8 +1,15 @@
-#include "modules/mpd.hpp"
+#include "modules/mpd/mpd.hpp"
 
 #include <fmt/chrono.h>
 #include <spdlog/spdlog.h>
 
+#include "modules/mpd/state.hpp"
+#if defined(MPD_NOINLINE)
+namespace waybar::modules {
+#include "modules/mpd/state.inl.hpp"
+}  // namespace waybar::modules
+#endif
+
 waybar::modules::MPD::MPD(const std::string& id, const Json::Value& config)
     : ALabel(config, "mpd", id, "{album} - {artist} - {title}", 5),
       module_name_(id.empty() ? "mpd" : "mpd#" + id),
@@ -10,7 +17,6 @@ waybar::modules::MPD::MPD(const std::string& id, const Json::Value& config)
       port_(config_["port"].isUInt() ? config["port"].asUInt() : 0),
       timeout_(config_["timeout"].isUInt() ? config_["timeout"].asUInt() * 1'000 : 30'000),
       connection_(nullptr, &mpd_connection_free),
-      alternate_connection_(nullptr, &mpd_connection_free),
       status_(nullptr, &mpd_status_free),
       song_(nullptr, &mpd_song_free) {
   if (!config_["port"].isNull() && !config_["port"].isUInt()) {
@@ -28,73 +34,33 @@ waybar::modules::MPD::MPD(const std::string& id, const Json::Value& config)
     server_ = config["server"].asCString();
   }
 
-  event_listener().detach();
-
   event_box_.add_events(Gdk::BUTTON_PRESS_MASK);
   event_box_.signal_button_press_event().connect(sigc::mem_fun(*this, &MPD::handlePlayPause));
 }
 
 auto waybar::modules::MPD::update() -> void {
-  std::lock_guard guard(connection_lock_);
-  tryConnect();
-
-  if (connection_ != nullptr) {
-    try {
-      bool wasPlaying = playing();
-      if(!wasPlaying) {
-        // Wait until the periodic_updater has stopped
-        std::lock_guard periodic_guard(periodic_lock_);
-      }
-      fetchState();
-      if (!wasPlaying && playing()) {
-        periodic_updater().detach();
-      }
-    } catch (const std::exception& e) {
-      spdlog::error("{}: {}", module_name_, e.what());
-      state_ = MPD_STATE_UNKNOWN;
-    }
-  }
-
-  setLabel();
+  context_.update();
 
   // Call parent update
   ALabel::update();
 }
 
-std::thread waybar::modules::MPD::event_listener() {
-  return std::thread([this] {
-    while (true) {
-      try {
-        if (connection_ == nullptr) {
-          // Retry periodically if no connection
-          dp.emit();
-          std::this_thread::sleep_for(interval_);
-        } else {
-          waitForEvent();
-          dp.emit();
-        }
-      } catch (const std::exception& e) {
-        if (strcmp(e.what(), "Connection to MPD closed") == 0) {
-          spdlog::debug("{}: {}", module_name_, e.what());
-        } else {
-          spdlog::warn("{}: {}", module_name_, e.what());
-        }
-      }
+void waybar::modules::MPD::queryMPD() {
+  if (connection_ != nullptr) {
+    spdlog::debug("{}: fetching state information", module_name_);
+    try {
+      fetchState();
+      spdlog::debug("{}: fetch complete", module_name_);
+    } catch (std::exception const& e) {
+      spdlog::error("{}: {}", module_name_, e.what());
+      state_ = MPD_STATE_UNKNOWN;
     }
-  });
+
+    dp.emit();
+  }
 }
 
-std::thread waybar::modules::MPD::periodic_updater() {
-  return std::thread([this] {
-    std::lock_guard guard(periodic_lock_);
-    while (connection_ != nullptr && playing()) {
-      dp.emit();
-      std::this_thread::sleep_for(std::chrono::seconds(1));
-    }
-  });
-}
-
-std::string waybar::modules::MPD::getTag(mpd_tag_type type, unsigned idx) {
+std::string waybar::modules::MPD::getTag(mpd_tag_type type, unsigned idx) const {
   std::string result =
       config_["unknown-tag"].isString() ? config_["unknown-tag"].asString() : "N/A";
   const char* tag = mpd_song_get_tag(song_.get(), type, idx);
@@ -133,7 +99,7 @@ void waybar::modules::MPD::setLabel() {
   auto format = format_;
 
   std::string          artist, album_artist, album, title, date;
-  int song_pos, queue_length;
+  int                  song_pos, queue_length;
   std::chrono::seconds elapsedTime, totalTime;
 
   std::string stateIcon = "";
@@ -149,8 +115,8 @@ void waybar::modules::MPD::setLabel() {
       label_.get_style_context()->add_class("playing");
       label_.get_style_context()->remove_class("paused");
     } else if (paused()) {
-      format =
-        config_["format-paused"].isString() ? config_["format-paused"].asString() : config_["format"].asString();
+      format = config_["format-paused"].isString() ? config_["format-paused"].asString()
+                                                   : config_["format"].asString();
       label_.get_style_context()->add_class("paused");
       label_.get_style_context()->remove_class("playing");
     }
@@ -216,7 +182,7 @@ void waybar::modules::MPD::setLabel() {
   }
 }
 
-std::string waybar::modules::MPD::getStateIcon() {
+std::string waybar::modules::MPD::getStateIcon() const {
   if (!config_["state-icons"].isObject()) {
     return "";
   }
@@ -238,7 +204,7 @@ std::string waybar::modules::MPD::getStateIcon() {
   }
 }
 
-std::string waybar::modules::MPD::getOptionIcon(std::string optionName, bool activated) {
+std::string waybar::modules::MPD::getOptionIcon(std::string optionName, bool activated) const {
   if (!config_[optionName + "-icons"].isObject()) {
     return "";
   }
@@ -261,15 +227,11 @@ void waybar::modules::MPD::tryConnect() {
   }
 
   connection_ =
-      unique_connection(mpd_connection_new(server_, port_, timeout_), &mpd_connection_free);
+      detail::unique_connection(mpd_connection_new(server_, port_, timeout_), &mpd_connection_free);
 
-  alternate_connection_ =
-      unique_connection(mpd_connection_new(server_, port_, timeout_), &mpd_connection_free);
-
-  if (connection_ == nullptr || alternate_connection_ == nullptr) {
+  if (connection_ == nullptr) {
     spdlog::error("{}: Failed to connect to MPD", module_name_);
     connection_.reset();
-    alternate_connection_.reset();
     return;
   }
 
@@ -279,7 +241,6 @@ void waybar::modules::MPD::tryConnect() {
   } catch (std::runtime_error& e) {
     spdlog::error("{}: Failed to connect to MPD: {}", module_name_, e.what());
     connection_.reset();
-    alternate_connection_.reset();
   }
 }
 
@@ -292,7 +253,6 @@ void waybar::modules::MPD::checkErrors(mpd_connection* conn) {
     case MPD_ERROR_CLOSED:
       mpd_connection_clear_error(conn);
       connection_.reset();
-      alternate_connection_.reset();
       state_ = MPD_STATE_UNKNOWN;
       throw std::runtime_error("Connection to MPD closed");
     default:
@@ -306,37 +266,20 @@ void waybar::modules::MPD::checkErrors(mpd_connection* conn) {
 }
 
 void waybar::modules::MPD::fetchState() {
+  if (connection_ == nullptr) {
+    spdlog::error("{}: Not connected to MPD", module_name_);
+    return;
+  }
+
   auto conn = connection_.get();
-  status_ = unique_status(mpd_run_status(conn), &mpd_status_free);
+
+  status_ = detail::unique_status(mpd_run_status(conn), &mpd_status_free);
   checkErrors(conn);
+
   state_ = mpd_status_get_state(status_.get());
   checkErrors(conn);
 
-  song_ = unique_song(mpd_run_current_song(conn), &mpd_song_free);
-  checkErrors(conn);
-}
-
-void waybar::modules::MPD::waitForEvent() {
-  auto conn = alternate_connection_.get();
-  // Wait for a player (play/pause), option (random, shuffle, etc.), or playlist
-  // change
-  if (!mpd_send_idle_mask(
-          conn, static_cast<mpd_idle>(MPD_IDLE_PLAYER | MPD_IDLE_OPTIONS | MPD_IDLE_QUEUE))) {
-    checkErrors(conn);
-    return;
-  }
-  // alternate_idle_ = true;
-
-  // See issue #277:
-  // https://github.com/Alexays/Waybar/issues/277
-  mpd_recv_idle(conn, /* disable_timeout = */ false);
-  // See issue #281:
-  // https://github.com/Alexays/Waybar/issues/281
-  std::lock_guard guard(connection_lock_);
-
-  checkErrors(conn);
-  mpd_response_finish(conn);
-
+  song_ = detail::unique_song(mpd_run_current_song(conn), &mpd_song_free);
   checkErrors(conn);
 }
 
@@ -346,24 +289,13 @@ bool waybar::modules::MPD::handlePlayPause(GdkEventButton* const& e) {
   }
 
   if (e->button == 1) {
-    std::lock_guard guard(connection_lock_);
-    if (stopped()) {
-      mpd_run_play(connection_.get());
-    } else {
-      mpd_run_toggle_pause(connection_.get());
-    }
+    if (state_ == MPD_STATE_PLAY)
+      context_.pause();
+    else
+      context_.play();
   } else if (e->button == 3) {
-    std::lock_guard guard(connection_lock_);
-    mpd_run_stop(connection_.get());
+    context_.stop();
   }
 
   return true;
 }
-
-bool waybar::modules::MPD::stopped() {
-  return connection_ == nullptr || state_ == MPD_STATE_UNKNOWN || state_ == MPD_STATE_STOP || status_ == nullptr;
-}
-
-bool waybar::modules::MPD::playing() { return connection_ != nullptr && state_ == MPD_STATE_PLAY; }
-
-bool waybar::modules::MPD::paused() { return connection_ != nullptr && state_ == MPD_STATE_PAUSE; }

src/modules/mpd/state.cpp

@@ -0,0 +1,382 @@
+#include "modules/mpd/state.hpp"
+
+#include <fmt/chrono.h>
+#include <spdlog/spdlog.h>
+
+#include "modules/mpd/mpd.hpp"
+#if defined(MPD_NOINLINE)
+namespace waybar::modules {
+#include "modules/mpd/state.inl.hpp"
+}  // namespace waybar::modules
+#endif
+
+namespace waybar::modules::detail {
+
+#define IDLE_RUN_NOIDLE_AND_CMD(...)                                      \
+  if (idle_connection_.connected()) {                                     \
+    idle_connection_.disconnect();                                        \
+    auto conn = ctx_->connection().get();                                 \
+    if (!mpd_run_noidle(conn)) {                                          \
+      if (mpd_connection_get_error(conn) != MPD_ERROR_SUCCESS) {          \
+        spdlog::error("mpd: Idle: failed to unregister for IDLE events"); \
+        ctx_->checkErrors(conn);                                          \
+      }                                                                   \
+    }                                                                     \
+    __VA_ARGS__;                                                          \
+  }
+
+void Idle::play() {
+  IDLE_RUN_NOIDLE_AND_CMD(mpd_run_play(conn));
+
+  ctx_->setState(std::make_unique<Playing>(ctx_));
+}
+
+void Idle::pause() {
+  IDLE_RUN_NOIDLE_AND_CMD(mpd_run_pause(conn, true));
+
+  ctx_->setState(std::make_unique<Paused>(ctx_));
+}
+
+void Idle::stop() {
+  IDLE_RUN_NOIDLE_AND_CMD(mpd_run_stop(conn));
+
+  ctx_->setState(std::make_unique<Stopped>(ctx_));
+}
+
+#undef IDLE_RUN_NOIDLE_AND_CMD
+
+void Idle::update() noexcept {
+  // This is intentionally blank.
+}
+
+void Idle::entry() noexcept {
+  auto            conn = ctx_->connection().get();
+  assert(conn != nullptr);
+
+  if (!mpd_send_idle_mask(
+          conn, static_cast<mpd_idle>(MPD_IDLE_PLAYER | MPD_IDLE_OPTIONS | MPD_IDLE_QUEUE))) {
+    ctx_->checkErrors(conn);
+    spdlog::error("mpd: Idle: failed to register for IDLE events");
+  } else {
+    spdlog::debug("mpd: Idle: watching FD");
+    sigc::slot<bool, Glib::IOCondition const&> idle_slot = sigc::mem_fun(*this, &Idle::on_io);
+    idle_connection_ =
+        Glib::signal_io().connect(idle_slot,
+                                  mpd_connection_get_fd(conn),
+                                  Glib::IO_IN | Glib::IO_PRI | Glib::IO_ERR | Glib::IO_HUP);
+  }
+}
+
+void Idle::exit() noexcept {
+  if (idle_connection_.connected()) {
+    idle_connection_.disconnect();
+    spdlog::debug("mpd: Idle: unwatching FD");
+  }
+}
+
+bool Idle::on_io(Glib::IOCondition const&) {
+  auto                         conn = ctx_->connection().get();
+
+  // callback should do this:
+  enum mpd_idle events = mpd_recv_idle(conn, /* ignore_timeout?= */ false);
+  spdlog::debug("mpd: Idle: recv_idle events -> {}", events);
+
+  mpd_response_finish(conn);
+  try {
+    ctx_->checkErrors(conn);
+  } catch (std::exception const& e) {
+    spdlog::warn("mpd: Idle: error: {}", e.what());
+    ctx_->setState(std::make_unique<Disconnected>(ctx_));
+    return false;
+  }
+
+  ctx_->fetchState();
+  mpd_state state = ctx_->state();
+
+  if (state == MPD_STATE_STOP) {
+    ctx_->emit();
+    ctx_->setState(std::make_unique<Stopped>(ctx_));
+  } else if (state == MPD_STATE_PLAY) {
+    ctx_->emit();
+    ctx_->setState(std::make_unique<Playing>(ctx_));
+  } else if (state == MPD_STATE_PAUSE) {
+    ctx_->emit();
+    ctx_->setState(std::make_unique<Paused>(ctx_));
+  } else {
+    ctx_->emit();
+    // self transition
+    ctx_->setState(std::make_unique<Idle>(ctx_));
+  }
+
+  return false;
+}
+
+void Playing::entry() noexcept {
+  sigc::slot<bool> timer_slot = sigc::mem_fun(*this, &Playing::on_timer);
+  timer_connection_ = Glib::signal_timeout().connect(timer_slot, /* milliseconds */ 1'000);
+  spdlog::debug("mpd: Playing: enabled 1 second periodic timer.");
+}
+
+void Playing::exit() noexcept {
+  if (timer_connection_.connected()) {
+    timer_connection_.disconnect();
+    spdlog::debug("mpd: Playing: disabled 1 second periodic timer.");
+  }
+}
+
+bool Playing::on_timer() {
+  // Attempt to connect with MPD.
+  try {
+    ctx_->tryConnect();
+
+    // Success?
+    if (!ctx_->is_connected()) {
+      ctx_->setState(std::make_unique<Disconnected>(ctx_));
+      return false;
+    }
+
+    ctx_->fetchState();
+
+    if (!ctx_->is_playing()) {
+      if (ctx_->is_paused()) {
+        ctx_->setState(std::make_unique<Paused>(ctx_));
+      } else {
+        ctx_->setState(std::make_unique<Stopped>(ctx_));
+      }
+      return false;
+    }
+
+    ctx_->queryMPD();
+    ctx_->emit();
+  } catch (std::exception const& e) {
+    spdlog::warn("mpd: Playing: error: {}", e.what());
+    ctx_->setState(std::make_unique<Disconnected>(ctx_));
+    return false;
+  }
+
+  return true;
+}
+
+void Playing::stop() {
+  if (timer_connection_.connected()) {
+    timer_connection_.disconnect();
+
+    mpd_run_stop(ctx_->connection().get());
+  }
+
+  ctx_->setState(std::make_unique<Stopped>(ctx_));
+}
+
+void Playing::pause() {
+  if (timer_connection_.connected()) {
+    timer_connection_.disconnect();
+
+    mpd_run_pause(ctx_->connection().get(), true);
+  }
+
+  ctx_->setState(std::make_unique<Paused>(ctx_));
+}
+
+void Playing::update() noexcept { ctx_->do_update(); }
+
+void Paused::entry() noexcept {
+  sigc::slot<bool> timer_slot = sigc::mem_fun(*this, &Paused::on_timer);
+  timer_connection_ = Glib::signal_timeout().connect(timer_slot, /* milliseconds */ 200);
+  spdlog::debug("mpd: Paused: enabled 200 ms periodic timer.");
+}
+
+void Paused::exit() noexcept {
+  if (timer_connection_.connected()) {
+    timer_connection_.disconnect();
+    spdlog::debug("mpd: Paused: disabled 200 ms periodic timer.");
+  }
+}
+
+bool Paused::on_timer() {
+  bool                         rc = true;
+
+  // Attempt to connect with MPD.
+  try {
+    ctx_->tryConnect();
+
+    // Success?
+    if (!ctx_->is_connected()) {
+      ctx_->setState(std::make_unique<Disconnected>(ctx_));
+      return false;
+    }
+
+    ctx_->fetchState();
+
+    ctx_->emit();
+
+    if (ctx_->is_paused()) {
+      ctx_->setState(std::make_unique<Idle>(ctx_));
+      rc = false;
+    } else if (ctx_->is_playing()) {
+      ctx_->setState(std::make_unique<Playing>(ctx_));
+      rc = false;
+    } else if (ctx_->is_stopped()) {
+      ctx_->setState(std::make_unique<Stopped>(ctx_));
+      rc = false;
+    }
+  } catch (std::exception const& e) {
+    spdlog::warn("mpd: Paused: error: {}", e.what());
+    ctx_->setState(std::make_unique<Disconnected>(ctx_));
+    rc = false;
+  }
+
+  return rc;
+}
+
+void Paused::play() {
+  if (timer_connection_.connected()) {
+    timer_connection_.disconnect();
+
+    mpd_run_play(ctx_->connection().get());
+  }
+
+  ctx_->setState(std::make_unique<Playing>(ctx_));
+}
+
+void Paused::stop() {
+  if (timer_connection_.connected()) {
+    timer_connection_.disconnect();
+
+    mpd_run_stop(ctx_->connection().get());
+  }
+
+  ctx_->setState(std::make_unique<Stopped>(ctx_));
+}
+
+void Paused::update() noexcept { ctx_->do_update(); }
+
+void Stopped::entry() noexcept {
+  sigc::slot<bool> timer_slot = sigc::mem_fun(*this, &Stopped::on_timer);
+  timer_connection_ = Glib::signal_timeout().connect(timer_slot, /* milliseconds */ 200);
+  spdlog::debug("mpd: Stopped: enabled 200 ms periodic timer.");
+}
+
+void Stopped::exit() noexcept {
+  if (timer_connection_.connected()) {
+    timer_connection_.disconnect();
+    spdlog::debug("mpd: Stopped: disabled 200 ms periodic timer.");
+  }
+}
+
+bool Stopped::on_timer() {
+  bool                         rc = true;
+
+  // Attempt to connect with MPD.
+  try {
+    ctx_->tryConnect();
+
+    // Success?
+    if (!ctx_->is_connected()) {
+      ctx_->setState(std::make_unique<Disconnected>(ctx_));
+      return false;
+    }
+
+    ctx_->fetchState();
+
+    ctx_->emit();
+
+    if (ctx_->is_stopped()) {
+      ctx_->setState(std::make_unique<Idle>(ctx_));
+      rc = false;
+    } else if (ctx_->is_playing()) {
+      ctx_->setState(std::make_unique<Playing>(ctx_));
+      rc = false;
+    } else if (ctx_->is_paused()) {
+      ctx_->setState(std::make_unique<Paused>(ctx_));
+      rc = false;
+    }
+  } catch (std::exception const& e) {
+    spdlog::warn("mpd: Stopped: error: {}", e.what());
+    ctx_->setState(std::make_unique<Disconnected>(ctx_));
+    rc = false;
+  }
+
+  return rc;
+}
+
+void Stopped::play() {
+  if (timer_connection_.connected()) {
+    timer_connection_.disconnect();
+
+    mpd_run_play(ctx_->connection().get());
+  }
+
+  ctx_->setState(std::make_unique<Playing>(ctx_));
+}
+
+void Stopped::pause() {
+  if (timer_connection_.connected()) {
+    timer_connection_.disconnect();
+
+    mpd_run_pause(ctx_->connection().get(), true);
+  }
+
+  ctx_->setState(std::make_unique<Paused>(ctx_));
+}
+
+void Stopped::update() noexcept { ctx_->do_update(); }
+
+void Disconnected::arm_timer(int interval) noexcept {
+  // unregister timer, if present
+  disarm_timer();
+
+  // register timer
+  sigc::slot<bool> timer_slot = sigc::mem_fun(*this, &Disconnected::on_timer);
+  timer_connection_ =
+      Glib::signal_timeout().connect(timer_slot, interval);
+  spdlog::debug("mpd: Disconnected: enabled interval timer.");
+}
+
+void Disconnected::disarm_timer() noexcept {
+  // unregister timer, if present
+  if (timer_connection_.connected()) {
+    timer_connection_.disconnect();
+    spdlog::debug("mpd: Disconnected: disabled interval timer.");
+  }
+}
+
+void Disconnected::entry() noexcept {
+  arm_timer(1'000);
+}
+
+void Disconnected::exit() noexcept {
+  disarm_timer();
+}
+
+bool Disconnected::on_timer() {
+  // Attempt to connect with MPD.
+  try {
+    ctx_->tryConnect();
+
+    // Success?
+    if (ctx_->is_connected()) {
+      ctx_->fetchState();
+      ctx_->emit();
+
+      if (ctx_->is_playing()) {
+        ctx_->setState(std::make_unique<Playing>(ctx_));
+      } else if (ctx_->is_paused()) {
+        ctx_->setState(std::make_unique<Paused>(ctx_));
+      } else {
+        ctx_->setState(std::make_unique<Stopped>(ctx_));
+      }
+
+      return false;  // do not rearm timer
+    }
+  } catch (std::exception const& e) {
+    spdlog::warn("mpd: Disconnected: error: {}", e.what());
+  }
+
+  arm_timer(ctx_->interval() * 1'000);
+
+  return false;
+}
+
+void Disconnected::update() noexcept { ctx_->do_update(); }
+
+}  // namespace waybar::modules::detail