very, very simple WP with midi CC out

include/libremidi/observer_configuration.hpp

@@ -0,0 +1,86 @@
+#pragma once
+#include <libremidi/config.hpp>
+#include <libremidi/error.hpp>
+
+#include <compare>
+#include <string>
+
+namespace libremidi
+{
+using client_handle = std::uint64_t;
+using port_handle = std::uint64_t;
+
+struct LIBREMIDI_EXPORT port_information
+{
+  // Handle to the client object:
+
+  // ALSA Raw: unused
+  // ALSA Seq: snd_seq_t*
+  // CoreMIDI: MidiClientRef
+  // WebMIDI: unused
+  // JACK: jack_client_t*
+  // PipeWire: unused
+  // WinMM: unused
+  // WinUWP: unused
+  client_handle client;
+
+  // ALSA Raw: { uint16_t card, device, sub, padding; }
+  // ALSA Seq: { uint32_t client, uint32_t port; }
+  // CoreMIDI: MidiObjectRef
+  // WebMIDI: unused
+  // JACK: jack_port_id_t
+  // PipeWire: port.id
+  // WinMM: unset, identified by port_name
+  // WinUWP: unused
+  port_handle port;
+
+  std::string manufacturer;
+  std::string device_name;
+  std::string port_name;
+  std::string display_name;
+
+  bool operator==(const port_information& other) const noexcept = default;
+  std::strong_ordering operator<=>(const port_information& other) const noexcept = default;
+};
+
+struct input_port : port_information
+{
+  bool operator==(const input_port& other) const noexcept = default;
+  std::strong_ordering operator<=>(const input_port& other) const noexcept = default;
+};
+struct output_port : port_information
+{
+  bool operator==(const output_port& other) const noexcept = default;
+  std::strong_ordering operator<=>(const output_port& other) const noexcept = default;
+};
+
+using input_port_callback = std::function<void(const input_port&)>;
+using output_port_callback = std::function<void(const output_port&)>;
+struct observer_configuration
+{
+  midi_error_callback on_error{};
+  midi_error_callback on_warning{};
+
+  input_port_callback input_added;
+  input_port_callback input_removed;
+  output_port_callback output_added;
+  output_port_callback output_removed;
+
+  // Observe hardware ports
+  uint32_t track_hardware : 1 = true;
+
+  // Observe software (virtual) ports if the API provides it
+  uint32_t track_virtual : 1 = false;
+
+  // Observe any port - some systems have other weird port types than hw / sw, this covers them
+  uint32_t track_any : 1 = false;
+
+  // Notify of the existing ports in the observer constructor
+  uint32_t notify_in_constructor : 1 = true;
+
+  bool has_callbacks() const noexcept
+  {
+    return input_added || input_removed || output_added || output_removed;
+  }
+};
+}