[core] Enable more conversion cases when creating midi_in objects

include/libremidi/api-c.h

@@ -29,7 +29,7 @@ typedef enum libremidi_api
   WINDOWS_MIDI_SERVICES, /*!< Windows API for MIDI 2.0. Requires Windows 11 */
   KEYBOARD_UMP,          /*!< Computer keyboard input */
 
-  DUMMY /*!< A compilable but non-functional API. */
+  DUMMY = 0xFFFF /*!< A compilable but non-functional API. */
 } libremidi_api;
 
 #if __cplusplus

include/libremidi/api.hpp

@@ -2,6 +2,7 @@
 #include <libremidi/api-c.h>
 #include <libremidi/config.hpp>
 
+#include <any>
 #include <string_view>
 #include <vector>
 
@@ -30,6 +31,9 @@ LIBREMIDI_EXPORT std::vector<libremidi::API> available_apis() noexcept;
 */
 LIBREMIDI_EXPORT std::vector<libremidi::API> available_ump_apis() noexcept;
 
+LIBREMIDI_EXPORT
+libremidi::API midi_api(const std::any& conf);
+
 //! A static function to determine the current version.
 LIBREMIDI_EXPORT std::string_view get_version() noexcept;
 
@@ -40,6 +44,17 @@ LIBREMIDI_EXPORT std::string_view get_api_display_name(libremidi::API api);
 //! Look-up an API through its name
 LIBREMIDI_EXPORT libremidi::API get_compiled_api_by_name(std::string_view api);
 
+inline constexpr bool is_midi1(libremidi::API api)
+{
+  return (static_cast<int>(api) >= 0x1 && static_cast<int>(api) < 0x1000)
+         || api == libremidi::API::DUMMY;
+}
+
+inline constexpr bool is_midi2(libremidi::API api)
+{
+  return static_cast<int>(api) >= 0x1000;
+}
+
 namespace midi1
 {
 //! Returns the default MIDI 1.0 backend to use for the target OS.

include/libremidi/libremidi.cpp

@@ -53,7 +53,20 @@ LIBREMIDI_INLINE libremidi::API get_compiled_api_by_name(std::string_view name)
   midi2::for_all_backends([&](auto b) { apis.push_back(b.API); });
   return apis;
 }
-
+LIBREMIDI_INLINE
+libremidi::API midi_api(const std::any& conf)
+{
+  libremidi::API ret = libremidi::API::UNSPECIFIED;
+  midi_any::for_all_backends([&]<typename T>(T) {
+    if (std::any_cast<typename T::midi_in_configuration>(&conf)
+        || std::any_cast<typename T::midi_out_configuration>(&conf)
+        || std::any_cast<typename T::midi_observer_configuration>(&conf))
+    {
+      ret = T::API;
+    }
+  });
+  return ret;
+}
 LIBREMIDI_INLINE
 std::any midi_in_configuration_for(libremidi::API api)
 {

include/libremidi/midi_in.cpp

@@ -124,14 +124,47 @@ make_midi1_in(const input_configuration& base_conf, const std::any& api_conf)
   {
     return make_midi1_in(base_conf);
   }
-  else if (auto api = std::any_cast<libremidi::API>(&api_conf))
+  else if (auto api_p = std::any_cast<libremidi::API>(&api_conf))
   {
-    return make_midi_in(base_conf, midi_in_configuration_for(*api), midi1::available_backends);
+    if (*api_p == libremidi::API::UNSPECIFIED)
+    {
+      if (auto backend = make_midi_in(
+              base_conf, midi_in_configuration_for(libremidi::midi1::default_api()),
+              midi1::available_backends))
+        return backend;
+
+      auto c2 = convert_midi1_to_midi2_input_configuration(base_conf);
+      if (auto backend = make_midi_in(
+              c2, midi_in_configuration_for(libremidi::midi2::default_api()),
+              midi2::available_backends))
+        return backend;
+    }
+    else if (is_midi1(*api_p))
+    {
+      // all good
+      return make_midi_in(base_conf, midi_in_configuration_for(*api_p), midi1::available_backends);
+    }
+    else if (is_midi2(*api_p))
+    {
+      auto c2 = convert_midi1_to_midi2_input_configuration(base_conf);
+      return make_midi_in(c2, midi_in_configuration_for(*api_p), midi2::available_backends);
+    }
   }
   else
   {
-    return make_midi_in(base_conf, api_conf, midi1::available_backends);
+    const auto api = libremidi::midi_api(api_conf);
+    if (libremidi::is_midi1(api))
+    {
+      return make_midi_in(base_conf, api_conf, midi1::available_backends);
+    }
+    else if (libremidi::is_midi2(api))
+    {
+      auto c2 = convert_midi1_to_midi2_input_configuration(base_conf);
+      return make_midi_in(c2, api_conf, midi2::available_backends);
+    }
   }
+
+  return std::make_unique<midi_in_dummy>(input_configuration{}, dummy_configuration{});
 }
 
 /// MIDI 1 constructors