Implement connection keycode logic (#25176)

quantum/connection/connection.h

@@ -0,0 +1,110 @@
+// Copyright 2025 QMK
+// SPDX-License-Identifier: GPL-2.0-or-later
+#pragma once
+
+#include <stdint.h>
+#include "util.h"
+
+/**
+ * \enum connection_host_t
+ *
+ * An enumeration of the possible hosts.
+ */
+typedef enum connection_host_t {
+    CONNECTION_HOST_AUTO,
+
+    CONNECTION_HOST_NONE,
+    CONNECTION_HOST_USB,
+    CONNECTION_HOST_BLUETOOTH,
+    CONNECTION_HOST_2P4GHZ
+} connection_host_t;
+
+/**
+ * \union connection_config_t
+ *
+ * Configuration structure for the connection subsystem.
+ */
+typedef union connection_config_t {
+    uint8_t           raw;
+    connection_host_t desired_host : 8;
+} PACKED connection_config_t;
+
+_Static_assert(sizeof(connection_config_t) == sizeof(uint8_t), "Connection EECONFIG out of spec.");
+
+/**
+ * \brief Initialize the subsystem.
+ *
+ * This function must be called only once, before any of the below functions can be called.
+ */
+void connection_init(void);
+
+/**
+ * \brief Get currently configured host. Does not resolve 'CONNECTION_HOST_AUTO'.
+ *
+ * \return 'connection_host_t' of the configured host.
+ */
+connection_host_t connection_get_host_raw(void);
+
+/**
+ * \brief Get current active host.
+ *
+ * \return 'connection_host_t' of the configured host.
+ */
+connection_host_t connection_auto_detect_host(void);
+
+/**
+ * \brief Get currently configured host. Resolves 'CONNECTION_HOST_AUTO' using 'connection_auto_detect_host()'.
+ *
+ * \return 'connection_host_t' of the configured host.
+ */
+connection_host_t connection_get_host(void);
+
+/**
+ * \brief Get current host. New state is not written to EEPROM.
+ *
+ * \param host The host to configure.
+ */
+void connection_set_host_noeeprom(connection_host_t host);
+
+/**
+ * \brief Get current host.
+ *
+ * \param host The host to configure.
+ */
+void connection_set_host(connection_host_t host);
+
+/**
+ * \brief Move to the next potential host. New state is not written to EEPROM.
+ *
+ */
+void connection_next_host_noeeprom(void);
+
+/**
+ * \brief Move to the next potential host.
+ *
+ */
+void connection_next_host(void);
+
+/**
+ * \brief Move to the previous potential host. New state is not written to EEPROM.
+ *
+ */
+void connection_prev_host_noeeprom(void);
+
+/**
+ * \brief Move to the previous potential host.
+ *
+ */
+void connection_prev_host(void);
+
+/**
+ * \brief user hook called when changing configured host
+ *
+ */
+void connection_host_changed_user(connection_host_t host);
+
+/**
+ * \brief keyboard hook called when changing configured host
+ *
+ */
+void connection_host_changed_kb(connection_host_t host);