Add send_unicode_hex_string function (#3828)

* Add send_string_unicode function

Co-authored-by: kdb424 <kdb424@gmail.com>
Co-authored-by: Konstantin <vomindoraan@gmail.com>

* Clean up code based on feedback

* Fix includes

quantum/process_keycode/process_unicode_common.c

@@ -16,6 +16,8 @@
 
 #include "process_unicode_common.h"
 #include "eeprom.h"
+#include <string.h>
+#include <ctype.h>
 
 static uint8_t input_mode;
 uint8_t mods;
@@ -120,3 +122,29 @@ void register_hex(uint16_t hex) {
     unregister_code(hex_to_keycode(digit));
   }
 }
+
+void send_unicode_hex_string(const char *str)
+{
+  if (!str) { return; } // Safety net
+
+  while (*str) {
+    // Find the next code point (token) in the string
+    for (; *str == ' '; str++);
+    size_t n = strcspn(str, " "); // Length of the current token
+    char code_point[n+1];
+    strncpy(code_point, str, n);
+    code_point[n] = '\0'; // Make sure it's null-terminated
+
+    // Normalize the code point: make all hex digits lowercase
+    for (char *p = code_point; *p; p++) {
+      *p = tolower((unsigned char)*p);
+    }
+
+    // Send the code point as a Unicode input string
+    unicode_input_start();
+    send_string(code_point);
+    unicode_input_finish();
+
+    str += n; // Move to the first ' ' (or '\0') after the current token
+  }
+}

quantum/process_keycode/process_unicode_common.h

@@ -31,6 +31,7 @@ uint8_t get_unicode_input_mode(void);
 void unicode_input_start(void);
 void unicode_input_finish(void);
 void register_hex(uint16_t hex);
+void send_unicode_hex_string(const char *str);
 
 #define UC_OSX 0  // Mac OS X
 #define UC_LNX 1  // Linux