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

docs/feature_unicode.md

@@ -19,7 +19,7 @@ table.
 TBD
 
 Unicode input in QMK works by inputing a sequence of characters to the OS,
-sort of like macro. Unfortunately, each OS has different ideas on how Unicode is inputted.
+sort of like macro. Unfortunately, each OS has different ideas on how Unicode is input.
 
 This is the current list of Unicode input method in QMK:
 
@@ -29,6 +29,11 @@ This is the current list of Unicode input method in QMK:
 * UC_WIN: (not recommended) Windows built-in Unicode input. To enable: create registry key under `HKEY_CURRENT_USER\Control Panel\Input Method\EnableHexNumpad` of type `REG_SZ` called `EnableHexNumpad`, set its value to 1, and reboot. This method is not recommended because of reliability and compatibility issue, use WinCompose method below instead.
 * UC_WINC: Windows Unicode input using WinCompose. Requires [WinCompose](https://github.com/samhocevar/wincompose). Works reliably under many (all?) variations of Windows.
 
+To type multiple characters for things like (ノಠ痊ಠ)ノ彡┻━┻, you can use `send_unicode_hex_string()` much like `SEND_STRING()` except you would use hex values seperated by spaces.
+For example, the table flip seen above would be `send_unicode_hex_string("0028 30CE 0CA0 75CA 0CA0 0029 30CE 5F61 253B 2501 253B")`
+
+There are many ways to get a hex code, but an easy one is [this site](https://r12a.github.io/app-conversion/). Just make sure to convert to hexadecimal, and that is your string.
+
 # Additional Language Support
 
 In `quantum/keymap_extras/`, you'll see various language files - these work the same way as the alternative layout ones do. Most are defined by their two letter country/language code followed by an underscore and a 4-letter abbreviation of its name. `FR_UGRV` which will result in a `ù` when using a software-implemented AZERTY layout. It's currently difficult to send such characters in just the firmware.

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