[Enhancement] More info on apply_autocorrect (#21056)

Co-authored-by: Drashna Jaelre <drashna@live.com>

quantum/process_keycode/process_autocorrect.c

@@ -1,5 +1,6 @@
 // Copyright 2021 Google LLC
 // Copyright 2021 @filterpaper
+// Copyright 2023 Pablo Martinez (@elpekenin) <elpekenin@elpekenin.dev>
 // SPDX-License-Identifier: Apache-2.0
 // Original source: https://getreuer.info/posts/keyboards/autocorrection
 
@@ -174,10 +175,12 @@ bool process_autocorrect_default_handler(uint16_t *keycode, keyrecord_t *record,
  *
  * @param backspaces number of characters to remove
  * @param str pointer to PROGMEM string to replace mistyped seletion with
+ * @param typo the wrong string that triggered a correction
+ * @param correct what it would become after the changes
  * @return true apply correction
  * @return false user handled replacement
  */
-__attribute__((weak)) bool apply_autocorrect(uint8_t backspaces, const char *str) {
+__attribute__((weak)) bool apply_autocorrect(uint8_t backspaces, const char *str, char *typo, char *correct) {
     return true;
 }
 
@@ -301,11 +304,57 @@ bool process_autocorrect(uint16_t keycode, keyrecord_t *record) {
 
         if (code & 128) { // A typo was found! Apply autocorrect.
             const uint8_t backspaces = (code & 63) + !record->event.pressed;
-            if (apply_autocorrect(backspaces, (char const *)(autocorrect_data + state + 1))) {
+            const char *  changes    = (const char *)(autocorrect_data + state + 1);
+
+            /* Gather info about the typo'd word
+             *
+             * Since buffer may contain several words, delimited by spaces, we
+             * iterate from the end to find the start and length of the typo
+             */
+            char typo[AUTOCORRECT_MAX_LENGTH + 1] = {0}; // extra char for null terminator
+
+            uint8_t typo_len   = 0;
+            uint8_t typo_start = 0;
+            bool    space_last = typo_buffer[typo_buffer_size - 1] == KC_SPC;
+            for (uint8_t i = typo_buffer_size; i > 0; --i) {
+                // stop counting after finding space (unless it is the last thing)
+                if (typo_buffer[i - 1] == KC_SPC && i != typo_buffer_size) {
+                    typo_start = i;
+                    break;
+                }
+
+                ++typo_len;
+            }
+
+            // when detecting 'typo:', reduce the length of the string by one
+            if (space_last) {
+                --typo_len;
+            }
+
+            // convert buffer of keycodes into a string
+            for (uint8_t i = 0; i < typo_len; ++i) {
+                typo[i] = typo_buffer[typo_start + i] - KC_A + 'a';
+            }
+
+            /* Gather the corrected word
+             *
+             * A) Correction of 'typo:' -- Code takes into account
+             * an extra backspace to delete the space (which we dont copy)
+             * for this reason the offset is correct to "skip" the null terminator
+             *
+             * B) When correcting 'typo' -- Need extra offset for terminator
+             */
+            char correct[AUTOCORRECT_MAX_LENGTH + 10] = {0}; // let's hope this is big enough
+
+            uint8_t offset = space_last ? backspaces : backspaces + 1;
+            strcpy(correct, typo);
+            strcpy_P(correct + typo_len - offset, changes);
+
+            if (apply_autocorrect(backspaces, changes, typo, correct)) {
                 for (uint8_t i = 0; i < backspaces; ++i) {
                     tap_code(KC_BSPC);
                 }
-                send_string_P((char const *)(autocorrect_data + state + 1));
+                send_string_P(changes);
             }
 
             if (keycode == KC_SPC) {