Fix up process_leader to be a bit more optimized (#4662)

* Fix up process_leader to be a bit more optimized

* Process dual function keys better

* Make leader start a callable function

* Fix per key timer call location

* Add escape if already leading

* Return false for KC_LEAD

* Add documentation

2 files changed, 32 insertions, 21 deletions

diff --git a/quantum/process_keycode/process_leader.c b/quantum/process_keycode/process_leader.c
index b32fc1db6..57fccdc7e 100644
--- a/quantum/process_keycode/process_leader.c
+++ b/quantum/process_keycode/process_leader.c
@@ -35,31 +35,42 @@ uint16_t leader_time = 0;
 uint16_t leader_sequence[5] = {0, 0, 0, 0, 0};
 uint8_t leader_sequence_size = 0;
 
+void qk_leader_start(void) {
+  if (leading) { return; }
+  leader_start();
+  leading = true;
+  leader_time = timer_read();
+  leader_sequence_size = 0;
+  leader_sequence[0] = 0;
+  leader_sequence[1] = 0;
+  leader_sequence[2] = 0;
+  leader_sequence[3] = 0;
+  leader_sequence[4] = 0;
+}
+
 bool process_leader(uint16_t keycode, keyrecord_t *record) {
   // Leader key set-up
   if (record->event.pressed) {
+    if (leading) {
+      if (timer_elapsed(leader_time) < LEADER_TIMEOUT) {
+#ifndef LEADER_KEY_STRICT_KEY_PROCESSING
+        if ((keycode >= QK_MOD_TAP && keycode <= QK_MOD_TAP_MAX) || (keycode >= QK_LAYER_TAP && keycode <= QK_LAYER_TAP_MAX)) {
+          keycode = keycode & 0xFF;
+        }
+#endif // LEADER_KEY_STRICT_KEY_PROCESSING
+        leader_sequence[leader_sequence_size] = keycode;
+        leader_sequence_size++;
 #ifdef LEADER_PER_KEY_TIMING
-    leader_time = timer_read();
+        leader_time = timer_read();
 #endif
-    if (!leading && keycode == KC_LEAD) {
-      leader_start();
-      leading = true;
-#ifndef LEADER_PER_KEY_TIMING
-      leader_time = timer_read();
-#endif
-      leader_time = timer_read();
-      leader_sequence_size = 0;
-      leader_sequence[0] = 0;
-      leader_sequence[1] = 0;
-      leader_sequence[2] = 0;
-      leader_sequence[3] = 0;
-      leader_sequence[4] = 0;
-      return false;
-    }
-    if (leading && timer_elapsed(leader_time) < LEADER_TIMEOUT) {
-      leader_sequence[leader_sequence_size] = keycode;
-      leader_sequence_size++;
-      return false;
+        return false;
+      }
+    } else {
+      if (keycode == KC_LEAD) {
+        qk_leader_start();
+        return false;
+      }
+      break;
     }
   }
   return true;
diff --git a/quantum/process_keycode/process_leader.h b/quantum/process_keycode/process_leader.h
index 59c3eed1b..15bccc3f6 100644
--- a/quantum/process_keycode/process_leader.h
+++ b/quantum/process_keycode/process_leader.h
@@ -24,7 +24,7 @@ bool process_leader(uint16_t keycode, keyrecord_t *record);
 
 void leader_start(void);
 void leader_end(void);
-
+void qk_leader_start(void);
 
 #define SEQ_ONE_KEY(key) if (leader_sequence[0] == (key) && leader_sequence[1] == 0 && leader_sequence[2] == 0 && leader_sequence[3] == 0 && leader_sequence[4] == 0)
 #define SEQ_TWO_KEYS(key1, key2) if (leader_sequence[0] == (key1) && leader_sequence[1] == (key2) && leader_sequence[2] == 0 && leader_sequence[3] == 0 && leader_sequence[4] == 0)