Process combos earlier & overlapping combos (#8591)

* Combo processing improvements.

Now it is possible to use ModTap and LayerTap keys as part of combos.
Overlapping combos also don't trigger all the combos, just exactly the
one that you press.

New settings:
- COMBO_MUST_HOLD_MODS
- COMBO_MOD_TERM
- COMBO_TERM_PER_COMBO
- COMBO_MUST_HOLD_PER_COMBO
- COMBO_STRICT_TIMER
- COMBO_NO_TIMER

* Remove the size flags from combo_t struct boolean members.

This in the end actually saves space as the members are accessed so many
times. The amount of operations needed to access the bits uses more
memory than setting the size saves.

* Fix `process_combo_key_release` not called correctly with tap-only combos

* Fix not passing a pointer when NO_ACTION_TAPPING is defined.

* Docs for `COMBO_ONLY_FROM_LAYER`

* Update docs/feature_combo.md

Co-authored-by: precondition <57645186+precondition@users.noreply.github.com>

* Update quantum/process_keycode/process_combo.c

Co-authored-by: precondition <57645186+precondition@users.noreply.github.com>

* Add `EXTRA_SHORT_COMBOS` option.

Stuff combo's `disabled` and `active` flags into `state`. Possibly can
save some space.

* Add more examples and clarify things with dict management system.

- Simple examples now has a combo that has modifiers included.
- The slightly more advanced examples now are actually more advanced
  instead of just `tap_code16(<modded-keycode>)`.
- Added a note that `COMBO_ACTION`s are not needed anymore as you can
  just use custom keycodes.
- Added a note that the `g/keymap_combo.h` macros use the
  `process_combo_event` function and that it is not usable in one's
  keymap afterwards.

* Update docs/feature_combo.md

Co-authored-by: precondition <57645186+precondition@users.noreply.github.com>

* Update docs/feature_combo.md

Co-authored-by: precondition <57645186+precondition@users.noreply.github.com>

* Update docs/feature_combo.md

Co-authored-by: precondition <57645186+precondition@users.noreply.github.com>

* Update docs/feature_combo.md

Co-authored-by: precondition <57645186+precondition@users.noreply.github.com>

* Update docs/feature_combo.md

Co-authored-by: precondition <57645186+precondition@users.noreply.github.com>

* Change "the" combo action example to "email" example.

* Update docs/feature_combo.md

Co-authored-by: precondition <57645186+precondition@users.noreply.github.com>

* Fix sneaky infinite loop with `combo_disable()`

No need to call `dump_key_buffer` when disabling combos because the
buffer is either being dumped if a combo-key was pressed, or the buffer is empty
if a non-combo-key is pressed.

* Update docs/feature_combo.md

Co-authored-by: precondition <57645186+precondition@users.noreply.github.com>

* Update docs/feature_combo.md

Co-authored-by: precondition <57645186+precondition@users.noreply.github.com>

Co-authored-by: precondition <57645186+precondition@users.noreply.github.com>
Co-authored-by: Drashna Jaelre <drashna@live.com>

11 files changed, 841 insertions, 165 deletions

diff --git a/docs/config_options.md b/docs/config_options.md
index 0c98b31010..78c1f70fd7 100644
--- a/docs/config_options.md
+++ b/docs/config_options.md
@@ -188,9 +188,21 @@ If you define these options you will enable the associated feature, which may in
     few ms of delay from this. But if you're doing chording on something with 3-4ms
     scan times? You probably want this.
 * `#define COMBO_COUNT 2`
-  * Set this to the number of combos that you're using in the [Combo](feature_combo.md) feature.
+  * Set this to the number of combos that you're using in the [Combo](feature_combo.md) feature. Or leave it undefined and programmatically set the count.
 * `#define COMBO_TERM 200`
   * how long for the Combo keys to be detected. Defaults to `TAPPING_TERM` if not defined.
+* `#define COMBO_MUST_HOLD_MODS`
+  * Flag for enabling extending timeout on Combos containing modifers
+* `#define COMBO_MOD_TERM 200`
+  * Allows for extending COMBO_TERM for mod keys while mid-combo. 
+* `#define COMBO_MUST_HOLD_PER_COMBO`
+  * Flag to enable per-combo COMBO_TERM extension and `get_combo_must_hold()` function
+* `#define COMBO_TERM_PER_COMBO`
+  * Flag to enable per-combo COMBO_TERM extension and `get_combo_term()` function
+* `#define COMBO_STRICT_TIMER`
+  * Only start the combo timer on the first key press instead of on all key presses.
+* `#define COMBO_NO_TIMER`
+  * Disable the combo timer completely for relaxed combos.
 * `#define TAP_CODE_DELAY 100`
   * Sets the delay between `register_code` and `unregister_code`, if you're having issues with it registering properly (common on VUSB boards). The value is in milliseconds.
 * `#define TAP_HOLD_CAPS_DELAY 80`
diff --git a/docs/feature_combo.md b/docs/feature_combo.md
index d831328f69..d98e6f2ac7 100644
--- a/docs/feature_combo.md
+++ b/docs/feature_combo.md
@@ -1,24 +1,39 @@
 # Combos
 
-The Combo feature is a chording type solution for adding custom actions.  It lets you hit multiple keys at once and produce a different effect.  For instance, hitting `A` and `S` within the tapping term would hit `ESC` instead, or have it perform even more complex tasks.
+The Combo feature is a chording type solution for adding custom actions. It lets you hit multiple keys at once and produce a different effect. For instance, hitting `A` and `S` within the combo term would hit `ESC` instead, or have it perform even more complex tasks.
 
 To enable this feature, you need to add `COMBO_ENABLE = yes` to your `rules.mk`.
 
-Additionally, in your `config.h`, you'll need to specify the number of combos that you'll be using, by adding `#define COMBO_COUNT 1` (replacing 1 with the number that you're using).
-<!-- At this time, this is necessary -->
+Additionally, in your `config.h`, you'll need to specify the number of combos that you'll be using, by adding `#define COMBO_COUNT 1` (replacing 1 with the number that you're using). It is also possible to not define this and instead set the variable `COMBO_LEN` yourself. There's a trick where we don't need to think about this variable at all. More on this later.
 
-Also, by default, the tapping term for the Combos is set to the same value as `TAPPING_TERM` (200 by default on most boards). But you can specify a different value by defining it in your `config.h`.  For instance: `#define COMBO_TERM 300` would set the time out period for combos to 300ms.
 
-Then, your `keymap.c` file, you'll need to define a sequence of keys, terminated with `COMBO_END`, and a structure to list the combination of keys, and it's resulting action.
+Then, in your `keymap.c` file, you'll need to define a sequence of keys, terminated with `COMBO_END`, and a structure to list the combination of keys, and its resulting action.
 
 ```c
-const uint16_t PROGMEM test_combo[] = {KC_A, KC_B, COMBO_END};
-combo_t key_combos[COMBO_COUNT] = {COMBO(test_combo, KC_ESC)};
+const uint16_t PROGMEM test_combo1[] = {KC_A, KC_B, COMBO_END};
+const uint16_t PROGMEM test_combo2[] = {KC_C, KC_D, COMBO_END};
+combo_t key_combos[COMBO_COUNT] = {
+    COMBO(test_combo1, KC_ESC),
+    COMBO(test_combo2, LCTL(KC_Z)), // keycodes with modifiers are possible too!
+};
 ```
 
-This will send "Escape" if you hit the A and B keys.
+This will send "Escape" if you hit the A and B keys, and Ctrl+Z when you hit the C and D keys.
+
+As of [PR#8591](https://github.com/qmk/qmk_firmware/pull/8591/), it is possible to fire combos from ModTap keys and LayerTap keys. So in the above example you could have keys `LSFT_T(KC_A)` and `LT(_LAYER, KC_B)` and it would work. So Home Row Mods and Home Row Combos at same time is now a thing!
 
-!> This method only supports [basic keycodes](keycodes_basic.md). See the examples for more control.
+It is also now possible to overlap combos. Before, with the example below both combos would activate when all three keys were pressed. Now only the three key combo will activate.
+
+```c
+const uint16_t PROGMEM test_combo1[] = {LSFT_T(KC_A), LT(_LAYER, KC_B), COMBO_END};
+const uint16_t PROGMEM test_combo2[] = {LSFT_T(KC_A), LT(_LAYER, KC_B), KC_C, COMBO_END};
+combo_t key_combos[COMBO_COUNT] = {
+    COMBO(test_combo1, KC_ESC)
+    COMBO(test_combo2, KC_TAB)
+};
+```
+
+Executing more complex keycodes like ModTaps and LayerTaps is now also possible.
 
 ## Examples
 
@@ -27,63 +42,68 @@ If you want to add a list, then you'd use something like this:
 ```c
 enum combos {
   AB_ESC,
-  JK_TAB
+  JK_TAB,
+  QW_SFT,
+  SD_LAYER,
 };
 
 const uint16_t PROGMEM ab_combo[] = {KC_A, KC_B, COMBO_END};
 const uint16_t PROGMEM jk_combo[] = {KC_J, KC_K, COMBO_END};
+const uint16_t PROGMEM qw_combo[] = {KC_Q, KC_W, COMBO_END};
+const uint16_t PROGMEM sd_combo[] = {KC_S, KC_D, COMBO_END};
 
 combo_t key_combos[COMBO_COUNT] = {
   [AB_ESC] = COMBO(ab_combo, KC_ESC),
-  [JK_TAB] = COMBO(jk_combo, KC_TAB)
+  [JK_TAB] = COMBO(jk_combo, KC_TAB),
+  [QW_SFT] = COMBO(qw_combo, KC_LSFT)
+  [SD_LAYER] = COMBO(layer_combo, MO(_LAYER)),
 };
 ```
 
 For a more complicated implementation, you can use the `process_combo_event` function to add custom handling.
+Additionally, this example shows how you can leave `COMBO_COUNT` undefined.
 
 ```c
 enum combo_events {
-  ZC_COPY,
-  XV_PASTE
+  EM_EMAIL,
+  BSPC_LSFT_CLEAR,
+  COMBO_LENGTH
 };
+uint16_t COMBO_LEN = COMBO_LENGTH; // remove the COMBO_COUNT define and use this instead!
 
-const uint16_t PROGMEM copy_combo[] = {KC_Z, KC_C, COMBO_END};
-const uint16_t PROGMEM paste_combo[] = {KC_X, KC_V, COMBO_END};
+const uint16_t PROGMEM email_combo[] = {KC_E, KC_M, COMBO_END};
+const uint16_t PROGMEM clear_line_combo[] = {KC_BSPC, KC_LSFT, COMBO_END};
 
-combo_t key_combos[COMBO_COUNT] = {
-  [ZC_COPY] = COMBO_ACTION(copy_combo),
-  [XV_PASTE] = COMBO_ACTION(paste_combo),
+combo_t key_combos[] = {
+  [EM_EMAIL] = COMBO_ACTION(email_combo),
+  [BSPC_LSFT_CLEAR] = COMBO_ACTION(clear_line_combo),
 };
+/* COMBO_ACTION(x) is same as COMBO(x, KC_NO) */
 
 void process_combo_event(uint16_t combo_index, bool pressed) {
   switch(combo_index) {
-    case ZC_COPY:
+    case EM_EMAIL:
       if (pressed) {
-        tap_code16(LCTL(KC_C));
+        SEND_STRING("john.doe@example.com");
       }
       break;
-    case XV_PASTE:
+    case BSPC_LSFT_CLEAR:
       if (pressed) {
-        tap_code16(LCTL(KC_V));
+        tap_code16(KC_END);
+        tap_code16(S(KC_HOME));
+        tap_code16(KC_BSPC);
       }
       break;
   }
 }
 ```
 
-This will send Ctrl+C if you hit Z and C, and Ctrl+V if you hit X and V.  But you could change this to do stuff like change layers, play sounds, or change settings.
-
-## Additional Configuration
+This will send "john.doe@example.com" if you chord E and M together, and clear the current line with Backspace and Left-Shift. You could change this to do stuff like play sounds or change settings.
 
-If you're using long combos, or even longer combos, you may run into issues with this, as the structure may not be large enough to accommodate what you're doing.
+It is worth noting that `COMBO_ACTION`s are not needed anymore. As of [PR#8591](https://github.com/qmk/qmk_firmware/pull/8591/), it is possible to run your own custom keycodes from combos. Just define the custom keycode, program its functionality in `process_record_user`, and define a combo with `COMBO(<key_array>, <your_custom_keycode>)`.
 
-In this case, you can add either `#define EXTRA_LONG_COMBOS` or `#define EXTRA_EXTRA_LONG_COMBOS` in your `config.h` file.
-
-You may also be able to enable action keys by defining `COMBO_ALLOW_ACTION_KEYS`.
-
-## Keycodes 
-
-You can enable, disable and toggle the Combo feature on the fly.  This is useful if you need to disable them temporarily, such as for a game. 
+## Keycodes
+You can enable, disable and toggle the Combo feature on the fly. This is useful if you need to disable them temporarily, such as for a game. The following keycodes are available for use in your `keymap.c`
 
 |Keycode   |Description                      |
 |----------|---------------------------------|
@@ -91,6 +111,187 @@ You can enable, disable and toggle the Combo feature on the fly.  This is useful
 |`CMB_OFF` |Turns off Combo feature          |
 |`CMB_TOG` |Toggles Combo feature on and off |
 
+# Advanced Configuration
+These configuration settings can be set in your `config.h` file.
+
+## Combo Term
+By default, the timeout for the Combos to be recognized is set to 50ms. This can be changed if accidental combo misfires are happening or if you're having difficulties pressing keys at the same time. For instance, `#define COMBO_TERM 40` would set the timeout period for combos to 40ms.
+
+## Buffer and state sizes
+If you're using long combos, or you have a lot of overlapping combos, you may run into issues with this, as the buffers may not be large enough to accommodate what you're doing. In this case, you can configure the sizes of the buffers used. Be aware, larger combo sizes and larger buffers will increase memory usage!
+
+To configure the amount of keys a combo can be composed of, change the following:
+
+| Keys | Define to be set                  |
+|------|-----------------------------------|
+| 6    | `#define EXTRA_SHORT_COMBOS`      |
+| 8    | QMK Default                       |
+| 16   | `#define EXTRA_LONG_COMBOS`       |
+| 32   | `#define EXTRA_EXTRA_LONG_COMBOS` |
+
+Defining `EXTRA_SHORT_COMBOS` combines a combo's internal state into just one byte. This can, in some cases, save some memory. If it doesn't, no point using it. If you do, you also have to make sure you don't define combos with more than 6 keys.
+
+Processing combos has two buffers, one for the key presses, another for the combos being activated. Use the following options to configure the sizes of these buffers:
+
+| Define                              | Default                                              |
+|-------------------------------------|------------------------------------------------------|
+| `#define COMBO_KEY_BUFFER_LENGTH 8` | 8 (the key amount `(EXTRA_)EXTRA_LONG_COMBOS` gives) |
+| `#define COMBO_BUFFER_LENGTH 4`     | 4                                                    |
+
+## Modifier Combos
+If a combo resolves to a Modifier, the window for processing the combo can be extended independently from normal combos. By default, this is disabled but can be enabled with `#define COMBO_MUST_HOLD_MODS`, and the time window can be configured with `#define COMBO_HOLD_TERM 150` (default: `TAPPING_TERM`). With `COMBO_MUST_HOLD_MODS`, you cannot tap the combo any more which makes the combo less prone to misfires.
+
+## Per Combo Timing, Holding and Tapping
+For each combo, it is possible to configure the time window it has to pressed in, if it needs to be held down, or if it needs to be tapped.
+
+For example, tap-only combos are useful if any (or all) of the underlying keys is a Mod-Tap or a Layer-Tap key. When you tap the combo, you get the combo result. When you press the combo and hold it down, the combo doesn't actually activate. Instead the keys are processed separately as if the combo wasn't even there.
+
+In order to use these features, the following configuration options and functions need to be defined. Coming up with useful timings and configuration is left as an exercise for the reader.
+
+| Config Flag                 | Function                                                  | Description                                                                                            |
+|-----------------------------|-----------------------------------------------------------|--------------------------------------------------------------------------------------------------------|
+| `COMBO_TERM_PER_COMBO`      | uint16_t get_combo_term(uint16_t index, combo_t \*combo)  | Optional per-combo timeout window. (default: `COMBO_TERM`)                                             |
+| `COMBO_MUST_HOLD_PER_COMBO` | bool get_combo_must_hold(uint16_t index, combo_t \*combo) | Controls if a given combo should fire immediately on tap or if it needs to be held. (default: `false`) |
+| `COMBO_MUST_TAP_PER_COMBO`  | bool get_combo_must_tap(uint16_t index, combo_t \*combo)  | Controls if a given combo should fire only if tapped within `COMBO_HOLD_TERM`. (default: `false`)      |
+
+Examples:
+```c
+uint16_t get_combo_term(uint16_t index, combo_t *combo) {
+    // decide by combo->keycode
+    switch (combo->keycode) {
+        case KC_X:
+            return 50;
+    }
+
+    // or with combo index, i.e. its name from enum.
+    switch (index) {
+        case COMBO_NAME_HERE:
+            return 9001;
+    }
+
+    // And if you're feeling adventurous, you can even decide by the keys in the chord,
+    // i.e. the exact array of keys you defined for the combo.
+    // This can be useful if your combos have a common key and you want to apply the
+    // same combo term for all of them.
+    if (combo->keys[0] == KC_ENTER) { // if first key in the array is KC_ENTER
+        return 150;
+    }
+
+    return COMBO_TERM;
+}
+
+bool get_combo_must_hold(uint16_t index, combo_t *combo) {
+    // Same as above, decide by keycode, the combo index, or by the keys in the chord.
+
+    if (KEYCODE_IS_MOD(combo->keycode) || 
+        (combo->keycode >= QK_MOMENTARY && combo->keycode <= QK_MOMENTARY_MAX) // MO(kc) keycodes
+        ) {
+        return true;
+    }
+
+    switch (index) {
+        case COMBO_NAME_HERE:
+            return true;
+    }
+
+    return false;
+}
+
+bool get_combo_must_tap(uint16_t index, combo_t *combo) {
+    // If you want all combos to be tap-only, just uncomment the next line
+    // return true
+
+    // If you want *all* combos, that have Mod-Tap/Layer-Tap/Momentary keys in its chord, to be tap-only, this is for you:
+    uint16_t key;
+    uint8_t idx = 0;
+    while ((key = pgm_read_word(&combo->keys[idx])) != COMBO_END) {
+        switch (key) {
+            case QK_MOD_TAP...QK_MOD_TAP_MAX:
+            case QK_LAYER_TAP...QK_LAYER_TAP_MAX:
+            case QK_MOMENTARY...QK_MOMENTARY_MAX:
+                return true;
+        }
+        idx += 1;
+    }
+    return false;
+
+}
+```
+
+## Variable Length Combos
+If you leave `COMBO_COUNT` undefined in `config.h`, it allows you to programmatically declare the size of the Combo data structure and avoid updating `COMBO_COUNT`. Instead a variable called `COMBO_LEN` has to be set. It can be set with something similar to the following in `keymap.c`: `uint16_t COMBO_LEN = sizeof(key_combos) / sizeof(key_combos[0]);` or by adding `COMBO_LENGTH` as the *last* entry in the combo enum and then `uint16_t COMBO_LEN = COMBO_LENGTH;` as such:
+```c
+enum myCombos {
+    ...,
+    COMBO_LENGTH
+};
+uint16_t COMBO_LEN = COMBO_LENGTH;
+```
+Regardless of the method used to declare `COMBO_LEN`, this also requires to convert the `combo_t key_combos[COMBO_COUNT] = {...};` line to `combo_t key_combos[] = {...};`.
+
+
+## Combo timer
+
+Normally, the timer is started on the first key press and then reset on every subsequent key press within the `COMBO_TERM`.
+Inputting combos is relaxed like this, but also slightly more prone to accidental misfires.
+
+The next two options alter the behaviour of the timer.
+
+### `#define COMBO_STRICT_TIMER`
+
+With `COMBO_STRICT_TIMER`, the timer is started only on the first key press.
+Inputting combos is now less relaxed; you need to make sure the full chord is pressed within the `COMBO_TERM`.
+Misfires are less common but if you type multiple combos fast, there is a
+chance that the latter ones might not activate properly.
+
+### `#define COMBO_NO_TIMER`
+
+By defining `COMBO_NO_TIMER`, the timer is disabled completely and combos are activated on the first key release.
+This also disables the "must hold" functionalities as they just wouldn't work at all.
+
+## Customizable key releases
+
+By defining `COMBO_PROCESS_KEY_RELEASE` and implementing the function `bool process_combo_key_release(uint16_t combo_index, combo_t *combo, uint8_t key_index, uint16_t keycode)`, you can run your custom code on each key release after a combo was activated. For example you could change the RGB colors, activate haptics, or alter the modifiers.
+
+You can also release a combo early by returning `true` from the function.
+
+Here's an example where a combo resolves to two modifiers, and on key releases the modifiers are unregistered one by one, depending on which key was released.
+
+```c
+enum combos {
+  AB_MODS,
+  COMBO_LENGTH
+};
+uint16_t COMBO_LEN = COMBO_LENGTH;
+
+const uint16_t PROGMEM ab_combo[] = {KC_A, KC_B, COMBO_END};
+
+combo_t key_combos[] = {
+  [AB_MODS] = COMBO(ab_combo, LCTL(KC_LSFT)),
+};
+
+bool process_combo_key_release(uint16_t combo_index, combo_t *combo, uint8_t key_index, uint16_t keycode) {
+    switch (combo_index) {
+        case AB_MODS:
+            switch(keycode) {
+                case KC_A:
+                    unregister_mods(MOD_MASK_CTRL);
+                    break;
+                case KC_B:
+                    unregister_mods(MOD_MASK_SHIFT);
+                    break;
+            }
+            return false; // do not release combo
+    }
+    return false;
+}
+```
+## Layer independent combos
+
+If you, for example, use multiple base layers for different key layouts, one for QWERTY, and another one for Colemak, you might want your combos to work from the same key positions on all layers. Defining the same combos again for another layout is redundant and takes more memory. The solution is to just check the keycodes from one layer.
+
+With `#define COMBO_ONLY_FROM_LAYER _LAYER_A` the combos' keys are always checked from layer `_LAYER_A` even though the active layer would be `_LAYER_B`.
+
 ## User callbacks
 
 In addition to the keycodes, there are a few functions that you can use to set the status, or check it:
@@ -101,3 +302,28 @@ In addition to the keycodes, there are a few functions that you can use to set t
 | `combo_disable()`    | Disables the combo feature, and clears the combo buffer |
 | `combo_toggle()`     | Toggles the state of the combo feature                  |
 | `is_combo_enabled()` | Returns the status of the combo feature state (true or false) |
+
+
+# Dictionary Management
+
+Having 3 places to update when adding new combos or altering old ones does become cumbersome when you have a lot of combos. We can alleviate this with some magic! ... If you consider C macros magic.
+First, you need to add `VPATH += keyboards/gboards` to your `rules.mk`. Next, include the file `g/keymap_combo.h` in your `keymap.c`.
+
+!> This functionality uses the same `process_combo_event` function as `COMBO_ACTION` macros do, so you cannot use the function yourself in your keymap. Instead, you have to define the `case`s of the `switch` statement by themselves within `inject.h`, which `g/keymap_combo.h` will then include into the function.
+
+Then, write your combos in `combos.def` file in the following manner:
+
+```c
+//   name     result    chord keys
+COMB(AB_ESC,   KC_ESC,   KC_A, KC_B)
+COMB(JK_TAB,   KC_TAB,   KC_J, KC_K)
+COMB(JKL_SPC,  KC_SPC,   KC_J, KC_K, KC_L)
+COMB(BSSL_CLR, KC_NO,    KC_BSPC, KC_LSFT) // using KC_NO as the resulting keycode is the same as COMBO_ACTION before.
+COMB(QW_UNDO,  C(KC_Z),  KC_Q, KC_W)
+SUBS(TH_THE,   "the",    KC_T, KC_H) // SUBS uses SEND_STRING to output the given string.
+...
+```
+
+Now, you can update only one place to add or alter combos. You don't even need to remember to update the `COMBO_COUNT` or the `COMBO_LEN` variables at all. Everything is taken care of. Magic!
+
+For small to huge ready made dictionaries of combos, you can check out http://combos.gboards.ca/.
diff --git a/keyboards/gboards/g/keymap_combo.h b/keyboards/gboards/g/keymap_combo.h
index 58e99863ea..b92b6a4bc4 100644
--- a/keyboards/gboards/g/keymap_combo.h
+++ b/keyboards/gboards/g/keymap_combo.h
@@ -28,7 +28,10 @@
 #define TOGG A_ENUM
 enum combos {
 #include "combos.def"
+    COMBO_LENGTH
 };
+// Export length to combo module
+uint16_t COMBO_LEN = COMBO_LENGTH;
 
 // Bake combos into mem
 #undef COMB
@@ -53,9 +56,6 @@ combo_t key_combos[] = {
 #undef SUBS
 #undef TOGG
 
-// Export length to combo module
-int COMBO_LEN = sizeof(key_combos) / sizeof(key_combos[0]);
-
 // Fill QMK hook
 #define COMB BLANK
 #define SUBS A_ACTI
diff --git a/quantum/keymap_common.c b/quantum/keymap_common.c
index e0fd6d4793..780c71ab9b 100644
--- a/quantum/keymap_common.c
+++ b/quantum/keymap_common.c
@@ -40,7 +40,10 @@ extern keymap_config_t keymap_config;
 action_t action_for_key(uint8_t layer, keypos_t key) {
     // 16bit keycodes - important
     uint16_t keycode = keymap_key_to_keycode(layer, key);
+    return action_for_keycode(keycode);
+};
 
+action_t action_for_keycode(uint16_t keycode) {
     // keycode remapping
     keycode = keycode_config(keycode);
 
diff --git a/quantum/process_keycode/process_combo.c b/quantum/process_keycode/process_combo.c
index 9e16292486..b4e698decd 100644
--- a/quantum/process_keycode/process_combo.c
+++ b/quantum/process_keycode/process_combo.c
@@ -16,114 +16,445 @@
 
 #include "print.h"
 #include "process_combo.h"
+#include "action_tapping.h"
 
-#ifndef COMBO_VARIABLE_LEN
-__attribute__((weak)) combo_t key_combos[COMBO_COUNT] = {};
+
+#ifdef COMBO_COUNT
+__attribute__((weak)) combo_t  key_combos[COMBO_COUNT];
+uint16_t COMBO_LEN = COMBO_COUNT;
 #else
 extern combo_t  key_combos[];
-extern int      COMBO_LEN;
+extern uint16_t COMBO_LEN;
 #endif
 
 __attribute__((weak)) void process_combo_event(uint16_t combo_index, bool pressed) {}
 
-static uint16_t timer               = 0;
-static uint16_t current_combo_index = 0;
-static bool     drop_buffer         = false;
-static bool     is_active           = false;
-static bool     b_combo_enable      = true;  // defaults to enabled
+#ifdef COMBO_MUST_HOLD_PER_COMBO
+__attribute__((weak)) bool get_combo_must_hold(uint16_t index, combo_t *combo) { return false; }
+#endif
+
+#ifdef COMBO_MUST_TAP_PER_COMBO
+__attribute__((weak)) bool get_combo_must_tap(uint16_t index, combo_t *combo) { return false; }
+#endif
 
-static uint8_t buffer_size = 0;
-#ifdef COMBO_ALLOW_ACTION_KEYS
-static keyrecord_t key_buffer[MAX_COMBO_LENGTH];
+#ifdef COMBO_TERM_PER_COMBO
+__attribute__((weak)) uint16_t get_combo_term(uint16_t index, combo_t *combo) { return COMBO_TERM; }
+#endif
+
+#ifdef COMBO_PROCESS_KEY_RELEASE
+__attribute__((weak)) bool process_combo_key_release(uint16_t combo_index, combo_t *combo, uint8_t key_index, uint16_t keycode) { return false; }
+#endif
+
+#ifndef COMBO_NO_TIMER
+static uint16_t timer                 = 0;
+#endif
+static bool     b_combo_enable        = true;  // defaults to enabled
+static uint16_t longest_term          = 0;
+
+typedef struct {
+    keyrecord_t record;
+    uint16_t combo_index;
+    uint16_t keycode;
+} queued_record_t;
+static uint8_t key_buffer_size = 0;
+static queued_record_t key_buffer[COMBO_KEY_BUFFER_LENGTH];
+
+typedef struct {
+    uint16_t combo_index;
+} queued_combo_t;
+static uint8_t combo_buffer_write= 0;
+static uint8_t combo_buffer_read = 0;
+static queued_combo_t combo_buffer[COMBO_BUFFER_LENGTH];
+
+#define INCREMENT_MOD(i) i = (i + 1) % COMBO_BUFFER_LENGTH
+
+#define COMBO_KEY_POS ((keypos_t){.col=254, .row=254})
+
+
+#ifndef EXTRA_SHORT_COMBOS
+/* flags are their own elements in combo_t struct. */
+#    define COMBO_ACTIVE(combo)   (combo->active)
+#    define COMBO_DISABLED(combo) (combo->disabled)
+#    define COMBO_STATE(combo)    (combo->state)
+
+#    define ACTIVATE_COMBO(combo)    do {combo->active = true;}while(0)
+#    define DEACTIVATE_COMBO(combo)  do {combo->active = false;}while(0)
+#    define DISABLE_COMBO(combo)     do {combo->disabled = true;}while(0)
+#    define RESET_COMBO_STATE(combo) do { \
+    combo->disabled = false; \
+    combo->state = 0; \
+}while(0)
 #else
-static uint16_t key_buffer[MAX_COMBO_LENGTH];
+/* flags are at the two high bits of state. */
+#    define COMBO_ACTIVE(combo)   (combo->state & 0x80)
+#    define COMBO_DISABLED(combo) (combo->state & 0x40)
+#    define COMBO_STATE(combo)    (combo->state & 0x3F)
+
+#    define ACTIVATE_COMBO(combo)    do {combo->state |= 0x80;}while(0)
+#    define DEACTIVATE_COMBO(combo)  do {combo->state &= ~0x80;}while(0)
+#    define DISABLE_COMBO(combo)     do {combo->state |= 0x40;}while(0)
+#    define RESET_COMBO_STATE(combo) do {combo->state &= ~0x7F;}while(0)
 #endif
 
-static inline void send_combo(uint16_t action, bool pressed) {
-    if (action) {
-        if (pressed) {
-            register_code16(action);
-        } else {
-            unregister_code16(action);
-        }
+static inline void release_combo(uint16_t combo_index, combo_t *combo) {
+    if (combo->keycode) {
+        keyrecord_t record = {
+            .event = {
+                .key = COMBO_KEY_POS,
+                .time = timer_read()|1,
+                .pressed = false,
+            },
+            .keycode = combo->keycode,
+        };
+#ifndef NO_ACTION_TAPPING
+        action_tapping_process(record);
+#else
+        process_record(&record);
+#endif
     } else {
-        process_combo_event(current_combo_index, pressed);
+        process_combo_event(combo_index, false);
+    }
+    DEACTIVATE_COMBO(combo);
+}
+
+static inline bool _get_combo_must_hold(uint16_t combo_index, combo_t *combo) {
+#ifdef COMBO_NO_TIMER
+    return false;
+#elif defined(COMBO_MUST_HOLD_PER_COMBO)
+    return get_combo_must_hold(combo_index, combo);
+#elif defined(COMBO_MUST_HOLD_MODS)
+    return (KEYCODE_IS_MOD(combo->keycode) ||
+            (combo->keycode >= QK_MOMENTARY && combo->keycode <= QK_MOMENTARY_MAX));
+#endif
+    return false;
+}
+
+static inline uint16_t _get_wait_time(uint16_t combo_index, combo_t *combo ) {
+    if (_get_combo_must_hold(combo_index, combo)
+#ifdef COMBO_MUST_TAP_PER_COMBO
+            || get_combo_must_tap(combo_index, combo)
+#endif
+       ) {
+        if (longest_term < COMBO_HOLD_TERM) {
+            return COMBO_HOLD_TERM;
+        }
+    }
+
+    return longest_term;
+}
+
+static inline uint16_t _get_combo_term(uint16_t combo_index, combo_t *combo) {
+
+#if defined(COMBO_TERM_PER_COMBO)
+        return get_combo_term(combo_index, combo);
+#endif
+
+    return COMBO_TERM;
+}
+
+void clear_combos(void) {
+    uint16_t index = 0;
+    longest_term = 0;
+    for (index = 0; index < COMBO_LEN; ++index) {
+        combo_t *combo = &key_combos[index];
+        if (!COMBO_ACTIVE(combo)) {
+            RESET_COMBO_STATE(combo);
+        }
     }
 }
 
-static inline void dump_key_buffer(bool emit) {
-    if (buffer_size == 0) {
+static inline void dump_key_buffer(void) {
+    if (key_buffer_size == 0) {
         return;
     }
 
-    if (emit) {
-        for (uint8_t i = 0; i < buffer_size; i++) {
-#ifdef COMBO_ALLOW_ACTION_KEYS
-            const action_t action = store_or_get_action(key_buffer[i].event.pressed, key_buffer[i].event.key);
-            process_action(&(key_buffer[i]), action);
+    for (uint8_t key_buffer_i = 0; key_buffer_i < key_buffer_size; key_buffer_i++) {
+
+        queued_record_t *qrecord = &key_buffer[key_buffer_i];
+        keyrecord_t *record = &qrecord->record;
+
+        if (IS_NOEVENT(record->event)) {
+            continue;
+        }
+
+        if (!record->keycode && qrecord->combo_index != (uint16_t)-1) {
+            process_combo_event(qrecord->combo_index, true);
+        } else {
+#ifndef NO_ACTION_TAPPING
+        action_tapping_process(*record);
 #else
-            register_code16(key_buffer[i]);
-            send_keyboard_report();
+        process_record(record);
 #endif
         }
+        record->event.time = 0;
     }
 
-    buffer_size = 0;
+    key_buffer_size = 0;
 }
 
-#define ALL_COMBO_KEYS_ARE_DOWN (((1 << count) - 1) == combo->state)
-#define KEY_STATE_DOWN(key)         \
-    do {                            \
-        combo->state |= (1 << key); \
+#define NO_COMBO_KEYS_ARE_DOWN (0 == COMBO_STATE(combo))
+#define ALL_COMBO_KEYS_ARE_DOWN(state, key_count) (((1 << key_count) - 1) == state)
+#define ONLY_ONE_KEY_IS_DOWN(state) !(state & (state - 1))
+#define KEY_NOT_YET_RELEASED(state, key_index) ((1 << key_index) & state)
+#define KEY_STATE_DOWN(state, key_index) \
+    do {                                 \
+        state |= (1 << key_index);       \
     } while (0)
-#define KEY_STATE_UP(key)            \
-    do {                             \
-        combo->state &= ~(1 << key); \
+#define KEY_STATE_UP(state, key_index) \
+    do {                               \
+        state &= ~(1 << key_index);    \
     } while (0)
 
-static bool process_single_combo(combo_t *combo, uint16_t keycode, keyrecord_t *record) {
-    uint8_t  count = 0;
-    uint16_t index = -1;
-    /* Find index of keycode and number of combo keys */
-    for (const uint16_t *keys = combo->keys;; ++count) {
-        uint16_t key = pgm_read_word(&keys[count]);
-        if (keycode == key) index = count;
+static inline void _find_key_index_and_count(const uint16_t *keys, uint16_t keycode, uint16_t *key_index, uint8_t *key_count) {
+    while (true) {
+        uint16_t key = pgm_read_word(&keys[*key_count]);
+        if (keycode == key) *key_index = *key_count;
         if (COMBO_END == key) break;
+        (*key_count)++;
+    }
+}
+
+void drop_combo_from_buffer(uint16_t combo_index) {
+    /* Mark a combo as processed from the buffer. If the buffer is in the
+     * beginning of the buffer, drop it.  */
+    uint8_t i = combo_buffer_read;
+    while (i != combo_buffer_write) {
+        queued_combo_t *qcombo = &combo_buffer[i];
+
+        if (qcombo->combo_index == combo_index) {
+            combo_t *combo = &key_combos[combo_index];
+            DISABLE_COMBO(combo);
+
+            if (i == combo_buffer_read) {
+                INCREMENT_MOD(combo_buffer_read);
+            }
+            break;
+        }
+        INCREMENT_MOD(i);
     }
+}
+
+void apply_combo(uint16_t combo_index, combo_t *combo) {
+    /* Apply combo's result keycode to the last chord key of the combo and
+     * disable the other keys. */
 
-    /* Continue processing if not a combo key */
-    if (-1 == (int8_t)index) return false;
+    if (COMBO_DISABLED(combo)) { return; }
 
-    bool is_combo_active = is_active;
+    // state to check against so we find the last key of the combo from the buffer
+#if defined(EXTRA_EXTRA_LONG_COMBOS)
+    uint32_t state = 0;
+#elif defined(EXTRA_LONG_COMBOS)
+    uint16_t state = 0;
+#else
+    uint8_t state = 0;
+#endif
+
+    for (uint8_t key_buffer_i = 0; key_buffer_i < key_buffer_size; key_buffer_i++) {
+
+        queued_record_t *qrecord = &key_buffer[key_buffer_i];
+        keyrecord_t *record = &qrecord->record;
+        uint16_t keycode = qrecord->keycode;
+
+        uint8_t key_count = 0;
+        uint16_t key_index = -1;
+        _find_key_index_and_count(combo->keys, keycode, &key_index, &key_count);
+
+        if (-1 == (int16_t)key_index) {
+            // key not part of this combo
+            continue;
+        }
 
-    if (record->event.pressed) {
-        KEY_STATE_DOWN(index);
+        KEY_STATE_DOWN(state, key_index);
+        if (ALL_COMBO_KEYS_ARE_DOWN(state, key_count)) {
+            // this in the end executes the combo when the key_buffer is dumped.
+            record->keycode = combo->keycode;
+            record->event.key = COMBO_KEY_POS;
 
-        if (is_combo_active) {
-            if (ALL_COMBO_KEYS_ARE_DOWN) { /* Combo was pressed */
-                send_combo(combo->keycode, true);
-                drop_buffer = true;
+            qrecord->combo_index = combo_index;
+            ACTIVATE_COMBO(combo);
+
+            break;
+        } else {
+            // key was part of the combo but not the last one, "disable" it
+            // by making it a TICK event.
+            record->event.time = 0;
+        }
+
+    }
+    drop_combo_from_buffer(combo_index);
+}
+
+static inline void apply_combos(void) {
+    // Apply all buffered normal combos.
+    for (uint8_t i = combo_buffer_read;
+            i != combo_buffer_write;
+            INCREMENT_MOD(i)) {
+
+        queued_combo_t *buffered_combo = &combo_buffer[i];
+        combo_t *combo = &key_combos[buffered_combo->combo_index];
+
+#ifdef COMBO_MUST_TAP_PER_COMBO
+        if (get_combo_must_tap(buffered_combo->combo_index, combo)) {
+            // Tap-only combos are applied on key release only, so let's drop 'em here.
+            drop_combo_from_buffer(buffered_combo->combo_index);
+            continue;
+        }
+#endif
+        apply_combo(buffered_combo->combo_index, combo);
+    }
+    dump_key_buffer();
+    clear_combos();
+}
+
+combo_t* overlaps(combo_t *combo1, combo_t *combo2) {
+    /* Checks if the combos overlap and returns the combo that should be
+     * dropped from the combo buffer.
+     * The combo that has less keys will be dropped. If they have the same
+     * amount of keys, drop combo1. */
+
+    uint8_t idx1 = 0, idx2 = 0;
+    uint16_t key1, key2;
+    bool overlaps = false;
+
+    while ((key1 = pgm_read_word(&combo1->keys[idx1])) != COMBO_END) {
+        idx2 = 0;
+        while ((key2 = pgm_read_word(&combo2->keys[idx2])) != COMBO_END) {
+            if (key1 == key2) overlaps = true;
+            idx2 += 1;
+        }
+        idx1 += 1;
+    }
+
+    if (!overlaps) return NULL;
+    if (idx2 < idx1) return combo2;
+    return combo1;
+}
+
+static bool process_single_combo(combo_t *combo, uint16_t keycode, keyrecord_t *record, uint16_t combo_index) {
+    uint8_t key_count = 0;
+    uint16_t key_index = -1;
+    _find_key_index_and_count(combo->keys, keycode, &key_index, &key_count);
+
+    /* Continue processing if key isn't part of current combo. */
+    if (-1 == (int16_t)key_index) {
+        return false;
+    }
+
+    bool key_is_part_of_combo = !COMBO_DISABLED(combo);
+
+    if (record->event.pressed && !COMBO_DISABLED(combo)) {
+        uint16_t time = _get_combo_term(combo_index, combo);
+        if (!COMBO_ACTIVE(combo)) {
+            KEY_STATE_DOWN(combo->state, key_index);
+            if (longest_term < time) {
+                longest_term = time;
             }
         }
+        if (ALL_COMBO_KEYS_ARE_DOWN(COMBO_STATE(combo), key_count)) {
+            /* Combo was fully pressed */
+            /* Buffer the combo so we can fire it after COMBO_TERM */
+
+#ifndef COMBO_NO_TIMER
+            /* Don't buffer this combo if its combo term has passed. */
+            if (timer && timer_elapsed(timer) > time) {
+                DISABLE_COMBO(combo);
+                return true;
+            } else
+#endif
+            {
+
+                // disable readied combos that overlap with this combo
+                combo_t *drop = NULL;
+                for (uint8_t combo_buffer_i = combo_buffer_read;
+                        combo_buffer_i != combo_buffer_write;
+                        INCREMENT_MOD(combo_buffer_i)) {
+
+                    queued_combo_t *qcombo = &combo_buffer[combo_buffer_i];
+                    combo_t *buffered_combo = &key_combos[qcombo->combo_index];
+
+                    if ((drop = overlaps(buffered_combo, combo))) {
+                        DISABLE_COMBO(drop);
+                        if (drop == combo) {
+                            // stop checking for overlaps if dropped combo was current combo.
+                            break;
+                        } else if (combo_buffer_i == combo_buffer_read && drop == buffered_combo) {
+                            /* Drop the disabled buffered combo from the buffer if
+                             * it is in the beginning of the buffer. */
+                            INCREMENT_MOD(combo_buffer_read);
+                        }
+                    }
+
+                }
+
+                if (drop != combo) {
+                    // save this combo to buffer
+                    combo_buffer[combo_buffer_write] = (queued_combo_t){
+                        .combo_index=combo_index,
+                    };
+                    INCREMENT_MOD(combo_buffer_write);
+
+                    // get possible longer waiting time for tap-/hold-only combos.
+                    longest_term = _get_wait_time(combo_index, combo);
+                }
+            } // if timer elapsed end
+
+        }
     } else {
-        if (ALL_COMBO_KEYS_ARE_DOWN) { /* Combo was released */
-            send_combo(combo->keycode, false);
+        // chord releases
+        if (!COMBO_ACTIVE(combo) && ALL_COMBO_KEYS_ARE_DOWN(COMBO_STATE(combo), key_count)) {
+            /* First key quickly released */
+            if (COMBO_DISABLED(combo) || _get_combo_must_hold(combo_index, combo)) {
+                // combo wasn't tappable, disable it and drop it from buffer.
+                drop_combo_from_buffer(combo_index);
+                key_is_part_of_combo = false;
+            }
+#ifdef COMBO_MUST_TAP_PER_COMBO
+            else if (get_combo_must_tap(combo_index, combo)) {
+                // immediately apply tap-only combo
+                apply_combo(combo_index, combo);
+                apply_combos(); // also apply other prepared combos and dump key buffer
+#    ifdef COMBO_PROCESS_KEY_RELEASE
+                if (process_combo_key_release(combo_index, combo, key_index, keycode)) {
+                    release_combo(combo_index, combo);
+                }
+#    endif
+            }
+#endif
+        } else if (COMBO_ACTIVE(combo)
+                && ONLY_ONE_KEY_IS_DOWN(COMBO_STATE(combo))
+                && KEY_NOT_YET_RELEASED(COMBO_STATE(combo), key_index)
+                ) {
+            /* last key released */
+            release_combo(combo_index, combo);
+            key_is_part_of_combo = true;
+
+#ifdef COMBO_PROCESS_KEY_RELEASE
+            process_combo_key_release(combo_index, combo, key_index, keycode);
+#endif
+        } else if (COMBO_ACTIVE(combo)
+                && KEY_NOT_YET_RELEASED(COMBO_STATE(combo), key_index)
+                ) {
+            /* first or middle key released */
+            key_is_part_of_combo = true;
+
+#ifdef COMBO_PROCESS_KEY_RELEASE
+            if (process_combo_key_release(combo_index, combo, key_index, keycode)) {
+                release_combo(combo_index, combo);
+            }
+#endif
         } else {
-            /* continue processing without immediately returning */
-            is_combo_active = false;
+            /* The released key was part of an incomplete combo */
+            key_is_part_of_combo = false;
         }
 
-        KEY_STATE_UP(index);
+        KEY_STATE_UP(combo->state, key_index);
     }
 
-    return is_combo_active;
+    return key_is_part_of_combo;
 }
 
-#define NO_COMBO_KEYS_ARE_DOWN (0 == combo->state)
-
 bool process_combo(uint16_t keycode, keyrecord_t *record) {
     bool is_combo_key          = false;
-    drop_buffer                = false;
     bool no_combo_keys_pressed = true;
 
     if (keycode == CMB_ON && record->event.pressed) {
@@ -144,62 +475,81 @@ bool process_combo(uint16_t keycode, keyrecord_t *record) {
     if (!is_combo_enabled()) {
         return true;
     }
-#ifndef COMBO_VARIABLE_LEN
-    for (current_combo_index = 0; current_combo_index < COMBO_COUNT; ++current_combo_index) {
-#else
-    for (current_combo_index = 0; current_combo_index < COMBO_LEN; ++current_combo_index) {
+
+#ifdef COMBO_ONLY_FROM_LAYER
+    /* Only check keycodes from one layer. */
+    keycode = keymap_key_to_keycode(COMBO_ONLY_FROM_LAYER, record->event.key);
 #endif
-        combo_t *combo = &key_combos[current_combo_index];
-        is_combo_key |= process_single_combo(combo, keycode, record);
-        no_combo_keys_pressed = no_combo_keys_pressed && NO_COMBO_KEYS_ARE_DOWN;
+
+    for (uint16_t idx = 0; idx < COMBO_LEN; ++idx) {
+        combo_t *combo = &key_combos[idx];
+        is_combo_key |= process_single_combo(combo, keycode, record, idx);
+        no_combo_keys_pressed = no_combo_keys_pressed && (NO_COMBO_KEYS_ARE_DOWN || COMBO_ACTIVE(combo) || COMBO_DISABLED(combo));
     }
 
-    if (drop_buffer) {
-        /* buffer is only dropped when we complete a combo, so we refresh the timer
-         * here */
-        timer = timer_read();
-        dump_key_buffer(false);
-    } else if (!is_combo_key) {
-        /* if no combos claim the key we need to emit the keybuffer */
-        dump_key_buffer(true);
-
-        // reset state if there are no combo keys pressed at all
-        if (no_combo_keys_pressed) {
-            timer     = 0;
-            is_active = true;
-        }
-    } else if (record->event.pressed && is_active) {
-        /* otherwise the key is consumed and placed in the buffer */
+    if (record->event.pressed && is_combo_key) {
+#ifndef COMBO_NO_TIMER
+#   ifdef COMBO_STRICT_TIMER
+        if (!timer) {
+            // timer is set only on the first key
+            timer = timer_read();
+        }
+#   else
         timer = timer_read();
+#   endif
+#endif
 
-        if (buffer_size < MAX_COMBO_LENGTH) {
-#ifdef COMBO_ALLOW_ACTION_KEYS
-            key_buffer[buffer_size++] = *record;
-#else
-            key_buffer[buffer_size++] = keycode;
+        if (key_buffer_size < COMBO_KEY_BUFFER_LENGTH) {
+            key_buffer[key_buffer_size++] = (queued_record_t){
+                .record = *record,
+                .keycode = keycode,
+                .combo_index = -1, // this will be set when applying combos
+            };
+        }
+    } else {
+        if (combo_buffer_read != combo_buffer_write) {
+            // some combo is prepared
+            apply_combos();
+        } else {
+            // reset state if there are no combo keys pressed at all
+            dump_key_buffer();
+#ifndef COMBO_NO_TIMER
+            timer = 0;
 #endif
+            clear_combos();
         }
     }
-
     return !is_combo_key;
 }
 
 void combo_task(void) {
-    if (b_combo_enable && is_active && timer && timer_elapsed(timer) > COMBO_TERM) {
-        /* This disables the combo, meaning key events for this
-         * combo will be handled by the next processors in the chain
-         */
-        is_active = false;
-        dump_key_buffer(true);
+    if (!b_combo_enable) {
+        return;
     }
+
+#ifndef COMBO_NO_TIMER
+    if (timer && timer_elapsed(timer) > longest_term) {
+        if (combo_buffer_read != combo_buffer_write) {
+            apply_combos();
+            longest_term = 0;
+            timer = 0;
+        } else {
+            dump_key_buffer();
+            timer = 0;
+            clear_combos();
+        }
+    }
+#endif
 }
 
 void combo_enable(void) { b_combo_enable = true; }
 
 void combo_disable(void) {
-    b_combo_enable = is_active = false;
+#ifndef COMBO_NO_TIMER
     timer                      = 0;
-    dump_key_buffer(true);
+#endif
+    b_combo_enable = false;
+    combo_buffer_read = combo_buffer_write;
 }
 
 void combo_toggle(void) {
diff --git a/quantum/process_keycode/process_combo.h b/quantum/process_keycode/process_combo.h
index 9af97588b2..43c36d79e6 100644
--- a/quantum/process_keycode/process_combo.h
+++ b/quantum/process_keycode/process_combo.h
@@ -20,23 +20,38 @@
 #include "quantum.h"
 #include <stdint.h>
 
-#ifdef EXTRA_EXTRA_LONG_COMBOS
+#ifdef EXTRA_SHORT_COMBOS
+#    define MAX_COMBO_LENGTH 6
+#elif defined(EXTRA_EXTRA_LONG_COMBOS)
 #    define MAX_COMBO_LENGTH 32
-#elif EXTRA_LONG_COMBOS
+#elif defined(EXTRA_LONG_COMBOS)
 #    define MAX_COMBO_LENGTH 16
 #else
 #    define MAX_COMBO_LENGTH 8
 #endif
 
+#ifndef COMBO_KEY_BUFFER_LENGTH
+#    define COMBO_KEY_BUFFER_LENGTH MAX_COMBO_LENGTH
+#endif
+#ifndef COMBO_BUFFER_LENGTH
+#    define COMBO_BUFFER_LENGTH 4
+#endif
+
 typedef struct {
     const uint16_t *keys;
     uint16_t        keycode;
-#ifdef EXTRA_EXTRA_LONG_COMBOS
+#ifdef EXTRA_SHORT_COMBOS
+    uint8_t state;
+#else
+    bool disabled;
+    bool active;
+#    if defined(EXTRA_EXTRA_LONG_COMBOS)
     uint32_t state;
-#elif EXTRA_LONG_COMBOS
+#    elif defined(EXTRA_LONG_COMBOS)
     uint16_t state;
-#else
+#    else
     uint8_t state;
+#    endif
 #endif
 } combo_t;
 
@@ -46,12 +61,15 @@ typedef struct {
     { .keys = &(ck)[0] }
 
 #define COMBO_END 0
-#ifndef COMBO_COUNT
-#    define COMBO_COUNT 0
-#endif
 #ifndef COMBO_TERM
-#    define COMBO_TERM TAPPING_TERM
+#    define COMBO_TERM 50
 #endif
+#ifndef COMBO_HOLD_TERM
+#    define COMBO_HOLD_TERM TAPPING_TERM
+#endif
+
+/* check if keycode is only modifiers */
+#define KEYCODE_IS_MOD(code) (IS_MOD(code) || (code >= QK_MODS && code <= QK_MODS_MAX && !(code & QK_BASIC_MAX)))
 
 bool process_combo(uint16_t keycode, keyrecord_t *record);
 void combo_task(void);
diff --git a/quantum/quantum.c b/quantum/quantum.c
index 3329c1146b..d173388714 100644
--- a/quantum/quantum.c
+++ b/quantum/quantum.c
@@ -143,7 +143,13 @@ void reset_keyboard(void) {
 }
 
 /* Convert record into usable keycode via the contained event. */
-uint16_t get_record_keycode(keyrecord_t *record, bool update_layer_cache) { return get_event_keycode(record->event, update_layer_cache); }
+uint16_t get_record_keycode(keyrecord_t *record, bool update_layer_cache) {
+#ifdef COMBO_ENABLE
+    if (record->keycode) { return record->keycode; }
+#endif
+    return get_event_keycode(record->event, update_layer_cache);
+}
+
 
 /* Convert event into usable keycode. Checks the layer cache to ensure that it
  * retains the correct keycode after a layer change, if the key is still pressed.
@@ -169,6 +175,18 @@ uint16_t get_event_keycode(keyevent_t event, bool update_layer_cache) {
         return keymap_key_to_keycode(layer_switch_get_layer(event.key), event.key);
 }
 
+/* Get keycode, and then process pre tapping functionality */
+bool pre_process_record_quantum(keyrecord_t *record) {
+    if (!(
+#ifdef COMBO_ENABLE
+        process_combo(get_record_keycode(record, true), record) &&
+#endif
+        true)) {
+        return false;
+    }
+    return true; // continue processing
+}
+
 /* Get keycode, and then call keyboard function */
 void post_process_record_quantum(keyrecord_t *record) {
     uint16_t keycode = get_record_keycode(record, false);
@@ -254,9 +272,6 @@ bool process_record_quantum(keyrecord_t *record) {
 #ifdef LEADER_ENABLE
             process_leader(keycode, record) &&
 #endif
-#ifdef COMBO_ENABLE
-            process_combo(keycode, record) &&
-#endif
 #ifdef PRINTING_ENABLE
             process_printer(keycode, record) &&
 #endif
diff --git a/tmk_core/common/action.c b/tmk_core/common/action.c
index bd41d28b66..d19fd2a045 100644
--- a/tmk_core/common/action.c
+++ b/tmk_core/common/action.c
@@ -55,6 +55,8 @@ __attribute__((weak)) bool get_ignore_mod_tap_interrupt(uint16_t keycode, keyrec
 __attribute__((weak)) bool get_retro_tapping(uint16_t keycode, keyrecord_t *record) { return false; }
 #endif
 
+__attribute__((weak)) bool pre_process_record_quantum(keyrecord_t *record) { return true; }
+
 #ifndef TAP_CODE_DELAY
 #    define TAP_CODE_DELAY 0
 #endif
@@ -106,9 +108,13 @@ void action_exec(keyevent_t event) {
 #endif
 
 #ifndef NO_ACTION_TAPPING
-    action_tapping_process(record);
+    if (IS_NOEVENT(record.event) || pre_process_record_quantum(&record)) {
+        action_tapping_process(record);
+    }
 #else
-    process_record(&record);
+    if (IS_NOEVENT(record.event) || pre_process_record_quantum(&record)) {
+        process_record(&record);
+    }
     if (!IS_NOEVENT(record.event)) {
         dprint("processed: ");
         debug_record(record);
@@ -206,7 +212,16 @@ void process_record(keyrecord_t *record) {
 }
 
 void process_record_handler(keyrecord_t *record) {
+#ifdef COMBO_ENABLE
+    action_t action;
+    if (record->keycode) {
+        action = action_for_keycode(record->keycode);
+    } else {
+        action = store_or_get_action(record->event.pressed, record->event.key);
+    }
+#else
     action_t action = store_or_get_action(record->event.pressed, record->event.key);
+#endif
     dprint("ACTION: ");
     debug_action(action);
 #ifndef NO_ACTION_LAYER
@@ -994,6 +1009,24 @@ bool is_tap_key(keypos_t key) {
  *
  * FIXME: Needs documentation.
  */
+bool is_tap_record(keyrecord_t *record) {
+#ifdef COMBO_ENABLE
+    action_t action;
+    if (record->keycode) {
+        action = action_for_keycode(record->keycode);
+    } else {
+        action = layer_switch_get_action(record->event.key);
+    }
+#else
+    action_t action = layer_switch_get_action(record->event.key);
+#endif
+    return is_tap_action(action);
+}
+
+/** \brief Utilities for actions. (FIXME: Needs better description)
+ *
+ * FIXME: Needs documentation.
+ */
 bool is_tap_action(action_t action) {
     switch (action.kind.id) {
         case ACT_LMODS_TAP:
diff --git a/tmk_core/common/action.h b/tmk_core/common/action.h
index 8cb4722c6e..3d357b33b8 100644
--- a/tmk_core/common/action.h
+++ b/tmk_core/common/action.h
@@ -53,6 +53,9 @@ typedef struct {
 #ifndef NO_ACTION_TAPPING
     tap_t tap;
 #endif
+#ifdef COMBO_ENABLE
+    uint16_t keycode;
+#endif
 } keyrecord_t;
 
 /* Execute action per keyevent */
@@ -60,6 +63,7 @@ void action_exec(keyevent_t event);
 
 /* action for key */
 action_t action_for_key(uint8_t layer, keypos_t key);
+action_t action_for_keycode(uint16_t keycode);
 
 /* macro */
 const macro_t *action_get_macro(keyrecord_t *record, uint8_t id, uint8_t opt);
@@ -111,6 +115,7 @@ void clear_keyboard_but_mods(void);
 void clear_keyboard_but_mods_and_keys(void);
 void layer_switch(uint8_t new_layer);
 bool is_tap_key(keypos_t key);
+bool is_tap_record(keyrecord_t *record);
 bool is_tap_action(action_t action);
 
 #ifndef NO_ACTION_TAPPING
diff --git a/tmk_core/common/action_tapping.c b/tmk_core/common/action_tapping.c
index 56044e096d..1701ae4717 100644
--- a/tmk_core/common/action_tapping.c
+++ b/tmk_core/common/action_tapping.c
@@ -18,11 +18,16 @@
 #    define IS_TAPPING_PRESSED() (IS_TAPPING() && tapping_key.event.pressed)
 #    define IS_TAPPING_RELEASED() (IS_TAPPING() && !tapping_key.event.pressed)
 #    define IS_TAPPING_KEY(k) (IS_TAPPING() && KEYEQ(tapping_key.event.key, (k)))
+#ifndef COMBO_ENABLE
+#    define IS_TAPPING_RECORD(r) (IS_TAPPING() && KEYEQ(tapping_key.event.key, (r->event.key)))
+#else
+#    define IS_TAPPING_RECORD(r) (IS_TAPPING() && KEYEQ(tapping_key.event.key, (r->event.key)) && tapping_key.keycode == r->keycode)
+#endif
 
 __attribute__((weak)) uint16_t get_tapping_term(uint16_t keycode, keyrecord_t *record) { return TAPPING_TERM; }
 
 #    ifdef TAPPING_TERM_PER_KEY
-#        define WITHIN_TAPPING_TERM(e) (TIMER_DIFF_16(e.time, tapping_key.event.time) < get_tapping_term(get_event_keycode(tapping_key.event, false), &tapping_key))
+#        define WITHIN_TAPPING_TERM(e) (TIMER_DIFF_16(e.time, tapping_key.event.time) < get_tapping_term(get_record_keycode(&tapping_key, false), &tapping_key))
 #    else
 #        define WITHIN_TAPPING_TERM(e) (TIMER_DIFF_16(e.time, tapping_key.event.time) < TAPPING_TERM)
 #    endif
@@ -103,7 +108,7 @@ bool process_tapping(keyrecord_t *keyp) {
     if (IS_TAPPING_PRESSED()) {
         if (WITHIN_TAPPING_TERM(event)) {
             if (tapping_key.tap.count == 0) {
-                if (IS_TAPPING_KEY(event.key) && !event.pressed) {
+                if (IS_TAPPING_RECORD(keyp) && !event.pressed) {
                     // first tap!
                     debug("Tapping: First tap(0->1).\n");
                     tapping_key.tap.count = 1;
@@ -122,14 +127,14 @@ bool process_tapping(keyrecord_t *keyp) {
 #    if defined(TAPPING_TERM_PER_KEY) || (TAPPING_TERM >= 500) || defined(PERMISSIVE_HOLD) || defined(PERMISSIVE_HOLD_PER_KEY)
                 else if (((
 #        ifdef TAPPING_TERM_PER_KEY
-                              get_tapping_term(get_event_keycode(tapping_key.event, false), keyp)
+                              get_tapping_term(get_record_keycode(&tapping_key, false), keyp)
 #        else
                               TAPPING_TERM
 #        endif
                               >= 500)
 
 #        ifdef PERMISSIVE_HOLD_PER_KEY
-                          || get_permissive_hold(get_event_keycode(tapping_key.event, false), keyp)
+                          || get_permissive_hold(get_record_keycode(&tapping_key, false), keyp)
 #        elif defined(PERMISSIVE_HOLD)
                           || true
 #        endif
@@ -177,7 +182,7 @@ bool process_tapping(keyrecord_t *keyp) {
             }
             // tap_count > 0
             else {
-                if (IS_TAPPING_KEY(event.key) && !event.pressed) {
+                if (IS_TAPPING_RECORD(keyp) && !event.pressed) {
                     debug("Tapping: Tap release(");
                     debug_dec(tapping_key.tap.count);
                     debug(")\n");
@@ -186,11 +191,15 @@ bool process_tapping(keyrecord_t *keyp) {
                     tapping_key = *keyp;
                     debug_tapping_key();
                     return true;
-                } else if (is_tap_key(event.key) && event.pressed) {
+                } else if (is_tap_record(keyp) && event.pressed) {
                     if (tapping_key.tap.count > 1) {
                         debug("Tapping: Start new tap with releasing last tap(>1).\n");
                         // unregister key
-                        process_record(&(keyrecord_t){.tap = tapping_key.tap, .event.key = tapping_key.event.key, .event.time = event.time, .event.pressed = false});
+                        process_record(&(keyrecord_t){.tap = tapping_key.tap, .event.key = tapping_key.event.key, .event.time = event.time, .event.pressed = false,
+#ifdef COMBO_ENABLE
+                                .keycode = tapping_key.keycode,
+#endif
+                                });
                     } else {
                         debug("Tapping: Start while last tap(1).\n");
                     }
@@ -218,17 +227,21 @@ bool process_tapping(keyrecord_t *keyp) {
                 debug_tapping_key();
                 return false;
             } else {
-                if (IS_TAPPING_KEY(event.key) && !event.pressed) {
+                if (IS_TAPPING_RECORD(keyp) && !event.pressed) {
                     debug("Tapping: End. last timeout tap release(>0).");
                     keyp->tap = tapping_key.tap;
                     process_record(keyp);
                     tapping_key = (keyrecord_t){};
                     return true;
-                } else if (is_tap_key(event.key) && event.pressed) {
+                } else if (is_tap_record(keyp) && event.pressed) {
                     if (tapping_key.tap.count > 1) {
                         debug("Tapping: Start new tap with releasing last timeout tap(>1).\n");
                         // unregister key
-                        process_record(&(keyrecord_t){.tap = tapping_key.tap, .event.key = tapping_key.event.key, .event.time = event.time, .event.pressed = false});
+                        process_record(&(keyrecord_t){.tap = tapping_key.tap, .event.key = tapping_key.event.key, .event.time = event.time, .event.pressed = false,
+#ifdef COMBO_ENABLE
+                                .keycode = tapping_key.keycode,
+#endif
+                                });
                     } else {
                         debug("Tapping: Start while last timeout tap(1).\n");
                     }
@@ -248,12 +261,12 @@ bool process_tapping(keyrecord_t *keyp) {
     } else if (IS_TAPPING_RELEASED()) {
         if (WITHIN_TAPPING_TERM(event)) {
             if (event.pressed) {
-                if (IS_TAPPING_KEY(event.key)) {
+                if (IS_TAPPING_RECORD(keyp)) {
 //#    ifndef TAPPING_FORCE_HOLD
 #    if !defined(TAPPING_FORCE_HOLD) || defined(TAPPING_FORCE_HOLD_PER_KEY)
                     if (
 #        ifdef TAPPING_FORCE_HOLD_PER_KEY
-                        !get_tapping_force_hold(get_event_keycode(tapping_key.event, false), keyp) &&
+                        !get_tapping_force_hold(get_record_keycode(&tapping_key, false), keyp) &&
 #        endif
                         !tapping_key.tap.interrupted && tapping_key.tap.count > 0) {
                         // sequential tap.
@@ -271,7 +284,7 @@ bool process_tapping(keyrecord_t *keyp) {
                     // FIX: start new tap again
                     tapping_key = *keyp;
                     return true;
-                } else if (is_tap_key(event.key)) {
+                } else if (is_tap_record(keyp)) {
                     // Sequential tap can be interfered with other tap key.
                     debug("Tapping: Start with interfering other tap.\n");
                     tapping_key = *keyp;
@@ -303,7 +316,7 @@ bool process_tapping(keyrecord_t *keyp) {
     }
     // not tapping state
     else {
-        if (event.pressed && is_tap_key(event.key)) {
+        if (event.pressed && is_tap_record(keyp)) {
             debug("Tapping: Start(Press tap key).\n");
             tapping_key = *keyp;
             process_record_tap_hint(&tapping_key);
diff --git a/tmk_core/common/action_tapping.h b/tmk_core/common/action_tapping.h
index 893ccb1ce1..7de8049c7f 100644
--- a/tmk_core/common/action_tapping.h
+++ b/tmk_core/common/action_tapping.h
@@ -30,6 +30,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #define WAITING_BUFFER_SIZE 8
 
 #ifndef NO_ACTION_TAPPING
+uint16_t get_record_keycode(keyrecord_t *record, bool update_layer_cache);
 uint16_t get_event_keycode(keyevent_t event, bool update_layer_cache);
 void     action_tapping_process(keyrecord_t record);