Adds oneshot layer and oneshot tap toggling (#308)

This commit is mostly a cherry-pick from `ahtn` at
https://github.com/tmk/tmk_keyboard/pull/255.

These are the changes:

* Adds ACTION_LAYER_ONESHOT
* Adds ONESHOT_TAP_TOGGLE
* Mentions sticky keys in the docs on oneshot.

4 files changed, 179 insertions, 13 deletions

diff --git a/tmk_core/common/action.c b/tmk_core/common/action.c
index f9e6c17dc..081e90b2d 100644
--- a/tmk_core/common/action.c
+++ b/tmk_core/common/action.c
@@ -74,6 +74,7 @@ void process_action_kb(keyrecord_t *record) {}
 
 void process_action(keyrecord_t *record)
 {
+    bool do_release_oneshot = false;
     keyevent_t event = record->event;
 #ifndef NO_ACTION_TAPPING
     uint8_t tap_count = record->tap.count;
@@ -81,6 +82,13 @@ void process_action(keyrecord_t *record)
 
     if (IS_NOEVENT(event)) { return; }
 
+#if (defined(ONESHOT_TIMEOUT) && (ONESHOT_TIMEOUT > 0))
+    if (has_oneshot_layer_timed_out()) {
+        dprintf("Oneshot layer: timeout\n");
+        clear_oneshot_layer_state(ONESHOT_OTHER_KEY_PRESSED);
+    }
+#endif
+
     process_action_kb(record);
 
     action_t action = store_or_get_action(event.pressed, event.key);
@@ -95,6 +103,15 @@ void process_action(keyrecord_t *record)
         // clear the potential weak mods left by previously pressed keys
         clear_weak_mods();
     }
+
+#ifndef NO_ACTION_ONESHOT
+    // notice we only clear the one shot layer if the pressed key is not a modifier.
+    if (is_oneshot_layer_active() && event.pressed && !IS_MOD(action.key.code)) {
+        clear_oneshot_layer_state(ONESHOT_OTHER_KEY_PRESSED);
+        do_release_oneshot = !is_oneshot_layer_active();
+    }
+#endif
+
     switch (action.kind.id) {
         /* Key and Mods */
         case ACT_LMODS:
@@ -139,24 +156,37 @@ void process_action(keyrecord_t *record)
                         // Oneshot modifier
                         if (event.pressed) {
                             if (tap_count == 0) {
+                                dprint("MODS_TAP: Oneshot: 0\n");
                                 register_mods(mods);
-                            }
-                            else if (tap_count == 1) {
+                            } else if (tap_count == 1) {
                                 dprint("MODS_TAP: Oneshot: start\n");
                                 set_oneshot_mods(mods);
-                            }
-                            else {
+                    #if defined(ONESHOT_TAP_TOGGLE) && ONESHOT_TAP_TOGGLE > 1
+                            } else if (tap_count == ONESHOT_TAP_TOGGLE) {
+                                dprint("MODS_TAP: Toggling oneshot");
+                                clear_oneshot_mods();
+                                set_oneshot_locked_mods(mods);
+                                register_mods(mods);
+                    #endif
+                            } else {
                                 register_mods(mods);
                             }
                         } else {
                             if (tap_count == 0) {
                                 clear_oneshot_mods();
                                 unregister_mods(mods);
-                            }
-                            else if (tap_count == 1) {
+                            } else if (tap_count == 1) {
                                 // Retain Oneshot mods
-                            }
-                            else {
+                    #if defined(ONESHOT_TAP_TOGGLE) && ONESHOT_TAP_TOGGLE > 1
+                                if (mods & get_mods()) {
+                                    clear_oneshot_locked_mods();
+                                    clear_oneshot_mods();
+                                    unregister_mods(mods);
+                                }
+                            } else if (tap_count == ONESHOT_TAP_TOGGLE) {
+                                // Toggle Oneshot Layer
+                    #endif
+                            } else {
                                 clear_oneshot_mods();
                                 unregister_mods(mods);
                             }
@@ -309,6 +339,44 @@ void process_action(keyrecord_t *record)
                     event.pressed ? layer_move(action.layer_tap.val) :
                                     layer_clear();
                     break;
+            #ifndef NO_ACTION_ONESHOT
+                case OP_ONESHOT:
+                    // Oneshot modifier
+                #if defined(ONESHOT_TAP_TOGGLE) && ONESHOT_TAP_TOGGLE > 1
+                    do_release_oneshot = false;
+                    if (event.pressed) {
+                        del_mods(get_oneshot_locked_mods());
+                        if (get_oneshot_layer_state() == ONESHOT_TOGGLED) {
+                            reset_oneshot_layer();
+                            layer_off(action.layer_tap.val);
+                            break;
+                        } else if (tap_count < ONESHOT_TAP_TOGGLE) {
+                            layer_on(action.layer_tap.val);
+                            set_oneshot_layer(action.layer_tap.val, ONESHOT_START);
+                        }
+                    } else {
+                        add_mods(get_oneshot_locked_mods());
+                        if (tap_count >= ONESHOT_TAP_TOGGLE) {
+                            reset_oneshot_layer();
+                            clear_oneshot_locked_mods();
+                            set_oneshot_layer(action.layer_tap.val, ONESHOT_TOGGLED);
+                        } else {
+                            clear_oneshot_layer_state(ONESHOT_PRESSED);
+                        }
+                    }
+                #else
+                    if (event.pressed) {
+                        layer_on(action.layer_tap.val);
+                        set_oneshot_layer(action.layer_tap.val, ONESHOT_START);
+                    } else {
+                        clear_oneshot_layer_state(ONESHOT_PRESSED);
+                        if (tap_count > 1) {
+                            clear_oneshot_layer_state(ONESHOT_OTHER_KEY_PRESSED);
+                        }
+                    }
+                #endif
+                    break;
+            #endif
                 default:
                     /* tap key */
                     if (event.pressed) {
@@ -372,6 +440,18 @@ void process_action(keyrecord_t *record)
         default:
             break;
     }
+
+#ifndef NO_ACTION_ONESHOT
+    /* Because we switch layers after a oneshot event, we need to release the
+     * key before we leave the layer or no key up event will be generated.
+     */
+    if (do_release_oneshot && !(get_oneshot_layer_state() & ONESHOT_PRESSED )   ) {
+        record->event.pressed = false;
+        layer_on(get_oneshot_layer());
+        process_action(record);
+        layer_off(get_oneshot_layer());
+    }
+#endif
 }
 
 
@@ -560,6 +640,7 @@ bool is_tap_key(keypos_t key)
             switch (action.layer_tap.code) {
                 case 0x00 ... 0xdf:
                 case OP_TAP_TOGGLE:
+                case OP_ONESHOT:
                     return true;
             }
             return false;
diff --git a/tmk_core/common/action_code.h b/tmk_core/common/action_code.h
index 2b0b0b077..ca729aaec 100644
--- a/tmk_core/common/action_code.h
+++ b/tmk_core/common/action_code.h
@@ -76,7 +76,8 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
  * 101E|LLLL|1111 0001   On/Off                 (0xF1)   [NOT TAP]
  * 101E|LLLL|1111 0010   Off/On                 (0xF2)   [NOT TAP]
  * 101E|LLLL|1111 0011   Set/Clear              (0xF3)   [NOT TAP]
- * 101E|LLLL|1111 xxxx   Reserved               (0xF4-FF)
+ * 101E|LLLL|1111 0100   One Shot Layer         (0xF4)   [TAP]
+ * 101E|LLLL|1111 xxxx   Reserved               (0xF5-FF)
  *   ELLLL: layer 0-31(E: extra bit for layer 16-31)
  *
  *
@@ -250,6 +251,7 @@ enum layer_pram_tap_op {
     OP_ON_OFF,
     OP_OFF_ON,
     OP_SET_CLEAR,
+    OP_ONESHOT,
 };
 #define ACTION_LAYER_BITOP(op, part, bits, on)      (ACT_LAYER<<12 | (op)<<10 | (on)<<8 | (part)<<5 | ((bits)&0x1f))
 #define ACTION_LAYER_TAP(layer, key)                (ACT_LAYER_TAP<<12 | (layer)<<8 | (key))
@@ -266,6 +268,7 @@ enum layer_pram_tap_op {
 #define ACTION_LAYER_ON_OFF(layer)                  ACTION_LAYER_TAP((layer), OP_ON_OFF)
 #define ACTION_LAYER_OFF_ON(layer)                  ACTION_LAYER_TAP((layer), OP_OFF_ON)
 #define ACTION_LAYER_SET_CLEAR(layer)               ACTION_LAYER_TAP((layer), OP_SET_CLEAR)
+#define ACTION_LAYER_ONESHOT(layer)                 ACTION_LAYER_TAP((layer), OP_ONESHOT)
 #define ACTION_LAYER_MODS(layer, mods)              ACTION_LAYER_TAP((layer), 0xe0 | ((mods)&0x0f))
 /* With Tapping */
 #define ACTION_LAYER_TAP_KEY(layer, key)            ACTION_LAYER_TAP((layer), (key))
diff --git a/tmk_core/common/action_util.c b/tmk_core/common/action_util.c
index a2d6577b2..61ff202be 100644
--- a/tmk_core/common/action_util.c
+++ b/tmk_core/common/action_util.c
@@ -18,6 +18,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include "report.h"
 #include "debug.h"
 #include "action_util.h"
+#include "action_layer.h"
 #include "timer.h"
 
 static inline void add_key_byte(uint8_t code);
@@ -47,11 +48,70 @@ report_keyboard_t *keyboard_report = &(report_keyboard_t){};
 
 #ifndef NO_ACTION_ONESHOT
 static int8_t oneshot_mods = 0;
+static int8_t oneshot_locked_mods = 0;
+int8_t get_oneshot_locked_mods(void) { return oneshot_locked_mods; }
+void set_oneshot_locked_mods(int8_t mods) { oneshot_locked_mods = mods; }
+void clear_oneshot_locked_mods(void) { oneshot_locked_mods = 0; }
 #if (defined(ONESHOT_TIMEOUT) && (ONESHOT_TIMEOUT > 0))
 static int16_t oneshot_time = 0;
+inline bool has_oneshot_mods_timed_out() {
+  return TIMER_DIFF_16(timer_read(), oneshot_time) >= ONESHOT_TIMEOUT;
+}
 #endif
 #endif
 
+/* oneshot layer */
+#ifndef NO_ACTION_ONESHOT
+/* oneshot_layer_data bits
+* LLLL LSSS
+* where:
+*   L => are layer bits
+*   S => oneshot state bits
+*/
+static int8_t oneshot_layer_data = 0;
+
+inline uint8_t get_oneshot_layer(void) { return oneshot_layer_data >> 3; }
+inline uint8_t get_oneshot_layer_state(void) { return oneshot_layer_data & 0b111; }
+
+#if (defined(ONESHOT_TIMEOUT) && (ONESHOT_TIMEOUT > 0))
+static int16_t oneshot_layer_time = 0;
+inline bool has_oneshot_layer_timed_out() {
+    return TIMER_DIFF_16(timer_read(), oneshot_layer_time) >= ONESHOT_TIMEOUT &&
+        !(get_oneshot_layer_state() & ONESHOT_TOGGLED);
+}
+#endif
+
+/* Oneshot layer */
+void set_oneshot_layer(uint8_t layer, uint8_t state)
+{
+    oneshot_layer_data = layer << 3 | state;
+    layer_on(layer);
+#if (defined(ONESHOT_TIMEOUT) && (ONESHOT_TIMEOUT > 0))
+    oneshot_layer_time = timer_read();
+#endif
+}
+void reset_oneshot_layer(void) {
+    oneshot_layer_data = 0;
+#if (defined(ONESHOT_TIMEOUT) && (ONESHOT_TIMEOUT > 0))
+    oneshot_layer_time = 0;
+#endif
+}
+void clear_oneshot_layer_state(oneshot_fullfillment_t state)
+{
+    uint8_t start_state = oneshot_layer_data;
+    oneshot_layer_data &= ~state;
+    if (!get_oneshot_layer_state() && start_state != oneshot_layer_data) {
+        layer_off(get_oneshot_layer());
+#if (defined(ONESHOT_TIMEOUT) && (ONESHOT_TIMEOUT > 0))
+    oneshot_layer_time = 0;
+#endif
+    }
+}
+bool is_oneshot_layer_active(void)
+{
+    return get_oneshot_layer_state();
+}
+#endif
 
 void send_keyboard_report(void) {
     keyboard_report->mods  = real_mods;
@@ -60,7 +120,7 @@ void send_keyboard_report(void) {
 #ifndef NO_ACTION_ONESHOT
     if (oneshot_mods) {
 #if (defined(ONESHOT_TIMEOUT) && (ONESHOT_TIMEOUT > 0))
-        if (TIMER_DIFF_16(timer_read(), oneshot_time) >= ONESHOT_TIMEOUT) {
+        if (has_oneshot_mods_timed_out()) {
             dprintf("Oneshot: timeout\n");
             clear_oneshot_mods();
         }
@@ -70,6 +130,7 @@ void send_keyboard_report(void) {
             clear_oneshot_mods();
         }
     }
+
 #endif
     host_keyboard_send(keyboard_report);
 }
@@ -143,11 +204,12 @@ void clear_oneshot_mods(void)
     oneshot_time = 0;
 #endif
 }
+uint8_t get_oneshot_mods(void)
+{
+    return oneshot_mods;
+}
 #endif
 
-
-
-
 /*
  * inspect keyboard state
  */
diff --git a/tmk_core/common/action_util.h b/tmk_core/common/action_util.h
index 1a95cec10..dd0c4c2bf 100644
--- a/tmk_core/common/action_util.h
+++ b/tmk_core/common/action_util.h
@@ -56,10 +56,30 @@ void clear_macro_mods(void);
 
 /* oneshot modifier */
 void set_oneshot_mods(uint8_t mods);
+uint8_t get_oneshot_mods(void);
 void clear_oneshot_mods(void);
 void oneshot_toggle(void);
 void oneshot_enable(void);
 void oneshot_disable(void);
+bool has_oneshot_mods_timed_out(void);
+
+int8_t get_oneshot_locked_mods(void);
+void set_oneshot_locked_mods(int8_t mods);
+void clear_oneshot_locked_mods(void);
+
+typedef enum {
+  ONESHOT_PRESSED = 0b01,
+  ONESHOT_OTHER_KEY_PRESSED = 0b10,
+  ONESHOT_START = 0b11,
+  ONESHOT_TOGGLED = 0b100
+} oneshot_fullfillment_t;
+void set_oneshot_layer(uint8_t layer, uint8_t state);
+uint8_t get_oneshot_layer(void);
+void clear_oneshot_layer_state(oneshot_fullfillment_t state);
+void reset_oneshot_layer(void);
+bool is_oneshot_layer_active(void);
+uint8_t get_oneshot_layer_state(void);
+bool has_oneshot_layer_timed_out(void);
 
 /* inspect */
 uint8_t has_anykey(void);