8 files changed, 165 insertions, 2 deletions

diff --git a/common_features.mk b/common_features.mk
index 0adf81afa..f405d5c07 100644
--- a/common_features.mk
+++ b/common_features.mk
@@ -104,6 +104,11 @@ ifeq ($(strip $(TAP_DANCE_ENABLE)), yes)
     SRC += $(QUANTUM_DIR)/process_keycode/process_tap_dance.c
 endif
 
+ifeq ($(strip $(KEY_LOCK_ENABLE)), yes)
+    OPT_DEFS += -DKEY_LOCK_ENABLE
+    SRC += $(QUANTUM_DIR)/process_keycode/process_key_lock.c
+endif
+
 ifeq ($(strip $(PRINTING_ENABLE)), yes)
     OPT_DEFS += -DPRINTING_ENABLE
     SRC += $(QUANTUM_DIR)/process_keycode/process_printer.c
@@ -156,4 +161,4 @@ QUANTUM_SRC:= \
 
 ifndef CUSTOM_MATRIX
     QUANTUM_SRC += $(QUANTUM_DIR)/matrix.c
-endif
\ No newline at end of file
+endif
diff --git a/keyboards/nyquist/keymaps/333fred/Makefile b/keyboards/nyquist/keymaps/333fred/Makefile
index 457a3d01d..471eac8b5 100644
--- a/keyboards/nyquist/keymaps/333fred/Makefile
+++ b/keyboards/nyquist/keymaps/333fred/Makefile
@@ -1,3 +1,5 @@
+KEY_LOCK_ENABLE = yes
+
 ifndef QUANTUM_DIR
         include ../../../../Makefile
 endif
diff --git a/keyboards/nyquist/keymaps/333fred/keymap.c b/keyboards/nyquist/keymaps/333fred/keymap.c
index 07434d93f..20bf29887 100644
--- a/keyboards/nyquist/keymaps/333fred/keymap.c
+++ b/keyboards/nyquist/keymaps/333fred/keymap.c
@@ -39,7 +39,7 @@ const uint16_t PROGMEM keymaps[][MATRIX_ROWS][MATRIX_COLS] = {
   KC_TAB,        KC_Q,         KC_W,  KC_E,    KC_R,           KC_T,    KC_Y,    KC_U,    KC_I,    KC_O,   KC_P,            KC_BSLASH, \
   KC_ESC,        KC_A,         KC_S,  KC_D,    LT(_VIM, KC_F), KC_G,    KC_H,    KC_J,    KC_K,    KC_L,   KC_SCLN,         KC_QUOT, \
   OSM(MOD_LSFT), LCTL_T(KC_Z), KC_X,  KC_C,    KC_V,           KC_B,    KC_N,    KC_M,    KC_COMM, KC_DOT, RCTL_T(KC_SLSH), OSM(MOD_RSFT), \
-  KC_LCTL,       KC_LALT,      KC_F4, KC_LGUI, OSL(_LOWER),    KC_BSPC, KC_SPC,  KC_ENT,  KC_RALT, KC_EQL, TG(_GAME),       KC_DEL \
+  KC_LCTL,       KC_LALT,      KC_F4, KC_LGUI, OSL(_LOWER),    KC_BSPC, KC_SPC,  KC_ENT,  KC_LOCK, KC_EQL, TG(_GAME),       KC_DEL \
 ),
 
 /* Lower
diff --git a/quantum/process_keycode/process_key_lock.c b/quantum/process_keycode/process_key_lock.c
new file mode 100644
index 000000000..60b0fcd9b
--- /dev/null
+++ b/quantum/process_keycode/process_key_lock.c
@@ -0,0 +1,120 @@
+/* Copyright 2017 Fredric Silberberg
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "inttypes.h"
+#include "stdint.h"
+#include "process_key_lock.h"
+
+#define SHIFT(shift) (((uint64_t)1) << (shift))
+#define GET_KEY_ARRAY(code) (((code) < 0x40) ? key_state[0] : \
+                             ((code) < 0x80) ? key_state[1] : \
+                             ((code) < 0xC0) ? key_state[2] : key_state[3])
+#define GET_CODE_INDEX(code) (((code) < 0x40) ? (code) : \
+                              ((code) < 0x80) ? (code) - 0x40 : \
+                              ((code) < 0xC0) ? (code) - 0x80 : (code) - 0xC0)
+#define KEY_STATE(code)  (GET_KEY_ARRAY(code) & SHIFT(GET_CODE_INDEX(code))) == SHIFT(GET_CODE_INDEX(code))
+#define SET_KEY_ARRAY_STATE(code, val) do { \
+    switch (code) { \
+        case 0x00 ... 0x3F: \
+            key_state[0] = (val); \
+            break; \
+        case 0x40 ... 0x7F: \
+            key_state[1] = (val); \
+            break; \
+        case 0x80 ... 0xBF: \
+            key_state[2] = (val); \
+            break; \
+        case 0xC0 ... 0xFF: \
+            key_state[3] = (val); \
+            break; \
+    } \
+} while(0)
+#define SET_KEY_STATE(code) SET_KEY_ARRAY_STATE(code, (GET_KEY_ARRAY(code) | SHIFT(GET_CODE_INDEX(code))))
+#define UNSET_KEY_STATE(code) SET_KEY_ARRAY_STATE(code, (GET_KEY_ARRAY(code)) & ~(SHIFT(GET_CODE_INDEX(code))))
+#define IS_STANDARD_KEYCODE(code) ((code) <= 0xFF)
+#define print_hex64(num) do { print_hex32((num & 0xFFFFFFFF00000000) >> 32); print_hex32(num & 0x00000000FFFFFFFF); } while (0)
+
+// Locked key state. This is an array of 256 bits, one for each of the standard keys supported qmk.
+uint64_t key_state[4] = { 0x0, 0x0, 0x0, 0x0 };
+bool watching = false;
+
+bool process_key_lock(uint16_t keycode, keyrecord_t *record) {
+    // We start by categorizing the keypress event. In the event of a down
+    // event, there are several possibilities:
+    // 1. The key is not being locked, and we are not watching for new keys.
+    //    In this case, we bail immediately. This is the common case for down events.
+    // 2. The key was locked, and we need to unlock it. In this case, we will
+    //    reset the state in our map and return false. When the user releases the
+    //    key, the up event will no longer be masked and the OS will observe the
+    //    released key.
+    // 3. KC_LOCK was just pressed. In this case, we set up the state machine
+    //    to watch for the next key down event, and finish processing
+    // 4. The keycode is below 0xFF, and we are watching for new keys. In this case,
+    //    we will send the key down event to the os, and set the key_state for that
+    //    key to mask the up event.
+    // 5. The keycode is above 0xFF, and we're wathing for new keys. In this case,
+    //    the user pressed a key that we cannot "lock", as it's a series of keys,
+    //    or a macro invocation, or a layer transition, or a custom-defined key, or
+    //    or some other arbitrary code. In this case, we bail immediately, reset
+    //    our watch state, and return true.
+    //
+    // In the event of an up event, there are these possibilities:
+    // 1. The key is not being locked. In this case, we return true and bail
+    //    immediately. This is the common case.
+    // 2. The key is being locked. In this case, we will mask the up event
+    //    by returning false, so the OS never sees that the key was released
+    //    until the user pressed the key again.
+    if (record->event.pressed) {
+        // Non-standard keycode, reset and return
+        if (!(IS_STANDARD_KEYCODE(keycode) || keycode == KC_LOCK)) {
+            watching = false;
+            return true;
+        }
+
+        // If we're already watching, turn off the watch.
+        if (keycode == KC_LOCK) {
+            watching = !watching;
+            return false;
+        }
+        
+        if (IS_STANDARD_KEYCODE(keycode)) {
+            // We check watching first. This is so that in the following scenario, we continue to
+            // hold the key: KC_LOCK, KC_F, KC_LOCK, KC_F
+            // If we checked in reverse order, we'd end up holding the key pressed after the second
+            // KC_F press is registered, when the user likely meant to hold F
+            if (watching) {
+                watching = false;
+                SET_KEY_STATE(keycode);
+                // Let the standard keymap send the keycode down event. The up event will be masked.
+                return true;
+            }
+            
+            if (KEY_STATE(keycode)) {
+                UNSET_KEY_STATE(keycode);
+                // The key is already held, stop this process. The up event will be sent when the user
+                // releases the key.
+                return false;
+            }
+        }
+        
+        // Either the key isn't a standard key, or we need to send the down event. Continue standard
+        // processing
+        return true;
+    } else {
+        // Stop processing if it's a standard key and we're masking up.
+        return !(IS_STANDARD_KEYCODE(keycode) && KEY_STATE(keycode));
+    }
+}
diff --git a/quantum/process_keycode/process_key_lock.h b/quantum/process_keycode/process_key_lock.h
new file mode 100644
index 000000000..237e103bc
--- /dev/null
+++ b/quantum/process_keycode/process_key_lock.h
@@ -0,0 +1,24 @@
+/* Copyright 2017 Fredric Silberberg
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef PROCESS_KEY_LOCK_H
+#define PROCESS_KEY_LOCK_H
+
+#include "quantum.h"
+
+bool process_key_lock(uint16_t keycode, keyrecord_t *record);
+
+#endif // PROCESS_KEY_LOCK_H
diff --git a/quantum/quantum.c b/quantum/quantum.c
index 1f8ce6c46..c71a97bf2 100644
--- a/quantum/quantum.c
+++ b/quantum/quantum.c
@@ -193,6 +193,10 @@ bool process_record_quantum(keyrecord_t *record) {
     // }
 
   if (!(
+  #if defined(KEY_LOCK_ENABLE)
+    // Must run first to be able to mask key_up events.
+    process_key_lock(keycode, record) &&
+  #endif
     process_record_kb(keycode, record) &&
   #if defined(MIDI_ENABLE) && defined(MIDI_ADVANCED)
     process_midi(keycode, record) &&
diff --git a/quantum/quantum.h b/quantum/quantum.h
index 453cb43f8..9a6d691a1 100644
--- a/quantum/quantum.h
+++ b/quantum/quantum.h
@@ -99,6 +99,10 @@ extern uint32_t default_layer_state;
         #include "process_combo.h"
 #endif
 
+#ifdef KEY_LOCK_ENABLE
+        #include "process_key_lock.h"
+#endif
+
 #define SEND_STRING(str) send_string(PSTR(str))
 extern const bool ascii_to_shift_lut[0x80];
 extern const uint8_t ascii_to_keycode_lut[0x80];
diff --git a/quantum/quantum_keycodes.h b/quantum/quantum_keycodes.h
index acdb9248d..1bb6706ba 100644
--- a/quantum/quantum_keycodes.h
+++ b/quantum/quantum_keycodes.h
@@ -419,6 +419,10 @@ enum quantum_keycodes {
     OUT_BT,
 #endif
 
+#ifdef KEY_LOCK_ENABLE
+    KC_LOCK,
+#endif
+
     // always leave at the end
     SAFE_RANGE
 };