From 3b3e683da859ed51cd179dd16635d481973dd3ec Mon Sep 17 00:00:00 2001
From: sheldonmlee <sheldon.m.lee@gmail.com>
Date: Tue, 3 Aug 2021 15:18:57 +0800
Subject: [PATCH] Custom oneshot functionality from qmk_firmware/users/callum.

---
 oneshot.c | 57 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 oneshot.h | 32 +++++++++++++++++++++++++++++++
 2 files changed, 89 insertions(+)
 create mode 100755 oneshot.c
 create mode 100755 oneshot.h

diff --git a/oneshot.c b/oneshot.c
new file mode 100755
index 0000000..33ec389
--- /dev/null
+++ b/oneshot.c
@@ -0,0 +1,57 @@
+#include "oneshot.h"
+
+void update_oneshot(
+    oneshot_state *state,
+    uint16_t mod,
+    uint16_t trigger,
+    uint16_t keycode,
+    keyrecord_t *record
+) {
+    if (keycode == trigger) {
+        if (record->event.pressed) {
+            // Trigger keydown
+            if (*state == os_up_unqueued) {
+                register_code(mod);
+            }
+            *state = os_down_unused;
+        } else {
+            // Trigger keyup
+            switch (*state) {
+            case os_down_unused:
+                // If we didn't use the mod while trigger was held, queue it.
+                *state = os_up_queued;
+                break;
+            case os_down_used:
+                // If we did use the mod while trigger was held, unregister it.
+                *state = os_up_unqueued;
+                unregister_code(mod);
+                break;
+            default:
+                break;
+            }
+        }
+    } else {
+        if (record->event.pressed) {
+            if (is_oneshot_cancel_key(keycode) && *state != os_up_unqueued) {
+                // Cancel oneshot on designated cancel keydown.
+                *state = os_up_unqueued;
+                unregister_code(mod);
+            }
+        } else {
+            if (!is_oneshot_ignored_key(keycode)) {
+                // On non-ignored keyup, consider the oneshot used.
+                switch (*state) {
+                case os_down_unused:
+                    *state = os_down_used;
+                    break;
+                case os_up_queued:
+                    *state = os_up_unqueued;
+                    unregister_code(mod);
+                    break;
+                default:
+                    break;
+                }
+            }
+        }
+    }
+}
diff --git a/oneshot.h b/oneshot.h
new file mode 100755
index 0000000..d341dd1
--- /dev/null
+++ b/oneshot.h
@@ -0,0 +1,32 @@
+// Taken from qmk_firmware/users/callum
+#pragma once
+
+#include QMK_KEYBOARD_H
+
+// Represents the four states a oneshot key can be in
+typedef enum {
+    os_up_unqueued,
+    os_up_queued,
+    os_down_unused,
+    os_down_used,
+} oneshot_state;
+
+// Custom oneshot mod implementation that doesn't rely on timers. If a mod is
+// used while it is held it will be unregistered on keyup as normal, otherwise
+// it will be queued and only released after the next non-mod keyup.
+void update_oneshot(
+    oneshot_state *state,
+    uint16_t mod,
+    uint16_t trigger,
+    uint16_t keycode,
+    keyrecord_t *record
+);
+
+// To be implemented by the consumer. Defines keys to cancel oneshot mods.
+bool is_oneshot_cancel_key(uint16_t keycode);
+
+// To be implemented by the consumer. Defines keys to ignore when determining
+// whether a oneshot mod has been used. Setting this to modifiers and layer
+// change keys allows stacking multiple oneshot modifiers, and carrying them
+// between layers.
+bool is_oneshot_ignored_key(uint16_t keycode);