[Core] Add Caps Word feature to core (#16588)

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

quantum/caps_word.c

@@ -0,0 +1,80 @@
+// Copyright 2021-2022 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "caps_word.h"
+
+/** @brief True when Caps Word is active. */
+static bool caps_word_active = false;
+
+#if CAPS_WORD_IDLE_TIMEOUT > 0
+// Constrain timeout to a sensible range. With 16-bit timers, the longest
+// timeout possible is 32768 ms, rounded here to 30000 ms = half a minute.
+#    if CAPS_WORD_IDLE_TIMEOUT < 100 || CAPS_WORD_IDLE_TIMEOUT > 30000
+#        error "CAPS_WORD_IDLE_TIMEOUT must be between 100 and 30000 ms"
+#    endif
+
+/** @brief Deadline for idle timeout. */
+static uint16_t idle_timer = 0;
+
+void caps_word_task(void) {
+    if (caps_word_active && timer_expired(timer_read(), idle_timer)) {
+        caps_word_off();
+    }
+}
+
+void caps_word_reset_idle_timer(void) {
+    idle_timer = timer_read() + CAPS_WORD_IDLE_TIMEOUT;
+}
+#endif // CAPS_WORD_IDLE_TIMEOUT > 0
+
+void caps_word_on(void) {
+    if (caps_word_active) {
+        return;
+    }
+
+    clear_mods();
+#ifndef NO_ACTION_ONESHOT
+    clear_oneshot_mods();
+#endif // NO_ACTION_ONESHOT
+#if CAPS_WORD_IDLE_TIMEOUT > 0
+    caps_word_reset_idle_timer();
+#endif // CAPS_WORD_IDLE_TIMEOUT > 0
+
+    caps_word_active = true;
+    caps_word_set_user(true);
+}
+
+void caps_word_off(void) {
+    if (!caps_word_active) {
+        return;
+    }
+
+    unregister_weak_mods(MOD_MASK_SHIFT); // Make sure weak shift is off.
+    caps_word_active = false;
+    caps_word_set_user(false);
+}
+
+void caps_word_toggle(void) {
+    if (caps_word_active) {
+        caps_word_off();
+    } else {
+        caps_word_on();
+    }
+}
+
+bool is_caps_word_on(void) {
+    return caps_word_active;
+}
+
+__attribute__((weak)) void caps_word_set_user(bool active) {}