feat(mouse): Initial mouse keys support.

* Add HID report/descriptor for a new report with mouse buttons,
  and x/y/wheel deltas.
* New mouse key press behavior for press/release of mouse keys.
* Add constants for HID main item values (e.g. data/array/absolute)
* Define and use constants for our HID report IDs.

app/src/hid.c

@@ -12,6 +12,7 @@ LOG_MODULE_DECLARE(zmk, CONFIG_ZMK_LOG_LEVEL);
 #include <dt-bindings/zmk/modifiers.h>
 
 static struct zmk_hid_keyboard_report keyboard_report = {
+
     .report_id = ZMK_HID_REPORT_ID_KEYBOARD, .body = {.modifiers = 0, ._reserved = 0, .keys = {0}}};
 
 static struct zmk_hid_consumer_report consumer_report = {.report_id = ZMK_HID_REPORT_ID_CONSUMER,
@@ -24,6 +25,13 @@ static uint8_t keys_held = 0;
 
 #endif /* IS_ENABLED(CONFIG_ZMK_USB_BOOT) */
 
+#if IS_ENABLED(CONFIG_ZMK_MOUSE)
+
+static struct zmk_hid_mouse_report mouse_report = {.report_id = ZMK_HID_REPORT_ID_MOUSE,
+                                                   .body = {.buttons = 0}};
+
+#endif // IS_ENABLED(CONFIG_ZMK_MOUSE)
+
 // Keep track of how often a modifier was pressed.
 // Only release the modifier if the count is 0.
 static int explicit_modifier_counts[8] = {0, 0, 0, 0, 0, 0, 0, 0};
@@ -357,6 +365,71 @@ bool zmk_hid_is_pressed(uint32_t usage) {
     return false;
 }
 
+#if IS_ENABLED(CONFIG_ZMK_MOUSE)
+
+// Keep track of how often a button was pressed.
+// Only release the button if the count is 0.
+static int explicit_button_counts[5] = {0, 0, 0, 0, 0};
+static zmk_mod_flags_t explicit_buttons = 0;
+
+#define SET_MOUSE_BUTTONS(btns)                                                                    \
+    {                                                                                              \
+        mouse_report.body.buttons = btns;                                                          \
+        LOG_DBG("Mouse buttons set to 0x%02X", mouse_report.body.buttons);                         \
+    }
+
+int zmk_hid_mouse_button_press(zmk_mouse_button_t button) {
+    if (button >= ZMK_HID_MOUSE_NUM_BUTTONS) {
+        return -EINVAL;
+    }
+
+    explicit_button_counts[button]++;
+    LOG_DBG("Button %d count %d", button, explicit_button_counts[button]);
+    WRITE_BIT(explicit_buttons, button, true);
+    SET_MOUSE_BUTTONS(explicit_buttons);
+    return 0;
+}
+
+int zmk_hid_mouse_button_release(zmk_mouse_button_t button) {
+    if (button >= ZMK_HID_MOUSE_NUM_BUTTONS) {
+        return -EINVAL;
+    }
+
+    if (explicit_button_counts[button] <= 0) {
+        LOG_ERR("Tried to release button %d too often", button);
+        return -EINVAL;
+    }
+    explicit_button_counts[button]--;
+    LOG_DBG("Button %d count: %d", button, explicit_button_counts[button]);
+    if (explicit_button_counts[button] == 0) {
+        LOG_DBG("Button %d released", button);
+        WRITE_BIT(explicit_buttons, button, false);
+    }
+    SET_MOUSE_BUTTONS(explicit_buttons);
+    return 0;
+}
+
+int zmk_hid_mouse_buttons_press(zmk_mouse_button_flags_t buttons) {
+    for (zmk_mouse_button_t i = 0; i < ZMK_HID_MOUSE_NUM_BUTTONS; i++) {
+        if (buttons & BIT(i)) {
+            zmk_hid_mouse_button_press(i);
+        }
+    }
+    return 0;
+}
+
+int zmk_hid_mouse_buttons_release(zmk_mouse_button_flags_t buttons) {
+    for (zmk_mouse_button_t i = 0; i < ZMK_HID_MOUSE_NUM_BUTTONS; i++) {
+        if (buttons & BIT(i)) {
+            zmk_hid_mouse_button_release(i);
+        }
+    }
+    return 0;
+}
+void zmk_hid_mouse_clear() { memset(&mouse_report.body, 0, sizeof(mouse_report.body)); }
+
+#endif // IS_ENABLED(CONFIG_ZMK_MOUSE)
+
 struct zmk_hid_keyboard_report *zmk_hid_get_keyboard_report() {
     return &keyboard_report;
 }
@@ -364,3 +437,11 @@ struct zmk_hid_keyboard_report *zmk_hid_get_keyboard_report() {
 struct zmk_hid_consumer_report *zmk_hid_get_consumer_report() {
     return &consumer_report;
 }
+
+#if IS_ENABLED(CONFIG_ZMK_MOUSE)
+
+struct zmk_hid_mouse_report *zmk_hid_get_mouse_report() {
+    return &mouse_report;
+}
+
+#endif // IS_ENABLED(CONFIG_ZMK_MOUSE)