QMK firmware Mod-Tab simulation with Tab-Dance for One-Shot-Modifier feature

keymap.c

typedef enum {
  SINGLE_TAP,
  SINGLE_HOLD,
} td_state_t;

static td_state_t td_state;

int cur_dance (qk_tap_dance_state_t *state);
void gui_control_finished (qk_tap_dance_state_t * state, void *user_data);
void gui_control_reset (qk_tap_dance_state_t* state, void *user_data);

int cur_dance (qk_tap_dance_state_t *state) {
  if (state->count ==  1) {
    if (state->interrupted || !state->pressed) {
      return SINGLE_TAP;
    } else {
      return SINGLE_HOLD;
    }
  } else {
    return 2;
  }
};

void gui_control_finished (qk_tap_dance_state_t *state, void *user_data) {
  td_state = cur_dance(state);
  switch (td_state) {
    case SINGLE_TAP:
      set_oneshot_mods(MOD_BIT(KC_LGUI));
      break;
    case SINGLE_HOLD:
      register_mods(MOD_BIT(KC_LCTL));
      break;
  }
};

void gui_control_reset (qk_tap_dance_state_t *state, void *user_data) {
  switch (td_state) {
    case SINGLE_TAP:
      clear_oneshot_mods();
      break;
    case SINGLE_HOLD:
      unregister_mods(MOD_BIT(KC_LCTL));
      break;
  }
};

enum tab_dance_codes {
  GUI_CONTROL = 0,
};

qk_tap_dance_action_t tap_dance_actions[] = {
  [GUI_CONTROL] = ACTION_TAP_DANCE_FN_ADVANCED(NULL, gui_control_finished, gui_control_reset),
};

const uint16_t PROGMEM keymaps[][MATRIX_ROWS][MATRIX_COLS] = {
  [LAYER_BASE] = LAYOUT_ergodox_pretty(
    TD(GUI_CONTROL), ....
  ),
};