shift-ctrl-keymap

// ---- ---- ---- ---- ----
//Functions associated with shift - ctrl tap dance
void shift_ctrl_toggle (qk_tap_dance_state_t *state, void *user_data);
void shift_ctrl_reset (qk_tap_dance_state_t *state, void *user_data);

//Initialize tap structure associated with example tap dance key
static tap lsft_tap_state = {
  .is_press_action = true,
  .state = 0
};

//single tap, single hold, double tap, double tap hold
//_         , Shift,     , _         , Ctrl
void shift_ctrl_toggle (qk_tap_dance_state_t *state, void *user_data) {
  lsft_tap_state.state = cur_dance(state);
  switch (lsft_tap_state.state) {
    case SINGLE_TAP:
      register_code(KC_LSFT);
      break;
    case SINGLE_HOLD:
      register_code(KC_LSFT);
      break;
    case DOUBLE_TAP:
      register_code(KC_LSFT);
      break;
    case DOUBLE_HOLD:
      register_code(KC_LCTL);
      break;
  }
}

void shift_ctrl_reset (qk_tap_dance_state_t *state, void *user_data) {
  // if key is held down it should work fine as LSFT
  if (lsft_tap_state.state==SINGLE_HOLD) {
    tap_code(KC_LSFT);
  }
  if (lsft_tap_state.state==SINGLE_TAP) {
    tap_code(KC_LSFT);
  }
}