Build a homepage for a Google Chat app

app.post('/', async (req, res) => {
  let event = req.body.chat;

  let body = {};
  if (event.type === 'APP_HOME') {
    // App home is requested
    body = { action: { navigations: [{
      pushCard: getHomeCard()
    }]}}
  } else if (event.type === 'SUBMIT_FORM') {
    // The update button from app home is clicked
    commonEvent = req.body.commonEventObject;
    if (commonEvent && commonEvent.invokedFunction === 'updateAppHome') {
      body = updateAppHome()
    }
  }

  return res.json(body);
});

// Create the app home card
function getHomeCard() {
  return { sections: [{ widgets: [
    { textParagraph: {
      text: "Here is the app home 🏠 It's " + new Date().toTimeString()
    }},
    { buttonList: { buttons: [{
      text: "Update app home",
      onClick: { action: {
        function: "updateAppHome"
      }}
    }]}}
  ]}]};
}

@app.route('/', methods=['POST'])
def post() -> Mapping[str, Any]:
  """Handle requests from Google Chat

  Returns:
      Mapping[str, Any]: the response
  """
  event = request.get_json()
  match event['chat'].get('type'):

    case 'APP_HOME':
      # App home is requested
      body = { "action": { "navigations": [{
        "pushCard": get_home_card()
      }]}}

    case 'SUBMIT_FORM':
      # The update button from app home is clicked
      event_object = event.get('commonEventObject')
      if event_object is not None:
        if 'update_app_home' == event_object.get('invokedFunction'):
          body = update_app_home()

    case _:
      # Other response types are not supported
      body = {}

  return json.jsonify(body)


def get_home_card() -> Mapping[str, Any]:
  """Create the app home card

  Returns:
      Mapping[str, Any]: the card
  """
  return { "sections": [{ "widgets": [
    { "textParagraph": {
      "text": "Here is the app home 🏠 It's " +
        datetime.datetime.now().isoformat()
    }},
    { "buttonList": { "buttons": [{
      "text": "Update app home",
      "onClick": { "action": {
        "function": "update_app_home"
      }}
    }]}}
  ]}]}

// Process Google Chat events
@PostMapping("/")
@ResponseBody
public GenericJson onEvent(@RequestBody JsonNode event) throws Exception {
  switch (event.at("/chat/type").asText()) {
    case "APP_HOME":
      // App home is requested
      GenericJson navigation = new GenericJson();
      navigation.set("pushCard", getHomeCard());

      GenericJson action = new GenericJson();
      action.set("navigations", List.of(navigation));

      GenericJson response = new GenericJson();
      response.set("action", action);
      return response;
    case "SUBMIT_FORM":
      // The update button from app home is clicked
      if (event.at("/commonEventObject/invokedFunction").asText().equals("updateAppHome")) {
        return updateAppHome();
      }
  }

  return new GenericJson();
}

// Create the app home card
GoogleAppsCardV1Card getHomeCard() {
  return new GoogleAppsCardV1Card()
    .setSections(List.of(new GoogleAppsCardV1Section()
      .setWidgets(List.of(
        new GoogleAppsCardV1Widget()
          .setTextParagraph(new GoogleAppsCardV1TextParagraph()
            .setText("Here is the app home 🏠 It's " + new Date())),
        new GoogleAppsCardV1Widget()
          .setButtonList(new GoogleAppsCardV1ButtonList().setButtons(List.of(new GoogleAppsCardV1Button()
            .setText("Update app home")
            .setOnClick(new GoogleAppsCardV1OnClick()
              .setAction(new GoogleAppsCardV1Action()
                .setFunction("updateAppHome"))))))))));
}

/**
 * Responds to a APP_HOME event in Google Chat.
 */
function onAppHome() {
  return { action: { navigations: [{
    pushCard: getHomeCard()
  }]}};
}

/**
 * Returns the app home card.
 */
function getHomeCard() {
  return { sections: [{ widgets: [
    { textParagraph: {
      text: "Here is the app home 🏠 It's " + new Date().toTimeString()
    }},
    { buttonList: { buttons: [{
      text: "Update app home",
      onClick: { action: {
        function: "updateAppHome"
      }}
    }]}}
  ]}]};
}

// Update the app home
function updateAppHome() {
  return { renderActions: { action: { navigations: [{
    updateCard: getHomeCard()
  }]}}}
};

def update_app_home() -> Mapping[str, Any]:
  """Update the app home

  Returns:
      Mapping[str, Any]: the update card render action
  """
  return { "renderActions": { "action": { "navigations": [{
    "updateCard": get_home_card()
  }]}}}

// Update the app home
GenericJson updateAppHome() {
  GenericJson navigation = new GenericJson();
  navigation.set("updateCard", getHomeCard());

  GenericJson action = new GenericJson();
  action.set("navigations", List.of(navigation));

  GenericJson renderActions = new GenericJson();
  renderActions.set("action", action);

  GenericJson response = new GenericJson();
  response.set("renderActions", renderActions);
  return response;
}

/**
 * Updates the home app.
 */
function updateAppHome() {
  return { renderActions: { action: { navigations: [{
    updateCard: getHomeCard()
  }]}}};
}