app.js

/**
 * Welcome to Pebble.js!
 *
 * This is where you write your app.
 */

var UI = require('ui');
var ajax = require('ajax');

function fetchJSON(url) {
  ajax(
    {
      url: url,
      type: 'json'
    }, function(data, status, request) {
      displayJSON(data);
    }, function(error, status, request) {
      var card = UI.Card({
        title: "Error",
        body: status
      });
      card.show();
    }
  );
}

function displayJSON (json) {
  if (json.hasOwnProperty('menu')) {
    var menu = new UI.Menu(json.menu);
    menu.on('select', function(e) {
      if (e.item.hasOwnProperty('url')) {
        fetchJSON(e.item.url);
      }
    });
    menu.show();
  } else if (json.hasOwnProperty('card')) {
    var card = new UI.Card(json.card);
    card.show();
  }
}

var menuUrl = "https://gist.githubusercontent.com/AlSquire/5b29d5c0ddbddac6e502/raw/menu.json";

fetchJSON(menuUrl);

card.json

{
  "card": {
    "title": "Hey you",
    "body": "Tralala\nAll right!"
  }
}

main.rb

require 'sinatra'
require 'json'
require 'net/http'

get '/' do
  "Hello World"
end

get '/velib.json' do
  stations = {
    2021 => 'OMTS',
    4013 => 'Home',
    4014 => 'Archives',
    3008 => 'Perle',
    4103 => 'BHV',
    4015 => 'Pont Louis',
    4012 => 'Ecouffes'
  }

  url = "http://opendata.paris.fr/api/records/1.0/search?dataset=stations-velib-disponibilites-en-temps-reel&q="
  url += 'number%3A' + stations.keys.join('+OR+number%3A')

  json = JSON.parse(Net::HTTP.get(URI(url)))

  body = stations.map do |key, val|
    fields = json['records'].detect { |r| r['fields']['number'] == key }['fields']
    "#{val}: #{fields['available_bikes']}/#{fields['available_bike_stands']}"
  end

  content_type :json
  {
    card: {
      title: "Velib",
      body: body.join("\n")
    }
  }.to_json
end

menu.json

{
  "menu": {
    "sections": [{
        "items": [
          {
            "title": "Velibs",
            "url": "http://alnet.herokuapp.com/velib.json"
          }, {
            "title": "Card test",
            "subtitle": "Yeah",
            "url": "https://gist.githubusercontent.com/AlSquire/5b29d5c0ddbddac6e502/raw/card.json"
          }, {
            "title": "Rien",
            "subtitle": "Gogogo"
          }
        ]
    }]
  }
}