Post pobrano z: Displaying the Weather With Serverless and Colors

I like to jog. Sometimes it’s cold out. Sometimes it’s cold out, but it looks like it isn’t. The sun is shining, the birds are chirping. Then you step outside in shorts and a t-shirt and realize you have roughly 2 minutes before exposure sets in.

I decided to solve this first world problem using a lightbulb to display a certain color based on what the temperature outside is. It works better than I expected, and that’s saying something because usually nothing works out like I want it to.

This was a fun project to build, and since it is essentially a hosted service running on a timer, it’s a perfect use case for Serverless.

Now you might be thinking, “um, wouldn’t it be easier to just check the weather?” Well, it would, but then I wouldn’t have an excuse to buy an expensive lightbulb or write an article with the word “Serverless.”

So let’s look at how you can build your own Weather Bulb. The final code is not complicated, but it does have some interesting pieces that are worth noting. By the way, did I mention that it’s Serverless?

Building the Weather Bulb

The first thing you are going to need is the bulb. You can’t have a Weather Bulb sans bulb. Say the word “bulb” out loud about 10 times and you’ll notice what a bizarre word it is. Bulb, bulb, bulb, bulb — see? Weird.

I am using the LIFX Mini Color. It’s not *too* expensive, but more importantly, it’s got an API that is wide open.

The API has two methods of authentication. The first contains the word “OAuth” and I’m already sorry that you had to read that. Don’t worry, there is an easier way that doesn’t involve OAu…. that which won’t be named.

The second way is to register an application with LIFX. You get back a key and all you have to do is pass that key with any HTTP request. That’s what I’m using for this demo.

For instance, if we wanted to change the bulb color to blue, we can just pass color: blue to the /state endpoint.

The API supports a few different color formats, including named colors (like red, blue), hex values, RBG, Kevlin, hue brightness and saturation. This is important because it factors into what proved to be the hardest part of this project: turning temperature into color.

Representing Temperature With Color

If you’ve ever watched a weather report, you’ll be familiar with the way that meteorology represents weather conditions with color on a map.

Usually, this is done to visualize precipitation. You have probably seen that ominous green strip of storms bearing down on you on a weather map while you try to figure out if you should get in the bathtub because you’re in the path of a tornado. Or maybe that’s just all of us unlucky souls here in America’s Tornado Alley.

Color is also used to represent temperature. This is precisely what I wanted to do with the bulb. The tough thing is that there doesn’t seem to be a standardized way to do this. Some maps show it as solid colors in bands. In this case, blue might represent the band from 0℉ – 32℉.

Others have it as a gradient scale which is more precise. This is what I was after for the Weather Bulb.

My first stab at solving this was just to Google “temperature color scale” and other various iterations of that search term. I got back a lot of information about Kelvin.

Kelvin is a representation of the temperature of a color. Literally. For any light source (light bulb, the sun, ect) the actual temperature of that source will affect the color of the light it emits. A fire burns a yellowish red color. The hotter that fire gets, the more it moves towards white. Hence the saying, “white hot”. So if someone ever says “red hot,” you can correct them in front of everyone because who doesn’t love a pedantic jerk?

The LIFX bulb supports Kelvin, so you might think that this would work. After all, this is the Kelvin scale….

The problem is that there is simply not enough color variation because these are not actual colors, but rather the tinge of color that a light is emitting based on it’s “temperature.” Here is the Kelvin color wheel that comes with the LIFX app.

These colors are barely distinguishable from one another on the bulb. Not exactly what I was after.

That leaves me with trying to convert the color to either Hex, RGB or some other format. This is tough because where do you begin? I spent an embarrassing amount of time adjust RGB scale values between blue for cold (0, 0, 255) and red for hot (255, 0, 0). It was about this time that it dawned on me that maybe HSL would be a better way to go here. Why? Because hue is a whole lot easier to understand.

Hue

Hue is a representation of color on a scale between 0 and 360. This is why we often see color represented on a wheel (360°). That’s a vast oversimplification, but unless you want me to start talking about wavelengths, let’s go with that definition.

The hue color wheel looks like this….

If we flatten it out, it’s easier to reason about.

We’re ready to convert temperature to color. The first thing we need to do is figure out a set temperature range. I went with 0℉ to 100℉. We can’t work with infinite temperature color combinations. Numbers go on forever, colors do not. It can only get so hot before our bulb is just bright red all the time, and that’s 100℉. The same is true for cold.

If light blue represents 0℉, I can start at about the 200 mark on the hue scale. Red will represent 100℉. You can see that red is at both extremes, so I can move either left OR right, depending on what colors I want to use to represent the temperature. It’s not the same as the colors they use in actual weather programs, but who cares? Obviously not me.

I chose to go right because there is no pink on the left and pink is my favorite color. I also felt like pink represents warm a bit better than green. Green is rain and tornadoes.

Now we can back into a hue based on temperature. Ready? Here we go.

Let’s pretend it’s a brisk 50℉ outside.

If 100℉ is the hottest we go (360) and 0℉ is the coldest (200), then we have a color scale of 160 points. To figure out where in that 160 point range we need to be, we can divide the current temperature by the upper bound of 100℉ which will give us the exact percentage we need to move in our range, or 50%. If we move 50% of the way into a 160 point range, that leaves us at 80. Since we are starting at 200, that gives us a hue of 280.

That sounds complicated, but only because word problems in math SUCK. Here’s how the code looks when it’s all said and done…

let hue = 200 + (160 * ( temperature / 100 ));

OK! We’ve got a dynamic color scale based on hue, and wouldn’t you know it, we can just pass the hue to LIFX as simply as we pass a named color.

Now we just need to find out what the current temperature is, back into a hue and do that every few minutes. Serverless, here we come!

Serverless Timer Functions

Serverless is all the rage. It’s like HTML5 used to be: it doesn’t matter what it is, it only matters that you know the word and are not afraid to use it in a blog post.

For this example, we’ll use Azure Functions because there is support for timer triggers, and we can test those timer triggers locally before we deploy using VS Code. One of the things about Serverless that irritates me to no end is when I can’t debug it locally.

Using the Azure Functions Core Tools and the Azure Functions Extension for VS Code, I can create a new Serverless project and select a Timer Trigger.

Timer Triggers in Azure Functions are specified as Cron Expressions. Don’t worry, I didn’t know what that was either.

Cron Expressions allow you to get very specific with interval definition. Cron breaks things down into second, minute, hour, day, month, year. So if you wanted to run something every second of every minute of every hour of every day of every year, your expression would look like this…

* * * * * *

If you wanted to run it every day at 10:15, it would look like this…

* 15 10 * * *

If you wanted to run it every 5 minutes (which is what Azure defaults to), you specify that by saying “when minutes is divisible by 5.”

0 */5 * * * *

For the purposes of this function, we set it to 2 minutes.

I am using a 2 minute interval because that’s how often we can call the weather API for free 💰.

Getting the Forecast From DarkSky

DarkSky has a wonderful weather API that you can call up to 1,000 times per day for free. If there are 1,440 minutes in a day (and there are), that means we can call DarkSky every 1.44 minutes per day and stay in the free zone. I just rounded up to 2 minutes because temperature doesn’t change that fast.

This is what our function looks like when we call the DarkSky API. All of my tokens, keys, latitude and longitude settings are in environment variables so they aren’t hardcoded. Those are set in the local.settings.json file. I used axios for my HTTP requests because it is a magical, magical package.

const axios = require('axios');

module.exports = function (context, myTimer) {
  // build up the DarkSky endpoint
  let endpoint = `${process.env.DS_API}/${process.env.DS_SECRET}/${process.env.LAT}, 
                  ${process.env.LNG}`;
  
  // use axios to call DarkSky for weather
  axios
    .get(endpoint)
    .then(response => {
      let temp = Math.round(response.data.currently.temperature);
    
      // TODO: Set the color of the LIFX bulb
    })
    .catch(err => {
      context.log(err.message);
    });
};

Now that I have the temperature, I need to call the LIFX API. And wouldn’t you know it, someone has already created an npm package to do this called lifx-http-api. This is why you love JavaScript.

Setting the Bulb Hue

After the weather result comes back, I need to use the LIFX API instance and call the setState method. This method returns a promise which means that we need to nest promises. Nesting promises can get out of hand and could land us right back in callback hell, which is what we’re trying to avoid with promises in the first place.

Instead, we’ll handle the first promise and then return Promise.all which we can handle at another top-level then. This just prevents us from nesting then statements.

Remember kids, promises are just socially acceptable callbacks.

const axios = require('axios');
const LIFX = require('lifx-http-api');

let client = new LIFX({
  bearerToken: process.env.LIFX_TOKEN
});

module.exports = function (context, myTimer) {
  // build up the DarkSky endpoint
  let endpoint = <code>${process.env.DS_API}/${process.env.DS_SECRET}/${
    process.env.LAT
    },${process.env.LNG}<code>;
    
  // use axios to call DarkSky for weather
  axios
    .get(endpoint)
    .then(response => {
      let temp = Math.round(response.data.currently.temperature);
      
      // make sure the temp isn't above 100 because that's as high as we can go
      temp = temp < 100 ? temp : 100;
      
      // determine the hue
      let hue = 200 + (160 * (temp / 100));

      // return Promise.all so we can resolve at the top level
      return Promise.all([
        data,
        client.setState('all', { color: <code>hue:${hue}<code> })
      ]);
    })
    .then(result => {
      // result[0] contains the darksky result
      // result[1] contains the LIFX result
      context.log(result[1]);
    })
    .catch(err => {
      context.log(err.message);
    });
};

Now we can run this thing locally and watch our timer do it’s thang.

That’s it! Let’s deploy it.

Deploying Weather Bulb

I can create a new Functions project from the VS Code extension.

I can right-click that to “Open in portal” where I can define a deployment source so it sucks my code in from Github and deploys it. This is ideal because now whenever I push a change to Github, my application automatically gets redeployed.

All Hail the Weather Bulb

Now just sit back and behold the soft glow of the Weather Bulb! Why look at the actual temperature when you can look at this beautiful shade of hot pink instead?

Can you guess what the temperature is based on what you know from this article? The person who leaves a comment and gets the closest will get a free LIFX lightbulb from me (because I ❤️ all of you), or the cost of the bulb if you are outside the U.S. (~$40).

You can grab all of the code for this project from Github.

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