Wednesday, January 02, 2019

A Hacker Friendly Weather Tool - The Singular Weather Service

I recently posted the start of a simple weather web service. And now I've got the rest of the code written.

Actual weather data is being pulled from the coder friendly DarkSky.net API. The code to do so is straightforward:

function forecast($loc, $time, $attr) {
  $key = DARKSKY_API_KEY;
  $url = "https://api.darksky.net/forecast/$key/{$loc['lat']},{$loc['lng']},$time";
  $ttl = $time < time() ? true : (60*60*6);

  if($time > (time() + (60*60*24*10))) {
    $ref_times = historic_times($time, 5);
    $result    = false;
    foreach($ref_times as $t) {
      $f  = forecast($loc, $t, $attr);
      if(is_numeric($f)) {
        $result = $result === false ? $f : (($result + $f) / 2);
      } else {
        $result = ($result == false ? $f : ("$result\n$f"));
      }
    }
    return $result;
  } else {
    $response = curl_get($url, ['exclude' => 'hourly,currently,flags'], ['ttl' => $ttl]);
    $data = $response['daily']['data'][0];
    return $attr === 'all' ? json_encode($data, JSON_PRETTY_PRINT) : $data[$attr];
  }
}

My code does have a few notable features:

  • To make my Darksky API quote last, I'm being careful to cache whatever data I can. If you ask for a historic forecast, the result is cached forever. If you ask for a forecast in the next 10 days, the results are cached for 6 hours.
  • The goal of my API is to return a single attribute, say temperatureHigh, however if you pass in the attribute all the entire forecast is returned as a JSON string. This is useful for debugging.
  • If you ask for the weather for a date more than 10 days into the future the code gets clever and returns a historic average of the last 5 years. Therefore, you can ask the system for any date and you'll get a sane response.

Here are some examples of the API in use:

# Quick access to one weather attribute. Note that any date allowed
# by strotime is legal.
$  curl -s "http://code.benjisimon.com/singular-weather-service/?loc=Arlington,VA&date=today&attr=temperatureHigh" ; echo
45.06

# See all attributes
$  curl -s "http://code.benjisimon.com/singular-weather-service/?loc=Arlington,VA&date=2019-01-02&attr=all" ; echo
{
    "time": 1546405200,
    "summary": "Light rain overnight.",
    "icon": "rain",
    "sunriseTime": 1546432095,
    "sunsetTime": 1546466329,
    "moonPhase": 0.9,
    "precipIntensity": 0.0042,
    "precipIntensityMax": 0.0375,
    "precipIntensityMaxTime": 1546488000,
    "precipProbability": 0.4,
    "precipType": "rain",
    "temperatureHigh": 45.06,
    "temperatureHighTime": 1546459200,
    "temperatureLow": 41.6,
    "temperatureLowTime": 1546491600,
    "apparentTemperatureHigh": 42.43,
    "apparentTemperatureHighTime": 1546459200,
    "apparentTemperatureLow": 37.09,
    "apparentTemperatureLowTime": 1546484400,
    "dewPoint": 33.69,
    "humidity": 0.73,
    "pressure": 1024.09,
    "windSpeed": 3.12,
    "windGust": 21.31,
    "windGustTime": 1546488000,
    "windBearing": 116,
    "cloudCover": 0.83,
    "uvIndex": 2,
    "uvIndexTime": 1546444800,
    "visibility": 10,
    "ozone": 273.7,
    "temperatureMin": 38.01,
    "temperatureMinTime": 1546430400,
    "temperatureMax": 45.06,
    "temperatureMaxTime": 1546459200,
    "apparentTemperatureMin": 36.13,
    "apparentTemperatureMinTime": 1546437600,
    "apparentTemperatureMax": 42.75,
    "apparentTemperatureMaxTime": 1546405200
}

# A month of high temps from the command line!
# This was on run on 2 Jan 2019. Therefore, some of these temps are predictions,
# some are historic and some are historic averages.
$ for d in `seq 1 31` ; do\
   echo -n "High Temp: $d Jan 2019: " ; \
   curl -s "http://code.benjisimon.com/singular-weather-service/?loc=Arlington,VA&date=2019-01-$d&attr=temperatureHigh" ; \
   echo "F" ; done
High Temp: 1 Jan 2019: 61.72F
High Temp: 2 Jan 2019: 45.06F
High Temp: 3 Jan 2019: 45.84F
High Temp: 4 Jan 2019: 49.45F
High Temp: 5 Jan 2019: 49.93F
High Temp: 6 Jan 2019: 53.85F
High Temp: 7 Jan 2019: 45.58F
High Temp: 8 Jan 2019: 53.14F
High Temp: 9 Jan 2019: 42.83F
High Temp: 10 Jan 2019: 44.97F
High Temp: 11 Jan 2019: 50.52F
High Temp: 12 Jan 2019: 41.88F
High Temp: 13 Jan 2019: 46.69F
High Temp: 14 Jan 2019: 41.600625F
High Temp: 15 Jan 2019: 43.900625F
High Temp: 16 Jan 2019: 41.5675F
High Temp: 17 Jan 2019: 41.451875F
High Temp: 18 Jan 2019: 34.704375F
High Temp: 19 Jan 2019: 44.614375F
High Temp: 20 Jan 2019: 49.164375F
High Temp: 21 Jan 2019: 36.860625F
High Temp: 22 Jan 2019: 29.885625F
High Temp: 23 Jan 2019: 32.618125F
High Temp: 24 Jan 2019: 31.099375F
High Temp: 25 Jan 2019: 39.45875F
High Temp: 26 Jan 2019: 37.8025F
High Temp: 27 Jan 2019: 44.05F
High Temp: 28 Jan 2019: 28.1475F
High Temp: 29 Jan 2019: 30.96F
High Temp: 30 Jan 2019: 35.040625F
High Temp: 31 Jan 2019: 45.15125F

Check out the code for the project here and feel free to experiment with the server over at http://code.benjisimon.com/singular-weather-service/.

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