weather.hs

weather.hs

{-# LANGUAGE OverloadedStrings #-}
module Main where

import System.Environment
import Data.Monoid
import Control.Monad
import Data.Aeson
import qualified Data.Text    as T
import qualified Data.Text.IO as T
import Network.HTTP.Client
import Data.ByteString.Lazy (ByteString)
type URL = String
type City = String
type Code = String
type Emoji = T.Text

data Weather = Weather { code :: String }

instance FromJSON Weather where
  parseJSON (Object o) = do
    weatherValues <- o .: "weather"
    case weatherValues of 
      [] -> mzero
      weatherValue:_ -> Weather <$> weatherValue .: "icon"
  parseJSON _ = mzero

apiUrl :: URL
apiUrl = "http://api.openweathermap.org/data/2.5/weather?q="

urlBuilder :: City -> URL
urlBuilder city = apiUrl <> city <> "&units=metric"

simplestHttp :: URL -> IO ByteString 
simplestHttp str = do 
  req <- parseUrl str
  withManager defaultManagerSettings $ \mgr -> do
     resp <- httpLbs req mgr
     return (responseBody resp)

getWeather :: City -> IO (Maybe Weather)
getWeather city = do   -- fmap decode . simplestHttp
  resp <- simplestHttp city
  return (decode resp :: Maybe Weather)

getEmoji :: Code -> Emoji
getEmoji code = case take 2 code of
  "01" -> "☀️" -- sun
  "02" -> "⛅️" -- sun with cloud
  "03" -> "☁️" -- cloud
  "04" -> "☁️" -- cloud
  "09" -> "💦" -- rain
  "10" -> "💦" -- rain
  "11" -> "⚡️" -- thunder
  "13" -> "❄️" -- snow
  "50" -> "♒︎" -- mist
  _ -> "⁉️"

parseArgs = do
  args <- getArgs
  case args of
    [s]-> return s
    _ -> error "No City given."
            

main = do
  city <- parseArgs
  response <- getWeather city
  case response of
    Just w -> T.putStrLn $ getEmoji (code w)
    Nothing  -> error "Failed to fetch weather info."