Move packagist check to a Haskell binary

app/Main.hs

@@ -0,0 +1,46 @@
+module Main
+    ( main
+    ) where
+
+import Data.Aeson.TH (defaultOptions, deriveJSON)
+import Data.HashMap.Strict (HashMap)
+import qualified Data.HashMap.Strict as HashMap
+import Data.Text (Text)
+import qualified Data.Text.IO as Text.IO
+import Data.Vector (Vector)
+import qualified Data.Vector as Vector
+import Network.HTTP.Req
+    ( runReq
+    , defaultHttpConfig
+    , req
+    , GET(..)
+    , https
+    , jsonResponse
+    , NoReqBody(..)
+    , (/:)
+    , responseBody
+    )
+import Data.Maybe (fromMaybe)
+
+newtype PackagistPackage = PackagistPackage
+    { version :: Text
+    } deriving (Eq, Show)
+
+$(deriveJSON defaultOptions ''PackagistPackage)
+
+newtype PackagistResponse = PackagistResponse
+    { packages :: HashMap Text (Vector PackagistPackage)
+    } deriving (Eq, Show)
+
+$(deriveJSON defaultOptions ''PackagistResponse)
+
+main :: IO ()
+main = do
+    packagistResponse <- runReq defaultHttpConfig $
+        let uri = https "repo.packagist.org" /: "p2" /: "composer" /: "composer.json"
+         in req GET uri NoReqBody jsonResponse mempty
+    let packagistPackages = packages $ responseBody packagistResponse
+
+    Text.IO.putStrLn $ fromMaybe ""
+        $ HashMap.lookup "composer/composer" packagistPackages
+        >>= fmap (version . fst) . Vector.uncons