[ETL in Haskell] Enrich a geojson file with attributes coming from an .xml #haskell #xml #geojson

etl.hs

#!/usr/bin/env stack
{-
stack
--install-ghc runghc
--package aeson
--package lens-aeson
--package xml-lens
-}
{-# Language OverloadedStrings #-}
import Control.Monad.Reader
import qualified Data.Text as T
import qualified Data.Text.IO as T
import qualified Data.ByteString.Lazy.Char8 as LB8
import qualified Data.Map as Map
import qualified Data.Vector as V
import Data.Scientific (Scientific)
import qualified Data.Aeson as Json
import Data.Aeson.Lens
import qualified Text.XML as XML
import Text.XML.Lens

records :: Reader XML.Document [(T.Text, Scientific)]
records =
  let
    field name = nodes . folded . _Element . named "field" . attributeIs "name" name
  in do
    magnify (root . named "Root" ./ named "data" ./ named "record") $ do
      record <- ask
      let name = record ^? (field "Country or Area" . attr "key")
      let year = record ^? (field "Year" . text)
      let val  = record ^? (field "Value" . text)
      return $ case (name, year, val) of
        (Just key, Just "2020", Just val) -> [ (key, read $ T.unpack val) ]
        _ -> []

features :: Map.Map T.Text Scientific -> Reader Json.Value [ Json.Value ]
features popMap = do
  magnify (key "features" . values) $ do
    feature <- ask
    let Just id = feature ^? (key "id" . _String)
    return $ case (Map.lookup id popMap) of
      Just pop -> [ feature & key "properties" . _Object . at "pop2020" ?~  Json.Number pop ]
      _ -> [ feature ]


main = do
  xml <- XML.readFile XML.def "population.xml"
  let pop2020Map = Map.fromList $ runReader records xml
  jsonBytes <- LB8.readFile "countries.geo.json"
  let Just json = Json.decode jsonBytes :: Maybe Json.Value
  let featureList = runReader (features pop2020Map) json :: [ Json.Value ]
  let newJson = json & key "features"  .~ (Json.Array $ V.fromList featureList)
  LB8.writeFile "countriesWithPopulation.geo.json" $ Json.encode newJson