Delaunay triangulation as a web service

delaunay-server.hs

{-# LANGUAGE OverloadedStrings #-}

-- Used packages: delaunay, scotty, aeson

import Graphics.Triangulation.Delaunay
import Data.Vector.V2
import Data.Aeson
import Data.ByteString (ByteString)
import Data.Text.Lazy.Encoding (encodeUtf8)
import Data.Text.Lazy (Text)
import qualified Data.Text.Lazy as TL
import Web.Scotty
import qualified Data.ByteString.Lazy.Char8 as BL
-- import Control.Monad.Trans (liftIO)


-- dat :: [Vector2]
-- dat = map (uncurry Vector2) [(1,2),(2,3),(2,5),(1,6)]

type Triangle = (Vector2, Vector2, Vector2)

conv :: Triangle -> Value
conv (Vector2 x1 y1, Vector2 x2 y2, Vector2 x3 y3) =
  toJSON [x1,y1,x2,y2,x3,y3] 

main = scotty 3000 $ do
  post "/programming/delaunay" $ do
    p <- param "data"
    j <- param "json"
    -- liftIO $ print p
    let f = if j == (1 :: Int) then Web.Scotty.json . map conv else csv
    case decode (encodeUtf8 p) of
      Just dat -> f $ triangulate $ map pnt dat
      _ -> Web.Scotty.text "[]"

csv :: [Triangle] -> ActionM ()
csv ts = Web.Scotty.text txt
  where
    txt = TL.intercalate "\n" $ map c ts
    c (Vector2 x1 y1, Vector2 x2 y2, Vector2 x3 y3)
      = TL.intercalate "," $ map (TL.pack . show) [x1,y1,x2,y2,x3,y3]    

pnt [a,b] = Vector2 a b