{-# OPTIONS_GHC -Wall #-}
module Main where

import           ALON.Diff.HTML (diffHTML)
import qualified Data.Text as T
import           Data.Text.Lazy (toStrict)
import           Data.Text.Lazy.Encoding (decodeUtf8)
import qualified Data.Aeson as DA
import qualified Data.ByteString.Lazy as L
import qualified Data.ByteString.Lazy.Char8 as LBC8
import           System.IO (hPutStrLn, stderr)
import           System.IO.Error (IOError)
import           System.Exit (exitFailure)
import           Control.Exception (catch)
import           System.Environment (getArgs)

readUTF8File :: String -> IO T.Text
readUTF8File filePath =
    L.readFile filePath `catch` errorHandler >>= return . toStrict . decodeUtf8
  where
    errorHandler e =
        let _ = (e :: IOError) in
            hPutStrLn stderr ("Error opening HTML file " ++ filePath) >> exitFailure

deltaFiles :: String -> String -> IO ()
deltaFiles sourceHtmlFile targetHtmlFile = do
    sourceHtml <- readUTF8File sourceHtmlFile
    targetHtml <- readUTF8File targetHtmlFile

    let diff      = diffHTML sourceHtml targetHtml
    let jsonValue = diff >>= return . DA.encode

    case jsonValue of
        (Just json) -> LBC8.putStr json
        Nothing     -> hPutStrLn stderr "Couldn't perform diff, is HTML in both source and target well formed?" >> exitFailure

main :: IO ()
main = do
    args <- getArgs
    case args of
        (sourceHtmlFile:targetHtmlFile:_) -> deltaFiles sourceHtmlFile targetHtmlFile
        _                                 -> hPutStrLn stderr "Expects 2 command line parameters" >> exitFailure