import Data.List.Split (sepBy)

import Control.Applicative ((<$>), (<*>))
import Data.List (isInfixOf)
import Distribution.InstalledPackageInfo (InstalledPackageInfo, InstalledPackageInfo_(..), parseInstalledPackageInfo, ParseResult(..))
import Distribution.Package (PackageIdentifier)
import Distribution.Text (display)
import System.Environment (getArgs)

display' :: PackageIdentifier -> String
display' = show . display

fromParseOk :: Show a => ParseResult a -> a
fromParseOk (ParseOk _ x) = x
fromParseOk e = error $ "Parse failed: " ++ show e

rels :: InstalledPackageInfo -> [String]
rels = fmap . (. display') . (++) . (++ " -> ") . display' . package <*> depends

fmain :: [String] -> String -> String
fmain maintainers input = unlines $ "digraph Packages {" : deps ++ ["}"]
    where
        deps :: [String]
	deps = (filteredRels . fromParseOk . parseInstalledPackageInfo) =<< sepBy "\n---\n" input
        filteredRels :: InstalledPackageInfo -> [String]
        filteredRels ipi
            | any (`isInfixOf` maintainer ipi) maintainers = ('\t' :) <$> rels ipi
            | otherwise                                    = []

main :: IO ()
main = do
    maintainers <- getArgs
    interact $ fmain maintainers