import Control.Applicative((<$>))
import Data.Char(isSpace)
import Data.ByteString.Lazy(readFile)
import Data.ByteString.Lazy.Char8(concat,singleton,split,init,last,unpack,lines)
import Data.Graph
import Data.List(intersperse,sort)
import System.Environment
import Prelude hiding (readFile,concat,init,last,lines)

x |> f = f x

dropWS = reverse . dropWhile isSpace . reverse . dropWhile isSpace

portify info
  = info |> lines |> (toPort <$>)
  where
    toPort line = line |> split ':' |> parse
    parse [package, deps] = (dropWS $ unpack package, filter (not . null) $ unpack <$> split ' ' deps)

generateGraph ports
  = map toNode ports |> graphFromEdges
  where toNode (name, deps) = (name, name, deps)

translate (name,_,_) = name
forward = id
backward = transposeG

depends graph port fromVertex toVertex tr
  = vertexed |> reachable graph |> map (tr . fromVertex) |> sort
  where
    vertexed = case (toVertex port) of
      Just id -> id
      Nothing -> error $ port ++ " cannot be found"

printLines = putStrLn . unlines

--
-- Calculate dependencies between ports based on a "describe file".  This
-- file contains information on which package depends the given package
-- (see hs-dependencies.sh).
--
-- The result is a list of all dependants according to the direction of
-- search: "forward" or "backward" (inverted).
--
calculateDependency describe port dir = do
  contents <- readFile describe
  let (h,f,g) = contents |> portify |> generateGraph
  return $ depends (dir h) port f g translate

showDependency describe port dir = do
  res <- calculateDependency describe port dir
  printLines res

--
-- Calculate a topology for ports -- it is an ordering between graph
-- elements.  It is ideal for determining the order of how ports should
-- be added/updated when committing them.
--
-- The result is a list ordered by their dependencies.
--
calculateTopology describe port dir = do
  contents <- readFile describe
  let (h,f,g) = contents |> portify |> generateGraph
  let (h1,f1,g1) = graphFromEdges $ depends (dir h) port f g id
  return $ topSort h1 |> map (translate . f1) |> reverse

showTopology describe port dir = do
  res <- calculateTopology describe port dir
  printLines res