module Dodge.Graph
  where
import Data.Function (on)
import Data.List

import Data.Graph

pairsToIncidence :: (Eq a,Ord a) => [(a,a)] -> [(a,[a])]
pairsToIncidence = map ((\(xs,ys) -> (head xs,ys)) . unzip)
                     . groupBy ( (==) `on` fst)
                     . sort

incidenceToFunction :: Eq a => [(a,[a])] -> a -> [a]
incidenceToFunction xs a = case lookup a xs of Just ys -> ys
                                               Nothing -> []

mkNode :: (a,[a]) -> (a,a,[a])
mkNode (x,xs) = (x,x,xs)

pairsToSCC :: (Eq a, Ord a) => [(a,a)] -> [SCC a]
pairsToSCC = stronglyConnComp . map mkNode . pairsToIncidence