-- | Representation of a directed graph. In Hakyll, this is used for dependency
-- tracking.
--
module Hakyll.Core.DirectedGraph
( DirectedGraph
, fromList
, toList
, member
, nodes
, neighbours
, reverse
, reachableNodes
) where
import Prelude hiding (reverse)
import Control.Arrow (second)
import Data.Monoid (mconcat)
import Data.Set (Set)
import Data.Maybe (fromMaybe)
import qualified Data.Map as M
import qualified Data.Set as S
import Hakyll.Core.DirectedGraph.Internal
-- | Construction of directed graphs
--
fromList :: Ord a
=> [(a, Set a)] -- ^ List of (node, reachable neighbours)
-> DirectedGraph a -- ^ Resulting directed graph
fromList = DirectedGraph . M.fromList . map (\(t, d) -> (t, Node t d))
-- | Deconstruction of directed graphs
--
toList :: DirectedGraph a
-> [(a, Set a)]
toList = map (second nodeNeighbours) . M.toList . unDirectedGraph
-- | Check if a node lies in the given graph
--
member :: Ord a
=> a -- ^ Node to check for
-> DirectedGraph a -- ^ Directed graph to check in
-> Bool -- ^ If the node lies in the graph
member n = M.member n . unDirectedGraph
-- | Get all nodes in the graph
--
nodes :: Ord a
=> DirectedGraph a -- ^ Graph to get the nodes from
-> Set a -- ^ All nodes in the graph
nodes = M.keysSet . unDirectedGraph
-- | Get a set of reachable neighbours from a directed graph
--
neighbours :: Ord a
=> a -- ^ Node to get the neighbours of
-> DirectedGraph a -- ^ Graph to search in
-> Set a -- ^ Set containing the neighbours
neighbours x = fromMaybe S.empty . fmap nodeNeighbours
. M.lookup x . unDirectedGraph
-- | Reverse a directed graph (i.e. flip all edges)
--
reverse :: Ord a
=> DirectedGraph a
-> DirectedGraph a
reverse = mconcat . map reverse' . M.toList . unDirectedGraph
where
reverse' (id', Node _ neighbours') = fromList $
zip (S.toList neighbours') $ repeat $ S.singleton id'
-- | Find all reachable nodes from a given set of nodes in the directed graph
--
reachableNodes :: Ord a => Set a -> DirectedGraph a -> Set a
reachableNodes set graph = reachable (setNeighbours set) set
where
reachable next visited
| S.null next = visited
| otherwise = reachable (sanitize neighbours') (next `S.union` visited)
where
sanitize = S.filter (`S.notMember` visited)
neighbours' = setNeighbours (sanitize next)
setNeighbours = S.unions . map (`neighbours` graph) . S.toList