-----------------------------------------------------------------------------
-- A representation of "compositional" graphs
-----------------------------------------------------------------------------

module Graph(Graph(..),Node(..),Edge(..),NodeId,
             joinGraphs,addNode,addEdge,isFinalizedGraph,showGraph) where

import DaVinci

-- A graph is a list of nodes and edges:
data Graph = Graph [Node] [Edge]

-- A node identifier is basically a natural number.
-- However, this data type is abstract so that the user cannot
-- explicitly construct node identifiers.
data NodeId = NodeId Int

-- A node is identified by a node identifier but more node infos
-- could be added:
data Node = Node NodeId

-- An edge consists of a source and a target node which are
-- identified by their node identifiers:
data Edge = Edge NodeId NodeId

-- Combine two graphs.
joinGraphs (Graph ns1 es1) (Graph ns2 es2) = Graph (ns1++ns2) (es1++es2)

-- Add a node two a graph.
addNode n (Graph ns es) = Graph (Node n : ns) es

-- Add a new edge between two nodes of a graph.
addEdge n1 n2 (Graph ns es) = Graph ns (Edge n1 n2 : es)

-- A graph is finalized for further processing if all nodes
-- have uniquely assigned node identifiers:
isFinalizedGraph :: Graph -> Success
isFinalizedGraph (Graph nodes _) = numberNodes 1 nodes
  where
     numberNodes _ [] = success
     numberNodes n (Node ni : ns)
         | ni =:= NodeId n  -- assign unique identifier
         = numberNodes (n+1) ns

-- As an example, we convert this representation into the daVinci
-- representation by grouping edges to their source node
-- and displaying the graph:
showGraph :: Graph -> IO ()
showGraph graph | isFinalizedGraph graph
                = (dvDisplay . graph2dv) graph

graph2dv (Graph nodes edges)
 | nodes==nodes  -- ensure that all nodeids are assigned
 = dvNewGraph 
   (map (\(dvid,nodeid)->
             dvNodeWithEdges dvid (make_label nodeid)
                             (map (\(Edge _ n2)->createEdge n2)
                                  (filter (\(Edge n1 _)->n1==nodeid)
                                          edges))
                             dvEmptyH)
        idnodes)
 where
   idnodes = map node2idnode nodes

   createEdge nodeid =
              dvSimpleEdge e
                           (fst (head (filter (\(_,n)->n==nodeid) idnodes)))
                           dvEmptyH
              where e free

   -- transform node into a DvId/NodeId pair:
   node2idnode (Node nodeid) = (dvid,nodeid)  where dvid free

   make_label (NodeId num) = "Node "++show num


-- end of Graph library