glance/app/GraphAlgorithms.hs

module GraphAlgorithms(
  collapseNodes,
  findTreeRoots,
  childCanBeEmbedded
  ) where

import qualified Data.Graph.Inductive.PatriciaTree as FGR
import qualified Data.Graph.Inductive.Graph as ING
import Types(SgNamedNode, Edge(..), SyntaxNode(..), sgNamedNodeToSyntaxNode, EdgeEnd(..), NameAndPort(..), IngSyntaxGraph)
import Data.Maybe(listToMaybe, catMaybes)
import Data.List(foldl', find)
import Diagrams.Prelude(toName)
import qualified Debug.Trace

import Util(printSelf, maybeBoolToBool)

-- See graph_algs.txt for pseudocode

type LabelledGraphEdge = ING.LEdge Edge

-- START collapseNodes helper functions --

-- | A syntaxNodeIsEmbeddable if it can be collapsed into another node
syntaxNodeIsEmbeddable :: SyntaxNode -> Bool
syntaxNodeIsEmbeddable n = case n of
  ApplyNode _ -> True
  -- TODO make PatternApplyNode embeddable
  PatternApplyNode _ _ -> False
  NameNode _ -> False
  LiteralNode _ -> True
  FunctionDefNode _ -> False
  GuardNode _ -> False
  CaseNode _ -> False
  BranchNode -> False
  CaseResultNode -> False
  -- Don't use a catch all (i.e. irrefutable) pattern here so that if other
  -- SyntaxNodes are added we will get a warning here.

-- | A syntaxNodeCanEmbed if it can contain other nodes
syntaxNodeCanEmbed :: SyntaxNode -> Bool
syntaxNodeCanEmbed n = case n of
  ApplyNode _ -> True
  x@(NestedApplyNode _ _) -> True -- This case should not happen
  -- TODO make PatternApplyNode embed
  PatternApplyNode _ _ -> False
  NameNode _ -> False
  LiteralNode _ -> False
  FunctionDefNode _ -> False
  GuardNode _ -> False
  CaseNode _ -> False
  BranchNode -> False
  CaseResultNode -> False
  -- Don't use a catch all (i.e. irrefutable) pattern here so that if other
  -- SyntaxNodes are added we will get a warning here.

extractSyntaxNode :: ING.LNode SgNamedNode -> SyntaxNode
extractSyntaxNode = snd . snd

findParents :: ING.Graph gr => gr a b -> ING.Node -> [ING.Node]
-- TODO, may need to use ING.pre or ING.neighbors instead of ING.suc'
findParents graph node = filter (/= node) $  ING.suc graph node

findChildren :: ING.Graph gr => gr a b -> ING.Node -> [ING.Node]
findChildren = ING.pre

-- | graphNodeCanEmbed returns true if the label (SyntaxNode) associated with the
-- node can be embedded in other SyntaxNodes (i.e. nodeCanEmbed is True)
graphNodeCanEmbed :: ING.Graph gr => IngSyntaxGraph gr -> ING.Node -> Bool
graphNodeCanEmbed graph node = maybeBoolToBool $ fmap syntaxNodeCanEmbed (lookupSyntaxNode graph node)

graphNodeIsEmbeddable :: ING.Graph gr => IngSyntaxGraph gr -> ING.Node -> Bool
graphNodeIsEmbeddable graph node = maybeBoolToBool $ fmap syntaxNodeIsEmbeddable (lookupSyntaxNode graph node)

lookupSyntaxNode :: ING.Graph gr => IngSyntaxGraph gr -> ING.Node -> Maybe SyntaxNode
lookupSyntaxNode gr node = fmap sgNamedNodeToSyntaxNode $ ING.lab gr node

-- | filterNodes returns a list of the nodes in the graph
-- where the filter function is true.
filterNodes :: ING.DynGraph gr => (ING.Node -> Bool) -> gr a b -> [ING.Node]
filterNodes pred gr = ING.nodes $ ING.nfilter pred gr

-- | Replace the a node's label
changeNodeLabel :: ING.DynGraph gr => gr a b -> ING.Node -> a -> gr a b
changeNodeLabel graph node newLabel = case ING.match node graph of
  (Just (inEdges, _, _, outEdges), restOfTheGraph) -> (inEdges, node, newLabel, outEdges) ING.& restOfTheGraph
  (Nothing, _) -> graph

findEdgeLabel :: ING.Graph gr => gr a b -> ING.Node -> ING.Node -> Maybe b
findEdgeLabel graph node1 node2 = fmap fst matchingEdges where
  labelledEdges = ING.lneighbors graph node1
  matchingEdges = find ((== node2) . snd) labelledEdges

-- END helper functions --

collapseNodes :: (ING.DynGraph gr) => IngSyntaxGraph gr -> IngSyntaxGraph gr
collapseNodes originalGraph = finalGraph where
  -- findTreeRoots returns a list of nodes that will embed other nodes, but are not embedded themselves.
  -- These nodes are thus each a root of a collapsed node tree.
  treeRoots = findTreeRoots originalGraph
  -- Now collapse each tree of nodes
  finalGraph = collapseRoots treeRoots originalGraph originalGraph treeRoots

-- START findTreeRoots functions --

-- |findTreeRoots returns a list of nodes that might embed other nodes, but are not embedded themselves.
-- These nodes are thus each a root of a collapsed node tree.
-- A node is a treeRoot if all of these conditions are true:
-- 1. The SyntaxNode can embed other nodes (i.e. syntaxNodeCanEmbed is true)
-- 2. The node has no parents that can embed it, or 2 or more parents that can embed it.
-- Note: A treeRoot may not actually have any embeddable children, since collapseTree will do nothing in that case.
findTreeRoots :: ING.DynGraph gr => IngSyntaxGraph gr -> [ING.Node]
findTreeRoots graph = filterNodes (isTreeRoot graph) graph

isTreeRoot :: ING.Graph gr => IngSyntaxGraph gr -> ING.Node -> Bool
isTreeRoot graph node = graphNodeCanEmbed graph node && rightNumberOfParentsCanEmbed where
  rightNumberOfParentsCanEmbed = numParentsThatCanEmbed == 0 || numParentsThatCanEmbed >= 2
  numParentsThatCanEmbed = length parentsThatCanEmbed
  parentsThatCanEmbed = filter (graphNodeCanEmbed graph) parents
  parents = findParents graph node

-- END findTreeRoots functions
-- START collapseRoots functions

collapseRoots :: ING.DynGraph gr => [ING.Node] -> IngSyntaxGraph gr -> IngSyntaxGraph gr -> [ING.Node] -> IngSyntaxGraph gr
collapseRoots treeRoots originalGraph = foldl' (collapseTree treeRoots originalGraph)

collapseTree :: ING.DynGraph gr => [ING.Node] -> IngSyntaxGraph gr -> IngSyntaxGraph gr -> ING.Node -> IngSyntaxGraph gr
collapseTree treeRoots originalGraph oldGraph rootNode = case childrenToEmbed of
  [] -> oldGraph
  _ -> finalGraph
  where
    -- Need to use the original graph for finding children, otherwise a node can be embedded when it is used twice in
    -- what will be a single embedding node. Examples:
    --  "y = foo (3 + bazOf2) bazOf2 where bazOf2 = baz 2",
    --  "y = foo (3 + bazOf2) (8 * bazOf2) where bazOf2 = baz 2"
    childrenToEmbed = findChildrenToEmbed treeRoots rootNode originalGraph
    -- Recursively collapse the children nodes
    graphWithCollapsedChildren = collapseRoots treeRoots originalGraph oldGraph childrenToEmbed
      -- Modify the rootNode label (i.e. SyntaxNode) to incorporate the children it is embedding
    graphWithEmbeddedChildren = embedChildSyntaxNodes rootNode childrenToEmbed graphWithCollapsedChildren
    -- Transfer the edges of the children to rootNode
    childEdgesToTransfer = findChildEdgesToTransfer rootNode childrenToEmbed graphWithEmbeddedChildren
    graphWithEdgesTransferred = ING.insEdges childEdgesToTransfer graphWithEmbeddedChildren
    -- Delete the children that have been embedded (and any or their remaining edges)
    finalGraph = deleteChildren childrenToEmbed graphWithEdgesTransferred

-- | findChildrenToEmbed returns a list of the node's children that can be embedded
-- A child can be embedded iff all of these conditions are true:
-- 1. The node is not a treeRoot (otherwise a cycle of embedding could occur)
-- 2. The SyntaxNode is embeddable (i.e. syntaxNodeIsEmbeddable is True)
-- 3. The node has exactly one parent that can embed (i.e. nodeCanEmbed is True for one parent)
findChildrenToEmbed :: ING.Graph gr => [ING.Node] -> ING.Node -> IngSyntaxGraph gr -> [ING.Node]
findChildrenToEmbed treeRoots node graph = if graphNodeCanEmbed graph node
  then childrenToEmbed
  else []
  where
    childrenToEmbed = filter (childCanBeEmbedded treeRoots graph) (findChildren graph node)

childCanBeEmbedded :: ING.Graph gr => [ING.Node] -> IngSyntaxGraph gr -> ING.Node -> Bool
childCanBeEmbedded treeRoots graph child = notTreeRoot && isEmbeddable && oneParentCanEmbed where
  notTreeRoot = notElem child treeRoots
  isEmbeddable = graphNodeIsEmbeddable graph child
  oneParentCanEmbed = case parentsThatCanEmbed of
    [_] -> True
    _ -> False
  parentsThatCanEmbed = filter (graphNodeCanEmbed graph) (findParents graph child)

-- TODO findChildEdgesToTransfer might add too many edges
findChildEdgesToTransfer :: ING.Graph gr => ING.Node -> [ING.Node] -> gr a b-> [ING.LEdge b]
findChildEdgesToTransfer parentNode nodes graph = concatMap makeLabelledGraphEdges nodes where
  makeLabelledGraphEdges childNode = fmap (changeEdgeToParent parentNode childNode) $ ING.inn graph childNode

changeEdgeToParent :: ING.Node -> ING.Node -> ING.LEdge b -> ING.LEdge b
changeEdgeToParent parentNode childNode (fromNode, toNode, edgeLabel)
  | childNode == fromNode = (parentNode, toNode, edgeLabel)
  | childNode == toNode = (fromNode, parentNode, edgeLabel)

-- | Change the node label of the parent to be nested.
embedChildSyntaxNodes :: ING.DynGraph gr => ING.Node -> [ING.Node] -> IngSyntaxGraph gr -> IngSyntaxGraph gr
embedChildSyntaxNodes parentNode childrenNodes oldGraph = case childrenNodes of
  [] -> oldGraph
  _ -> newGraph
  where
    maybeOldNodeLabel = ING.lab oldGraph parentNode
    newGraph = case maybeOldNodeLabel of
      Nothing -> oldGraph
      Just oldNodeLabel -> changeNodeLabel oldGraph parentNode newNodeLabel
        where
          (nodeName, oldSyntaxNode) = oldNodeLabel
          newNodeLabel = (nodeName, newSyntaxNode)
          newSyntaxNode = case oldSyntaxNode of
            -- TODO Add PatternApplyNode, and NestedApplyNode
            ApplyNode x -> NestedApplyNode x childrenAndEdgesToParent
            _ -> oldSyntaxNode
    childrenAndEdgesToParent = catMaybes $ fmap findChildAndEdge childrenNodes
    findChildAndEdge childNode =
      (,) <$> ING.lab oldGraph childNode <*> findEdgeLabel oldGraph parentNode childNode


deleteChildren :: ING.Graph gr => [ING.Node] -> IngSyntaxGraph gr -> IngSyntaxGraph gr
deleteChildren = ING.delNodes

-- END collapseRoots functions