"""
Extend the Node and Edge classes to control rendering.

Add nodes by calling graph#nodes passing in the new node. Note that this function de-duplicates based upon the uid of the node; returning the existing node if possible.

Add edges in the same style; calling graph#edges. Again, this de-duplicates based on the uid of the edge.

Extension points for Node:

uid: determines if a node is the same as another node in the graph. Default: random 16 word characters.
id: graphviz node id; must return an identifier.
label: display name for the node; any graphviz label is valid. Default: id.
shape: graphviz shape. Default: 'oval'.
colour: line colour for the node. Default: 'black'

Extension points for Edge:

uid: determines if an edge is the same as another edge. Useful for de-duplicating edges. Default: random 16 word characters.
label: display name for the node; any graphviz label is valid. Default: '' [empty string].
colour: line colour for the node. Default: 'black'

"""
module YaGraph
  class Element
    def to_graphviz(out) "" end

    """
    an id that is unique in the context of the element type. Subtypes should override this.
    """
    def uid()
      @uid ||= random_id()
    end

    def random_id()
      (0...16).map { (65 + rand(26)).chr }.join
    end
  end

  class Graph < Element
    RANKDIR_LR = "LR"

    def initialize()
      @nodes = {}
      @edges = {}
      @subgraphs = {}
    end

    def edges(edge)
      @edges[edge.uid] ||= edge
    end

    def edge?(s, e)
      @edges.any? do |k, v|
        v.start == s and v.finish == e
      end
    end

    def nodes(node)
      @nodes[node.uid] ||= node
    end

    def subgraph(subgraph)
      @subgraphs[subgraph.uid] ||= subgraph
    end

    def rankdir(mode)
      @rankdir = mode
    end

    def initial_nodes()
      initial = {}
      @nodes.each {|k, n| initial[k] = n}
      @edges.each do |k, e|
        initial.delete(e.finish.uid)
      end
      initial.values
    end

    def terminal_nodes()
      terminal = {}
      @nodes.each {|k, n| terminal[k] = n}
      @edges.each do |k, e|
        terminal.delete(e.start.uid)
      end
      terminal.values
    end

    def to_graphviz(out)
      out.puts("digraph main {\n")
      out.puts("  rankdir=#{@rankdir}") if @rankdir
      @subgraphs.each {|k, s| s.to_graphviz(out) }
      @nodes.each {|k, n| n.to_graphviz(out) }
      @edges.each {|k, e| e.to_graphviz(out) }
      out.puts("}")
    end
  end

  class SubGraph < Graph
    def initialize()
      super()
    end

    def is_cluster() false end

    def to_graphviz(out)
      out.puts("  subgraph #{if is_cluster() then "cluster_" else "" end}#{uid()} {")
      if label() then out.puts("    label=\"#{label()}\"") end
      @nodes.each {|k, n| out.write("  "); n.to_graphviz(out) }
      @edges.each {|k, e| out.write("  "); e.to_graphviz(out) }
      out.puts("  }")
    end

    def label() nil end
  end

  class Node < Element
    def id() "" end
    def to_graphviz(out)
      out.puts("  #{id} [ color=\"#{colour}\" label=\"#{label}\" shape=\"#{shape}\" ]")
    end
    def label() id end
    def shape() "oval" end
    def colour() "black" end
  end

  class Edge < Element
    attr_reader :start, :finish
    def to_graphviz(out)
      out.puts("  #{start.id} -> #{finish.id} [ color=\"#{colour}\" label=\"#{label}\"]")
    end
    def label() "" end
    def colour() "black" end
  end
end

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