# A dot edge that links two nodes
#
# Edges can be created from scratch
# ~~~
# var a1 = new DotNode("a1")
# var b1 = new DotNode("b1")
# var edge = new DotEdge(a1, b1)
# edge["color"] = "blue"
# ~~~
# Then added to a graph
# ~~~
# var graph = new DotGraph("G", "digraph")
# graph.add edge
# ~~~
# Or can be created directly from an existing graph
# ~~~
# var a2 = graph.add_node("a2")
# var b2 = graph.add_node("b2")
# var edge2 = graph.add_edge(a2, b2)
# edge2["color"] = "red"
# ~~~
class DotEdge
	super DotElement
	autoinit from, to

	# Node this edge is from
	var from: DotElement

	# Node this edge goes to
	var to: DotElement

	# Is this edge directed?
	var directed = true is writable

	redef fun id do return "{from.id}--{to.id}"

	redef fun to_dot do
		var res = new Buffer
		res.append "\"{from.escape_id}\" "
		if directed then
			res.append "->"
		else
			res.append "--"
		end
		res.append " \"{to.escape_id}\" "
		if attrs.not_empty then res.append "[{attrs.to_dot(",")}]"
		return res.write_to_string
	end
end