redef class NeoGraph
	super Serializable

	# Retrieve the graph from the specified JSON document.
	#
	# For the expected format, see `JsonGraphStore`.
	#
	# ~~~nit
	# import neo4j::graph::sequential_id
	#
	# var graph = new NeoGraph(new SequentialNodeCollection("node_id"))
	# var a = new NeoNode
	# a.labels.add "Foo"
	# a["answer"] = 42
	# a["Ultimate question of"] = new JsonArray.from(["life",
	#		"the Universe", "and Everything."])
	# graph.nodes.register a
	# var b = graph.create_node
	# b.labels.add "Foo"
	# b.labels.add "Bar"
	# graph.edges.add new NeoEdge(a, "BAZ", b)
	#
	# graph = new NeoGraph.from_json(
	#		new SequentialNodeCollection("node_id"), graph.to_json)
	# assert 1 == graph.edges.length
	# for edge in graph.edges do
	#	assert "BAZ" == edge.rel_type
	#	assert a.labels == edge.from.labels
	#	for k, v in a.properties do assert v == edge.from.properties[k]
	#	assert b.labels == edge.to.labels
	#	for k, v in b.properties do assert v == edge.to.properties[k]
	# end
	# assert 2 == graph.nodes.length
	# ~~~
	init from_json(nodes: NeoNodeCollection, t: Text) do
		from_json_object(nodes, t.parse_json.as(JsonObject))
	end

	# Retrieve the graph from the specified JSON object.
	#
	# For the expected format, see `JsonGraphStore`.
	init from_json_object(nodes: NeoNodeCollection, o: JsonObject) do
		init(nodes)
		load_json_object(o)
	end

	# Retrieve a part of the graph from the specified JSON document.
	#
	# For the expected format, see `JsonGraphStore`.
	fun load_json(t: Text) do
		load_json_object(t.parse_json.as(JsonObject))
	end

	# Retrieve a part of the graph from the specified JSON object.
	#
	# For the expected format, see `JsonGraphStore`.
	fun load_json_object(o: JsonObject) do
		var json_nodes = o["nodes"].as(JsonArray)
		var nodes = self.nodes
		nodes.enlarge(nodes.length)
		for json_node in json_nodes do
			assert json_node isa JsonObject
			var node = new NeoNode.from_json_object(json_node)
			nodes.add node
		end

		var json_edges = o["edges"].as(JsonArray)
		var edges = self.edges
		if edges isa AbstractArray[NeoEdge] then edges.enlarge(edges.length)
		for json_edge in json_edges do
			assert json_edge isa JsonObject
			var from = nodes[nodes.id_from_jsonable(json_edge["from"])]
			var to = nodes[nodes.id_from_jsonable(json_edge["to"])]
			var rel_type = json_edge["type"].as(String)
			var json_properties = json_edge["properties"].as(JsonObject)
			var edge = new NeoEdge(from, rel_type, to)
			edge.properties.add_all(json_properties)
			edges.add edge
		end
	end

	redef fun accept_json_serializer(v) do
		v.stream.write "\{\"nodes\":["
		append_entities_json(nodes, v)
		v.stream.write "],\"edges\":["
		append_entities_json(edges, v)
		v.stream.write "]\}"
	end

	# Encode `self` in JSON.
	#
	# For a description of the format, see `JsonGraphStore`.
	private fun append_entities_json(entities: Collection[NeoEntity], v: JsonSerializer) do
		var i = entities.iterator
		if i.is_ok then
			i.item.append_json_for(self, v)
			i.next
			for entity in i do
				v.stream.write ","
				entity.append_json_for(self, v)
			end
		end
	end
end