# View of an object in a poset
# This class is a helper to handle specific queries on a same object
#
# For instance, one common usage is to add a specific attribute for each poset a class belong.
#
# ~~~nitish
# class Thing
#     var in_some_relation: POSetElement[Thing]
#     var in_other_relation: POSetElement[Thing]
# end
# var t: Thing
# # ...
# t.in_some_relation.greaters
# ~~~
class POSetElement[E]
	super Serializable

	# The poset self belong to
	var poset: POSet[E]

	# The real object behind the view
	var element: E

	private var tos = new HashSet[E]
	private var froms = new HashSet[E]
	private var dtos = new HashSet[E]
	private var dfroms = new HashSet[E]

	# The rank of the
	# This attribute is used to force a total order for POSet#compare
	private var count: Int

	# Return the set of all elements `t` that have an edge from `element` to `t`.
	# Since the POSet is reflexive, element is included in the set.
	#
	# ~~~~
	# var pos = new POSet[String]
	# pos.add_chain(["A", "B", "C", "D"])
	# assert pos["B"].greaters.has_exactly(["B", "C", "D"])
	# ~~~~
	fun greaters: Collection[E]
	do
		return self.tos
	end

	# Return the set of all elements `t` that have a direct edge from `element` to `t`.
	#
	# ~~~~
	# var pos = new POSet[String]
	# pos.add_chain(["A", "B", "C", "D"])
	# assert pos["B"].direct_greaters.has_exactly(["C"])
	# ~~~~
	fun direct_greaters: Collection[E]
	do
		return self.dtos
	end

	# Return the set of all elements `f` that have an edge from `f` to `element`.
	# Since the POSet is reflexive, element is included in the set.
	#
	# ~~~~
	# var pos = new POSet[String]
	# pos.add_chain(["A", "B", "C", "D"])
	# assert pos["C"].smallers.has_exactly(["A", "B", "C"])
	# ~~~~
	fun smallers: Collection[E]
	do
		return self.froms
	end

	# Return the set of all elements `f` that have an edge from `f` to `element`.
	#
	# ~~~~
	# var pos = new POSet[String]
	# pos.add_chain(["A", "B", "C", "D"])
	# assert pos["C"].direct_smallers.has_exactly(["B"])
	# ~~~~
	fun direct_smallers: Collection[E]
	do
		return self.dfroms
	end

	# Is there an edge from `element` to `t`?
	#
	# ~~~~
	# var pos = new POSet[String]
	# pos.add_chain(["A", "B", "C", "D"])
	# assert     pos["B"] <= "D"
	# assert     pos["B"] <= "C"
	# assert     pos["B"] <= "B"
	# assert not pos["B"] <= "A"
	# ~~~~
	fun <=(t: E): Bool
	do
		return self.tos.has(t)
	end

	# Is `t != element` and is there an edge from `element` to `t`?
	#
	# ~~~~
	# var pos = new POSet[String]
	# pos.add_chain(["A", "B", "C", "D"])
	# assert     pos["B"] < "D"
	# assert     pos["B"] < "C"
	# assert not pos["B"] < "B"
	# assert not pos["B"] < "A"
	# ~~~~
	fun <(t: E): Bool
	do
		return t != self.element and self.tos.has(t)
	end

	# The length of the shortest path to the root of the poset hierarchy
	#
	# ~~~~
	# var pos = new POSet[String]
	# pos.add_chain(["A", "B", "C", "D"])
	# assert pos["A"].depth == 3
	# assert pos["D"].depth == 0
	# ~~~~
	fun depth: Int do
		if direct_greaters.is_empty then
			return 0
		end
		var min = -1
		for p in direct_greaters do
			var d = poset[p].depth + 1
			if min == -1 or d < min then
				min = d
			end
		end
		return min
	end

	redef fun core_serialize_to(serializer)
	do
		serializer.serialize_attribute("poset", poset)
		serializer.serialize_attribute("element", element)
		serializer.serialize_attribute("tos", tos)
		serializer.serialize_attribute("froms", froms)
		serializer.serialize_attribute("dtos", dtos)
		serializer.serialize_attribute("dfroms", dfroms)
		serializer.serialize_attribute("count", count)

		# Don't serialize `froms`, `dtos` and `tos` as they duplicate information.
		# TODO serialize them if a flag for extra info is set on `serializer`.
	end

	redef init from_deserializer(v)
	do
		# Code generated by the serialization_phase from the compiler frontend,
		# copied here for compatibility with nith.

		super
		v.notify_of_creation self

		var poset = v.deserialize_attribute("poset", "POSet[nullable Object]")
		if v.deserialize_attribute_missing then
			v.errors.add new Error("Deserialization Error: attribute `{class_name}::poset` missing from JSON object")
		else if not poset isa POSet[E] then
			v.errors.add new AttributeTypeError(self, "poset", poset, "POSet[nullable Object]")
			if v.keep_going == false then return
		else
			self.poset = poset
		end

		var element = v.deserialize_attribute("element", "nullable Object")
		if v.deserialize_attribute_missing then
			v.errors.add new Error("Deserialization Error: attribute `{class_name}::element` missing from JSON object")
		else if not element isa E then
			v.errors.add new AttributeTypeError(self, "element", element, "nullable Object")
			if v.keep_going == false then return
		else
			self.element = element
		end

		var tos = v.deserialize_attribute("tos", "HashSet[nullable Object]")
		if v.deserialize_attribute_missing then
		else if not tos isa HashSet[E] then
			v.errors.add new AttributeTypeError(self, "tos", tos, "HashSet[nullable Object]")
			if v.keep_going == false then return
		else
			self.tos = tos
		end

		var froms = v.deserialize_attribute("froms", "HashSet[nullable Object]")
		if v.deserialize_attribute_missing then
		else if not froms isa HashSet[E] then
			v.errors.add new AttributeTypeError(self, "froms", froms, "HashSet[nullable Object]")
			if v.keep_going == false then return
		else
			self.froms = froms
		end

		var dtos = v.deserialize_attribute("dtos", "HashSet[nullable Object]")
		if v.deserialize_attribute_missing then
		else if not dtos isa HashSet[E] then
			v.errors.add new AttributeTypeError(self, "dtos", dtos, "HashSet[nullable Object]")
			if v.keep_going == false then return
		else
			self.dtos = dtos
		end

		var dfroms = v.deserialize_attribute("dfroms", "HashSet[nullable Object]")
		if v.deserialize_attribute_missing then
		else if not dfroms isa HashSet[E] then
			v.errors.add new AttributeTypeError(self, "dfroms", dfroms, "HashSet[nullable Object]")
			if v.keep_going == false then return
		else
			self.dfroms = dfroms
		end

		var count = v.deserialize_attribute("count", "Int")
		if v.deserialize_attribute_missing then
			v.errors.add new Error("Deserialization Error: attribute `{class_name}::count` missing from JSON object")
		else if not count isa Int then
			v.errors.add new AttributeTypeError(self, "count", count, "Int")
			if v.keep_going == false then return
		else
			self.count = count
		end
	end
end