# Define contract facet for MMethod in the given mclassdef. The facet represents the entry point with contracts (expect, ensure) of the method.
	# If a contract is given adapt the contract facet.
	#
	# `classdef`: Indicates the class where we want to introduce our facet
	# `exist_contract`: Indicates if it is necessary to define a new facet for the contract. If `exist_contract_facet and exist_contract` it's not necessary to add a facet.
	#
	# Exemple:
	# ~~~nitish
	# from:
	#	classe A
	#		i :Int
	#		fun add_one is ensure(old(i) + 1 == i)
	#	end
	# to:
	#	classe A
	#		fun add_one is ensure(old(i) + 1 == i)
	#
	#		# The contract facet
	#		fun contract_add_one do
	#			add_one
	#			ensure_add_one(old_add_one)
	#		end
	#	end
	# ~~
	private fun define_contract_facet(v: ContractsVisitor, classdef: MClassDef, mcontract: nullable MContract)
	do
		var exist_contract_facet = has_contract_facet
		var contract_facet = build_contract_facet
		# Do nothing the contract and the contract facet already exist
		if mcontract != null and mcontract.is_already_applied(contract_facet) then return

		var n_contract_facet: AMethPropdef
		if not exist_contract_facet then
			# If has no contract facet in intro just create it
			if classdef != intro_mclassdef then
				var n_intro_face = create_facet(v, intro_mclassdef, contract_facet, self)
				n_intro_face.location = self.intro.location
				n_intro_face.do_all(v.toolcontext)
			end
			n_contract_facet = create_facet(v, classdef, contract_facet, self)
		else
			# Check if the contract facet already exist in this context (in this classdef)
			if classdef.mpropdefs_by_property.has_key(contract_facet) then
				# get the definition
				n_contract_facet = v.toolcontext.modelbuilder.mpropdef2node(classdef.mpropdefs_by_property[contract_facet]).as(AMethPropdef)
			else
				# create a new contract facet definition
				n_contract_facet = create_facet(v, classdef, contract_facet, self)
				var block = v.ast_builder.make_block
				# super call to the contract facet
				var args = n_contract_facet.n_signature.make_parameter_read(v.ast_builder)
				var n_super_call = v.ast_builder.make_super_call(args)
				# verification for add a return or not
				if self.intro.msignature.return_mtype != null then
					block.add(v.ast_builder.make_return(n_super_call))
				else
					block.add(n_super_call)
				end
				n_contract_facet.n_block = block
			end
		end
		if mcontract != null then mcontract.adapt_method_to_contract(v, contract_facet, n_contract_facet)

		n_contract_facet.location = v.current_location
		n_contract_facet.do_all(v.toolcontext)
	end