class Steep::Interface::Builder::Config

def self.empty
  new(self_type: nil, variable_bounds: {})
end

def initialize(self_type:, class_type: nil, instance_type: nil, variable_bounds:)
  @self_type = self_type
  @class_type = class_type
  @instance_type = instance_type
  @variable_bounds = variable_bounds
  validate
end

def subst
  if self_type || class_type || instance_type
    Substitution.build([], [], self_type: self_type, module_type: class_type, instance_type: instance_type)
  end
end

def upper_bound(a)
  variable_bounds.fetch(a, nil)
end

def validate
  validate_fvs(:self_type, self_type)
  validate_fvs(:instance_type, instance_type)
  validate_fvs(:class_type, class_type)
  self
end

def validate_fvs(name, type)
  if type
    fvs = type.free_variables
    if fvs.include?(AST::Types::Self.instance)
      raise "#{name} cannot include 'self' type: #{type}"
    end
    if fvs.include?(AST::Types::Instance.instance)
      raise "#{name} cannot include 'instance' type: #{type}"
    end
    if fvs.include?(AST::Types::Class.instance)
      raise "#{name} cannot include 'class' type: #{type}"
    end
  end
end