class RBS::AST::TypeParam

def self.rename(params, new_names:)
  raise unless params.size == new_names.size
  subst = Substitution.build(new_names, Types::Variable.build(new_names))
  params.map.with_index do |param, index|
    new_name = new_names[index]
    TypeParam.new(
      name: new_name,
      variance: param.variance,
      upper_bound: param.upper_bound&.map_type {|type| type.sub(subst) },
      location: param.location
    ).unchecked!(param.unchecked?)
  end
end

def self.resolve_variables(params)
  return if params.empty?
  vars = Set.new(params.map(&:name))
  params.map! do |param|
    param.map_type {|bound| _ = subst_var(vars, bound) }
  end
end

def self.subst_var(vars, type)
  case type
  when Types::ClassInstance
    namespace = type.name.namespace
    if namespace.relative? && namespace.empty? && vars.member?(type.name.name)
      return Types::Variable.new(name: type.name.name, location: type.location)
    end
  end
  type.map_type {|t| subst_var(vars, t) }
end

def ==(other)
  other.is_a?(TypeParam) &&
    other.name == name &&
    other.variance == variance &&
    other.upper_bound == upper_bound &&
    other.unchecked? == unchecked?
end

def hash
  self.class.hash ^ name.hash ^ variance.hash ^ upper_bound.hash ^ unchecked?.hash
end

def initialize(name:, variance:, upper_bound:, location:)
  @name = name
  @variance = variance
  @upper_bound = upper_bound
  @location = location
  @unchecked = false
end

def map_type(&block)
  if b = upper_bound
    _upper_bound = yield(b)
  end
  TypeParam.new(
    name: name,
    variance: variance,
    upper_bound: _upper_bound,
    location: location
  ).unchecked!(unchecked?)
end

def rename(name)
  TypeParam.new(
    name: name,
    variance: variance,
    upper_bound: upper_bound,
    location: location
  ).unchecked!(unchecked?)
end

def to_json(state = JSON::State.new)
  {
    name: name,
    variance: variance,
    unchecked: unchecked?,
    location: location,
    upper_bound: upper_bound
  }.to_json(state)
end

def to_s
  s = +""
  if unchecked?
    s << "unchecked "
  end
  case variance
  when :invariant
    # nop
  when :covariant
    s << "out "
  when :contravariant
    s << "in "
  end
  s << name.to_s
  if type = upper_bound
    s << " < #{type}"
  end
  s
end

def unchecked!(value = true)
  @unchecked = value ? true : false
  self
end

def unchecked?
  @unchecked
end