class T::Types::Base

def self.method_added(method_name)
  super(method_name)
  # What is now `subtype_of_single?` used to be named `subtype_of?`. Make sure people don't
  # override the wrong thing.
  #
  # NB: Outside of T::Types, we would enforce this by using `sig` and not declaring the method
  # as overridable, but doing so here would result in a dependency cycle.
  if method_name == :subtype_of? && self != T::Types::Base
    raise "`subtype_of?` should not be overridden. You probably want to override " \
          "`subtype_of_single?` instead."
  end
end

def ==(other)
  (T::Utils.resolve_alias(other).class == T::Utils.resolve_alias(self).class) &&
    other.name == self.name
end

def describe_obj(obj)
  # Would be redundant to print class and value in these common cases.
  case obj
  when nil, true, false
    return "type #{obj.class}"
  end
  # In rare cases, obj.inspect may fail, or be undefined, so rescue.
  begin
    # Default inspect behavior of, eg; `#<Object:0x0...>` is ugly; just print the hash instead, which is more concise/readable.
    if obj.method(:inspect).owner == Kernel
      "type #{obj.class} with hash #{obj.hash}"
    elsif T::Configuration.include_value_in_type_errors?
      "type #{obj.class} with value #{T::Utils.string_truncate_middle(obj.inspect, 30, 30)}"
    else
      "type #{obj.class}"
    end
  rescue StandardError, SystemStackError
    "type #{obj.class} with unprintable value"
  end
end

def error_message_for_obj(obj)
  if valid?(obj)
    nil
  else
    "Expected type #{self.name}, got #{describe_obj(obj)}"
  end
end

def error_message_for_obj_recursive(obj)
  if recursively_valid?(obj)
    nil
  else
    "Expected type #{self.name}, got #{describe_obj(obj)}"
  end
end

def hash
  name.hash
end

def name
  raise NotImplementedError
end

def recursively_valid?(obj)
  valid?(obj)
end

def subtype_of?(t2)
  t1 = self
  if t2.is_a?(T::Private::Types::TypeAlias)
    t2 = t2.aliased_type
  end
  if t1.is_a?(T::Private::Types::TypeAlias)
    return t1.aliased_type.subtype_of?(t2)
  end
  # pairs to cover: 1  (_, _)
  #                 2  (_, And)
  #                 3  (_, Or)
  #                 4  (And, _)
  #                 5  (And, And)
  #                 6  (And, Or)
  #                 7  (Or, _)
  #                 8  (Or, And)
  #                 9  (Or, Or)
  # Note: order of cases here matters!
  if t1.is_a?(T::Types::Union) # 7, 8, 9
    # this will be incorrect if/when we have Type members
    return t1.types.all? {|t1_member| t1_member.subtype_of?(t2)}
  end
  if t2.is_a?(T::Types::Intersection) # 2, 5
    # this will be incorrect if/when we have Type members
    return t2.types.all? {|t2_member| t1.subtype_of?(t2_member)}
  end
  if t2.is_a?(T::Types::Union)
    if t1.is_a?(T::Types::Intersection) # 6
      # dropping either of parts eagerly make subtype test be too strict.
      # we have to try both cases, when we normally try only one
      return t2.types.any? {|t2_member| t1.subtype_of?(t2_member)} ||
          t1.types.any? {|t1_member| t1_member.subtype_of?(t2)}
    end
    return t2.types.any? {|t2_member| t1.subtype_of?(t2_member)} # 3
  end
  if t1.is_a?(T::Types::Intersection) # 4
    # this will be incorrect if/when we have Type members
    return t1.types.any? {|t1_member| t1_member.subtype_of?(t2)}
  end
  # 1; Start with some special cases
  if t1.is_a?(T::Private::Types::Void)
    return t2.is_a?(T::Private::Types::Void)
  end
  if t1.is_a?(T::Types::Untyped) || t2.is_a?(T::Types::Untyped)
    return true
  end
  # Rest of (1)
  subtype_of_single?(t2)
end

def subtype_of_single?(type)
NotImplementedError

def to_s
  name
end

def valid?(obj)
  raise NotImplementedError
end

def validate!(obj)
  err = error_message_for_obj(obj)
  raise TypeError.new(err) if err
end