class Enumerator::Lazy

def __set_inspect(method, args = nil, receiver = nil)
  @method = method
  @args = args
  @receiver = receiver if receiver
  self
end

def chunk(*)
  super.lazy
end if Enumerable.method_defined?(:chunk) && ![].lazy.chunk{}.is_a?(Lazy)

def drop(n)
  n = Backports::coerce_to_int(n)
  Lazy.new(self) do |yielder, *values|
    data = yielder.backports_memo ||= {:remain => n}
    if data[:remain] > 0
      data[:remain] -= 1
    else
      yielder.yield(*values)
    end
  end.__set_inspect :drop, [n]
end

def drop_while
  raise ArgumentError, "tried to call lazy drop_while without a block" unless block_given?
  Lazy.new(self) do |yielder, *values|
    data = yielder.backports_memo ||= {:dropping => true}
    yielder.yield(*values) unless data[:dropping] &&= yield(*values)
  end.__set_inspect :drop_while
end

def flat_map
  raise ArgumentError, "tried to call lazy flat_map without a block" unless block_given?
  Lazy.new(self) do |yielder, *values|
    result = yield(*values)
    ary = Backports.is_array?(result)
    if ary || (result.respond_to?(:each) && result.respond_to?(:force))
      (ary || result).each{|x| yielder << x }
    else
      yielder << result
    end
  end.__set_inspect :flat_map
end

def grep(pattern)
  if block_given?
    # Split for performance
    Lazy.new(self) do |yielder, *values|
      values = values.first unless values.size > 1
      yielder.yield(yield(values)) if pattern === values
    end
  else
    Lazy.new(self) do |yielder, *values|
      values = values.first unless values.size > 1
      yielder.yield(values) if pattern === values
    end
  end.__set_inspect :grep, [pattern]
end

def initialize(obj)
  if obj.is_a?(@@lazy_with_no_block)
    @inspect_info = obj
    return super(@receiver = obj.object, @method = obj.method || :each, * @args = obj.args)
  end
  raise ArgumentError, "must supply a block" unless block_given?
  @receiver = obj
  super() do |yielder, *args|
    catch @@done do
      obj.each(*args) do |*x|
        yield yielder, *x
      end
    end
  end
end

def inspect
  suff = ''
  suff << ":#{@method}" unless @method.nil? || @method == :each
  suff << "(#{@args.inspect[1...-1]})" if @args && !@args.empty?
  "#<#{self.class}: #{@receiver.inspect}#{suff}>"
end

def lazy
  self
end

def map
  raise ArgumentError, "tried to call lazy map without a block" unless block_given?
  Lazy.new(self) do |yielder, *values|
    yielder << yield(*values)
  end.__set_inspect :map
end

def reject
  raise ArgumentError, "tried to call lazy reject without a block" unless block_given?
  Lazy.new(self) do |yielder, *values|
    values = values.first unless values.size > 1
    yielder.yield(values) unless yield values
  end.__set_inspect :reject
end

def select
  raise ArgumentError, "tried to call lazy select without a block" unless block_given?
  Lazy.new(self) do |yielder, *values|
    values = values.first unless values.size > 1
    yielder.yield values if yield values
  end.__set_inspect :select
end

def take(n)
  n = Backports::coerce_to_int(n)
  raise ArgumentError, 'attempt to take negative size' if n < 0
  Lazy.new(n == 0 ? [] : self) do |yielder, *values|
    data = yielder.backports_memo ||= {:remain => n}
    yielder.yield(*values)
    throw @@done if (data[:remain] -= 1) == 0
  end.__set_inspect :take, [n], self
end

def take_while
  raise ArgumentError, "tried to call lazy take_while without a block" unless block_given?
  Lazy.new(self) do |yielder, *values|
    throw @@done unless yield(*values)
    yielder.yield(*values)
  end.__set_inspect :take_while
end

def to_enum(method = :each, *args)
  Lazy.new(@@lazy_with_no_block.new(self, method, args))
end

def zip(*args)
  return super if block_given?
  arys = args.map{ |arg| Backports.is_array?(arg) }
  if arys.all?
    # Handle trivial case of multiple array arguments separately
    # by avoiding Enumerator#next for efficiency & compatibility
    Lazy.new(self) do |yielder, *values|
      data = yielder.backports_memo ||= {:iter => 0}
      values = values.first unless values.size > 1
      yielder << arys.map{|ary| ary[data[:iter]]}.unshift(values)
      data[:iter] += 1
    end
  else
    args.each do |a|
      raise TypeError, "wrong argument type #{a.class} (must respond to :each)" unless a.respond_to? :each
    end
    Lazy.new(self) do |yielder, *values|
      enums = yielder.backports_memo ||= args.map(&:to_enum)
      values = values.first unless values.size > 1
      others = enums.map do |arg|
        begin
          arg.next
        rescue StopIteration
          nil
        end
      end
      yielder << others.unshift(values)
    end
  end.__set_inspect :zip, args
end