class RSpec::Matchers::BuiltIn::YieldProbe

def self.assert_valid_expect_block!(block)
  return if block.arity == 1
  raise "Your expect block must accept an argument to be used with this " +
        "matcher. Pass the argument as a block on to the method you are testing."
end

def self.probe(block)
  probe = new
  assert_valid_expect_block!(block)
  block.call(probe)
  probe.assert_used!
  probe
end

def assert_used!
  return if @used
  raise "You must pass the argument yielded to your expect block on " +
        "to the method-under-test as a block. It acts as a probe that " +
        "allows the matcher to detect whether or not the method-under-test " +
        "yields, and, if so, how many times, and what the yielded arguments " +
        "are."
end

def initialize
  @used = false
  self.num_yields, self.yielded_args = 0, []
end

def single_yield_args
  yielded_args.first
end

def successive_yield_args
  yielded_args.map do |arg_array|
    arg_array.size == 1 ? arg_array.first : arg_array
  end
end

def to_proc
  @used = true
  probe = self
  Proc.new do |*args|
    probe.num_yields += 1
    probe.yielded_args << args
  end
end

def yielded_once?(matcher_name)
  case num_yields
  when 1 then true
  when 0 then false
  else
    raise "The #{matcher_name} matcher is not designed to be used with a " +
          "method that yields multiple times. Use the yield_successive_args " +
          "matcher for that case."
  end
end