class RSpec::Matchers::BuiltIn::BeWithin

def description
  "be within #{@delta}#{@unit} of #{@expected}"
end

def failure_message_for_should
  "expected #{@actual} to #{description}"
end

def failure_message_for_should_not
  "expected #{@actual} not to #{description}"
end

def initialize(delta)
  @delta = delta
end

def matches?(actual)
  @actual = actual
  raise needs_expected     unless defined? @expected
  raise needs_subtractable unless @actual.respond_to? :-
  (@actual - @expected).abs <= @tolerance
end

def needs_expected
  ArgumentError.new "You must set an expected value using #of: be_within(#{@delta}).of(expected_value)"
end

def needs_subtractable
  ArgumentError.new "The actual value (#{@actual.inspect}) must respond to `-`"
end

def of(expected)
  @expected  = expected
  @tolerance = @delta
  @unit      = ''
  self
end

def percent_of(expected)
  @expected  = expected
  @tolerance = @delta * @expected.abs / 100.0
  @unit      = '%'
  self
end

def supports_block_expectations?
  false
end