class RSpec::Matchers::BuiltIn::Change

def actual_delta
  @actual_after - @actual_before
end

def by(expected_delta)
  @expected_delta = expected_delta
  self
end

def by_at_least(minimum)
  @minimum = minimum
  self
end

def by_at_most(maximum)
  @maximum = maximum
  self
end

def change_expected?
  @expected_delta != 0
end

def changed?
  @actual_before != @actual_after
end

def description
  "change ##{message}"
end

def does_not_match?(event_proc, &block)
  expression = if @expected_delta
    "by()"
  elsif @minimum
    "by_at_least()"
  elsif @maximum
    "by_at_most()"
  elsif @eval_after
    "to()"
  end
  if expression
    RSpec.deprecate("`expect { }.not_to change { }.#{expression}`")
  end
  matched_positively = matches?(event_proc, &block)
  unless matches_before?
    RSpec.warn_deprecation(<<-EOS.gsub(/^\s+\|/, ''))
      |The semantics of `expect { }.not_to change { }.from()` are changing
      |in RSpec 3. In RSpec 2.x, this would pass if the value changed but
      |the starting value was not what you specified with `from()`. In
      |RSpec 3, this will only pass if the starting value matches your
      |`from()` value _and_ it has not changed.
      |
      |You have an expectation that relies upon the old RSpec 2.x semantics
      |at: #{CallerFilter.first_non_rspec_line}"
    EOS
  end
  !matched_positively
end

def evaluate_value_proc
  case val = @value_proc.call
  when Enumerable, String
    val.dup
  else
    val
  end
end

def expected_matches_actual?(expected, actual)
  expected === actual || actual == expected
end

def failure_message_for_expected_after
  if RSpec::Matchers.is_a_matcher?(@expected_after)
    @expected_after.description
  else
    @expected_after.inspect
  end
end

def failure_message_for_should
  if @eval_before && !expected_matches_actual?(@expected_before, @actual_before)
    "#{message} should have initially been #{@expected_before.inspect}, but was #{@actual_before.inspect}"
  elsif @eval_after && !expected_matches_actual?(@expected_after, @actual_after)
    "#{message} should have been changed to #{failure_message_for_expected_after}, but is now #{@actual_after.inspect}"
  elsif @expected_delta
    "#{message} should have been changed by #{@expected_delta.inspect}, but was changed by #{actual_delta.inspect}"
  elsif @minimum
    "#{message} should have been changed by at least #{@minimum.inspect}, but was changed by #{actual_delta.inspect}"
  elsif @maximum
    "#{message} should have been changed by at most #{@maximum.inspect}, but was changed by #{actual_delta.inspect}"
  else
    "#{message} should have changed, but is still #{@actual_before.inspect}"
  end
end

def failure_message_for_should_not
  "#{message} should not have changed, but did change from #{@actual_before.inspect} to #{@actual_after.inspect}"
end

def from (before)
  @eval_before = true
  @expected_before = before
  self
end

def initialize(receiver=nil, message=nil, &block)
  @message = message
  @value_proc = block || lambda {receiver.__send__(message)}
  @expected_after = @expected_before = @minimum = @maximum = @expected_delta = nil
  @eval_before = @eval_after = false
end

def matches?(event_proc)
  raise_block_syntax_error if block_given?
  @actual_before = evaluate_value_proc
  event_proc.call
  @actual_after = evaluate_value_proc
  (!change_expected? || changed?) && matches_before? && matches_after? && matches_expected_delta? && matches_min? && matches_max?
end

def matches_after?
  @eval_after ? expected_matches_actual?(@expected_after, @actual_after) : true
end

def matches_before?
  @eval_before ? expected_matches_actual?(@expected_before, @actual_before) : true
end

def matches_expected_delta?
  @expected_delta ? (@actual_before + @expected_delta == @actual_after) : true
end

def matches_max?
  @maximum ? (@actual_after - @actual_before <= @maximum) : true
end

def matches_min?
  @minimum ? (@actual_after - @actual_before >= @minimum) : true
end

def message
  @message || "result"
end

def raise_block_syntax_error
  raise SyntaxError.new(<<-MESSAGE)
ssed to should or should_not change must use {} instead of do/end
end

def supports_block_expectations?
  true
end

def to(to)
  @eval_after = true
  @expected_after = to
  self
end