require 'mspec/capture'

class ComplainMatcher
  def initialize(complaint)
    @complaint = complaint
  end
  
  def matches?(proc)
    @saved_err = $stderr
    @stderr = $stderr = CaptureOutput.new
    @verbose = $VERBOSE
    $VERBOSE = false
    
    proc.call
    
    unless @complaint.nil?
      case @complaint
      when Regexp
        return false unless $stderr =~ @complaint
      else
        return false unless $stderr == @complaint
      end
    end

    return $stderr.empty? ? false : true
  ensure
    $VERBOSE = @verbose
    $stderr = @saved_err
  end
  
  def failure_message
    if @complaint.nil?
      ["Expected a warning", "but received none"]
    elsif @complaint.kind_of? Regexp
      ["Expected warning to match:", @complaint.inspect]
    else
      ["Expected warning: #{@complaint.inspect}", "but got: #{@stderr.chomp.inspect}"]
    end
  end
  
  def negative_failure_message
    if @complaint.nil?
      ["Unexpected warning: ", @stderr.chomp.inspect]
    elsif @complaint.kind_of? Regexp
      ["Expected warning not to match:", @complaint.inspect]
    else
      ["Expected warning: #{@complaint.inspect}", "but got: #{@stderr.chomp.inspect}"]
    end
  end
end

class Object
  def complain(complaint=nil)
    ComplainMatcher.new(complaint)
  end
end
