class AssertionError < StandardError; end

class MustAssertions < ExtraBlankSlate
  attr_reader :obj
  
  def initialize obj
    @obj = obj
  end
  
  def == o
    @obj == o
  end
  
  def =~ o
    @obj =~ o
  end
  
  def never_called
    false
  end
  
  def nil
    @obj.equal? nil
  end
  
  def defined
    !nil
  end
  
  def respond_to method
    @obj.respond_to? method
  end
    
  def a klass
    if klass.class == Array
      klass.any?{|k| @obj.is_a? k}
    else
      @obj.is_a? klass
    end
  end
  alias_method :an, :a
        
  # def be klass = nil
  #   if klass.class == Array
  #     klass.any?{|k| @obj.respond_to :is?, k}
  #   else
  #     @obj.respond_to :is?, klass
  #   end
  # end
    
  def include o
    @obj.include? o
  end
    
  def in *args
    if args.size == 1 
      obj = args.first
      if obj.is_a?(Array) or obj.is_a?(Range)
        obj.include? @obj
      else
        args.include? @obj
      end
    else
      args.include? @obj
    end
  end

  def true
    !!@obj
  end

  def false
    !@obj
  end

  def empty
    @obj.empty?
  end
  
  def blank
    @obj.blank?
  end
  
  def present
    !@obj.blank?
  end
  
  def > o
    @obj > o
  end
  
  def < o
    @obj < o
  end
  
  def >= o
    @obj >= o
  end
  
  def <= o
    @obj <= o
  end
  
  def exist arg
    @obj.exist? arg
  end
  
  def be
    @prefix = 'be'
    self
  end
  
  def have
    @prefix = 'have'
    self
  end
  
  def self.assertions
    special = %w{be have}
    instance_methods.select{|m| m !~ /^__/ and m != 'be'}
  end

  protected
    def method_missing m, *args, &b
      raise RuntimeError, "Assertion '#{m}' is unknown!", caller[1..-1]
    end
  
    def failed method, negative, *args
      stack = caller.sfilter('must.rb')
      
      unless args.empty?
        Kernel.raise AssertionError, "
  ASSERTION FAILED (#{stack.first}):
  #{@obj.inspect} must #{'not ' if negative}#{"#{@prefix} " if @prefix}#{method} #{args.first.inspect}
        ", stack
      else
        Kernel.raise AssertionError, "
  ASSERTION FAILED (#{stack.first}):
  #{@obj.inspect} must #{'not ' if negative}#{"#{@prefix} " if @prefix}#{method}
        ", stack
      end
    end
end

class Must < MustAssertions
  assertions.each do |m|
    desition = "_#{m}"
    alias_method desition, m
    define_method m do |*args|
      failed m, false, *args unless __send__(desition, *args)      
      @obj
    end
  end
end

class MustNot < MustAssertions
  assertions.each do |m|
    desition = "_#{m}"
    alias_method desition, m
    define_method m do |*args|
      failed m, true, *args if __send__(desition, *args)
      @obj
    end
  end
end

Object.class_eval do
  
  def must
    Must.new(self)
  end
  
  def must_not
    MustNot.new(self)
  end
  
  def must_be
    must.be
  end
  
  def must_not_be
    must_not.be
  end
  
  # def must_have
  #   must.have
  # end
  # 
  # def must_not_have
  #   must_not.have
  # end
end