class AssertionError < RuntimeError; end

class MustAssertions < BasicObject
  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
    @obj != nil
  end

  def respond_to method
    @obj.respond_to? method
  end

  def a *args
    if args.class == ::Array
      args.any?{|k| @obj.is_a? k}
    else
      @obj.is_a? args
    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 *args
    @obj.exist? *args
  end

  def be
    @prefix = 'be'
    self
  end

  def have
    @prefix = 'have'
    self
  end

  def self.assertions
    special = [:be, :have]
    public_instance_methods.select{|m| m !~ /^__/ and !special.include?(m)}
  end

  protected
    # def method_missing m, *args, &b
    #   raise ::RuntimeError, "Assertion '#{m}' is unknown!", caller[1..-1]
    # end

    def failed method, negative, *args
      stack = ::Object.send(:caller).sfilter('must.rb')

      unless args.empty?
        ::Object.send :raise, ::AssertionError, "
  ASSERTION FAILED (#{stack.first}):
  #{@obj.inspect} must #{'not ' if negative}#{"#{@prefix} " if @prefix}#{method} #{args.collect{|a| a.inspect}.join(', ')}
        ", stack
      else
        ::Object.send :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

  def inspect
    "<#Must>"
  end
end

class MustNot < MustAssertions
  assertions.each do |m|
    desition = "_#{m}".to_sym
    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