require 'shoulda/private_helpers'

module Shoulda # :nodoc:
  module Macros
    # Macro that creates a test asserting a change between the return value
    # of an expression that is run before and after the current setup block
    # is run. This is similar to Active Support's <tt>assert_difference</tt>
    # assertion, but supports more than just numeric values.  See also
    # should_not_change.
    #
    # Example:
    #
    #   context "Creating a post" do
    #     setup { Post.create }
    #     should_change "Post.count", :by => 1
    #   end
    #
    # As shown in this example, the <tt>:by</tt> option expects a numeric
    # difference between the before and after values of the expression.  You
    # may also specify <tt>:from</tt> and <tt>:to</tt> options:
    #
    #   should_change "Post.count", :from => 0, :to => 1
    #   should_change "@post.title", :from => "old", :to => "new"
    #
    # Combinations of <tt>:by</tt>, <tt>:from</tt>, and <tt>:to</tt> are allowed:
    #
    #   should_change "@post.title"                # => assert the value changed in some way
    #   should_change "@post.title", :from => "old" # => assert the value changed to anything other than "old"
    #   should_change "@post.title", :to   => "new" # => assert the value changed from anything other than "new"
    def should_change(expression, options = {})
      by, from, to = get_options!([options], :by, :from, :to)
      stmt = "change #{expression.inspect}"
      stmt << " from #{from.inspect}" if from
      stmt << " to #{to.inspect}" if to
      stmt << " by #{by.inspect}" if by

      expression_eval = lambda { eval(expression) }
      before = lambda { @_before_should_change = expression_eval.bind(self).call }
      should stmt, :before => before do
        old_value = @_before_should_change
        new_value = expression_eval.bind(self).call
        assert_operator from, :===, old_value, "#{expression.inspect} did not originally match #{from.inspect}" if from
        assert_not_equal old_value, new_value, "#{expression.inspect} did not change" unless by == 0
        assert_operator to, :===, new_value, "#{expression.inspect} was not changed to match #{to.inspect}" if to
        assert_equal old_value + by, new_value if by
      end
    end

    # Macro that creates a test asserting no change between the return value
    # of an expression that is run before and after the current setup block
    # is run. This is the logical opposite of should_change.
    #
    # Example:
    #
    #   context "Updating a post" do
    #     setup { @post.update_attributes(:title => "new") }
    #     should_not_change "Post.count"
    #   end
    def should_not_change(expression)
      expression_eval = lambda { eval(expression) }
      before = lambda { @_before_should_not_change = expression_eval.bind(self).call }
      should "not change #{expression.inspect}", :before => before do
        new_value = expression_eval.bind(self).call
        assert_equal @_before_should_not_change, new_value, "#{expression.inspect} changed"
      end
    end

    private

    include Shoulda::Private
  end
end