module ActiveSupport
  module Testing
    module Assertions
      UNTRACKED = Object.new # :nodoc:

      # Asserts that an expression is not truthy. Passes if <tt>object</tt> is
      # +nil+ or +false+. "Truthy" means "considered true in a conditional"
      # like <tt>if foo</tt>.
      #
      #   assert_not nil    # => true
      #   assert_not false  # => true
      #   assert_not 'foo'  # => Expected "foo" to be nil or false
      #
      # An error message can be specified.
      #
      #   assert_not foo, 'foo should be false'
      def assert_not(object, message = nil)
        message ||= "Expected #{mu_pp(object)} to be nil or false"
        assert !object, message
      end

      # Test numeric difference between the return value of an expression as a
      # result of what is evaluated in the yielded block.
      #
      #   assert_difference 'Article.count' do
      #     post :create, params: { article: {...} }
      #   end
      #
      # An arbitrary expression is passed in and evaluated.
      #
      #   assert_difference 'Article.last.comments(:reload).size' do
      #     post :create, params: { comment: {...} }
      #   end
      #
      # An arbitrary positive or negative difference can be specified.
      # The default is <tt>1</tt>.
      #
      #   assert_difference 'Article.count', -1 do
      #     post :delete, params: { id: ... }
      #   end
      #
      # An array of expressions can also be passed in and evaluated.
      #
      #   assert_difference [ 'Article.count', 'Post.count' ], 2 do
      #     post :create, params: { article: {...} }
      #   end
      #
      # A lambda or a list of lambdas can be passed in and evaluated:
      #
      #   assert_difference ->{ Article.count }, 2 do
      #     post :create, params: { article: {...} }
      #   end
      #
      #   assert_difference [->{ Article.count }, ->{ Post.count }], 2 do
      #     post :create, params: { article: {...} }
      #   end
      #
      # An error message can be specified.
      #
      #   assert_difference 'Article.count', -1, 'An Article should be destroyed' do
      #     post :delete, params: { id: ... }
      #   end
      def assert_difference(expression, difference = 1, message = nil, &block)
        expressions = Array(expression)

        exps = expressions.map { |e|
          e.respond_to?(:call) ? e : lambda { eval(e, block.binding) }
        }
        before = exps.map(&:call)

        retval = yield

        expressions.zip(exps).each_with_index do |(code, e), i|
          error  = "#{code.inspect} didn't change by #{difference}"
          error  = "#{message}.\n#{error}" if message
          assert_equal(before[i] + difference, e.call, error)
        end

        retval
      end

      # Assertion that the numeric result of evaluating an expression is not
      # changed before and after invoking the passed in block.
      #
      #   assert_no_difference 'Article.count' do
      #     post :create, params: { article: invalid_attributes }
      #   end
      #
      # An error message can be specified.
      #
      #   assert_no_difference 'Article.count', 'An Article should not be created' do
      #     post :create, params: { article: invalid_attributes }
      #   end
      def assert_no_difference(expression, message = nil, &block)
        assert_difference expression, 0, message, &block
      end

      # Assertion that the result of evaluating an expression is changed before
      # and after invoking the passed in block.
      #
      #   assert_changes 'Status.all_good?' do
      #     post :create, params: { status: { ok: false } }
      #   end
      #
      # You can pass the block as a string to be evaluated in the context of
      # the block. A lambda can be passed for the block as well.
      #
      #   assert_changes -> { Status.all_good? } do
      #     post :create, params: { status: { ok: false } }
      #   end
      #
      # The assertion is useful to test side effects. The passed block can be
      # anything that can be converted to string with #to_s.
      #
      #   assert_changes :@object do
      #     @object = 42
      #   end
      #
      # The keyword arguments :from and :to can be given to specify the
      # expected initial value and the expected value after the block was
      # executed.
      #
      #   assert_changes :@object, from: nil, to: :foo do
      #     @object = :foo
      #   end
      #
      # An error message can be specified.
      #
      #   assert_changes -> { Status.all_good? }, 'Expected the status to be bad' do
      #     post :create, params: { status: { incident: true } }
      #   end
      def assert_changes(expression, message = nil, from: UNTRACKED, to: UNTRACKED, &block)
        exp = expression.respond_to?(:call) ? expression : -> { eval(expression.to_s, block.binding) }

        before = exp.call
        retval = yield

        unless from == UNTRACKED
          error = "#{expression.inspect} isn't #{from}"
          error = "#{message}.\n#{error}" if message
          assert from === before, error
        end

        after = exp.call

        if to == UNTRACKED
          error = "#{expression.inspect} didn't changed"
          error = "#{message}.\n#{error}" if message
          assert_not_equal before, after, error
        else
          message = "#{expression.inspect} didn't change to #{to}"
          error = "#{message}.\n#{error}" if message
          assert to === after, error
        end

        retval
      end

      # Assertion that the result of evaluating an expression is changed before
      # and after invoking the passed in block.
      #
      #   assert_no_changes 'Status.all_good?' do
      #     post :create, params: { status: { ok: true } }
      #   end
      #
      # An error message can be specified.
      #
      #   assert_no_changes -> { Status.all_good? }, 'Expected the status to be good' do
      #     post :create, params: { status: { ok: false } }
      #   end
      def assert_no_changes(expression, message = nil, &block)
        exp = expression.respond_to?(:call) ? expression : -> { eval(expression.to_s, block.binding) }

        before = exp.call
        retval = yield
        after = exp.call

        error = "#{expression.inspect} did change to #{after}"
        error = "#{message}.\n#{error}" if message
        assert_equal before, after, error

        retval
      end
    end
  end
end