# -*- encoding: utf-8 -*-
# Copyright © 2010, 2011, 2012 José Pablo Fernández

module AssertDifference
  VERSION = "0.4.1" unless defined?(::AssertDifference::VERSION)

  # 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, :article => {...}
  #     end
  #
  # An arbitrary expression is passed in and evaluated.
  #
  #     assert_difference "assigns(:article).comments(:reload).size" do
  #       post :create, :comment => {...}
  #     end
  #
  # An arbitrary positive or negative difference can be specified. The default is +1.
  #
  #     assert_difference "Article.count", -1 do
  #       post :delete, :id => ...
  #     end
  #
  # An array of expressions can also be passed in and evaluated.
  #
  #     assert_difference [ "Article.count", "Post.count" ], +2 do
  #       post :create, :article => {...}
  #     end
  #
  # A error message can be specified.
  #
  #     assert_difference "Article.count", -1, "An Article should be destroyed" do
  #       post :delete, :id => ...
  #     end
  #
  # Various assertions can be combined into one, instead of writing:
  #
  #     assert_difference "Company.count" do
  #       assert_difference "User.count", +5 do
  #         assert_difference "Article.count", -1 do
  #           post :something
  #         end
  #       end
  #     end
  #
  # you can *now* write:
  #
  #     assert_difference "Article.count" => 1, "assigns(:article).comments(:reload).size" => 1, "Article.count" => -1 do
  #       post :something
  #     end
  #
  # the results of the block is the result of the assert, so you can write
  #
  #     email = assert_difference "ActionMailer::Base.deliveries.count" => +1 do
  #         Mailer.reset_password_email(@user).deliver
  #     end
  #     assert_equal [@user.email], email.to
  #
  # @param [Array, Hash] expressions array of expressions to evaluate or hash
  #   table of expressions and expected difference.
  # @param [Integer] difference expected difference when using an array or single expression.
  # @param [String, nil] message error message to display. One would be constructed if nil.
  # @return whatever the block returned
  def assert_difference(expressions, difference = 1, message = nil, &block)
    b = block.send(:binding)
    if !expressions.is_a? Hash
      exps = Array.wrap(expressions)
      expressions = {}
      exps.each { |e| expressions[e] = difference }
    end

    before = {}
    expressions.each { |exp, _| before[exp] = eval(exp, b) }

    result = yield

    error_messages = []
    expressions.each do |exp, diff|
      expected = before[exp] + diff
      actual = eval(exp, b)
      if expected != actual
        error = "#{exp.inspect} didn't change by #{diff} (expecting #{expected}, but got #{actual})"
        error = "#{message}.\n#{error}" if message
        error_messages << error
      end
    end

    if error_messages.any?
      fail error_messages.join(error_message.any? { |m| m.includes? "\n" } ? "\n\n" : ". ").strip
    end

    return result
  end
end