require 'singleton'
require 'timecop/time_extensions'
require 'timecop/time_stack_item'

# Timecop
# * Wrapper class for manipulating the extensions to the Time, Date, and DateTime objects
# * Allows us to "freeze" time in our Ruby applications.
# * Optionally allows time travel to simulate a running clock, such time is not technically frozen.
#
# This is very useful when your app's functionality is dependent on time (e.g.
# anything that might expire).  This will allow us to alter the return value of
# Date.today, Time.now, and DateTime.now, such that our application code _never_ has to change.
class Timecop
  include Singleton

  class << self
    attr_accessor :active_support

    # Allows you to run a block of code and "fake" a time throughout the execution of that block.
    # This is particularly useful for writing test methods where the passage of time is critical to the business
    # logic being tested.  For example:
    #
    #   joe = User.find(1)
    #   joe.purchase_home()
    #   assert !joe.mortgage_due?
    #   Timecop.freeze(2008, 10, 5) do
    #     assert joe.mortgage_due?
    #   end
    #
    # freeze and travel will respond to several different arguments:
    # 1. Timecop.freeze(time_inst)
    # 2. Timecop.freeze(datetime_inst)
    # 3. Timecop.freeze(date_inst)
    # 4. Timecop.freeze(offset_in_seconds)
    # 5. Timecop.freeze(year, month, day, hour=0, minute=0, second=0)
    #
    # When a block is also passed, Time.now, DateTime.now and Date.today are all reset to their
    # previous values after the block has finished executing.  This allows us to nest multiple
    # calls to Timecop.travel and have each block maintain it's concept of "now."
    #
    # * Note: Timecop.freeze will actually freeze time.  This can cause unanticipated problems if
    #   benchmark or other timing calls are executed, which implicitly expect Time to actually move
    #   forward.
    #
    # * Rails Users: Be especially careful when setting this in your development environment in a
    #   rails project.  Generators will load your environment, including the migration generator,
    #   which will lead to files being generated with the timestamp set by the Timecop.freeze call
    #   in your dev environment
    #
    # Returns the frozen time.
    def freeze(*args, &block)
      instance().send(:travel, :freeze, *args, &block)
      Time.now
    end

    # Allows you to run a block of code and "fake" a time throughout the execution of that block.
    # See Timecop#freeze for a sample of how to use (same exact usage syntax)
    #
    # * Note: Timecop.travel will not freeze time (as opposed to Timecop.freeze).  This is a particularly
    #   good candidate for use in environment files in rails projects.
    #
    # Returns the 'new' current Time.
    def travel(*args, &block)
      instance().send(:travel, :travel, *args, &block)
      Time.now
    end

    def baseline
      instance().send(:baseline)
    end

    def baseline=(baseline)
      instance().send(:baseline=, baseline)
    end

    # Reverts back to system's Time.now, Date.today and DateTime.now (if it exists).
    #
    # Returns Time.now, which is now the real current time.
    def return
      instance().send(:unmock!)
      Time.now
    end

    def return_to_baseline
      instance().send(:return_to_baseline)
      Time.now
    end

    def top_stack_item #:nodoc:
      instance().instance_variable_get(:@_stack).last
    end
  end

  protected

    def baseline=(baseline)
      @baseline = baseline
      @_stack << TimeStackItem.new(:travel, baseline)
    end

    def initialize #:nodoc:
      @_stack = []
    end

    def travel(mock_type, *args, &block) #:nodoc:
      stack_item = TimeStackItem.new(mock_type, *args)

      # store this time traveling on our stack...
      @_stack << stack_item

      if block_given?
        begin
          yield stack_item.time
        ensure
          # pull it off the stack...
          @_stack.pop
        end
      end
    end

    def unmock! #:nodoc:
      @baseline = nil
      @_stack = []
    end

    def return_to_baseline
      if @baseline
        @_stack = [@_stack.shift]
      else
        unmock!
      end
    end
end