module ActiveSupport #:nodoc:
  module CoreExtensions #:nodoc:
    module Time #:nodoc:
      # Enables the use of time calculations within Time itself
      module Calculations
        def self.included(base) #:nodoc:
          base.extend ClassMethods

          base.class_eval do
            alias_method :plus_without_duration, :+
            alias_method :+, :plus_with_duration
            
            alias_method :minus_without_duration, :-
            alias_method :-, :minus_with_duration
            
            alias_method :minus_without_coercion, :-
            alias_method :-, :minus_with_coercion
            
            alias_method :compare_without_coercion, :<=>
            alias_method :<=>, :compare_with_coercion
          end
        end

        COMMON_YEAR_DAYS_IN_MONTH = [nil, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]

        module ClassMethods
          # Overriding case equality method so that it returns true for ActiveSupport::TimeWithZone instances
          def ===(other)
            other.is_a?(::Time)
          end
          
          # Return the number of days in the given month. 
          # If no year is specified, it will use the current year. 
          def days_in_month(month, year = now.year)
            return 29 if month == 2 && ::Date.gregorian_leap?(year)
            COMMON_YEAR_DAYS_IN_MONTH[month]
          end

          # Returns a new Time if requested year can be accommodated by Ruby's Time class
          # (i.e., if year is within either 1970..2038 or 1902..2038, depending on system architecture);
          # otherwise returns a DateTime
          def time_with_datetime_fallback(utc_or_local, year, month=1, day=1, hour=0, min=0, sec=0, usec=0)
            ::Time.send(utc_or_local, year, month, day, hour, min, sec, usec)
          rescue
            offset = utc_or_local.to_sym == :local ? ::DateTime.local_offset : 0
            ::DateTime.civil(year, month, day, hour, min, sec, offset)
          end

          # Wraps class method +time_with_datetime_fallback+ with +utc_or_local+ set to <tt>:utc</tt>.
          def utc_time(*args)
            time_with_datetime_fallback(:utc, *args)
          end

          # Wraps class method +time_with_datetime_fallback+ with +utc_or_local+ set to <tt>:local</tt>.
          def local_time(*args)
            time_with_datetime_fallback(:local, *args)
          end
        end

        # Seconds since midnight: Time.now.seconds_since_midnight
        def seconds_since_midnight
          self.to_i - self.change(:hour => 0).to_i + (self.usec/1.0e+6)
        end

        # Returns a new Time where one or more of the elements have been changed according to the +options+ parameter. The time options
        # (hour, minute, sec, usec) reset cascadingly, so if only the hour is passed, then minute, sec, and usec is set to 0. If the hour and
        # minute is passed, then sec and usec is set to 0.
        def change(options)
          ::Time.send(
            self.utc? ? :utc_time : :local_time,
            options[:year]  || self.year,
            options[:month] || self.month,
            options[:day]   || self.day,
            options[:hour]  || self.hour,
            options[:min]   || (options[:hour] ? 0 : self.min),
            options[:sec]   || ((options[:hour] || options[:min]) ? 0 : self.sec),
            options[:usec]  || ((options[:hour] || options[:min] || options[:sec]) ? 0 : self.usec)
          )
        end

        # Uses Date to provide precise Time calculations for years, months, and days.
        # The +options+ parameter takes a hash with any of these keys: <tt>:years</tt>,
        # <tt>:months</tt>, <tt>:weeks</tt>, <tt>:days</tt>, <tt>:hours</tt>,
        # <tt>:minutes</tt>, <tt>:seconds</tt>.
        def advance(options)
          d = to_date.advance(options)
          time_advanced_by_date = change(:year => d.year, :month => d.month, :day => d.day)
          seconds_to_advance = (options[:seconds] || 0) + (options[:minutes] || 0) * 60 + (options[:hours] || 0) * 3600
          seconds_to_advance == 0 ? time_advanced_by_date : time_advanced_by_date.since(seconds_to_advance)
        end

        # Returns a new Time representing the time a number of seconds ago, this is basically a wrapper around the Numeric extension
        def ago(seconds)
          self.since(-seconds)
        end

        # Returns a new Time representing the time a number of seconds since the instance time, this is basically a wrapper around
        # the Numeric extension.
        def since(seconds)
          f = seconds.since(self)
          if ActiveSupport::Duration === seconds
            f
          else
            initial_dst = self.dst? ? 1 : 0
            final_dst   = f.dst? ? 1 : 0
            (seconds.abs >= 86400 && initial_dst != final_dst) ? f + (initial_dst - final_dst).hours : f
          end
        rescue
          self.to_datetime.since(seconds)          
        end
        alias :in :since

        # Returns a new Time representing the time a number of specified months ago
        def months_ago(months)
          advance(:months => -months)
        end

        # Returns a new Time representing the time a number of specified months in the future
        def months_since(months)
          advance(:months => months)
        end

        # Returns a new Time representing the time a number of specified years ago
        def years_ago(years)
          advance(:years => -years)
        end

        # Returns a new Time representing the time a number of specified years in the future
        def years_since(years)
          advance(:years => years)
        end

        # Short-hand for years_ago(1)
        def last_year
          years_ago(1)
        end

        # Short-hand for years_since(1)
        def next_year
          years_since(1)
        end


        # Short-hand for months_ago(1)
        def last_month
          months_ago(1)
        end

        # Short-hand for months_since(1)
        def next_month
          months_since(1)
        end

        # Returns a new Time representing the "start" of this week (Monday, 0:00)
        def beginning_of_week
          days_to_monday = self.wday!=0 ? self.wday-1 : 6
          (self - days_to_monday.days).midnight
        end
        alias :monday :beginning_of_week
        alias :at_beginning_of_week :beginning_of_week

        # Returns a new Time representing the end of this week (Sunday, 23:59:59)
        def end_of_week
          days_to_sunday = self.wday!=0 ? 7-self.wday : 0
          (self + days_to_sunday.days).end_of_day
        end
        alias :at_end_of_week :end_of_week

        # Returns a new Time representing the start of the given day in next week (default is Monday).
        def next_week(day = :monday)
          days_into_week = { :monday => 0, :tuesday => 1, :wednesday => 2, :thursday => 3, :friday => 4, :saturday => 5, :sunday => 6}
          since(1.week).beginning_of_week.since(days_into_week[day].day).change(:hour => 0)
        end

        # Returns a new Time representing the start of the day (0:00)
        def beginning_of_day
          (self - self.seconds_since_midnight).change(:usec => 0)
        end
        alias :midnight :beginning_of_day
        alias :at_midnight :beginning_of_day
        alias :at_beginning_of_day :beginning_of_day

        # Returns a new Time representing the end of the day (23:59:59)
        def end_of_day
          change(:hour => 23, :min => 59, :sec => 59)
        end

        # Returns a new Time representing the start of the month (1st of the month, 0:00)
        def beginning_of_month
          #self - ((self.mday-1).days + self.seconds_since_midnight)
          change(:day => 1,:hour => 0, :min => 0, :sec => 0, :usec => 0)
        end
        alias :at_beginning_of_month :beginning_of_month

        # Returns a new Time representing the end of the month (last day of the month, 0:00)
        def end_of_month
          #self - ((self.mday-1).days + self.seconds_since_midnight)
          last_day = ::Time.days_in_month( self.month, self.year )
          change(:day => last_day, :hour => 23, :min => 59, :sec => 59, :usec => 0)
        end
        alias :at_end_of_month :end_of_month
		
        # Returns  a new Time representing the start of the quarter (1st of january, april, july, october, 0:00)
        def beginning_of_quarter
          beginning_of_month.change(:month => [10, 7, 4, 1].detect { |m| m <= self.month })
        end
        alias :at_beginning_of_quarter :beginning_of_quarter

        # Returns a new Time representing the end of the quarter (last day of march, june, september, december, 23:59:59)
        def end_of_quarter
          change(:month => [3, 6, 9, 12].detect { |m| m >= self.month }).end_of_month
        end
        alias :at_end_of_quarter :end_of_quarter

        # Returns  a new Time representing the start of the year (1st of january, 0:00)
        def beginning_of_year
          change(:month => 1,:day => 1,:hour => 0, :min => 0, :sec => 0, :usec => 0)
        end
        alias :at_beginning_of_year :beginning_of_year

        # Returns a new Time representing the end of the year (31st of december, 23:59:59)
        def end_of_year
          change(:month => 12,:day => 31,:hour => 23, :min => 59, :sec => 59)
        end
        alias :at_end_of_year :end_of_year

        # Convenience method which returns a new Time representing the time 1 day ago
        def yesterday
          advance(:days => -1)
        end

        # Convenience method which returns a new Time representing the time 1 day since the instance time
        def tomorrow
          advance(:days => 1)
        end

        def plus_with_duration(other) #:nodoc:
          if ActiveSupport::Duration === other
            other.since(self)
          else
            plus_without_duration(other)
          end
        end

        def minus_with_duration(other) #:nodoc:
          if ActiveSupport::Duration === other
            other.until(self)
          else
            minus_without_duration(other)
          end
        end
        
        # Time#- can also be used to determine the number of seconds between two Time instances.
        # We're layering on additional behavior so that ActiveSupport::TimeWithZone instances
        # are coerced into values that Time#- will recognize
        def minus_with_coercion(other)
          other = other.comparable_time if other.respond_to?(:comparable_time)
          minus_without_coercion(other)
        end
        
        # Layers additional behavior on Time#<=> so that DateTime and ActiveSupport::TimeWithZone instances
        # can be chronologically compared with a Time
        def compare_with_coercion(other)
          # if other is an ActiveSupport::TimeWithZone, coerce a Time instance from it so we can do <=> comparision
          other = other.comparable_time if other.respond_to?(:comparable_time)
          if other.acts_like?(:date)
            # other is a Date/DateTime, so coerce self #to_datetime and hand off to DateTime#<=>
            to_datetime.compare_without_coercion(other)
          else
            compare_without_coercion(other)
          end
        end
      end
    end
  end
end