module ActiveSupport::CoreExtensions::Time::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

def advance(options)
  unless options[:weeks].nil?
    options[:weeks], partial_weeks = options[:weeks].divmod(1)
    options[:days] = (options[:days] || 0) + 7 * partial_weeks
  end
  
  unless options[:days].nil?
    options[:days], partial_days = options[:days].divmod(1)
    options[:hours] = (options[:hours] || 0) + 24 * partial_days
  end
  
  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

def ago(seconds)
  self.since(-seconds)
end

def beginning_of_day
  #(self - seconds_since_midnight).change(:usec => 0)
  change(:hour => 0, :min => 0, :sec => 0, :usec => 0)
end

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

def beginning_of_quarter
  beginning_of_month.change(:month => [10, 7, 4, 1].detect { |m| m <= self.month })
end

def beginning_of_week
  days_to_monday = self.wday!=0 ? self.wday-1 : 6
  (self - days_to_monday.days).midnight
end

def beginning_of_year
  change(:month => 1,:day => 1,:hour => 0, :min => 0, :sec => 0, :usec => 0)
end

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

def compare_with_coercion(other)
  # if other is an ActiveSupport::TimeWithZone, coerce a Time instance from it so we can do <=> comparison
  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

def end_of_day
  change(:hour => 23, :min => 59, :sec => 59, :usec => 999999.999)
end

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 => 999999.999)
end

def end_of_quarter
  beginning_of_month.change(:month => [3, 6, 9, 12].detect { |m| m >= self.month }).end_of_month
end

def end_of_week
  days_to_sunday = self.wday!=0 ? 7-self.wday : 0
  (self + days_to_sunday.days).end_of_day
end

def end_of_year
  change(:month => 12, :day => 31, :hour => 23, :min => 59, :sec => 59, :usec => 999999.999)
end

def future?
  self > ::Time.current
end

def last_month # :nodoc:
  ActiveSupport::Deprecation.warn("Time#last_month is deprecated and has been removed in Rails 3, please use Time#prev_month instead", caller)
  prev_month
end

def last_year # :nodoc:
  ActiveSupport::Deprecation.warn("Time#last_year is deprecated and has been removed in Rails 3, please use Time#prev_year instead", caller)
  prev_year
end

def minus_with_coercion(other)
  other = other.comparable_time if other.respond_to?(:comparable_time)
  other.is_a?(::DateTime) ? to_f - other.to_f : minus_without_coercion(other)
end

def minus_with_duration(other) #:nodoc:
  if ActiveSupport::Duration === other
    other.until(self)
  else
    minus_without_duration(other)
  end
end

def months_ago(months)
  advance(:months => -months)
end

def months_since(months)
  advance(:months => months)
end

def next_month
  months_since(1)
end

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

def next_year
  years_since(1)
end

def past?
  self < ::Time.current
end

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

def prev_month
  months_ago(1)
end

def prev_year
  years_ago(1)
end

def seconds_since_midnight
  self.to_i - self.change(:hour => 0).to_i + (self.usec/1.0e+6)
end

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

def today?
  self.to_date == ::Date.current
end

def tomorrow
  advance(:days => 1)
end

def years_ago(years)
  advance(:years => -years)
end

def years_since(years)
  advance(:years => years)
end

def yesterday
  advance(:days => -1)
end