Overlapping issues with time slots in Ruby

When i was working for a client on a Ruby on Rails application dealing with multiples time slots, i find myself with a rather complex problem.

Time Slots

To manage user schedules, the application has an object TimeSlot which represents a period of time between start_date and end_date.

class TimeSlot < ActiveRecord::Base
  belongs_to :user
  attr_accessible :end_date, :start_date
end

Simple enough right ? But the user can have several TimeSlot at the same time, and of course it can midway between two days.

And i need to calculate the number of hours used by days.

But i have a main problem : Overlapping time slots.

Overlapping Issue

Range of DateTime

Luckily we can solve this rather complex problem using the ruby Range class.

A Range represents an interval—a set of values with a start and an end.

Ranges can be constructed using objects of any type, as long as the objects can be compared using their <=> operator and they support the succ method to return the next object in sequence.

So we can convert all ours TimeSlot objects into Range of DateTime with a little helper.

def to_time_range
  (self.start_date..self.end_date)
end

We’re going to need some utility methods for check if a range overlap another and for merging two range together.

def ranges_overlap?(a, b)
  a.cover?(b.begin) || b.cover?(a.begin)
end

def merge_ranges(a, b)
  [a.begin, b.begin].min..[a.end, b.end].max
end

Now we just need to check inside the array of ranges, if some range overlap another and merge it.

def merge_overlapping_ranges(ranges)
  ranges.sort_by(&:begin).inject([]) do |ranges, range|
    if !ranges.empty? && ranges_overlap?(ranges.last, range)
      ranges[0...-1] + [merge_ranges(ranges.last, range)]
    else
      ranges + [range]
    end
  end
end

Thank to this thread on Stackoverflow.