Gemfile

source 'https://rubygems.org'
gem 'activesupport'
gem 'rspec-rails'

main.rb

require 'active_support'
require 'active_support/core_ext'

class Schedule
  NO_REPEAT = 0
  R_DAY = 1
  R_WDAY = 2
  R_WEEK = 3
  R_MONTH = 4
  EOL = 10.years.since

  attr_accessor :current_start, :current_end

  def initialize start_time:, end_time:, repeat: 0, last_time: nil
    @start_time = start_time
    @end_time = end_time
    @repeat = repeat
    @last_time = last_time
    @current_start = @start_time
    @current_end = @end_time
  end
  # return: nil if no next, else a schedule start from next date
  def next_time!
    return if @current_start.nil?
    return @current_start = nil if @repeat == NO_REPEAT
    offset = 0
    case @repeat
    when R_DAY then offset = 1.day
    when R_WDAY then offset = @current_start.wday == 5 ? 3.days : 1.day
    when R_WEEK then offset = 7.days
    when R_MONTH then offset = find_next_month_offset
    end
    duration = @current_end - @current_start
    @current_start += offset
    @current_end = @current_start + duration
    return @current_start = nil if @last_time && @current_start > @last_time
    return @current_start = nil if @current_start > EOL
    @current_start
  end

  # next month at the end of the month could be more than 1 month offset
  # next month of 3/31 is 5/31
  def find_next_month_offset
    length = 0
    this_month = @current_start
    loop do
      length += 1
      next_month = this_month + length.months
      break if next_month.day == this_month.day
    end
    length.month
  end

  def conflicts? sch
    # @start within sch?
    return true if @current_start >= sch.current_start && @current_start <= sch.current_end
    # @end within sch?
    return true if @current_end >= sch.current_start && @current_end <= sch.current_end
    # @ contains sch?
    return true if @current_start <= sch.current_start && @current_end >= sch.current_end
    # safe
    false
  end
end

class ScheduleService
  def self.conflicts? s1, s2
    # if both schedule exists?
    while !s1.current_start.nil? && !s2.current_start.nil?
      # check if they conflicts
      return true if s1.conflicts? s2
      # find the next date to compare
      if s1.current_start < s2.current_start
        s1.next_time!
      else
        s2.next_time!
      end
    end
    false
  end
end

main_spec.rb

require './main'

describe Schedule do
  it 'generates future events by month' do
    t = Time.new(2015,1,31)
    s = Schedule.new start_time: t, end_time: t + 40.minutes, repeat: 4, last_time: t + 1.year
    tlist = []
    while !s.current_start.nil? do
      tlist << s.current_start
      s.next_time!
    end
    expect(tlist.size).to eq 8
  end
  it 'generates future events by week' do
    t = Time.new(2015,1,31)
    s = Schedule.new start_time: t, end_time: t + 40.minutes, repeat: 3, last_time: t + 1.year
    tlist = []
    while !s.current_start.nil? do
      tlist << s.current_start
      s.next_time!
    end
    expect(tlist.size).to eq 53
  end
  it 'generates future events by workday' do
    t = Time.new(2015,2,2) # It's monday
    s = Schedule.new start_time: t, end_time: t + 40.minutes, repeat: 2, last_time: t + 1.month
    tlist = []
    while !s.current_start.nil? do
      tlist << s.current_start
      s.next_time!
    end
    expect(tlist.size).to eq 21
  end
  it 'generates future events by day' do
    t = Time.new(2015,1,31)
    s = Schedule.new start_time: t, end_time: t + 40.minutes, repeat: 1, last_time: t + 1.month
    tlist = []
    while !s.current_start.nil? do
      tlist << s.current_start
      s.next_time!
    end
    expect(tlist.size).to eq 29
  end
end

describe ScheduleService do
  it '日程【2015-07-08 16:00:00，2015-07-08 17:00:00，不重复】与日程【2015-07-06 16:00:00，2015-07-06 16:30:00，每天重复，没有截止日期】冲突' do
    s1 = Schedule.new start_time: Time.new(2015, 7, 8, 16), end_time: Time.new(2015, 7, 8, 17)
    s2 = Schedule.new start_time: Time.new(2015, 7, 6, 16), end_time: Time.new(2015, 7, 6, 16, 30), repeat: Schedule::R_DAY
    expect(ScheduleService.conflicts? s1, s2).to be true
  end
  it '日程【2015-07-08 16:00:00，2015-07-08 17:00:00，每工作日重复，没有截止日期】与日程【2015-07-11 16:00:00，2015-07-11 17:00:00，每周重复，没有截止日期】 不冲突' do
    s1 = Schedule.new start_time: Time.new(2015, 7, 8, 16), end_time: Time.new(2015, 7, 8, 17), repeat: Schedule::R_WDAY
    s2 = Schedule.new start_time: Time.new(2015, 7, 11, 16), end_time: Time.new(2015, 7, 11, 17), repeat: Schedule::R_WEEK
    expect(ScheduleService.conflicts? s1, s2).to be false
  end
  it '日程【2015-05-31 16:00:00，2015-05-31 17:00:00，每月重复，截止2015-07-15】与日程【2015-06-10 16:00:00，2015-06-10 17:00:00，每天重复，没有截止日期】不冲突' do
    s1 = Schedule.new start_time: Time.new(2015, 5, 31, 16), end_time: Time.new(2015, 5, 31, 17), repeat: Schedule::R_MONTH, last_time: Time.new(2015, 7, 15)
    s2 = Schedule.new start_time: Time.new(2015, 6, 10, 16), end_time: Time.new(2015, 6, 10, 17), repeat: Schedule::R_DAY
    expect(ScheduleService.conflicts? s1, s2).to be false
  end
end