Scrapes module info from CORS and converts it into iCal. Not working right

cors_scraper.rb

#!/usr/bin/ruby
#

require 'mechanize'
require 'icalendar'
include Icalendar

def create_datetime(day_str,time_str)
	if(time_str.length<4)
		time_str = "0"+time_str
	end
	return DateTime.strptime("#{day_str} #{time_str}","%A %H%M")
end
def create_exam(cal,module_name,date_str)
	exam_date = Date.strptime(date_str,"%d-%m-%Y")

	event = Event.new
	event.start = exam_date
#	event.end = exam_date.next_day
	event.summary = "#{module_name} Exam"
	cal.add_event(event)
	return exam_date
end
def create_event(cal,module_name,slot_name,arr,end_date)
	day = arr[0]
	start_time = arr[1]
	end_time = arr[2]
	venue = arr[3]
	repeats = arr[4]
			
	event = Event.new
	event.start=create_datetime(day,start_time)
	event.end=create_datetime(day,end_time)
	event.location = venue
	event.recurrence_rules = ["FREQ=WEEKLY;INTERVAL=1"]
	event.tzid="Asia/Singapore"

	if(end_date) 
		event.recurrence_rules[0] = "#{event.recurrence_rules[0]};UNTIL=#{end_date.to_ical}"
	end
	event.summary="#{module_name} #{slot_name}"
	cal.add_event(event)
end





exam_xpath = "//div[@id='wrapper']/table[1]/tr[2]/td[1]/table[1]/tr[3]/td[1]/table[1]/tr[6]/td[2]"
lecture_xpath = "//div[@id='wrapper']/table[1]/tr[2]/td[1]/table[1]/tr[3]/td[1]/table[3]/tr[2]/td[1]/div[1]/table[1]/tr[1]/td[1]"
tutorial_xpath = "//div[@id='wrapper']/table[1]/tr[2]/td[1]/table[1]/tr[3]/td[1]/table[4]/tr[3]/td[1]/div[1]/table/tr[1]/td[1]"

agent = Mechanize.new

cal = Calendar.new
cal.timezone do
	timezone_id "Asia/Singapore"
	standard do
		timezone_offset_from "+0800"
		timezone_offset_to	"+0800"
		timezone_name "SGT"
		dtstart "19700101T000000"
	end
end


ARGV.each do|module_name|
url = "https://aces01.nus.edu.sg/cors/jsp/report/ModuleDetailedInfo.jsp?acad_y=2010/2011&sem_c=2&mod_c=#{module_name}"
puts "#Downloading..."
page = agent.get(url)
puts "#DONE"

exam_element = page.search(exam_xpath)

if(exam_element[0])
	exam_str = exam_element[0].to_str
	exam_date = nil
	if(/\s*(\d{2}-\d{2}-\d{4})\s+(AM|PM)/.match(exam_str))
		exam_date = create_exam(cal,module_name,$1)
		end_date = exam_date.prev_day(exam_date.wday).prev_day(7)
	end
end


lecture_elements = page.search(lecture_xpath)
lecture_elements.each do |e|
	schedule = e.to_str
	if (/(.*)[\n\r](.*)/.match(schedule)) 
		slot_name = $1
		schedule_string = $2
		matches = schedule_string.scan(/\s*(\w+) From (\d+) hrs to (\d+) hrs in (\w+), Week\(s\): ([\s\w\d]*)\./)
		matches.each do |arr|
				create_event(cal,module_name,slot_name,arr,end_date)
		end
	end
	
end

tutorial_elements = page.search(tutorial_xpath)
tutorial_elements.each do |e|
	schedule = e.to_str
	if (/(.*)[\n\r](.*)/.match(schedule)) 
#		puts $1
		slot_name = $1
		schedule_string = $2
		matches = schedule_string.scan(/(\w+) From (\d+) hrs to (\d+) hrs in (.*), Week\(s\): ([\s\w\d]*)\./)
		arr = matches[0];
		if(arr)
			create_event(cal,module_name,slot_name,arr,end_date)
		end	
	end
end
end
puts cal.to_ical