require 'rubygems'
require 'open-uri'
require 'icalendar'
require 'date'
require 'net/smtp'
require 'erb'
require 'yaml'

ICAL_URL = "http://www.google.com/calendar/ical...path_to_your_ical_file"
FROM_EMAIL = 'your_email_address@domain.com'
MAIL_TEMPLATE_FILE = 'mail_template.html.erb'
SENT_NOTIFICATIONS_FILE = 'sent_notifications.yml'
GROUP_LIST_FILE = 'group_list.txt'
DAYS_BEFORE_TO_SEND = 2

@logger = Logger.new('notification.log')
@logger.datetime_format = "%Y-%m-%d %H:%M:%S "
@logger.info 'Start'

def init
  begin
  @logger.info '  Reading ical from google'
  myFile = open(ICAL_URL).read

  cals = Icalendar.parse(myFile)
  cal = cals.first

  cal.events.each{ |e|
    time_diff = e.dtstart - DateTime.now
    
    if time_diff < (DAYS_BEFORE_TO_SEND * 24 * 60 * 60) && time_diff > 0
      @logger.info "  Event: #{e.summary} in #{round_f((e.dtstart - DateTime.now).to_f)} days."
      
      if notified?(e.uid)
        @logger.info '    notification previousy sent.'
      
      else
        send_to = group_list
        msg = ERB.new(File.read( MAIL_TEMPLATE_FILE )).result( binding )
        send_email('Notifications', FROM_EMAIL, send_to, e.summary, msg)
        @logger.info "    sending Email {recipients: #{send_to.length}}"

        add_notification_to_list(e.uid)
        @logger.info "    adding to notification list {uid:#{uid}}"
        
      end
    end
    }
  
  rescue
    @logger.error 'ERROR: ' + $!.message + ', ' + $!.backtrace.join("\n")
  end
end


def format_date(dt)
  dt.strftime('%a %b %d, %Y - %I:%M %p')
end

def round_f(num)
  (num * 100).round / 100.0
end


def add_notification_to_list(uid)
  if File.exists?( SENT_NOTIFICATIONS_FILE )
    y_content = YAML.load( File.open( SENT_NOTIFICATIONS_FILE ) )
  end
  
  y_content = [] unless y_content.is_a?( Array )
  
  File.open( SENT_NOTIFICATIONS_FILE, 'w+' ) { |yf|
    y_content.concat [ :date => Time.now, :uid => "#{uid}" ]
    YAML.dump( y_content, yf )
  }
end


def notified?(uid)
  if File.exist?( SENT_NOTIFICATIONS_FILE )
    File.open( SENT_NOTIFICATIONS_FILE ) { |yf|
      y_content = YAML.load( yf )

      if y_content.is_a? Array
        y_content.each{ |e| return true if e[:uid] == uid }
      end
    }
  end

  return false  #not found
end


def group_list
  begin
    IO.read( GROUP_LIST_FILE ).split(/\n/)
  rescue
    return Array['default_email@domain.com']
  end
end

def send_email(from_alias, from, to_array, subject, message)
	msg = <<END_OF_MESSAGE
From: #{from_alias} <#{from}>
To: #{to_array.collect{ |item| '<' + item + '>' }.join(',')}
Subject: [NOTIFICATION]#{subject}
Content-Type: text/html

#{message}
END_OF_MESSAGE

	Net::SMTP.start( 'mail.your.domain.com', 25 ) do |smtp|
		smtp.send_message msg, from, to_array
	end
end


init()
@logger.info 'Stopped'
@logger.close