Within this kata you should create a class UrlShortener which accepts an url to shorten shorten(String url) and returns an shortened link.

Example from bit.ly:

• Each main-point or sub-point below should create at least one new test or an addition to an existing test
• Follow them line by line
• Please do not forget to refactor!
• Do not implement any other public methods than listed above and create them as you need them!
  • int size()
  • String shorten(String)
  • String unshorten(String)
  • int countUnshortenings(String)
  • String statisctics(String)

• A newly created UrlShortener is empty:
  • The size is empty int size() returns 0
• There is a method which can be called to shorten an url String shorten(String longUrl):
  • The size increases to 1
  • The shortened urls should start with https://sho.rt
  • The shortened url should follow the format https://sho.rt/ID, the format of the id is free to choose. Hint: think about using an ascending number.
• The full url behind a shortened url can be retrieved through String unshorten(String shortUrl)
  • given the shortUrl it will return the long url
• The url shortener should handle multiple urls
• The url shortener should handle 1000 urls
• An url that has the same domain https://sho.rt can not be shortened (again)
• if given an unknown shortUrl to unshorten(String shortUrl) it will throw an RuntimeException
• If the same url should be shortened more than once it will return the same short url. It should fail with RuntimeException.
• The id should be of consist of 3 digits with [0-9]. Example: 001, 345, ...
• The count of unshortenings int unshorteningsFor(String shortUrl) of an url should be counted:
  • When a short url is created the count is 0
  • When a short url is unshortend the count increases by one
  • When the short url given does not exist throw an RuntimeException
• The id should be random and independend of the given url. (number between 0 and 999) Hint: two instances of the UrlShortener should return different ids for same url.
• The method int unshorteningsFor(String shortUrl) should be changed to int unshorteningsFor(String shortOrLongUrl) so that it does not matter if the short url or long url were given. Hint: urls starting with https://sho.rt/ can not be shortened:
  • unknown long urls should throw a RuntimeException
• The method String shorten(String url) should only accept urls starting with https://. If other urls are given, it should throw a RuntimeException
• Create a statistics method String String statisctics(String shortOrLongUrl) which returns a string like: Short URL: https://sho.rt/123, long URL: https://www.google.de, visits: 12:
  • short/long url can be given
  • given an unknown url it throws an RuntimeException