Discussion on: Daily Challenge #89 - Extract domain name from URL

[Amin]

Haskell

Note: Assuming the string will always start with either http:// or https:// or nothing but not supporting any other protocols (by lazyness).

Note2: This won't work for the URIs that have a dot in their name, still working on it.

Note3: Working all good but the end is a mess haha...

import Control.Arrow
import Data.List (isPrefixOf)

removeProtocol :: String -> String
removeProtocol "" = ""
removeProtocol string@(firstCharacter : rest)
    | isPrefixOf https string = removeProtocol (drop (length https) string)
    | isPrefixOf http string = removeProtocol (drop (length http) string)
    | otherwise = firstCharacter : removeProtocol rest
    where
        https = "https://"
        http = "http://"

countDots :: String -> Int
countDots =
    filter (== '.') >>> length

dropUntilWithDot :: String -> String
dropUntilWithDot =
    dropWhile (/= '.') >>> drop 1 

domainName :: String -> String
domainName url 
    | countDots url == 1 = takeWhile (/= '.') urlWithoutProtocol
    | otherwise = takeWhile (/= '.') $ iterate dropUntilWithDot url !! (countDots (takeWhile (/= '/') urlWithoutProtocol) - 1)
    where urlWithoutProtocol = removeProtocol url

main :: IO ()
main = do
    print $ domainName "domain.com"                                 -- domain
    print $ domainName "http://domain.com"                          -- domain
    print $ domainName "https://domain.com"                         -- domain
    print $ domainName "api.domain.com"                             -- domain
    print $ domainName "http://api.domain.com"                      -- domain
    print $ domainName "https://api.domain.com"                     -- domain
    print $ domainName "dev.api.domain.com"                         -- domain
    print $ domainName "http://dev.api.domain.com"                  -- domain
    print $ domainName "https://dev.api.domain.com"                 -- domain
    print $ domainName "https://dev.api.domain.com/something.cool"  -- domain

Try it online

Hosted on Repl.it.

[Gab]

Have you tried it using a .co.uk TLD? :D

[Amin]

No I didn't and I assume it will fail for this particular case. Do you have any way on improving this one?

[Gab]

Unfortunately, I think the only way to improve on it is to use the list of all TLDs to find how much of the end of the domain is TLD.