--
-- Lets pretty print a Book!
--

-- A couple of type synonyms for readability.
type Title = String
type Authors = [String]

-- Our Book data type.
-- A book consists of an isbn number, a title and a list of authors.
data Book = Book {isbn :: Int,
                  title :: Title, 
                  authors :: Authors} 
                  deriving (Show)
                    
-- A convenience method for empty String.                           
emptyString = ""                                            
                                               
-- This is our book.              
myBook = Book 42 "Secrets of The Universe" ["Author no. 1", "Authour no. 2"]

-- Constructs a string of authors from the Authors list.
-- Delimiter is a /
getAuthorsString :: String -> Authors -> String
getAuthorsString x xs  = if length x == 0 && length xs == 0
                   then emptyString
                   else if length x == 0 && length xs == 1
                   then head xs
                   else if length x == 0 && length xs > 1
                   then getAuthorsString (x ++ head xs) (tail xs)
                   else if length x > 0 && length xs == 1
                   then x ++ " / " ++ head xs
                   else if length x > 0 && length xs > 1
                   then getAuthorsString (x ++ " / " ++  head xs) (tail xs)
                   else x

-- Take a Book and return it as a prettyfied String representation.
prettyPrint :: Book -> String
prettyPrint b = "The book " ++ 
                title b ++ 
                " (isbn " ++ 
                show (isbn b) ++ 
                ") is written by " ++ 
                getAuthorsString (emptyString) (authors b)