/* 

  Twelve Days of Christmas using DCG in Picat.

  From
  https://www.reddit.com/r/prolog/comments/kip3wg/coding_challenge_27_2_weeks_the_twelve_days_of/
  """
  The task is to output some version of the lyrics of the cumulative song 
  The Twelve Days of Christmas.
  """

  This is a port of Markus Triska's DCG version.

  But it don't work in Picat, or rather: I have not been able to make it work in Picat.

  This model was created by Hakan Kjellerstrand, hakank@gmail.com
  See also my Picat page: http://www.hakank.org/picat/

*/

import v3_utils.

main => go.


go ?=>
  lyrics(Ls,[]),
  println(Ls.flatten),
  
  nl.

go => true.


day(first)    --> "A partridge in a pear tree.".
day(second)   --> "Two turtle doves".
day(third)    --> "Three french hens".
day(fourth)   --> "Four calling birds".
day(fifth)    --> "Five golden rings".
day(sixth)    --> "Six geese a-laying".
day(seventh)  --> "Seven swans a-swimming".
day(eight)    --> "Eight maids a-milking".
day(ninth)    --> "Nine ladies dancing".
day(tenth)    --> "Ten lords a-leaping".
day(eleventh) --> "Eleven pipers piping".
day(twelth)   --> "Twelve drummers drumming".

lyrics -->
        { Days = findall(D, $day(D,_,[])) },       
        stanzas(Days, []).

stanzas([], _) --> [].
stanzas([Day|Days], Prevs) -->
        "On the ", [Day.to_string], " day of Christmas\n", % convert atom day to string
        "My true love gave to me:\n",
        day(Day), 
        previous_days(Prevs),
        "\n\n",
        stanzas(Days, [Day|Prevs]).

previous_days([]) --> [].
previous_days([D|Ds]) --> previous_days_(Ds, D).

previous_days_([], D) --> " and\n", day(D).
previous_days_([D|Ds], Prev) --> "\n",
        day(Prev),
        previous_days_(Ds, D).