USING: arrays circular io.encodings.utf8 io.files kernel math
math.parser math.vectors prettyprint sequences sequences.rotated
;
IN: aoc.20

: I ( -- seq ) "~/factor/aoc/20/test.in" utf8 file-lines [ dec> ] map ;

: remove-elt ( seq     idx -- seq elt ) over length rem cut unclip [ append ] dip ;
: add-elt    ( seq elt idx -- seq     ) 1 - pick length rem 1 + swapd cut rot prefix append ;
: move-elt   ( seq     idx -- seq     ) [ remove-elt dup first ] keep + add-elt ;

: (mix)   ( seq       -- seq ) dup length [ over [ second ] map index move-elt ] each-integer ;
: mix     ( seq times -- seq ) [ [ 2array ] map-index ] dip [ (mix) ] times [ first ] map ;
: decrypt ( seq times -- n   ) mix 0 over index <rotated> <circular> { 1000 2000 3000 } swap nths sum ;

: part1 ( -- n ) I               1  decrypt ;
: part2 ( -- n ) I 811589153 v*n 10 decrypt ;
: solve ( --   ) part1 . part2 . ;