! Copyright (C) 2017 Jon Harper.
! See http://factorcode.org/license.txt for BSD license.
USING: arrays circular grouping io.encodings.ascii
io.encodings.string kernel math math.parser math.ranges
sequences splitting ;
IN: aoc.2017.10

CONSTANT: input "46,41,212,83,1,255,157,65,139,52,39,254,2,86,0,204"

: rev! ( start length circular -- )
    [ over + [a,b) ] dip
    [ nths reverse ] [ [ set-nth ] curry 2each ] 2bi ;

: round ( skip start lengths circular -- skip' start' )
    [ [ rev! ] [ drop [ 2drop 1 + ] [ + + ] 3bi ] 3bi ] curry each
    ;
: p1 ( str -- n )
    "," split [ string>number ] map
    [ 0 0 ] dip
    256 <iota> >array [
    <circular> round 2drop
    ] keep first2 * ;

: p2 ( str -- hash )
    ascii encode { 17 31 73 47 23 } append
    [ 0 0 ] dip
    256 <iota> >array [
        <circular>
        [ round ] 2curry 64 swap times 2drop
    ] keep 16 group [ unclip [ bitxor ] reduce ] map
    bytes>hex-string ;