USING: combinators io io.encodings.binary io.files kernel math
ranges sbufs sequences strings ;
IN: ulz

: copy-forward ( sbuf to from -- )
    [a..b) dupd -rot '[ _ nth _ push ] each ;

: cpy-start ( decoder offset -- i ) neg swap length + ;

: (cpy) ( sbuf length offset -- )
    swap [ dup ] [ cpy-start ] [ over + ] tri* copy-forward ;

: lit ( sbuf op -- sbuf )
    1 + over '[ read1 _ push ] times ;

: cpy ( sbuf op -- sbuf )
    dupd 63 192 [ bitand ] bi-curry@ bi 0xc0 = [
        8 shift read1 bitor
    ] when 4 + read1 1 + (cpy) ;

: interpret ( sbuf -- sbuf )
    read1 [ 
        dup 63 bitand 0 = [ lit ] [ cpy ] if interpret
    ] when* ; recursive

: decode ( file -- string )
    binary <file-reader> [ 
        0 <sbuf> interpret 
    ] with-input-stream >string ;