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

: copy-forward ( buffer to from -- )
    [a..b) dupd [ swap nth swap push ] 2with each ;

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

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

: lit ( buffer op -- buffer )
    dupd 1 + [ read1 suffix! ] times drop ;

: cpy1 ( buffer op -- buffer )
    dupd 0x3F bitand 4 + read1 1 + cpy ;

: cpy2 ( buffer op -- buffer )
    dupd 8 shift 0x3FFF bitand 4 + read1 1 + cpy ;

: interpret ( buffer -- buffer )
    read1 [ 
        dup 0xc0 bitand {
            { 0x00 [ lit  ] }
            { 0x80 [ cpy1 ] }
            { 0xc0 [ cpy2 ] }
        } case interpret
    ] when* ; recursive 

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