if [ "$1" = "-v" ]; then
    VERBOSE=true
    shift
else
    VERBOSE=false
fi

if [ "$1" = "-n" ]; then
    DECOMPRESS=false
    shift
else
    DECOMPRESS=true
fi


if [ ! -f "$1" ]; then
    echo "Usage: $0 [-v] [-n] FILE"
    echo "  -v   display raw content and NBT dump"
    echo "  -n   don't decompress"
    exit 1
fi

# pointer data
OFFSET_HEX="0x$(dd bs=1 if="$1" count=3 2>/dev/null | hexdump -e '3/1 "%02x" "\n"')"
OFFSET="$(baseconvert -d $OFFSET_HEX)"
echo "  offset: $OFFSET ($OFFSET_HEX)"
LENGTH_HEX="0x$(dd bs=1 if="$1" count=1 skip=3 2>/dev/null | hexdump -e '1/1 "%02x" "\n"')"
LENGTH="$(baseconvert -d $LENGTH_HEX)"
echo "  length: $LENGTH ($LENGTH_HEX)"

#TODO: last modified

# chunk
DATA="$(dd if="$1" bs=4096 count=$LENGTH skip=$OFFSET 2>/dev/null | hexdump -v -e '16/1 "%02x" "\n"' | tr -d '
')"

# blob header
# bs=2 because each byte is two digits hex
COMPRESSED_LENGTH_HEX="0x$(dd bs=2 count=4 2> /dev/null <<< $DATA)"
COMPRESSED_LENGTH="$(baseconvert -d $COMPRESSED_LENGTH_HEX)"
echo "  compressed length in bytes: $COMPRESSED_LENGTH ($COMPRESSED_LENGTH_HEX)"
FORMAT_HEX="0x$(dd bs=2 skip=4 count=1 2> /dev/null <<< $DATA)"
case $FORMAT_HEX in
"0x01")
    FORMAT="gzip"
    function UNCOMPRESS {
        gzip -dc
    }
    ;;
"0x02")
    FORMAT="zlib"
    function UNCOMPRESS {
        cat > /tmp/chunk_zlib_decompress
        python3 <<< "
import zlib,sys
a = open('/tmp/chunk_zlib_decompress', 'rb')
data = a.read()
a.close()
sys.stdout.buffer.write(zlib.decompress(data))
sys.stdout.buffer.flush()
"
        rm /tmp/chunk_zlib_decompress
    }
    ;;
*)
    FORMAT="unknown"
    function UNCOMPRESS {
        false
    }
    ;;
esac
echo "  format: $FORMAT ($FORMAT_HEX)"


if $DECOMPRESS; then
  dd if="$1" bs=4096 count=$LENGTH skip=$OFFSET 2>/dev/null | dd bs=1 skip=5 count=$(($COMPRESSED_LENGTH-1)) 2>/dev/null | UNCOMPRESS > /tmp/chunk_uncompressed_nbt
else
  dd if="$1" bs=4096 count=$LENGTH skip=$OFFSET 2>/dev/null | dd bs=1 skip=5 count=$(($COMPRESSED_LENGTH-1)) 2>/dev/null > /tmp/chunk_compressed_nbt
fi

if $VERBOSE; then
    echo "Raw chunk data:"
    echo "$DATA"
    echo "NBT dump:"

    #TODO: use pipes instead of a file
    #TODO: fix this up to work with both compressed and uncompressed NBT
    dumpnbt /tmp/chunk_uncompressed_nbt
    rm /tmp/chunk_uncompressed_nbt
fi