"""Functions that read and write gzipped files.

The user of the file doesn't have to worry about the compression,

but random access is not allowed."""

# based on Andrew Kuchling's minigzip.py distributed with the zlib module

import struct, sys, time

import zlib

import __builtin__

__all__ = ["GzipFile","open"]

FTEXT, FHCRC, FEXTRA, FNAME, FCOMMENT = 1, 2, 4, 8, 16

READ, WRITE = 1, 2

def U32(i):

    """Return i as an unsigned integer, assuming it fits in 32 bits.

    If it's >= 2GB when viewed as a 32-bit unsigned int, return a long.

    """

    if i < 0:

        i += 1L << 32

    return i

def LOWU32(i):

    """Return the low-order 32 bits of an int, as a non-negative int."""

    return i & 0xFFFFFFFFL

def write32(output, value):

    output.write(struct.pack("<l", value))

def write32u(output, value):

    # The L format writes the bit pattern correctly whether signed

    # or unsigned.

    output.write(struct.pack("<L", value))

def read32(input):

    return struct.unpack("<l", input.read(4))[0]

def open(filename, mode="rb", compresslevel=9):

    """Shorthand for GzipFile(filename, mode, compresslevel).

    The filename argument is required; mode defaults to 'rb'

    and compresslevel defaults to 9.

    """

    return GzipFile(filename, mode, compresslevel)

class GzipFile:

    """The GzipFile class simulates most of the methods of a file object with

    the exception of the readinto() and truncate() methods.

    """

    myfileobj = None

    max_read_chunk = 10 * 1024 * 1024   # 10Mb

    def __init__(self, filename=None, mode=None,

                 compresslevel=9, fileobj=None):

        """Constructor for the GzipFile class.

        At least one of fileobj and filename must be given a

        non-trivial value.

        The new class instance is based on fileobj, which can be a regular

        file, a StringIO object, or any other object which simulates a file.

        It defaults to None, in which case filename is opened to provide

        a file object.

        When fileobj is not None, the filename argument is only used to be

        included in the gzip file header, which may includes the original

        filename of the uncompressed file.  It defaults to the filename of

        fileobj, if discernible; otherwise, it defaults to the empty string,

        and in this case the original filename is not included in the header.

        The mode argument can be any of 'r', 'rb', 'a', 'ab', 'w', or 'wb',

        depending on whether the file will be read or written.  The default

        is the mode of fileobj if discernible; otherwise, the default is 'rb'.

        Be aware that only the 'rb', 'ab', and 'wb' values should be used

        for cross-platform portability.

        The compresslevel argument is an integer from 1 to 9 controlling the

        level of compression; 1 is fastest and produces the least compression,

        and 9 is slowest and produces the most compression.  The default is 9.

        """

        # guarantee the file is opened in binary mode on platforms

        # that care about that sort of thing

        if mode and 'b' not in mode:

            mode += 'b'

        if fileobj is None:

            fileobj = self.myfileobj = __builtin__.open(filename, mode or 'rb')

        if filename is None:

            if hasattr(fileobj, 'name'): filename = fileobj.name

            else: filename = ''

        if mode is None:

            if hasattr(fileobj, 'mode'): mode = fileobj.mode

            else: mode = 'rb'

        if mode[0:1] == 'r':

            self.mode = READ

            # Set flag indicating start of a new member

            self._new_member = True

            self.extrabuf = ""

            self.extrasize = 0

            self.filename = filename

            # Starts small, scales exponentially

            self.min_readsize = 100

        elif mode[0:1] == 'w' or mode[0:1] == 'a':

            self.mode = WRITE

            self._init_write(filename)

            self.compress = zlib.compressobj(compresslevel,

                                             zlib.DEFLATED,

                                             -zlib.MAX_WBITS,

                                             zlib.DEF_MEM_LEVEL,

                                             0)

        else:

            raise IOError, "Mode " + mode + " not supported"

        self.fileobj = fileobj

        self.offset = 0

        if self.mode == WRITE:

            self._write_gzip_header()

    def __repr__(self):

        s = repr(self.fileobj)

        return '<gzip ' + s[1:-1] + ' ' + hex(id(self)) + '>'

    def _init_write(self, filename):

        if filename[-3:] != '.gz':

            filename = filename + '.gz'

        self.filename = filename

        self.crc = zlib.crc32("")

        self.size = 0

        self.writebuf = []

        self.bufsize = 0

    def _write_gzip_header(self):

        self.fileobj.write('\037\213')             # magic header

        self.fileobj.write('\010')                 # compression method

        fname = self.filename[:-3]

        flags = 0

        if fname:

            flags = FNAME

        self.fileobj.write(chr(flags))

        write32u(self.fileobj, long(time.time()))

        self.fileobj.write('\002')

        self.fileobj.write('\377')

        if fname:

            self.fileobj.write(fname + '\000')

    def _init_read(self):

        self.crc = zlib.crc32("")

        self.size = 0

    def _read_gzip_header(self):

        magic = self.fileobj.read(2)

        if magic != '\037\213':

            raise IOError, 'Not a gzipped file'

        method = ord( self.fileobj.read(1) )

        if method != 8:

            raise IOError, 'Unknown compression method'

        flag = ord( self.fileobj.read(1) )

        # modtime = self.fileobj.read(4)

        # extraflag = self.fileobj.read(1)

        # os = self.fileobj.read(1)

        self.fileobj.read(6)

        if flag & FEXTRA:

            # Read & discard the extra field, if present

            xlen = ord(self.fileobj.read(1))

            xlen = xlen + 256*ord(self.fileobj.read(1))

            self.fileobj.read(xlen)

        if flag & FNAME:

            # Read and discard a null-terminated string containing the filename

            while True:

                s = self.fileobj.read(1)

                if not s or s=='\000':

                    break

        if flag & FCOMMENT:

            # Read and discard a null-terminated string containing a comment

            while True:

                s = self.fileobj.read(1)

                if not s or s=='\000':

                    break

        if flag & FHCRC:

            self.fileobj.read(2)     # Read & discard the 16-bit header CRC

    def write(self,data):

        if self.mode != WRITE:

            import errno

            raise IOError(errno.EBADF, "write() on read-only GzipFile object")

        if self.fileobj is None:

            raise ValueError, "write() on closed GzipFile object"

        if len(data) > 0:

            self.size = self.size + len(data)

            self.crc = zlib.crc32(data, self.crc)

            self.fileobj.write( self.compress.compress(data) )

            self.offset += len(data)

    def read(self, size=-1):

        if self.mode != READ:

            import errno

            raise IOError(errno.EBADF, "read() on write-only GzipFile object")

        if self.extrasize <= 0 and self.fileobj is None:

            return ''

        readsize = 1024

        if size < 0:        # get the whole thing

            try:

                while True:

                    self._read(readsize)

                    readsize = min(self.max_read_chunk, readsize * 2)

            except EOFError:

                size = self.extrasize

        else:               # just get some more of it

            try:

                while size > self.extrasize:

                    self._read(readsize)

                    readsize = min(self.max_read_chunk, readsize * 2)

            except EOFError:

                if size > self.extrasize:

                    size = self.extrasize

        chunk = self.extrabuf[:size]

        self.extrabuf = self.extrabuf[size:]

        self.extrasize = self.extrasize - size

        self.offset += size

        return chunk

    def _unread(self, buf):

        self.extrabuf = buf + self.extrabuf

        self.extrasize = len(buf) + self.extrasize

        self.offset -= len(buf)

    def _read(self, size=1024):

        if self.fileobj is None:

            raise EOFError, "Reached EOF"

        if self._new_member:

            # If the _new_member flag is set, we have to

            # jump to the next member, if there is one.

            #

            # First, check if we're at the end of the file;

            # if so, it's time to stop; no more members to read.

            pos = self.fileobj.tell()   # Save current position

            self.fileobj.seek(0, 2)     # Seek to end of file

            if pos == self.fileobj.tell():

                raise EOFError, "Reached EOF"

            else:

                self.fileobj.seek( pos ) # Return to original position

            self._init_read()

            self._read_gzip_header()

            self.decompress = zlib.decompressobj(-zlib.MAX_WBITS)

            self._new_member = False

        # Read a chunk of data from the file

        buf = self.fileobj.read(size)

        # If the EOF has been reached, flush the decompression object

        # and mark this object as finished.

        if buf == "":

            uncompress = self.decompress.flush()

            self._read_eof()

            self._add_read_data( uncompress )

            raise EOFError, 'Reached EOF'

        uncompress = self.decompress.decompress(buf)

        self._add_read_data( uncompress )

        if self.decompress.unused_data != "":

            # Ending case: we've come to the end of a member in the file,

            # so seek back to the start of the unused data, finish up

            # this member, and read a new gzip header.

            # (The number of bytes to seek back is the length of the unused

            # data, minus 8 because _read_eof() will rewind a further 8 bytes)

            self.fileobj.seek( -len(self.decompress.unused_data)+8, 1)

            # Check the CRC and file size, and set the flag so we read

            # a new member on the next call

            self._read_eof()

            self._new_member = True

    def _add_read_data(self, data):

        self.crc = zlib.crc32(data, self.crc)

        self.extrabuf = self.extrabuf + data

        self.extrasize = self.extrasize + len(data)

        self.size = self.size + len(data)

    def _read_eof(self):

        # We've read to the end of the file, so we have to rewind in order

        # to reread the 8 bytes containing the CRC and the file size.

        # We check the that the computed CRC and size of the

        # uncompressed data matches the stored values.  Note that the size

        # stored is the true file size mod 2**32.

        self.fileobj.seek(-8, 1)

        crc32 = read32(self.fileobj)

        isize = U32(read32(self.fileobj))   # may exceed 2GB

        if U32(crc32) != U32(self.crc):

            raise IOError, "CRC check failed"

        elif isize != LOWU32(self.size):

            raise IOError, "Incorrect length of data produced"

    def close(self):

        if self.mode == WRITE:

            self.fileobj.write(self.compress.flush())

            # The native zlib crc is an unsigned 32-bit integer, but

            # the Python wrapper implicitly casts that to a signed C

            # long.  So, on a 32-bit box self.crc may "look negative",

            # while the same crc on a 64-bit box may "look positive".

            # To avoid irksome warnings from the `struct` module, force

            # it to look positive on all boxes.

            write32u(self.fileobj, LOWU32(self.crc))

            # self.size may exceed 2GB, or even 4GB

            write32u(self.fileobj, LOWU32(self.size))

            self.fileobj = None

        elif self.mode == READ:

            self.fileobj = None

        if self.myfileobj:

            self.myfileobj.close()

            self.myfileobj = None

    def __del__(self):

        try:

            if (self.myfileobj is None and

                self.fileobj is None):

                return

        except AttributeError:

            return

        self.close()

    def flush(self,zlib_mode=zlib.Z_SYNC_FLUSH):

        if self.mode == WRITE:

            # Ensure the compressor's buffer is flushed

            self.fileobj.write(self.compress.flush(zlib_mode))

        self.fileobj.flush()

    def fileno(self):

        """Invoke the underlying file object's fileno() method.

        This will raise AttributeError if the underlying file object

        doesn't support fileno().

        """

        return self.fileobj.fileno()

    def isatty(self):

        return False

    def tell(self):

        return self.offset

    def rewind(self):

        '''Return the uncompressed stream file position indicator to the

        beginning of the file'''

        if self.mode != READ:

            raise IOError("Can't rewind in write mode")

        self.fileobj.seek(0)

        self._new_member = True

        self.extrabuf = ""

        self.extrasize = 0

        self.offset = 0

    def seek(self, offset):

        if self.mode == WRITE:

            if offset < self.offset:

                raise IOError('Negative seek in write mode')

            count = offset - self.offset

            for i in range(count // 1024):

                self.write(1024 * '\0')

            self.write((count % 1024) * '\0')

        elif self.mode == READ:

            if offset < self.offset:

                # for negative seek, rewind and do positive seek

                self.rewind()

            count = offset - self.offset

            for i in range(count // 1024):

                self.read(1024)

            self.read(count % 1024)

    def readline(self, size=-1):

        if size < 0:

            size = sys.maxint

            readsize = self.min_readsize

        else:

            readsize = size

        bufs = []

        while size != 0:

            c = self.read(readsize)

            i = c.find('\n')

            # We set i=size to break out of the loop under two

            # conditions: 1) there's no newline, and the chunk is

            # larger than size, or 2) there is a newline, but the

            # resulting line would be longer than 'size'.

            if (size <= i) or (i == -1 and len(c) > size):

                i = size - 1

            if i >= 0 or c == '':

                bufs.append(c[:i + 1])    # Add portion of last chunk

                self._unread(c[i + 1:])   # Push back rest of chunk

                break

            # Append chunk to list, decrease 'size',

            bufs.append(c)

            size = size - len(c)

            readsize = min(size, readsize * 2)

        if readsize > self.min_readsize:

            self.min_readsize = min(readsize, self.min_readsize * 2, 512)

        return ''.join(bufs) # Return resulting line

    def readlines(self, sizehint=0):

        # Negative numbers result in reading all the lines

        if sizehint <= 0:

            sizehint = sys.maxint

        L = []

        while sizehint > 0:

            line = self.readline()

            if line == "":

                break

            L.append(line)

            sizehint = sizehint - len(line)

        return L

    def writelines(self, L):

        for line in L:

            self.write(line)

    def __iter__(self):

        return self

    def next(self):

        line = self.readline()

        if line:

            return line

        else:

            raise StopIteration

def _test():

    # Act like gzip; with -d, act like gunzip.

    # The input file is not deleted, however, nor are any other gzip

    # options or features supported.

    args = sys.argv[1:]

    decompress = args and args[0] == "-d"

    if decompress:

        args = args[1:]

    if not args:

        args = ["-"]

    for arg in args:

        if decompress:

            if arg == "-":

                f = GzipFile(filename="", mode="rb", fileobj=sys.stdin)

                g = sys.stdout

            else:

                if arg[-3:] != ".gz":

                    print "filename doesn't end in .gz:", repr(arg)

                    continue

                f = open(arg, "rb")

                g = __builtin__.open(arg[:-3], "wb")

        else:

            if arg == "-":

                f = sys.stdin

                g = GzipFile(filename="", mode="wb", fileobj=sys.stdout)

            else:

                f = __builtin__.open(arg, "rb")

                g = open(arg + ".gz", "wb")

        while True:

            chunk = f.read(1024)

            if not chunk:

                break

            g.write(chunk)

        if g is not sys.stdout:

            g.close()

        if f is not sys.stdin:

            f.close()

if __name__ == '__main__':

    _test()