#!/usr/bin/python -t

import gzip
import types
import struct
import sys
from dumpMetadata import byteranges

BUF_SIZE = 32768
    

def get_signature_from_file(sigfile):
    f = open(sigfile, "r")
    sig = f.read()
    f.close()
    return sig
    
def make_delta_from_sig(src_delta, sigfile, dst_delta):
    # Open source deltarpm and read/write header
    (range_start, range_end) = byteranges(src_delta)
    
    sfd = open(src_delta, "r")
    dfd = open(dst_delta, "w")
    
    dfd.write(sfd.read(range_end))

    # Switch to compressed mode
    try:
        scfd = gzip.GzipFile("", "rb", 9, sfd)
    except:
        raise zlibError("Data not stored in gzip format")

    if scfd.read(4) != "DLT3":
        raise Exception("Not a deltarpm")
    
    dcfd = gzip.GzipFile("", "wb", 9, dfd)
    dcfd.write("DLT3")
    
    # Get nevr and write it
    len_str     = scfd.read(4)
    (length, )  = struct.unpack('>I', len_str)
    nevr_length = len_str
    nevr        = scfd.read(length)

    dcfd.write("%s%s" % (nevr_length, nevr))
    
    # Read sequence and write it
    len_str = scfd.read(4)
    (length, ) = struct.unpack('>I', len_str)
    dcfd.write(len_str + scfd.read(length))

    # Read md5 and discard, replacing with \x00's.  New versions of deltarpm
    # will see this and use the rpm's md5 checksum rather than this one.
    scfd.read(16)
    dcfd.write("\x00" * 16)
    
    # Read and write target size
    dcfd.write(scfd.read(4))
    
    # Read and write other data
    dcfd.write(scfd.read(12))
    len_str = scfd.read(4)
    (length, ) = struct.unpack('>I', len_str)
    dcfd.write(len_str + scfd.read(length*2*4))
    dcfd.write(scfd.read(4))
    
    # Read and write lead
    dcfd.write(scfd.read(96))
    
    # Write signature from signature file and skip signature in src deltarpm
    signature = get_signature_from_file(sigfile)
    dcfd.write(signature)
    
    scfd.read(8)
    binindex = scfd.read(4)
    (sigindex, ) = struct.unpack('>I', binindex)
    bindata = scfd.read(4)
    (sigdata, ) = struct.unpack('>I', bindata)
    # each index is 4 32bit segments - so each is 16 bytes
    sigindexsize = sigindex * 16
    sigsize = sigdata + sigindexsize
    # we have to round off to the next 8 byte boundary
    disttoboundary = (sigsize % 8)
    if disttoboundary != 0:
        disttoboundary = 8 - disttoboundary
    scfd.read(sigsize + disttoboundary)
    
    data = scfd.read(BUF_SIZE)
    while data != "":
        dcfd.write(data)
        data = scfd.read(BUF_SIZE)
        
def main():
    if len(sys.argv) != 4:
        print "Usage: %s <original deltarpm> <signature> <new deltarpm>" % sys.argv[0]
        sys.exit(1)
        
    make_delta_from_sig(sys.argv[1], sys.argv[2], sys.argv[3])

if __name__ == '__main__':
    main()