# Cache information based on a logfile

import os
from stat import *
from cPickle import Pickler, Unpickler

class Cache:
    def __init__(self, filename, usename, version, location):
        self.cache_name="%s/%s.cache" % (location, usename)
        self.filename=filename
        self.usename=usename
        try:
            in_file=open(self.cache_name, "r")
            p=Unpickler(in_file)
            self.stat_ino=p.load()
	    self.version=p.load()
            seek_pos=p.load()
            self.data=p.load()
            in_file.close()
            if self.stat_ino!=os.stat(filename)[ST_INO] or \
	       self.version!=version:
                raise IOError # The cache doesn't match the logfile
	except (IOError, EOFError):
            self.stat_ino=os.stat(filename)[ST_INO]
	    self.version=version
            seek_pos=0
            self.data=None
        self.file=open(filename, "r")
        self.file.seek(seek_pos, 0)
    def close(self, data):
        out_file=open(self.cache_name, "w")
        p=Pickler(out_file, 1)
        p.dump(self.stat_ino)
	p.dump(self.version)
        p.dump(self.file.tell())
        p.dump(data)
        out_file.close()
        self.file.close()
    def abort(self):
        self.file.close()