# This file is part of Rubber and thus covered by the GPL

# (c) Emmanuel Beffara, 2002--2006

"""

This module contains utility functions and classes used by the main system and

by the modules for various tasks.

"""

try:

    import hashlib

except ImportError:

    # Fallback for python 2.4:

    import md5 as hashlib

import os

from msg import _, msg

def md5_file(fname):

    """

    Compute the MD5 sum of a given file.

    """

    m = hashlib.md5()

    file = open(fname)

    for line in file.readlines():

        m.update(line)

    file.close()

    return m.digest()

class Watcher:

    """

    Watch for any changes of the files to survey, by checking the file MD5 sums.

    """

    def __init__(self):

        self.files = {}

    def watch(self, file):

        if os.path.exists(file):

            self.files[file] = md5_file(file)

        else:

            self.files[file] = None

    def update(self):

        """

        Update the MD5 sums of all files watched, and return the name of one

        of the files that changed, or None of they didn't change.

        """

        changed = []

        for file in self.files.keys():

            if os.path.exists(file):

                new = md5_file(file)

                if self.files[file] != new:

                    msg.debug(_("%s MD5 checksum changed") % \

                              os.path.basename(file))

                    changed.append(file)

                self.files[file] = new

        return changed