#!/usr/bin/env python

# rybackup -- rsync based backup script with rotating backup-snapshots,
#             based on the idea and implementation found on mikerubel.org
# Copyright (C) 2010 Adrian C. <anrxc sysphere.org>

# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.

# crontab
#   0 */4 * * * ~/.backup/rybackup.py hourly  # every 4 hours
#   0 18 * * *  ~/.backup/rybackup.py daily   # once a day at 18h
#   58 3 * * 0  ~/.backup/rybackup.py weekly  # every sunday at 3:58
#   53 3 1 * *  ~/.backup/rybackup.py monthly # first day of every month
#
# crontab eCryptfs (i.e. less frequent)
#   @daily  ID=bak-daily  ~/.backup/rybackup.py hourly # job runs first chance,
#   @weekly ID=bak-weekly ~/.backup/rybackup.py daily  # and retries on EAGAIN


from sys import argv
from shutil import rmtree
from subprocess import call
from os import getuid
from os import path, rename
from os import listdir, makedirs


# Configuration
#
# Local backup mount point and sources to backup
bak = {
    "dst" : "/mnt/nfs/backup",
    "src" : [ "/etc/", "/root/", "/home/user/", "/mnt/storage/Documents/" ],
    "efs" : False,             # eCryptfs support
}

# Remote backup server, or removable storage
rmt = {
    "fst" : "-t nfs",          # file-system type
    "opt" : "-o async,vers=3", # mount options, if any
    "dev" : "192.168.0.10",    # device node or NFS host
    "dst" : "/mnt/backup/clientname" # remote NFS export
}

# Number of backup snapshots to keep
count = {
    "hourly"  : 4,
    "daily"   : 3,
    "weekly"  : 2,
    "monthly" : 2,
}

# Files with a role in the backup procedure
files = {
    "mounts"  : "/proc/mounts",
    "exclude" : "/root/.backup/exclude.lst",
}

# System commands used by this program
bin = {
    "cp"     : "/bin/cp",
    "mount"  : "/bin/mount",
    "umount" : "/bin/umount",
    "grep"   : "/bin/grep",
    "touch"  : "/bin/touch",
    "rsync"  : "/usr/bin/rsync",
}



# Functions
#
# Snapshot rotation
def rotate(arg):
    rotation = {  # Interval relations
        "hourly"  : ["hourly", 1, 2],
        "daily"   : ["hourly", count['hourly'], 1],
        "weekly"  : ["daily",  count['daily'],  1],
        "monthly" : ["weekly", count['weekly'], 1],
    }

    # Delete the oldest snapshot
    if path.isdir("%s/%s.%s" % (bak['dst'], arg, count[arg])):
        rmtree("%s/%s.%s" % (bak['dst'], arg, count[arg]))

    # Shift the middle snapshot(s) back by one
    for i in reversed(range(2, count[arg]+1)):
        if i-1 == 1 and arg == "hourly": break

        if path.isdir("%s/%s.%s" % (bak['dst'], arg, i-1)):
            rename("%s/%s.%s" % (bak['dst'], arg, i-1),
                   "%s/%s.%s" % (bak['dst'], arg, i))

    # Make a hard-link-only copy of the latest snapshot
    if path.isdir("%s/%s.%s" % (bak['dst'], rotation[arg][0], rotation[arg][1])):
        call("%s -al %s/%s.%s %s/%s.%s" % (bin['cp'], bak['dst'], rotation[arg][0],
                                           rotation[arg][1], bak['dst'], arg,
                                           rotation[arg][2]), shell=True)

# Rsync backup synchronization
def sync(arg):
    rsyncopt = (             # Mirroring options:
        "--archive",         #  use the archive mode,
        "--verbose",         #  increase verbosity,
        "--delete",          #  delete extraneous files,
        "--delete-excluded", #  delete excluded files
        "--exclude-from=%s" % files['exclude'],
    )

    for i in bak['src']:
        # Create directories from source names
        if not path.isdir("%s/%s.1/%s" % (bak['dst'], arg, i[1:])):
            makedirs("%s/%s.1/%s" % (bak['dst'], arg, i[1:]))

        # Mirror directories with rsync and unlink files that changed
        call("%s %s %s %s/%s.1/%s" % (bin['rsync'], " ".join(rsyncopt),
                                      i, bak['dst'], arg, i[1:]), shell=True)

    # Make the backup reflect the snapshot time
    if path.isdir("%s/%s.1" % (bak['dst'], arg)):
        call("%s %s/%s.1" % (bin['touch'], bak['dst'], arg), shell=True)


# Managing mount points
def mount(action, arg=""):
    if action == "mount":
        if bak['efs'] and arg == "hourly":
            # Exit with EAGAIN if eCryptfs is mounted
            if call("%s -qs ecryptfs %s"
                    % (bin['grep'], files['mounts']), shell=True) == 0:
                raise SystemExit(11)

        # Include the export for NFS
        if rmt['fst'] == "-t nfs":
            rmt['dev'] = "%s:%s" % (rmt['dev'], rmt['dst'])

        # Attempt to mount the destination
        if call("%s %s %s %s %s" % (bin[action], rmt['fst'], rmt['opt'],
                                    rmt['dev'], bak['dst']), shell=True) != 0:
            raise SystemExit("Error: could not mount destination")
    elif action == "umount":
        # Unmount the snapshot mountpoint (should never be writeable)
        if call("%s %s" % (bin[action], bak['dst']), shell=True) != 0:
            raise SystemExit("Error: could not unmount destination")



# Backup procedure
def main():
    usage = "Usage: %s {hourly|daily|weekly|monthly}" % path.split(argv[0])[1]

    if getuid() != 0:
        raise SystemExit("Error: super user privileges required")
    try:
        if argv[1] in count:
            mount("mount", argv[1])
            rotate(argv[1])
            if argv[1] == "hourly":
                sync(argv[1])
            mount("umount")
        else:
            raise SystemExit(usage)
    except IndexError:
        raise SystemExit(usage)

if __name__ == "__main__":
    main()