#!/bin/bash
# Backs up a Subversion repository using incremental dumps relative to the
# previous one, or if there aren't any, a full backup made by 'svnadmin
# hotcopy'.  
# Version 1.0
#
# This script is designed to be run by a daily (or more often) incremental
# backup script.  It doesn't compress anything as the backup software (or tape
# drives) will hopefully do that anyway.
#
# Note that currently, this script doesn't create the full backups.  They
# should be created manually or by a cron job using svn-hot-backup (part of the
# 'subversion-tools' package in Debian) a.k.a. hot-backup.py.  Don't forget to
# set the SVN_HOTBACKUP_BACKUPS_NUMBER environment variable or use the
# --num-backups option, so that old backups are removed.
#
# directory structure is as follows:
#   backupdir/
#     full/
#       repo-6/
#       repo-7/
#       repo-8/
#       repo-8-1/
#       repo-9/
#     incr-10-14.svndump
#     incr-15.svndump
#     incr-16-19.svndump
#     incr-20.svndump
#     old_incrementals/
#       incr-5.svndump
#       incr-6-9.svndump
#
# TO-DO:
#   option to delete old incrementals instead of moving them
#     (or just check for presence of old_incrementals/)
#   warn if there is a dump (e.g. 7-12) that spans a hot backup (e.g. test-11)
#     (can only happen if svn-hot-backup is run simultaneously with this script)

self=${0##*/}
declare -i verbose=1


incr_latest_rev()
{
  local name_sans_ext=${1%.svndump}
  # remove everything up to and including the last hyphen,
  # e.g. incr-10-14 becomes 14
  echo ${name_sans_ext##*-}
}


show_old_incr()
{
  echo $1 is old
}


move_old_incr()
{
  mv `if [ $verbose -ge 1 ] ; then echo -v ; fi` $1 $backupdir/old_incrementals
}


# *** MAINLINE ***
# == Command-line handling ==
if [ $# -lt 2 ]; then
  echo "Usage: $self <repodir> <backupdir>"
  exit 1
fi
repodir=$1
backupdir=$2


# == Sanity checking ==
full_backup_name=`ls -v $backupdir/full | tail -n 1`
if [ -z $full_backup_name ] ; then
  echo "$self: Error: no full backups present" 2>&1
  exit 3
fi

declare -i full_backup_rev=`svnlook youngest $backupdir/full/$full_backup_name`
if [ -z $full_backup_rev ] ; then
  echo "$self: Error: $full_backup_name doesn't appear to be a hotcopy" 2>&1
  exit 4
fi

declare -i youngest_rev=`svnlook youngest $repodir`
if [ -z $youngest_rev ] ; then
  echo "$self: Error: $repodir doesn't appear to be a repository" 2>&1
  exit 5
fi


# == Preparation ==
handle_old_incr=show_old_incr
if [ -d $backupdir/old_incrementals ] ; then
  handle_old_incr=move_old_incr
fi


# == Processing ==
if [ $youngest_rev -gt $full_backup_rev ] ; then
  # incremental backup possibly required
  if [ $verbose -ge 2 ] ; then echo $self: checking existing incrementals ; fi

  # find the most recent incremental
  # (uses GNU ls' version sorting to remove the need for zero padding in names)
  newest=`ls -v $backupdir | grep '^incr-.*\.svndump$' | tail -n 1`
  if [ -z $newest ] ; then
    if [ $verbose -ge 1 ] ; then echo $self: no existing incrementals ; fi
    incr_present=n
    declare -i first_dump_rev=$((full_backup_rev + 1))
    declare -i last_dump_rev=$youngest_rev
    backup=y
  else
    incr_present=y
    declare -i latest_incr_rev=`incr_latest_rev $newest`
    if [ $verbose -ge 2 ] ; then echo $self: latest incremental rev is $latest_incr_rev ; fi
    if [ $youngest_rev -gt $latest_incr_rev ] ; then
      declare -i first_dump_rev=$((latest_incr_rev + 1))
      declare -i last_dump_rev=$youngest_rev
      backup=y
    else
      backup=n
      echo "$self: Notice: nothing to back up (youngest rev is $youngest_rev and newest incremental is $newest)"
    fi
  fi

  # a backup is only needed if there is not already an incremental that
  # covers $youngest_rev (this was established by checking $latest_incr_rev)
  if [ $backup = y ] ; then
    if [ $verbose -ge 2 ] ; then echo $self: revs to dump are $first_dump_rev-$last_dump_rev ; fi

    if [ $first_dump_rev -eq $last_dump_rev ] ; then
      revparam=$first_dump_rev
      dumpfile_name=incr-$first_dump_rev.svndump
    else
      revparam=$first_dump_rev:$last_dump_rev
      dumpfile_name=incr-$first_dump_rev-$last_dump_rev.svndump
    fi

    # svnadmin dump puts its informational messages to stderr to redirect them
    # to stdout
    # (doesn't affect the actual output due to the fact that shell redirects
    # actually copy file descriptors)
    if ! svnadmin dump --incremental -r $revparam $repodir 2>&1 > $backupdir/$dumpfile_name
    then
      echo "$self: Error: \"svnadmin dump\" failed with error code $?" 2>&1
      ## exit 6
    fi
  fi

  # move old incrementals even if there was no backup done
  if [ $incr_present = y ] ; then
    for incr in $backupdir/incr-*.svndump ; do
      declare -i current_incr_rev=`incr_latest_rev ${incr##*/}`
      if [ $current_incr_rev -le $full_backup_rev ] ; then
        $handle_old_incr $incr
      fi
    done
  fi
else
  echo "$self: Notice: nothing to back up (youngest rev is $youngest_rev and full backup is $full_backup_name)"
fi