#!/bin/bash

source /usr/local/lib/err

usage() {
  cat <<EOF
Usage: ${0##*/} OLD_HOST NEW_HOST

Turn off mail receiving on OLD_HOST, run btrbk to move mail to NEW_HOST,
turn on mail receiving on NEW_HOST.  Assumes we want to move all
filesystems unless passing -o.

-o         Only btrbk /o, instead of all filesystems.
-h|--help  Print help and exit.

I used to adjust home network dns so NEW_HOST resolves locally if it is
on the local network, but its simpler just not to and just rely
on the internet. Email can wait.

Note: Uses GNU getopt options parsing style
EOF
  exit $1
}

restore_new_btrbk=false
restore_old_btrbk=false
cleanup() {
  if $restore_new_btrbk; then
    m $new_shell sudo systemctl start btrbk.timer
  fi
  if $restore_old_btrbk; then
    m $old_shell sudo systemctl start btrbk.timer
  fi
}
_errcatch_cleanup=cleanup # used by sourced err

pre="${0##*/}:"
m() { printf "$pre %s\n"  "$*"; "$@"; }
e() { printf "$pre %s\n"  "$*"; }

##### begin command line parsing ########

temp=$(getopt -l help owh "$@") || usage 1
mp_args="-m /o,/q,/a"
eval set -- "$temp"
while true; do
  case $1 in
    -o) mp_args="-m /o"; shift ;;
    -h|--help) usage ;;
    --) shift; break ;;
    *) echo "$0: Internal error! unexpected args: $*" ; exit 1 ;;
  esac
done


(( $# == 2 )) || usage 1

old_host=$1
new_host=$2
source /a/bin/bash_unpublished/source-state

if [[ $old_host != "$MAIL_HOST" ]]; then
  read -r -p "warning: \$old_host != \$MAIL_HOST: $old_host != $MAIL_HOST, proceed? y/N "
  if [[ $REPLY != [yY] ]]; then
    exit 1
  fi
fi

if [[ $new_host == "$HOSTNAME" ]]; then
  localhost_new=true
  new_shell=
else
  localhost_new=false
  new_shell="ssh $new_host"
fi

old_shell="ssh $old_host"
if [[ $old_host == "$HOSTNAME" ]]; then
  old_shell=
fi

if [[ ! $new_host || ! $old_host ]]; then
  echo "$0: bad args. see script"
  exit 1
fi

e $new_shell hostname
new_hostname=$($new_shell hostname)

########### end initial processing, begin actually modifying things ##########

if $new_shell systemctl is-active btrbk.timer; then
  m $new_shell sudo systemctl stop btrbk.timer
  restore_new_btrbk=true
fi
if $old_shell systemctl is-active btrbk.timer; then
  m $old_shell sudo systemctl stop btrbk.timer
  restore_old_btrbk=true
fi

btrbk_test="systemctl is-active btrbk.service"
while true; do
  for shell in "$new_shell" "$old_shell"; do
    e $shell $btrbk_test
    status=$($shell $btrbk_test) ||:
    case $status in
      inactive|failed) : ;;
      *)
        e "btrbk active on shell:$shell, status:$status, sleeping 8 seconds"
        sleep 8
        continue
        ;;
    esac
  done
  break
done

# ensure these are unused before doing anything

e "umounting /m and /o via $new_shell"
$new_shell bash -xs <<'EOF'
set -eE
if mountpoint -q /m; then sudo umount /m; fi
if mountpoint -q /o; then sudo umount /o; fi
EOF

# previously, I was checking to see if the new mail host
# is on my home network, then changing my home dns
# to resolve on the local network, so that I didnt
# have to send traffic out to the internet or rely
# on that. However, that breaks for a laptop that roams.
# So, we could have a cronjob that updates that dns,
# however, another solution is to just use ipv6,
# and I prefer that.
#
# TODO: enable ipv6 for email. exim config setting disables it.
# need to add vpn support. need to add firewall / routing.
# I think exim will try ipv6 first, so no need to disable
# ipv6 i think.

m $old_shell /a/exe/primary-setup $new_hostname

if $localhost_new; then
  m btrbk-run -v -s $old_host $mp_args
else
  m btrbk-run -v -t $new_host $mp_args
fi

m $new_shell /a/exe/primary-setup $new_hostname