#!/bin/bash

source /usr/local/lib/err

usage() {
  cat <<EOF
Usage: switch-mail-host|switch-host2 [OPTIONS] push|pull 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.

-a         Avoid snapshot /a, /q, and similar. If we haven't
           made any changes in the last hour, there is no
           need to snapshot anything but /o, and we will
           just do that once.
-i         Disallow incremental backup.
-o         Only btrbk /o, instead of all filesystems.
--force    Run even though our local state does not say that MAIL_HOST is
           us when pushing or HOST when pulling.
-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
}

script_name="${BASH_SOURCE[0]}"
script_name="${script_name##*/}"

restore_new_btrbk=false
restore_old_btrbk=false
err-cleanup() {
  if $restore_new_btrbk; then
    e WARNING: due to failure, btrbk.timer may need manual restoration:
    e $new_shell systemctl start btrbk.timer btrbk-spread.timer  || (( $? == 5 ))
  fi
  if $restore_old_btrbk; then
    e WARNING: due to failure, btrbk.timer may need manual restoration:
    e $old_shell systemctl start btrbk.timer btrbk-spread.timer  || (( $? == 5 ))
  fi
}

pre="${SSH_CLIENT:+$HOSTNAME} $script_name:"
m() { printf "$pre %s\n"  "$*"; "$@"; }
e() { printf "$pre %s\n"  "$*"; }
err() { echo "$pre ERROR: $*" >&2; }

if [[ $EUID != 0 ]]; then
  err "requires running as root"
  exit 1
fi


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

mail_only=false
host2_only=false
force=false
mp_args="-m /o,/a,/ar,/q,/qr"
temp=$(getopt -l force,help aioh "$@") || usage 1
eval set -- "$temp"
while true; do
  case $1 in
    -a) snapshot_arg=resume ;;
    --force) force=true ;;
    -i) incremental_arg="-i" ;;
    -o)
      mail_only=true ;;
    -h|--help) usage ;;
    --) shift; break ;;
    *) echo "$0: Internal error! unexpected args: $*" ; exit 1 ;;
  esac
  shift
done


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

if [[ ! $HOSTNAME ]]; then
  err "\$HOSTNAME is unset"
  exit 1
fi

source /a/bin/bash_unpublished/source-state

direction=$1
host=$2
case $direction in
  push)
    old_host=$HOSTNAME
    old_hostname=$HOSTNAME
    new_host=$host
    bbk_args="-t $new_host"
    new_shell="ssh -F $HOME/.ssh/confighome root@$new_host"
    if ! new_hostname=$($new_shell hostname); then
      echo "$pre: error: failed ssh. retrying failed $new_shell with -v for more info:"
      $new_shell -v hostname
    fi
    ;;
  pull)
    old_host=$host
    new_host=$HOSTNAME
    new_hostname=$HOSTNAME
    bbk_args="-s $old_host"
    old_shell="ssh -F $HOME/.ssh/confighome root@$old_host"
    old_shelliank="ssh -F $HOME/.ssh/confighome iank@$old_host"
    # tests ssh connection. crafted this to not need to do escape chars
    f=/a/bin/bash_unpublished/source-state
    if ! old_info=($($old_shell "hostname; sed -n s,.*MAIL_HOST=,,p $f; sed -n s,.*HOST2=,,p $f")); then
      echo "$pre: error: failed ssh. retrying failed $old_shell with -v for more info:"
      $old_shell -v hostname
      exit 1
    fi
    old_hostname=${old_info[0]}
    MAIL_HOST=${old_info[1]}
    HOST2=${old_info[2]}
    ;;
  *)
    err invalid first argument
    exit 1
    ;;
esac

case $script_name in
  switch-mail-host)
    if [[ $MAIL_HOST != "$HOST2" ]]; then
      mail_only=true
    fi
    ;;
  switch-host2)
    host2_only=true
    ;;
  *)
    err unexpected script name
    ;;
esac

if $mail_only; then
  mp_args="-m /o"
elif $host2_only; then
  mp_args="-m /a,/ar,/q,/qr"
fi

if ! $force; then
  if $host2_only; then
    if [[ $old_hostname != "$HOST2" ]]; then
      err "\$old_hostname($old_hostname) != \$HOST2($HOST2). Rerun with --force if you really want this."
      exit 1
    fi
  elif [[ $old_hostname != "$MAIL_HOST" ]]; then
    err "\$old_hostname($old_hostname) != \$MAIL_HOST($MAIL_HOST). Rerun with --force if you really want this."
    exit 1
  fi
fi

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


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

if $new_shell systemctl is-active btrbk.timer; then
  m $new_shell systemctl stop btrbk.timer btrbk-spread.timer || (( $? == 5 ))
  restore_new_btrbk=true
fi
if $old_shell systemctl is-active btrbk.timer; then
  m $old_shell systemctl stop btrbk.timer btrbk-spread.timer || (( $? == 5 ))
  restore_old_btrbk=true
fi

btrbk_test="systemctl is-active btrbk.service"
active=true
while $active; do
  active=false
  for shell in "$new_shell" "$old_shell"; do
    e $shell $btrbk_test
    status=$($shell $btrbk_test) ||:
    case $status in
      inactive|failed) : ;;
      *)
        # This covers conditions like "activating", which still return 3 from
        # systemctl is-active.
        active=true
        e "btrbk active on shell:$shell, status:$status, sleeping 8 seconds"
        sleep 8
        break
        ;;
    esac
  done
done

# ensure these are unused before doing anything
e "On $new_host: umounting /m and /o, checking emacs"
{
  cat <<'EOF'
set -eE
if pgrep -G iank -u iank -f 'emacs --daemon' &>/dev/null; then
  bufs="$(sudo -u iank env XDG_RUNTIME_DIR=/run/user/1000 emacsclient --eval "$(cat /a/bin/ds/unsaved-buffers.el)"| sed '/^"nil"$/d;s/^"(/E: /;s/)"$//')"
  if [[ $bufs ]]; then
    echo "error: on $HOSTNAME, unsaved emacs files: $bufs" >&2
    exit 1
  fi
fi
EOF
  if ! $host2_only; then
    cat <<EOF
for dir in m o; do
  if mountpoint -q /\$dir; then
    echo On $new_host: umount /\$dir
    umount /\$dir
  fi
done
EOF
  fi
} | $new_shell bash -s

$old_shell bash -s <<'EOF'
if pgrep -G iank -u iank -f 'emacs --daemon' &>/dev/null; then
  bufs="$(sudo -u iank env XDG_RUNTIME_DIR=/run/user/1000 emacsclient --eval "$(cat /a/bin/ds/unsaved-buffers.el)"| sed '/^"nil"$/d;s/^"(/E: /;s/)"$//')"
  if [[ $bufs ]]; then
    echo "error: on $HOSTNAME, unsaved emacs files: $bufs" >&2
    exit 1
  fi
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.


e Running initial btrbk
m btrbk-run -v $bbk_args $incremental_arg $mp_args $snapshot_arg || ret=$?
if (( ret )); then
  err "failed initial btrbk"
  exit $ret
fi

if ! $mail_only; then
  m $old_shell sed -ri "s/HOST2=.*/HOST2=$new_hostname/" /a/bin/bash_unpublished/source-state
  m $new_shell sed -ri "s/HOST2=.*/HOST2=$new_hostname/" /a/bin/bash_unpublished/source-state
fi

if $host2_only; then
  if [[ $old_hostname != "$MAIL_HOST" && $old_hostname != kd ]]; then
    # most systems dont have btrbk-spread, systemctl exits 5 on unknown unit
    m $old_shell systemctl --now disable btrbk.timer btrbk-spread.timer || (( $? == 5 ))
  fi
  m $new_shell systemctl --now enable btrbk.timer btrbk-spread.timer  || (( $? == 5 ))
  exit 0
fi

m $old_shell /a/exe/primary-setup $new_hostname || ret=$?
if (( ret )); then
  err "failed \$old_shell primary-setup \$new_hostname. fix and rerun $script_name"
  exit $ret
fi

# Try to prevent emacs from saving stale data it has in memory to disk. eg: files, recentf list, etc.
# But if emacs ignores the signal, let it live.
m $new_shell killall -q emacs ||:

e Running main btrbk
m btrbk-run -v --fast $bbk_args $incremental_arg -m /o || ret=$?
if (( ret )); then
  bang="$(printf "$(tput setaf 5)█$(tput sgr0)%.0s" 1 2 3 4 5 6 7)"
  e $bang failed btrbk of /o. restoring old host as primary
  m $old_shell /a/exe/primary-setup localhost
  exit $ret
fi

# new system is usable at this point
printf "$(tput setaf 5 2>/dev/null ||:)█$(tput sgr0 2>/dev/null||:)%.0s" $(eval echo "{1..${COLUMNS:-60}}")
echo

# once I accidentally accepted incoming mail on old host. I used this script to copy over that mail:
#
# die=false; for d in o.leaf.2021-05-29T10:02:08-0400/m/{4e,md,4e2}/{,l/}!(*myarchive)/new; do if $die; then break; fi; find $d -type f -mtime -5 | while read -r f; do dir="${f%new/*}"; dir="btrbk/o.20210530T000011-0400/${dir#*/}"; fname="${f##*/}"; [[ -e $dir/new/$fname || -e $dir/cur/$fname ]] && continue; if ! e cp -a $f /${dir#*/*/}new; then echo failed cp; die=true; break; fi ; done; done

# once I accidentally sent mail from non-main mail host. to copy into the main mail host's sent dir, cd into dir of non-mail mail host Sent/cur, then
#
# shopt -s nullglob; find . -type f -mtime -2 | while read -r f; do a=( /m/4e/Sent/cur/${f%,*}* ); if (( ${#a[@]} )); then e exists $a; else m cp -a $f /m/4e/Sent/cur; fi; done

m $new_shell /a/exe/primary-setup localhost || ret=$?
if (( ret )); then
  err "failed final primary-setup, just fix and rerun: $new_shell /a/exe/primary-setup localhost"
  exit $ret
fi

m exit 0