#!/bin/bash
# I, Ian Kelling, follow the GNU license recommendations at
# https://www.gnu.org/licenses/license-recommendations.en.html. They
# recommend that small programs, < 300 lines, be licensed under the
# Apache License 2.0. This file contains or is part of one or more small
# programs. If a small program grows beyond 300 lines, I plan to switch
# its license to GPL.

# Copyright 2024 Ian Kelling

# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at

#     http://www.apache.org/licenses/LICENSE-2.0

# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.


set -e; . /usr/local/lib/bash-bear; set +e

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 0
}

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
  fi
  if $restore_old_btrbk; then
    e WARNING: due to failure, btrbk.timer may need manual restoration:
    e $old_shell systemctl start btrbk.timer
  fi
}

pre="$script_name:"
m() { printf "$pre %s\n"  "$*"; "$@"; }
e() { printf "$pre %s\n"  "$*"; }
err() { echo "$pre ERROR: $*" >&2; }
die() { printf "%s\n" "$*" >&2; echo "exiting with status 1" >&2; exit 1; }

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


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

mail_only=false
host2_only=false
force=false
force_arg=
pull_reexec=false
mp_args="-m /o,/a,/q,/qd,/qr"
check_installed=false
orig_args=("$@")
if ! temp=$(getopt -l check-installed,force,pull-reexec,help afioh "$@"); then
  err "args invalid. args=$*"
fi
eval set -- "$temp"
while true; do
  case $1 in
    -a) snapshot_arg=resume ;;
    --force|-f)
      force=true
      force_arg=-f
      ;;
    --check-installed)
      check_installed=true
      ;;
    -i) incremental_arg="-i" ;;
    # internal option for rerunning under newer old_host when doing pull
    --pull-reexec) pull_reexec=true;;
    -o)
      mail_only=true ;;
    -h|--help) usage ;;
    --) shift; break ;;
    *) echo "$0: Internal error! unexpected args: $*" ; exit 1 ;;
  esac
  shift
done


if (( $# != 2 )) && ! $check_installed; then
  err expected 2 args, got $#
fi

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

uninstalled-file-die() {
  die "on host=$HOSTNAME, uninstalled file $1. run install-my-scripts or rerun with -f"
}


source /a/bin/bash_unpublished/source-state

direction=$1
host=$2

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,/q,/qd,/qr"
fi


if ! $force && { $check_installed || [[ $direction == push ]]; } ; then
  install_bin_files=(
    mount-latest-subvol
    check-subvol-stale
    btrbk-run
    switch-mail-host
  )
  for f in ${install_bin_files[@]}; do
    if ! diff -q /a/bin/ds/$f /usr/local/bin/$f; then
      uninstalled-file-die $f
    fi
  done
  if ! diff -q /a/bin/bash-bear-trap/bash-bear /usr/local/lib/bash-bear; then
    uninstalled-file-die err
  fi
  if $check_installed; then
    exit 0
  fi
fi


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"
    # tests ssh connection. crafted this to not need to do escape chars

    if ! $mail_only && ! $pull_reexec ; then
      if ! $force; then
        if ! $old_shell switch-mail-host --check-installed; then
          die "failed: $old_shell switch-mail-host --check-installed"
        fi
      fi
      tmpd=$(mktemp -d)
      files=(
        /usr/local/{bin/{unsaved-buffers{,.el},switch-mail-host},lib/bash-bear}
      )
      m scp -F $HOME/.ssh/confighome \
        ${files[@]/#/root@$old_host:} $tmpd
      diff=false
      for f in ${files[@]}; do
        if ! diff -q $tmpd/${f##*/} $f; then
          m install -T $tmpd/${f##*/} $f
          diff=true
        fi
      done
      if $diff; then
        e "found different version on old_host=$old_host, reexecing"
        m /usr/local/bin/switch-mail-host --pull-reexec "${orig_args[@]}"
        exit 0
      fi
      rm -r -- $tmpd
    fi

    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:"
      $old_shell -v hostname
      exit 1
    fi
    read -d '' -r old_hostname MAIL_HOST HOST2 <<<"$old_info" || (( $? == 1 ))

    ;;
  *)
    err invalid first argument
    exit 1
    ;;
esac


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

if ! $host2_only; then
  # ensure these are unused before doing anything
  e "On $new_host: umounting /m and /o, checking emacs"
  {
    cat /usr/local/bin/unsaved-buffers
    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
fi

if ! $mail_only; then
  cat /usr/local/bin/unsaved-buffers - <<'EOF' |  $old_shell bash -s

# 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.
pkill -xf 'emacs( --daemon| -f znc-all)' ||:

if [[ -e /p/profanity-here ]]; then
  systemctl disable --now profanity
fi
EOF
fi

# 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 $force_arg $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
    m $old_shell systemctl --now disable btrbk.timer
  fi
  m $new_shell systemctl --now enable btrbk.timer
  if [[ -e /p/profanity-here ]]; then
    m $new_shell systemctl --now enable profanity
  fi
  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


e Running main btrbk
m btrbk-run -v --fast $bbk_args $force_arg $incremental_arg -m /o || ret=$?
if (( ret )); then
  bang="███████"
  e $bang failed btrbk of /o. restoring old host as primary
  if ! m $old_shell /a/exe/primary-setup localhost; then
    die "due to failed btrbk of /o, we tried to restore old host as primary, but then we failed at that too. To resolve: Fix & rerun switch-mail-host, or fix and rerun primary-setup localhost on old shell so you have a working mail server and then rerun switch-mail-host."
  fi
  e finished restoring old host as primary, now exiting $ret due to earlier failed btrbk of /o.
  exit $ret
fi

# new system is usable at this point
blocks=██████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████
printf "%s\n" "${blocks:0:${COLUMNS:-100}}"

# 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

if ! $mail_only && [[ -e /p/profanity-here ]]; then
  m $new_shell systemctl --now enable profanity || ret=$?
  if (( ret )); then
    err "failed final systemctl --now enable profanity, just fix and rerun"
    exit $ret
  fi
fi

m exit 0