#!/bin/bash


[[ $EUID == 0 ]] || exec sudo -E "${BASH_SOURCE[0]}" "$@"

source /a/bin/errhandle/err

# inspired from
# https://github.com/kdave/btrfsmaintenance


# Man page says we could also use a range, i suppose it would be
# logical to use a pattern like 5..10 10..20,
# but I don't know if this would help us at all.
dusage="5 10"
musage="5"

e() {
  echo "cron: $*"
  if ! $dryrun; then
    "$@"
  fi
}

check-idle() {
  type -p xprintidle &>/dev/null || return 0
  export DISPLAY=:0
  # a hours, a movie could run that long.
  idle_limit=$((1000 * 60 * 60 * 2))
  idle_time=$idle_limit
  while read -r user; do
    new_idle_time=$(sudo -u $user xprintidle 2>/dev/null) ||:
    if [[ $new_idle_time && $new_idle_time -lt $idle_time ]]; then
      idle_time=$new_idle_time
    fi
  done < <(users | tr " " "\n" | sort -u)
  if (( idle_time < idle_limit )); then
    idle=false
  else
    idle=true
  fi
}


usage() {
  cat <<EOF
Usage: ${0##*/} [ARGS]
Do btrfs maintence or stop if xprintidle shows a user

force  Run regardless of user idle status
check  Only check if an existing maintence should be cancelled due to
         nonidle user. Also, runs in a loop every 20 seconds for 10
         minutes.

Note: Uses util-linux getopt option parsing: spaces between args and
options, short options can be combined, options before args.
EOF
  exit $1
}


force=false
check=false
dryrun=false
if [[ $1 ]]; then
  case $1 in
    check)
      check=true
      ;;
    force)
      force=true
      ;;
    dryrun)
      dryrun=true
      ;;
    *)
      echo "$0: error: unexpected arg" >&2
      usage 1
      ;;
  esac
fi


main() {
  idle=true
  if ! $force; then
    check-idle
  fi

  tmp=$(mktemp)

  fnd="findmnt --types btrfs --noheading"
  for x in $($fnd --output "SOURCE" --nofsroot | sort -u); do
    mnt=$($fnd --output "TARGET" --first-only --source $x)
    [[ $mnt ]] || continue

    if ! btrfs dev stats -c $mnt >$tmp; then
      if diff -q $mnt/btrfs-dev-stats $tmp; then
        diff -u $mnt/btrfs-dev-stats $tmp | mail -s "$HOSTNAME: error: btrfs dev stats -c $mnt" root@localhost
        cat $tmp >$mnt/btrfs-dev-stats
      fi
    fi

    if ! $idle; then
      if $dryrun; then
        echo "$0: not idle. if this wasnt a dry run, btrfs scrub cancel $mnt"
      else
        btrfs scrub cancel $mnt &>/dev/null ||:
        continue
      fi
    fi
    if $check; then
      continue
    fi

    # for comparing before and after balance.
    # the log is already fairly verbose, so commented.
    # e btrfs filesystem df $mnt
    # e df -H $mnt
    if btrfs filesystem df $mnt | grep -q "Data+Metadata"; then
      for usage in $dusage; do
        e ionice -c 3 btrfs balance start -dusage=$usage -musage=$usage $mnt
      done
    else
      e ionice -c 3 btrfs balance start -dusage=0 $mnt
      for usage in $dusage; do
        e ionice -c 3 btrfs balance start -dusage=$usage $mnt
      done
      e ionice -c 3 btrfs balance start -musage=0 $mnt
      for usage in $musage; do
        e ionice -c 3 btrfs balance start -musage=$usage $mnt
      done
    fi
    date=
    scrub_status=$(btrfs scrub status $mnt)
    if printf "%s\n" "$scrub_status" | grep -i '^status:[[:space:]]*finished$' &>/dev/null; then
      date=$(printf "%s\n" "$scrub_status" | sed -rn 's/^Scrub started:[[:space:]]*(.*)/\1/p')
    fi
    if [[ ! $date ]]; then
      # output from older versions, at least btrfs v4.15.1
      date=$(
        printf "%s\n" "$scrub_status" | \
          sed -rn 's/^\s*scrub started at (.*) and finished.*/\1/p'
          )
    fi
    if [[ $date ]]; then
      if $dryrun; then
        echo "$0: last scrub finish for $mnt: $date"
      fi
      date=$(date --date="$date" +%s)
      # if date is sooner than 90 days ago
      # the wiki recommends 30 days or so, but
      # it makes the comp lag like shit for a day,
      # so I'm going with 90 days.
      if (( date > EPOCHSECONDS - 60*60*24*30 )); then
        if $dryrun; then
          echo "$0: skiping scrub of $mnt, last was $(( (EPOCHSECONDS - date) / 60/60/24 )) days ago, < 30 days"
        fi
        continue
      fi
    fi
    # -c 2 -n 4 is from btrfsmaintenance, does ionice
    e btrfs scrub start -Bd -c 2 -n 4 $mnt
  done
}

loop-main() {
  while true; do
    main
    sleep 60
  done
}

if $check; then
  loop-main
else
  main
fi