#!/bin/bash
set -eE -o pipefail
trap 'echo "$0:$LINENO:error: \"$BASH_COMMAND\" returned $?" >&2' 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="1 5 10 20 30 40 50"
musage="1 5 10 20 30"

e() { echo "cron: $*"; "$@"; }

check-idle() {
    export DISPLAY=:0
    # 3 hours, assume a movie might run that long.
    idle_limit=$((1000 * 60 * 60 * 3))
    idle_time=$idle_limit
    id=999
    while id $((++id)) &>/dev/null; do
        new_idle_time=$(sudo -u \#$id xprintidle 2>/dev/null) ||:
        if [[ $new_idle_time && $new_idle_time -lt $idle_time ]]; then
            idle_time=$new_idle_time
        fi
    done
    if (( idle_time < idle_limit )); then
        idle=false
    else
        idle=true
    fi
}

if [[ $1 == check ]]; then
    check=true
else
    check=false
fi

check-idle

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 ! $idle; then
        btrfs scrub cancel $mnt &>/dev/null ||:
        continue
    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 $dusage; do
            e btrfs balance start -dusage=$usage -musage=$usage $mnt
        done
    else
        e btrfs balance start -dusage=0 $mnt
        for usage in $dusage; do
            e btrfs balance start -dusage=$usage $mnt
        done
        e btrfs balance start -musage=0 $mnt
        for usage in $musage; do
            e btrfs balance start -musage=$usage $mnt
        done
    fi
    # e btrfs filesystem df $mnt
    # e df -H $mnt
    date=$(
        btrfs scrub status $mnt | \
            sed -rn 's/^\s*scrub started at (.*) and finished.*/\1/p'
        )
    if [[ $date ]]; then
        date=$(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 > `date +%s` - 60*60*24*30 )); then
            echo "cron: skiping scrub of $mnt"
            continue
        fi
    fi
    e btrfs scrub start -Bd $mnt
done