#!/bin/dash

usage()
{
    echo "usage: $0 [--unscan] [btrfs options] <btrfs filesystem> <mountpoint>"
}

get_prop()
{
    local prop="$1"
    btrfs inspect-internal dump-super "$2" | sed -E -ne "s/^${prop}	+//p"
}

device_count()
{
    btrfs inspect-internal dump-super "$1" | grep -c '^dev_item.devid	'
}

competing_devices()
{
    local uuid
    uuid=$1
    btrfs filesystem show "$uuid" | sed -E -ne 's/^    devid.* //p'
}

remove_competition()
{
    competing_devices "$1" | while read dev
    do
        [ "$dev" = "$source" ] || btrfs device scan -u "$dev" || true
    done
}

getend()
{
    eval "echo \${$(($#-$1))}"
}

btrfs_mount()
{
    [ $# -ge 2 ] || { usage; exit 1; }

    destdir=$(getend 0 "$@")
    source=$(getend 1 "$@")

    [ -e "$source" ]
    [ -r "$source" ]
    [ -d "$destdir" ]

    for args
    do
        case "$1" in
                --unscan) unscan=y;;
                *) set -- "$@" "$1";;
        esac
        shift
    done

    if [ "$unscan" ]
    then
        device_count=$(device_count "$source")
        if [ $device_count -eq 1 ]
        then
            source_uuid=$(get_prop fsid "$source")
            remove_competition "$source_uuid"
        fi
    fi

    mount "$@"
}

set -e

btrfs_mount "$@"