#!/bin/sh

. ./var.sh
. ./btrfs-functions.sh

create_image()
{
    $(ARGS_NE megs filename)
    [ ! -e "$filename" ] || return
    truncate -s "$megs"M "$filename"
}

make_seed_fs()
{
    $(ARGS_NE input_dir img)
    local mountpoint dev seed_subvol root_subvol

    mountpoint=$img.mnt
    mkdir "$mountpoint"                    || die 'mkdir failed'
    dev=$(lodev "$img")                    || die 'lodev failed'
    mkfs.btrfs "$dev"                      || die 'mkfs failed'
    mount "$dev" "$mountpoint"             || die 'mount failed'

    seed_subvol=$mountpoint/SEED
    root_subvol=$mountpoint/ROOT
    btrfs subvolume create "$root_subvol"                     || die
    rsync -aP "$input_dir"/ "$root_subvol"/                   || die 'rsync failed'
    btrfs subvolume snapshot -r "$root_subvol" "$seed_subvol" || die
    btrfs_subvolume_set_default "$root_subvol" || die

    umount "$mountpoint"                   || die 'umount failed'
    rmdir "$mountpoint"
    btrfstune -S 1 "$dev"                  || die 'btrfstune failed'
    unlodev "$dev"
}

btrfs_subvolume_set_default()
{
    $(ARGS_NE path)
    local subvol_id
    subvol_id=$(btrfs_show_subvolume_id "$path")       || return
    btrfs subvolume set-default "$subvol_id" "$path"
}

loop_is_attached()
{
    [ "$(losetup -l  "$1" -O BACK-FILE -n 2>/dev/null)" ]
}

lodev() { lodev_helper false "$@"; }
lodev_readonly() { lodev_helper true "$@"; }

lodev_helper()
{
    $(ARGS_NE readonly img)
    local link b dev opt_ro
    link=$img.b
    if $readonly; then
        opt_ro=-r
    else
        opt_ro=
    fi
    if [ -L "$link" ]; then
        b="$(readlink "$link")"
        loop_is_attached "$b" || losetup $opt_ro "$b" "$img" || return
    else
        dev=$(unused_dev) || return
        losetup $opt_ro "$dev" "$img" || return
        ln -sf "$dev" "$img".b || return
    fi >/dev/null
    printf '%s\n' $link
}

unused_dev()
{
    local do_not_use f d no
    do_not_use=$(for f in *.b; do [ -L "$f" ] || continue; readlink $f; done)
    for n in $(seq 10 20); do
        d=/dev/loop$n
        for no in $do_not_use; do
            [ "$d" != "$no" ] || continue 2
        done
        echo $d
        return
    done
}

unlodev()
{
    $(ARGS_NE link)
    [ -L "$link" ] || return
    losetup -d "$(readlink "$link")" # && rm -f "$link"
}

plant_seed()
{
    $(ARGS_NE seed_img overlay_img mountpoint)
    local overlay_dev seed_dev

    overlay_dev=$(lodev "$overlay_img")             || die 'lodev failed'
    seed_dev=$(lodev_readonly "$seed_img")          || die 'lodev failed'

    mount "$seed_dev" "$mountpoint"                 || die 'mount failed'

    btrfs device add "$overlay_dev" "$mountpoint"   || die 'btrfs-device-add failed'
    mount -o rw,remount "$mountpoint"               || die 'remount failed'
    btrfs device delete "$seed_dev" "$mountpoint"   || die 'btrfs-device-delete failed'

    unlodev "$seed_dev"

    umount "$mountpoint"
    unlodev "$overlay_dev"
}

generate_seed_helper()
{
    $(ARGS_NE seed_layer keep_old_seeds size seed_img snapshot_mountpoint overlay_img_output)
    local mountpoint overlay_dev seed_dev snapshot_default
    mountpoint=${overlay_img_output}.mnt

    mountpoint -q "$snapshot_mountpoint" || die
    [ -d "$mountpoint" ]  || mkdir "$mountpoint" || die

    filemaker "$overlay_img_output" create_image "$size" || die

    overlay_dev=$(lodev "$overlay_img_output") || die
    seed_dev=$(lodev_read_only "$seed_img") || die

    mount -o subvol=/ "$seed_dev" "$mountpoint" || die
    btrfs device add "$overlay_dev" "$mountpoint" || die
    mount -o rw,remount "$mountpoint" || die

    snapshot_default=$(btrfs_show_default_path "$snapshot_mountpoint") || die

    push_simple "$snapshot_mountpoint"/SEED_NEW "$snapshot_mountpoint"/SEED "$snapshot_default" "$mountpoint"

    if $keep_old_seeds; then
        sex mv -T --backup=numbered "$mountpoint"/SEED_NEW "$mountpoint"/SEED || die
    else
        btrfs subvolume delete "$mountpoint"/SEED || die
        sex mv "$mountpoint"/SEED_NEW "$mountpoint"/SEED || die
    fi

    if ! $seed_layer; then
        btrfs device remove "$seed_dev" "$mountpoint" || die
    fi

    umount "$mountpoint" || die
    rmdir "$mountpoint"

    btrfstune -S 1 "$overlay_img_output"                  || die 'btrfstune failed'
}

generate_seed_overlay() # NB. uses non-local variables set in <..>_helper
{
    generate_seed_helper true true "$@"
}

regenerate_toplevel_seed()
{
    generate_seed_helper false true "$@"
}

regenerate_from_master()
{
    regenerate_toplevel_seed 256 seed.img master overlay.img
    remove_image seed.img || die
    mv overlay.img seed.img || die
    mv overlay.img.b seed.img.b || die
}

plant_seed_mount()
{
    plant_seed "$1" "$2" "$3"
    mount "$(lodev "$2")" "$3"
}

plant_seed_mount_rootvol()
{
    plant_seed "$1" "$2" "$3"
    mount -o subvol=/ "$(lodev "$2")" "$3"
}

remove_image()
{
    unlodev "$1.b"
    rm -f "$1" "$1.b"
}

IMAGES='master.img slave.img seed.img overlay.img'
MNTPOINTS='master slave/mnt slave seed.img.mnt overlay.img.mnt'

mounter()
{
    $(ARGS_NE mp)
    shift
    mountpoint -q "$mp" && return
    mkdir "$mp" 2>/dev/null
    "$@" "$mp"
}

filemaker()
{
    $(ARGS_NE f)
    shift
    [ -f "$f" ] && return
    ! [ -e "$f" ] || return
    "$@" "$f"
}

in_dir()
{
    (set -e
     cd "$1"
     shift
     "$@")
}

pull()
{
    $(ARGS_NE mnt src dst)
    local src_subvol
    src_subvol=$(btrfs_show_default_path "$src") || die

    die 'unimplemented'
}

push_slave()
{
    local mnt img img_dev
    mnt=slave/mnt
    img=slave.img
    mkdir "$mnt" 2>/dev/null
    img_dev=$(lodev "$img") || die
    mounter "$mnt" mount -o subvol=/ "$img_dev" || die

    push "$mnt" slave master
    umount "$mnt"
    losetup -D
}

main()
{
    local img

    mkdir inp
    touch inp/file.txt

    for img in $IMAGES; do
        filemaker $img create_image 256 || die            # Note: btrfs kernel task hangs if image is too small!
    done

    make_seed_fs inp seed.img || die

    mounter slave   plant_seed_mount         seed.img slave.img
    mounter master  plant_seed_mount_rootvol seed.img master.img
}

cleanup()
{
    local img m

    for img in $IMAGES; do
        remove_image "$img"
    done
    for m in $MNTPOINTS; do
        umount "$m" 2>/dev/null
        rmdir "$m" 2>/dev/null
    done
    losetup -D 2>/dev/null
    true
}

case "$1" in
    clean|cleanup) cleanup ;;
    testclean) main; cleanup ;;
    cleantest) cleanup; main ;;
    push) push_slave ;;
    regen) regenerate_from_master ;;
    '') main ;;
    *) die "Unknown command: $1" ;;
esac