#! /usr/bin/env bash

# Upload new or upgrade existing machine subvolume on a Build OS build host.
#
# -k            - keep the old subvolume on the build host
#
# <host>        - build host to upload to (as user 'build')
# <new-subvol>  - machine subvolume to upload
# <old-subvol>  - previous machine subvolume (btrfs send -p)
#
usage="usage: $0 [<options>] <host> <new-subvol> [<old-subvol>]"

machines=/build/machines/default

owd="$(pwd)"
trap "{ cd '$owd'; exit 1; }" ERR
set -o errtrace # Trap in functions.

function info () { echo "$*" 1>&2; }
function error () { info "$*"; exit 1; }

keep=false

while [ "$#" -gt 0 ]; do
  case "$1" in
    -k)
      keep=true
      shift
      ;;
    -*)
      error "unknown option: $1"
      ;;
    *)
      break
      ;;
  esac
done

host="$1"
newsv="${2%/}"
oldsv="${3%/}"

if [ -z "$host" -o -z "$newsv" ]; then
  error "$usage"
fi

host="build@$host"

newsv_name="$(sed -n -re 's%^(.*/)?([^/]+)$%\2%p' <<<"$newsv")"
oldsv_name="$(sed -n -re 's%^(.*/)?([^/]+)$%\2%p' <<<"$oldsv")"

if [ -z "$newsv_name" ]; then
  error "unable to extract subvolume name from '$newsv'"
fi

if [ -n "$oldsv" -a -z "$oldsv_name" ]; then
  error "unable to extract subvolume name from '$oldsv'"
fi

# Get the machine link (<name>-<P>) and name.
#
mlink="$(sed -n -re 's/^(.+-[0-9]+)\.[0-9]+$/\1/p' <<<"$newsv_name")"
mname="$(sed -n -re 's/^(.+)-[0-9]+$/\1/p' <<<"$mlink")"

if [ -z "$mlink" -o -z "$mname" ]; then
  error "unable to extract machine link/name from '$newsv'"
fi

# Subvolume paths on build host.
#
newsv_host="$machines/$mname/$newsv_name"
oldsv_host="$machines/$mname/$oldsv_name"

# Make sure subvolumes are read-only.
#
function check_ro () # <subvol>
{
  local r;
  r="$(btrfs property get -ts "$1" ro)"
  if [ "$r" != "ro=true" ]; then
    info "subvolume '$1' is not read-only; to change, run:"
    info "  btrfs property set -ts $1 ro true"
    exit 1
  fi
}

check_ro "$newsv"
if [ -n "$oldsv" ]; then
  check_ro "$oldsv"
fi

# btrfs send command
#
send=(sudo btrfs send)
if [ -n "$oldsv" ]; then
  send+=(-p "$oldsv")
fi
send+=("$newsv")

set -x

# Make sure the machine directory exists.
#
ssh "$host" mkdir -p "$machines/$mname"

# Send the snapshot over.
#
sudo "${send[@]}" | ssh "$host" sudo btrfs receive "$machines/$mname/"

# Adjust machine ownership.
#
ssh "$host" sudo btrfs property set -ts "$newsv_host" ro false
ssh "$host" sudo chown build:build "$newsv_host"
ssh "$host" sudo chown build:build "$newsv_host/*"
ssh "$host" btrfs property set -ts "$newsv_host" ro true

# Atomically switch the current machine.
#
ssh "$host" "cd $machines/$mname && ln -s $newsv_name new-$mlink"
ssh "$host" "cd $machines/$mname && mv -T new-$mlink $mlink"

# Remove the old machine subvolume.
#
{ set +x; } 2>/dev/null
if [ -z "$oldsv" -o "$keep" = true ]; then
  exit 0
fi

set -x
ssh "$host" btrfs property set -ts "$oldsv_host" ro false
ssh "$host" btrfs subvolume delete "$oldsv_host"