#!/usr/bin/env bash
# Update the running Pi over SSH without reflashing.
#
#   ./deploy-rpi.sh                 build rpi4.scm, copy, switch, reboot
#   ./deploy-rpi.sh --no-reboot     ... activate only (services restart on reboot)
#   ./deploy-rpi.sh switch N        make existing generation N the default
#                                   (roll back), activate, reboot
#   ./deploy-rpi.sh list            show the Pi's system generations
#
# The system is cross-built here (--target, like the image) and sent with
# `guix copy'; extlinux.conf is generated here too (scripts/extlinux-conf.scm),
# because `guix system reconfigure/switch-generation' on the Pi would need
# native aarch64 builds (PITFALLS #28).  Old generations stay in the U-Boot
# menu: pick one from the console if a new one doesn't boot.
#
# Needs: ~/.ssh/config entry for $PI, /etc/guix/signing-key.* on this host,
# and that key in the Pi's guix-service-type authorized-keys (rpi4.scm).
set -euo pipefail
cd "$(dirname "$0")"
export PATH=$HOME/.local/bin:$PATH
export GUIX_PACKAGE_PATH="$PWD/packages:$HOME/channels/nonguix"
PI=${PI:-pirouter}
PROFILES=/var/guix/profiles

# -n: never read stdin (it would swallow `while read` loop input).
pi() { ssh -n -o BatchMode=yes "$PI" "$@"; }

# "N /gnu/store/…-system" for each generation, ascending.
generations() {
  pi "cd $PROFILES && for l in system-*-link; do n=\${l#system-}; echo \"\${n%-link} \$(readlink \$l)\"; done" |
    sort -n
}

current() { pi "readlink -f $PROFILES/system"; }

# Write extlinux.conf with generation $1 (store path) as default and every
# other generation as fallback entries, newest first; install it on the Pi.
install_bootcfg() {
  local default=$1 tmp params=() n path conf
  tmp=$(mktemp -d)
  pi "cat $default/parameters" > "$tmp/default"
  while read -r n path; do
    [ "$path" = "$default" ] && continue
    pi "cat $path/parameters" > "$tmp/$n"
    params=("$path" "$tmp/$n" "${params[@]}")     # newest first
  done < <(generations)
  conf=$(guix repl -L packages -L "$HOME/channels/nonguix" -- \
           scripts/extlinux-conf.scm rpi4.scm \
           "$default" "$tmp/default" "${params[@]}" | tail -1)
  rm -rf "$tmp"
  [ -f "$conf" ] || { echo "extlinux.conf generation failed" >&2; exit 1; }
  scp -q -o BatchMode=yes "$conf" "$PI:/boot/extlinux/extlinux.conf.new"
  pi "mv /boot/extlinux/extlinux.conf.new /boot/extlinux/extlinux.conf && sync"
  echo "extlinux.conf: default $default, $(( ${#params[@]} / 2 )) fallback(s)"
}

# Point the system profile at generation $1, activate it.
switch_to() {
  local n=$1 path
  path=$(pi "readlink $PROFILES/system-$n-link")
  install_bootcfg "$path"
  pi "ln -sfn system-$n-link $PROFILES/system.new && mv -T $PROFILES/system.new $PROFILES/system"
  echo "activating generation $n ($path)"
  # activate.scm picks the system from GUIX_NEW_SYSTEM (set by reconfigure
  # and at boot); without it, it re-activates /run/current-system.
  pi "GUIX_NEW_SYSTEM=$path $path/activate" ||
    echo "warning: activation reported errors" >&2
}

reboot_pi() {
  echo "rebooting $PI"
  pi "sync; (sleep 1; reboot) >/dev/null 2>&1 &" || true
}

case "${1:-deploy}" in
  list)
    cur=$(current)
    generations | while read -r n path; do
      echo "$n $path$( [ "$path" = "$cur" ] && echo '  (current)')"
    done ;;
  switch)
    n=${2:?usage: deploy-rpi.sh switch N}
    switch_to "$n"
    [ "${3:-}" = --no-reboot ] || reboot_pi ;;
  deploy|--no-reboot)
    sys=$(guix system build --target=aarch64-linux-gnu rpi4.scm | tail -1)
    echo "built $sys"
    if [ "$sys" = "$(current)" ]; then echo "already running $sys"; exit 0; fi
    guix copy --to="$PI" "$sys"
    last=$(generations | tail -1 | cut -d' ' -f1)
    n=$((last + 1))
    pi "ln -sfn $sys $PROFILES/system-$n-link"
    echo "registered generation $n"
    switch_to "$n"
    [ "${1:-deploy}" = --no-reboot ] || reboot_pi ;;
  *)
    sed -n '2,10p' "$0"; exit 1 ;;
esac