#!/usr/bin/env bash
# Updates NixOS from a throwaway worktree of this repo, so the checkout you edit in
# is left alone until the update is done. Started from the "Desktop" half of the
# control centre's update tile in a kitty window (installed as `nixos-update`,
# modules/home/packages.nix, which sets DOT_REPO).
#
#   1. a temporary worktree of main, with the commits git.granstrm.com made since
#      (the nightly CachyOS kernel, flake.nix's `ci`)
#   2. nix flake update of every input but the kernel's, committed there: the kernel
#      is the one git.granstrm.com built, and comes from its binary cache
#   3. nixos-rebuild build, then nvd's list of what changed against the running system
#   4. asks before going on; then pushes the commit, installs it as the next boot
#      entry (nixos-rebuild boot), brings your checkout's main up to date and reboots
#
# If anything fails, the window stays open until you press Enter, and nothing is
# rebooted.
set -E

repo=${DOT_REPO:-$HOME/git/dot}
tmp=""

step() { printf '\n\e[1;34m==> %s\e[0m\n' "$*"; }
note() { printf '\e[1;33m%s\e[0m\n' "$*"; }
wait_close() { read -rp "Press Enter to close. " _ || true; }

die() {
  trap - ERR
  printf '\n\e[1;31m%s\e[0m\n' "$*"
  wait_close
  exit 1
}

cleanup() {
  if [ -n "$tmp" ]; then
    git -C "$repo" worktree remove --force "$tmp" 2>/dev/null || true
    rm -rf "$tmp"
    tmp=""
  fi
}

trap 'die "The update failed (see above). Nothing was rebooted."' ERR
trap cleanup EXIT

step "Fetching $repo"
git -C "$repo" worktree prune
git -C "$repo" fetch origin main
main=$(git -C "$repo" rev-parse main)
# git.granstrm.com's own commits (the kernel) are taken as they are; your own on
# main that it doesn't have yet are pushed with the update.
if git -C "$repo" merge-base --is-ancestor main origin/main; then
  base=$(git -C "$repo" rev-parse origin/main)
elif git -C "$repo" merge-base --is-ancestor origin/main main; then
  base=$main
else
  die "main in $repo and origin/main have diverged; rebase main first."
fi
ahead=$(git -C "$repo" rev-list --count origin/main..main)
dirty=$(git -C "$repo" status --porcelain)

tmp=$(mktemp -d -t dot-update.XXXXXX)
step "Creating a worktree of main in $tmp"
git -C "$repo" worktree add --detach "$tmp" "$base"
cd "$tmp" || die "Could not enter $tmp."

step "Updating flake inputs (all but the kernel's)"
mapfile -t inputs < <(jq -r '.nodes.root.inputs | keys[] | select(. != "nix-cachyos-kernel")' flake.lock)
nix flake update --commit-lock-file "${inputs[@]}"

kernel=$(nix eval --raw "$tmp#nixosConfigurations.desktop.config.boot.kernelPackages.kernel")
if ! nix path-info "$kernel" >/dev/null 2>&1 &&
  ! nix path-info --store https://cache.git.granstrm.com "$kernel" >/dev/null 2>&1; then
  note "The kernel isn't in git.granstrm.com's cache: its CI hasn't built it yet, or failed"
  note "(https://git.granstrm.com/dot). It would compile here, which takes a while."
  read -rp "Compile it here? [y/N] " answer || answer=""
  case $answer in
    [yY]*) ;;
    *)
      echo "Nothing was changed."
      sleep 1
      exit 0
      ;;
  esac
fi

step "Building"
nixos-rebuild build --flake "$tmp"
if [ "$(readlink -f "$tmp/result")" = "$(readlink -f /run/current-system)" ]; then
  printf '\nEverything is already up to date.\n'
  wait_close
  exit 0
fi

step "What changes"
git --no-pager log --format='%s%n%n%b' "$main..HEAD"
nvd diff /run/current-system "$tmp/result"

echo
[ -z "$dirty" ] || note "Uncommitted changes in $repo are not part of this update."
[ "$ahead" -eq 0 ] || note "main has $ahead commit(s) not on git.granstrm.com yet; they are pushed too."
read -rp "Commit, push, install and reboot? [y/N] " answer || answer=""
case $answer in
  [yY]*) ;;
  *)
    echo "Nothing was changed."
    sleep 1
    exit 0
    ;;
esac

step "Pushing"
git push origin HEAD:main

step "Installing as the next boot entry"
nixos-rebuild boot --sudo --flake "$tmp"

step "Updating main in $repo"
commit=$(git rev-parse HEAD)
if [ "$(git -C "$repo" symbolic-ref --quiet --short HEAD)" = main ]; then
  git -C "$repo" merge --ff-only "$commit"
else
  git -C "$repo" update-ref refs/heads/main "$commit" "$main"
fi
cd "$repo"
cleanup

trap 'printf "\nReboot cancelled. The update boots next time.\n"; wait_close; exit 0' INT
step "Rebooting in 5 seconds (Ctrl+C to cancel)"
sleep 5
systemctl reboot