#! /usr/bin/env sh

# This is the remote side of `update_hosts.sh`, it will be copied to the remote host
# and is responsible for performing the update.

set -e

PATH_add() {
    nix_expr="$1"
    what="$(nix build "nixpkgs#$nix_expr.out" --print-out-paths --no-link)"

    printf "Adding '%s' (%s/bin) to PATH..\n" "$nix_expr" "$what"

    PATH="$what/bin:$PATH"
    export PATH
}

branch="$1"
flake_path="${2-""}"

# We don't have access to git by default, so evaluate it here
PATH_add git

# By-default these systems use cppnix, which can't build our config. So let's switch to
# lix.
PATH_add lixPackageSets.latest.lix

# We might or might not have python, and we need it, because we use the unwrapped
# `nixos-update`.
PATH_add python3
PATH_add nixos-rebuild

if [ -z "$flake_path" ]; then
    set -x
    cd /etc/nixos

    sudo git fetch --all --prune
    sudo git switch "$branch"
    sudo git pull --rebase

    flake_path="git+file:/etc/nixos/"
fi

# we use the unwrapped one, to make sure that we are really using lix (otherwise it might
# be wrapped with cppnix).
PYTHONNOUSERSITE='true' sudo --preserve-env=PATH --preserve-env=PYTHONNOUSERSITE ".nixos-rebuild-wrapped" --flake "$flake_path" --no-reexec boot

sudo reboot