#!/usr/bin/env bash
set -euo pipefail
# your hostname (flake target)
hostname="$(hostname)"
old_gen=$(nixos-rebuild list-generations | grep current | awk '{print $1}')
gen=$((old_gen + 1))
timestamp=$(date '+%Y-%m-%d %H:%M:%S')
nix_dir="$HOME/.nix"
logfile="$nix_dir/.nixos-switch-log"

pushd "$nix_dir" >/dev/null

# function to get current nixos generation
get_current_generation() {
    nixos-rebuild list-generations
}

echo "diffs:"
git diff
git status --short
read -rp "commit message: " commit_msg
echo "rebuilding nixos with flake.nix..."
if ! sudo nixos-rebuild switch --flake .#"$hostname" 2>&1 | tee "$logfile"; then
    echo "rebuild failed; exited with no commit"
    exit 1
fi
if sed -n '3p' flake.nix | grep -q '^# generation:'; then
    # replace the comment on line 3
    sed -i "3s|^# generation:.*|# generation: $gen, timestamp: $timestamp|" flake.nix
else
    # insert comment on line 3
    sed -i "3i# generation: $gen, timestamp: $timestamp" flake.nix
fi
echo "committing..."
git add $nix_dir 
git commit -m "$commit_msg"
echo "flake rebuild and commit fin"