#!/usr/bin/env bash
# The NixOS Operations Script (NOS) is a wrapper script for nixos-rebuild and Flake-based configurations.
# It handles pulling the latest version of your repository using Git, running system updates, and pushing changes back up.

# Configuration parameters
operation="switch"                              # The nixos-rebuild operation to use
hostname=$(/run/current-system/sw/bin/hostname) # The name of the host to build
flakeDir="${FLAKE_DIR}"                         # Path to the flake file (and optionally the hostname)
update=false                                    # Whether to update and commmit flake.lock
user=$(/run/current-system/sw/bin/whoami)       # Which user account to use for git commands
remainingArgs=""                                # All remaining arguments that haven't yet been processed (will be passed to nixos-rebuild)

function usage() {
	echo "The NixOS Operations Script (NOS) is a nixos-rebuild wrapper for system maintenance."
	echo ""
	echo "Running the script with no parameters performs the following operations:"
	echo "  1. Pull the latest version of your Nix config repository"
	echo "  2. Run 'nixos-rebuild switch'."
	echo ""
	echo "Advanced usage: nixos-operations-script.sh [-h | --hostname hostname-to-build] [-o | --operation operation] [-f | --flake path-to-flake] [extra nixos-rebuild parameters]"
	echo ""
	echo "Options:"
	echo " --help                       Show this help screen."
	echo " -f, --flake [path]           The path to your flake.nix file (defualts to the FLAKE_DIR environment variable)."
	echo " -h, --hostname [hostname]    The name of the host to build (defaults to the current system's hostname)."
	echo " -o, --operation [operation]  The nixos-rebuild operation to perform (defaults to 'switch')."
	echo " -U, --update                 Update and commit the flake.lock file."
	echo " -u, --user [username]        Which user account to run git commands under (defaults to the user running this script)."
	echo ""
	exit 0
}

# Argument processing logic shamelessly stolen from https://stackoverflow.com/questions/192249/how-do-i-parse-command-line-arguments-in-bash
POSITIONAL_ARGS=()
while [[ $# -gt 0 ]]; do
  case "$1" in
	--flake|-f)
		flakeDir="$2"
		shift
		shift
		;;
	--hostname|-h)
	    hostname="$2"
	    shift
	    shift
	    ;;
	--update|--upgrade|-U)
		update=true
		shift
		;;
	--operation|-o)
		operation="$2"
		shift
		shift
		;;
	--user|-u)
		user="$2"
		shift
		shift
		;;
	--help)
		usage
		;;
	*)
		POSITIONAL_ARGS+=("$1") # save positional arg
		shift
		;;
	esac
done
remainingArgs=${POSITIONAL_ARGS[@]}
set -- "${POSITIONAL_ARGS[@]}" # restore positional parameters

if [ -z "${flakeDir}" ]; then
	echo "Flake directory not specified. Use '--flake <path>' or set \$FLAKE_DIR."
	exit 1
fi

cd $flakeDir

echo "Pulling the latest version of the repository..."
/run/wrappers/bin/sudo -u $user git pull

if [ $update = true ]; then
	echo "Updating flake.lock..."
	/run/wrappers/bin/sudo -u $user nix flake update --commit-lock-file && /run/wrappers/bin/sudo -u $user git push
else
	echo "Skipping 'nix flake update'..."
fi

options="--flake ${flakeDir}#${hostname} ${remainingArgs} --use-remote-sudo --log-format multiline-with-logs"

echo "Running this operation: nixos-rebuild ${operation} ${options}"
/run/wrappers/bin/sudo -u $user /run/current-system/sw/bin/nixos-rebuild $operation $options

exit 0