#!/usr/bin/env bash

# a small useful script for quickly accessing different nix and nixos commands
# through a single nice interface.
# run `nx help` for command list!

set -euo pipefail

config="/etc/configuration"
current_hostname="$(hostname)"

run() {
	echo -ne "* \033[1;33m"
	echo "$@"
	echo -ne "\033[0m"
	$@
}

error() {
	echo -ne "\033[1;31m"
	echo -n "error: "
	echo -ne "\033[0m"
	echo "$@"
}

rebuild() {
	local target="$1"
	local tool="$2"

	run nixos-rebuild --sudo --builders "\"\"" --flake "$config#$target" "$tool"
}

flag() {
	local f="$1"

	case "$f" in
	-h | --here)
		config="."
		;;
	*)
		error "unknown flag '$f'"
		exit 1
		;;
	esac
}

apply_command() {
	rebuild "$current_hostname" "switch"
}

apply_boot_command() {
	rebuild "$current_hostname" "boot"
}

test_command() {
	local given_host="${1:-}"

	local target

	if [ -z "$given_host" ]; then
		target="$current_hostname"
	else
		target="$given_host"
	fi

	run nix build "$config#nixosConfigurations.$target.config.system.build.toplevel" --dry-run
}

repl_command() {
	local given_host="${1:-}"

	local target

	if [ -z "$given_host" ]; then
		target="$current_hostname"
	else
		target="$given_host"
	fi

	rebuild "$target" "repl"
}

garbage_command() {
	local given_period="${1:-}"

	if [ -z "$given_period" ]; then
		run sudo nix-collect-garbage -d
	else
		run sudo nix-collect-garbage --delete-older-than "$given_period"
	fi
}

help_command() {
	echo "usage: nx <command> [args] [flags]"
	echo ""
	echo "commands:"
	echo "  apply         apply nixos configuration and switch to it"
	echo "  apply-boot    apply nixos configuration on next boot"
	echo "  test [host]   try building configuration of a host (default: current host)"
	echo "  repl [host]   start repl with host configuration (default: current host)"
	echo "  garbage [age] collect garbage (default: all)"
	echo ""
	echo "flags:"
	echo "  --here, -h    evaluate configuration in current directory"
}

args=()
for arg in "$@"; do
	if [[ "$arg" == -* ]]; then
		flag "$arg"
	else
		args+=("$arg")
	fi
done

command="${args[0]:-}"

if [ -z "$command" ]; then
	error "no command given!"
	echo ""
	help_command
	exit 1
fi

case "$command" in
help)
	help_command
	;;
apply)
	apply_command
	;;
apply-boot)
	apply_boot_command
	;;
test)
	test_command "${args[1]:-}"
	;;
repl)
	repl_command "${args[1]:-}"
	;;
garbage)
	garbage_command "${args[1]:-}"
	;;
*)
	error "unknown command '$command'"
	exit 1
	;;
esac