# `router-install`: write a prebuilt router system to a disk. Nothing is built
# on the box; the system closure travels with the installer.
{
  config,
  lib,
  pkgs,
  ...
}:
let
  cfg = config.router.installer;

  installScript = pkgs.writeShellApplication {
    name = "router-install";
    runtimeInputs = [
      config.system.build.nixos-install
      pkgs.coreutils
      pkgs.dosfstools
      pkgs.e2fsprogs
      pkgs.gptfdisk
      pkgs.util-linux
    ];
    text = ''
      usage() {
        echo "usage: router-install [--yes] [--secrets DIR] <disk>" >&2
        echo "  Wipes <disk> (e.g. /dev/nvme0n1) and installs ${cfg.system}." >&2
        echo "  --secrets DIR  copied to /var/lib/router (PPPoE password, WireGuard keys, ...)" >&2
        exit 2
      }

      yes=0
      secrets=
      disk=
      while [ $# -gt 0 ]; do
        case $1 in
          --yes) yes=1 ;;
          --secrets) shift; [ $# -gt 0 ] || usage; secrets=$1 ;;
          -*) usage ;;
          *) [ -z "$disk" ] || usage; disk=$1 ;;
        esac
        shift
      done
      [ -n "$disk" ] || usage

      [ "$(id -u)" -eq 0 ] || { echo "router-install: must run as root" >&2; exit 1; }
      [ -b "$disk" ] || { echo "router-install: $disk is not a block device" >&2; exit 1; }
      if [ -n "$secrets" ] && [ ! -d "$secrets" ]; then
        echo "router-install: $secrets is not a directory" >&2
        exit 1
      fi
      if lsblk -nr -o MOUNTPOINTS "$disk" | grep -q .; then
        echo "router-install: $disk or one of its partitions is mounted; refusing" >&2
        exit 1
      fi
      [ -d /sys/firmware/efi ] || echo "warning: not booted in UEFI mode; the box itself must boot UEFI" >&2

      echo "About to ERASE $disk:"
      lsblk -o NAME,SIZE,MODEL,FSTYPE,LABEL "$disk"
      if [ "$yes" -ne 1 ]; then
        printf 'Type the device name (%s) to continue: ' "$disk"
        read -r answer
        [ "$answer" = "$disk" ] || { echo "aborted" >&2; exit 1; }
      fi

      part() {
        case $disk in
          *[0-9]) echo "''${disk}p$1" ;;
          *) echo "$disk$1" ;;
        esac
      }

      echo ">> partitioning"
      sgdisk --zap-all "$disk" >/dev/null
      sgdisk -n 1:0:+512M -t 1:ef00 -c 1:boot -n 2:0:0 -t 2:8300 -c 2:nixos "$disk" >/dev/null
      partprobe "$disk" || true
      udevadm settle

      echo ">> formatting"
      mkfs.fat -F 32 -n boot "$(part 1)" >/dev/null
      mkfs.ext4 -q -F -L nixos "$(part 2)"

      echo ">> mounting"
      mkdir -p /mnt
      mount "$(part 2)" /mnt
      mkdir -p /mnt/boot
      mount -o umask=0077 "$(part 1)" /mnt/boot

      if [ -n "$secrets" ]; then
        echo ">> copying secrets"
        install -d -m 0700 /mnt/var/lib/router
        cp -rT "$secrets" /mnt/var/lib/router
        chown -R root:root /mnt/var/lib/router
        chmod -R go-rwx /mnt/var/lib/router
      else
        echo "note: no --secrets given; put the PPPoE password etc. in /var/lib/router later" >&2
      fi

      echo ">> installing ${cfg.system}"
      nixos-install --system ${cfg.system} --root /mnt --no-root-passwd --no-channel-copy

      echo ">> unmounting"
      umount -R /mnt
      sync
      echo "Done. Remove the installer and reboot."
    '';
  };
in
{
  options.router.installer.system = lib.mkOption {
    type = lib.types.package;
    description = "The system (a `system.build.toplevel`) `router-install` writes to disk.";
  };

  config = {
    environment.systemPackages = [ installScript ];
    # The closure must be on the installer itself.
    system.extraDependencies = [ cfg.system ];
  };
}