#! @shell@ -e

# Allow the location of NixOS sources and the system configuration
# file to be overridden.

: ${mountPoint=/mnt}
: ${NIXOS_PATH=/etc/nixos/nixos}
: ${NIXOS_CONFIG=/etc/nixos/configuration.nix}
: ${NIXPKGS=/etc/nixos/nixpkgs}
export NIXOS_PATH

usage () {
  echo 1>&2 "
Usage: $0 [--install] [-v] [-d] [-l] OPTION_NAME
       $0 [--install]

This program is used to explore NixOS options by looking at their values or
by looking at their description.  It is helpful for understanding the how
your configuration is working.

Options:

  -i | --install        Use the configuration on
                        ${mountPoint:+$mountPoint/}$NIXOS_CONFIG instead of
                        the current system configuration.  Generate a
                        template configuration if no option name is
                        specified.
  -v | --value          Display the current value, based on your
                        configuration.
  -d | --default        Display the default value, the example and the
                        description.
  -l | --lookup         Display where the option is defined and where it
                        is declared.
  --help                Show this message.

Environment variables affecting $0:

  \$mountPoint          Path to the target file system.
  \$NIXOS_PATH          Path where the NixOS repository is located.
  \$NIXOS_CONFIG        Path to your configuration file.
  \$NIXPKGS             Path to Nix packages.

"

  exit 1;
}

#####################
# Process Arguments #
#####################

desc=false
defs=false
value=false
install=false
verbose=false

option=""

argfun=""
for arg; do
  if test -z "$argfun"; then
    case $arg in
      -*)
        longarg=""
        sarg="$arg"
        while test "$sarg" != "-"; do
          case $sarg in
            --*) longarg=$arg;;
            -d*) longarg="$longarg --description";;
            -v*) longarg="$longarg --value";;
            -l*) longarg="$longarg --lookup";;
            -i*) longarg="$longarg --install";;
            -*) usage;;
          esac
          sarg="-${sarg#??}"
        done
        ;;
      *) longarg=$arg;;
    esac
    for larg in $longarg; do
      case $larg in
        --description) desc=true;;
        --value) value=true;;
        --lookup) defs=true;;
        --install) install=true;;
        --verbose) verbose=true;;
        --help) usage;;
        -*) usage;;
        *) if test -z "$option"; then
             option="$larg"
           else
             usage
           fi;;
      esac
    done
  else
    case $argfun in
      set_*)
        var=$(echo $argfun | sed 's,^set_,,')
        eval $var=$arg
        ;;
    esac
    argfun=""
  fi
done

# --install cannot be used with -d -v -l without option name.
if $value || $desc || $defs && $install && test -z "$option"; then
  usage
fi

generate=false
if ! $defs && ! $desc && ! $value && $install && test -z "$option"; then
  generate=true
fi

if ! $defs && ! $desc; then
  value=true
fi

if $verbose; then
  set -x
else
  set +x
fi

#############################
# Process the configuration #
#############################

evalAttr(){
  local prefix=$1
  local suffix=$2
  local strict=$3
  echo "(import $NIXOS_PATH {}).$prefix${option:+.$option}${suffix:+.$suffix}" |
    nix-instantiate - --eval-only ${strict:+--strict}
}

evalOpt(){
  evalAttr "eval.options" "$@"
}

evalCfg(){
  evalAttr "config" "$@"
}

findSources(){
  local suffix=$1
  echo "builtins.map (f: f.source) (import $NIXOS_PATH {}).eval.options${option:+.$option}.$suffix" |
    nix-instantiate - --eval-only --strict
}

if $install; then
  if test -e "$mountPoint$NIXOS_PATH"; then
    export NIXOS_PATH="$mountPoint$NIXOS_PATH"
  fi
  if test -e "$mountPoint$NIXPKGS"; then
    export NIXPKGS="$mountPoint$NIXPKGS"
  fi
  export NIXOS_CONFIG="$mountPoint$NIXOS_CONFIG"
fi

if $generate; then
  mkdir -p $(dirname "$NIXOS_CONFIG")

  # Scan the hardware and add the result to /etc/nixos/hardware-scan.nix.
  hardware_config="${NIXOS_CONFIG%/configuration.nix}/hardware-configuration.nix"
  if test -e "$hardware_config"; then
    echo "A hardware configuration file exists, generation skipped."
  else
    echo "Scan your hardware to generate a hardware configuration file."
    nixos-hardware-scan > "$hardware_config"
  fi

  if test -e "$NIXOS_CONFIG"; then
    echo 1>&2 "error: Cannot generate a template configuration because a configuration file exists."
    exit 1
  fi

  echo "Generate a template configuration that you should edit."

  # Generate a template configuration file where the user has to
  # fill the gaps.
  echo > "$NIXOS_CONFIG" \
'# Edit this configuration file which defines what would be installed on the
# system.  To Help while choosing option value, you can watch at the manual
# page of configuration.nix or at the last chapter of the manual available
# on the virtual console 8 (Alt+F8).

{config, pkgs, ...}:

{
  require = [
    # Include the configuration for part of your system which have been
    # detected automatically.  In addition, it includes the same
    # configuration as the installation device that you used.
    ./hardware-configuration.nix
  ];

  boot.initrd.kernelModules = [
    # Specify all kernel modules that are necessary for mounting the root
    # file system.
    #
    # "ext4" "ata_piix"
  ];

  boot.loader.grub = {
    # Use grub 2 as boot loader.
    enable = true;
    version = 2;

    # Define on which hard drive you want to install Grub.
    # device = "/dev/sda";
  };

  networking = {
    # hostName = "nixos"; # Define your hostname.
    interfaceMonitor.enable = true; # Watch for plugged cable.
    enableWLAN = true;  # Enables Wireless.
  };

  # Add file system entries for each partition that you want to see mounted
  # at boot time.  You can add filesystems which are not mounted at boot by
  # adding the noauto option.
  fileSystems = [
    # Mount the root file system
    #
    # { mountPoint = "/";
    #   device = "/dev/sda2";
    # }

    # Copy & Paste & Uncomment & Modify to add any other file system.
    #
    # { mountPoint = "/data"; # where you want to mount the device
    #   device = "/dev/sdb"; # the device or the label of the device
    #   # label = "data";
    #   fsType = "ext3";      # the type of the partition.
    #   options = "data=journal";
    # }
  ];

  swapDevices = [
    # List swap partitions that are mounted at boot time.
    #
    # { device = "/dev/sda1"; }
  ];

  # Select internationalisation properties.
  # i18n = {
  #   consoleFont = "lat9w-16";
  #   consoleKeyMap = "us";
  #   defaultLocale = "en_US.UTF-8";
  # };

  # List services that you want to enable:

  # Add an OpenSSH daemon.
  # services.openssh.enable = true;

  # Add CUPS to print documents.
  # services.printing.enable = true;

  # Add XServer (default if you have used a graphical iso)
  # service.xserver = {
  #   enable = true;
  #   layout = "us";
  #   xkbOptions = "eurosign:e";
  # };

  # Add the NixOS Manual on virtual console 8
  services.nixosManual.showManual = true;
}
'

  exit 0
fi;

if test "$(evalOpt "_type" 2> /dev/null)" = '"option"'; then
  $value && evalCfg;

  if $desc; then
    $value && echo;

    if default=$(evalOpt "default" - 2> /dev/null); then
      echo "Default: $default"
    else
      echo "Default: <None>"
    fi
    if example=$(evalOpt "example" - 2> /dev/null); then
      echo "Example: $example"
    fi
    echo "Description:"
    eval printf $(evalOpt "description")
  fi

  if $defs; then
    $desc || $value && echo;

    echo "Declared by:"
    for f in $(findSources "declarations"); do
      test $f = '[' -o $f = ']' && continue;
      echo "  $f"
    done
    echo ""
    echo "Defined by:"
    for f in $(findSources "definitions"); do
      test $f = '[' -o $f = ']' && continue;
      echo "  $f"
    done
    echo ""
  fi

else
  # echo 1>&2 "Warning: This value is not an option."

  result=$(evalCfg)
  if names=$(echo "builtins.attrNames $result" | sed 's,<CODE>,"<CODE>",g' | nix-instantiate - --eval-only --strict 2> /dev/null); then
    echo 1>&2 "This attribute set contains:" 
    for attr in $names; do
      test $attr = '[' -o $attr = ']' && continue;
      eval echo $attr # escape extra double-quotes in the attribute name.
    done
  else
    echo $result
  fi
fi