{ config, lib, pkgs, ... }:

with lib;

let

  inherit (pkgs) stdenv writeText procps;

  udev = config.systemd.package;

  cfg = config.services.udev;

  extraUdevRules = pkgs.writeTextFile {
    name = "extra-udev-rules";
    text = cfg.extraRules;
    destination = "/etc/udev/rules.d/10-local.rules";
  };

  nixosRules = ''
    # Miscellaneous devices.
    KERNEL=="kvm",                  MODE="0666"
    KERNEL=="kqemu",                MODE="0666"

    # Needed for gpm.
    SUBSYSTEM=="input", KERNEL=="mice", TAG+="systemd"
  '';

  # Perform substitutions in all udev rules files.
  udevRules = stdenv.mkDerivation {
    name = "udev-rules";

    preferLocalBuild = true;
    allowSubstitutes = false;

    buildCommand = ''
      mkdir -p $out
      shopt -s nullglob
      set +o pipefail

      # Set a reasonable $PATH for programs called by udev rules.
      echo 'ENV{PATH}="${udevPath}/bin:${udevPath}/sbin"' > $out/00-path.rules

      # Add the udev rules from other packages.
      for i in ${toString cfg.packages}; do
        echo "Adding rules for package $i"
        for j in $i/{etc,lib}/udev/rules.d/*; do
          echo "Copying $j to $out/$(basename $j)"
          cat $j > $out/$(basename $j)
        done
      done

      # Fix some paths in the standard udev rules.  Hacky.
      for i in $out/*.rules; do
        substituteInPlace $i \
          --replace \"/sbin/modprobe \"${config.system.sbin.modprobe}/sbin/modprobe \
          --replace \"/sbin/mdadm \"${pkgs.mdadm}/sbin/mdadm \
          --replace \"/sbin/blkid \"${pkgs.utillinux}/sbin/blkid \
          --replace \"/bin/mount \"${pkgs.utillinux}/bin/mount
      done

      echo -n "Checking that all programs called by relative paths in udev rules exist in ${udev}/lib/udev... "
      import_progs=$(grep 'IMPORT{program}="[^/$]' $out/* |
        sed -e 's/.*IMPORT{program}="\([^ "]*\)[ "].*/\1/' | uniq)
      run_progs=$(grep -v '^[[:space:]]*#' $out/* | grep 'RUN+="[^/$]' |
        sed -e 's/.*RUN+="\([^ "]*\)[ "].*/\1/' | uniq)
      for i in $import_progs $run_progs; do
        if [[ ! -x ${udev}/lib/udev/$i && ! $i =~ socket:.* ]]; then
          echo "FAIL"
          echo "$i is called in udev rules but not installed by udev"
          exit 1
        fi
      done
      echo "OK"

      echo -n "Checking that all programs called by absolute paths in udev rules exist... "
      import_progs=$(grep 'IMPORT{program}="\/' $out/* |
        sed -e 's/.*IMPORT{program}="\([^ "]*\)[ "].*/\1/' | uniq)
      run_progs=$(grep -v '^[[:space:]]*#' $out/* | grep 'RUN+="/' |
        sed -e 's/.*RUN+="\([^ "]*\)[ "].*/\1/' | uniq)
      for i in $import_progs $run_progs; do
        if [[ ! -x $i ]]; then
          echo "FAIL"
          echo "$i is called in udev rules but not installed by udev"
          exit 1
        fi
      done
      echo "OK"

      echo "Consider fixing the following udev rules:"
      for i in ${toString cfg.packages}; do
        grep -l '\(RUN+\|IMPORT{program}\)="\(/usr\)\?/s\?bin' $i/*/udev/rules.d/* || true
      done

      ${optionalString config.networking.usePredictableInterfaceNames ''
        cp ${./80-net-setup-link.rules} $out/80-net-setup-link.rules
      ''}

      # If auto-configuration is disabled, then remove
      # udev's 80-drivers.rules file, which contains rules for
      # automatically calling modprobe.
      ${optionalString (!config.boot.hardwareScan) ''
        ln -s /dev/null $out/80-drivers.rules
      ''}
    ''; # */
  };

  # Udev has a 512-character limit for ENV{PATH}, so create a symlink
  # tree to work around this.
  udevPath = pkgs.buildEnv {
    name = "udev-path";
    paths = cfg.path;
    pathsToLink = [ "/bin" "/sbin" ];
    ignoreCollisions = true;
  };

in

{

  ###### interface

  options = {

    boot.hardwareScan = mkOption {
      type = types.bool;
      default = true;
      description = ''
        Whether to try to load kernel modules for all detected hardware.
        Usually this does a good job of providing you with the modules
        you need, but sometimes it can crash the system or cause other
        nasty effects.
      '';
    };

    services.udev = {

      packages = mkOption {
        type = types.listOf types.path;
        default = [];
        description = ''
          List of packages containing <command>udev</command> rules.
          All files found in
          <filename><replaceable>pkg</replaceable>/etc/udev/rules.d</filename> and
          <filename><replaceable>pkg</replaceable>/lib/udev/rules.d</filename>
          will be included.
        '';
      };

      path = mkOption {
        type = types.listOf types.path;
        default = [];
        description = ''
          Packages added to the <envar>PATH</envar> environment variable when
          executing programs from Udev rules.
        '';
      };

      extraRules = mkOption {
        default = "";
        example = ''
          KERNEL=="eth*", ATTR{address}=="00:1D:60:B9:6D:4F", NAME="my_fast_network_card"
        '';
        type = types.lines;
        description = ''
          Additional <command>udev</command> rules. They'll be written
          into file <filename>10-local.rules</filename>. Thus they are
          read before all other rules.
        '';
      };

    };

    hardware.firmware = mkOption {
      type = types.listOf types.package;
      default = [];
      description = ''
        List of packages containing firmware files.  Such files
        will be loaded automatically if the kernel asks for them
        (i.e., when it has detected specific hardware that requires
        firmware to function).  If multiple packages contain firmware
        files with the same name, the first package in the list takes
        precedence.  Note that you must rebuild your system if you add
        files to any of these directories.
      '';
      apply = list: pkgs.buildEnv {
        name = "firmware";
        paths = list;
        pathsToLink = [ "/lib/firmware" ];
        ignoreCollisions = true;
      };
    };

    networking.usePredictableInterfaceNames = mkOption {
      default = true;
      type = types.bool;
      description = ''
        Whether to assign <link
        xlink:href='http://www.freedesktop.org/wiki/Software/systemd/PredictableNetworkInterfaceNames'>predictable
        names to network interfaces</link>.  If enabled, interfaces
        are assigned names that contain topology information
        (e.g. <literal>wlp3s0</literal>) and thus should be stable
        across reboots.  If disabled, names depend on the order in
        which interfaces are discovered by the kernel, which may
        change randomly across reboots; for instance, you may find
        <literal>eth0</literal> and <literal>eth1</literal> flipping
        unpredictably.
      '';
    };

  };


  ###### implementation

  config = mkIf (!config.boot.isContainer) {

    services.udev.extraRules = nixosRules;

    services.udev.packages = [ extraUdevRules ];

    services.udev.path = [ pkgs.coreutils pkgs.gnused pkgs.gnugrep pkgs.utillinux udev ];

    environment.etc =
      [ { source = udevRules;
          target = "udev/rules.d";
        }
      ];

    system.requiredKernelConfig = with config.lib.kernelConfig; [
      (isEnabled "UNIX")
      (isYes "INOTIFY_USER")
      (isYes "NET")
    ];

    boot.extraModprobeConfig = "options firmware_class path=${config.hardware.firmware}/lib/firmware";

    system.activationScripts.udevd =
      ''
        # The deprecated hotplug uevent helper is not used anymore
        if [ -e /proc/sys/kernel/hotplug ]; then
          echo "" > /proc/sys/kernel/hotplug
        fi

        # Regenerate the hardware database /var/lib/udev/hwdb.bin
        # whenever systemd changes.
        if [ ! -e /var/lib/udev/prev-systemd -o "$(readlink /var/lib/udev/prev-systemd)" != ${config.systemd.package} ]; then
          echo "regenerating udev hardware database..."
          ${config.systemd.package}/bin/udevadm hwdb --update && ln -sfn ${config.systemd.package} /var/lib/udev/prev-systemd
        fi

        # Allow the kernel to find our firmware.
        if [ -e /sys/module/firmware_class/parameters/path ]; then
          echo -n "${config.hardware.firmware}/lib/firmware" > /sys/module/firmware_class/parameters/path
        fi
      '';

    systemd.services.systemd-udevd =
      { environment.MODULE_DIR = "/run/booted-system/kernel-modules/lib/modules";
      };

  };
}