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

with lib;

let
  inherit (utils) systemdUtils escapeSystemdPath;
  inherit (systemdUtils.lib)
    generateUnits
    pathToUnit
    serviceToUnit
    sliceToUnit
    socketToUnit
    targetToUnit
    timerToUnit
    mountToUnit
    automountToUnit;


  cfg = config.boot.initrd.systemd;

  upstreamUnits = [
    "basic.target"
    "ctrl-alt-del.target"
    "debug-shell.service"
    "emergency.service"
    "emergency.target"
    "final.target"
    "halt.target"
    "initrd-cleanup.service"
    "initrd-fs.target"
    "initrd-parse-etc.service"
    "initrd-root-device.target"
    "initrd-root-fs.target"
    "initrd-switch-root.service"
    "initrd-switch-root.target"
    "initrd.target"
    "kexec.target"
    "kmod-static-nodes.service"
    "local-fs-pre.target"
    "local-fs.target"
    "multi-user.target"
    "paths.target"
    "poweroff.target"
    "reboot.target"
    "rescue.service"
    "rescue.target"
    "rpcbind.target"
    "shutdown.target"
    "sigpwr.target"
    "slices.target"
    "sockets.target"
    "swap.target"
    "sysinit.target"
    "sys-kernel-config.mount"
    "syslog.socket"
    "systemd-ask-password-console.path"
    "systemd-ask-password-console.service"
    "systemd-fsck@.service"
    "systemd-halt.service"
    "systemd-hibernate-resume.service"
    "systemd-journald-audit.socket"
    "systemd-journald-dev-log.socket"
    "systemd-journald.service"
    "systemd-journald.socket"
    "systemd-kexec.service"
    "systemd-modules-load.service"
    "systemd-poweroff.service"
    "systemd-reboot.service"
    "systemd-sysctl.service"
    "systemd-tmpfiles-setup-dev.service"
    "systemd-tmpfiles-setup.service"
    "timers.target"
    "umount.target"
    "systemd-bsod.service"
  ] ++ cfg.additionalUpstreamUnits;

  upstreamWants = [
    "sysinit.target.wants"
  ];

  enabledUpstreamUnits = filter (n: ! elem n cfg.suppressedUnits) upstreamUnits;
  enabledUnits = filterAttrs (n: v: ! elem n cfg.suppressedUnits) cfg.units;
  jobScripts = concatLists (mapAttrsToList (_: unit: unit.jobScripts or []) (filterAttrs (_: v: v.enable) cfg.services));

  stage1Units = generateUnits {
    type = "initrd";
    units = enabledUnits;
    upstreamUnits = enabledUpstreamUnits;
    inherit upstreamWants;
    inherit (cfg) packages package;
  };

  kernel-name = config.boot.kernelPackages.kernel.name or "kernel";
  # Determine the set of modules that we need to mount the root FS.
  modulesClosure = pkgs.makeModulesClosure {
    rootModules = config.boot.initrd.availableKernelModules ++ config.boot.initrd.kernelModules;
    kernel = config.system.modulesTree;
    firmware = config.hardware.firmware;
    allowMissing = false;
  };

  initrdBinEnv = pkgs.buildEnv {
    name = "initrd-bin-env";
    paths = map getBin cfg.initrdBin;
    pathsToLink = ["/bin" "/sbin"];
    postBuild = concatStringsSep "\n" (mapAttrsToList (n: v: "ln -sf '${v}' $out/bin/'${n}'") cfg.extraBin);
  };

  initialRamdisk = pkgs.makeInitrdNG {
    name = "initrd-${kernel-name}";
    inherit (config.boot.initrd) compressor compressorArgs prepend;
    inherit (cfg) strip;

    contents = map (path: { object = path; symlink = ""; }) (subtractLists cfg.suppressedStorePaths cfg.storePaths)
      ++ mapAttrsToList (_: v: { object = v.source; symlink = v.target; }) (filterAttrs (_: v: v.enable) cfg.contents);
  };

in {
  options.boot.initrd.systemd = {
    enable = mkEnableOption "systemd in initrd" // {
      description = ''
        Whether to enable systemd in initrd. The unit options such as
        {option}`boot.initrd.systemd.services` are the same as their
        stage 2 counterparts such as {option}`systemd.services`,
        except that `restartTriggers` and `reloadTriggers` are not
        supported.
      '';
    };

    package = lib.mkOption {
      type = lib.types.package;
      default = config.systemd.package;
      defaultText = lib.literalExpression "config.systemd.package";
      description = ''
        The systemd package to use.
      '';
    };

    extraConfig = mkOption {
      default = "";
      type = types.lines;
      example = "DefaultLimitCORE=infinity";
      description = ''
        Extra config options for systemd. See systemd-system.conf(5) man page
        for available options.
      '';
    };

    managerEnvironment = mkOption {
      type = with types; attrsOf (nullOr (oneOf [ str path package ]));
      default = {};
      example = { SYSTEMD_LOG_LEVEL = "debug"; };
      description = ''
        Environment variables of PID 1. These variables are
        *not* passed to started units.
      '';
    };

    contents = mkOption {
      description = "Set of files that have to be linked into the initrd";
      example = literalExpression ''
        {
          "/etc/hostname".text = "mymachine";
        }
      '';
      default = {};
      type = utils.systemdUtils.types.initrdContents;
    };

    storePaths = mkOption {
      description = ''
        Store paths to copy into the initrd as well.
      '';
      type = with types; listOf (oneOf [ singleLineStr package ]);
      default = [];
    };

    strip = mkOption {
      description = ''
        Whether to completely strip executables and libraries copied to the initramfs.

        Setting this to false may save on the order of 30MiB on the
        machine building the system (by avoiding a binutils
        reference), at the cost of ~1MiB of initramfs size. This puts
        this option firmly in the territory of micro-optimisation.
      '';
      type = types.bool;
      default = true;
    };

    extraBin = mkOption {
      description = ''
        Tools to add to /bin
      '';
      example = literalExpression ''
        {
          umount = ''${pkgs.util-linux}/bin/umount;
        }
      '';
      type = types.attrsOf types.path;
      default = {};
    };

    suppressedStorePaths = mkOption {
      description = ''
        Store paths specified in the storePaths option that
        should not be copied.
      '';
      type = types.listOf types.singleLineStr;
      default = [];
    };

    root = lib.mkOption {
      type = lib.types.enum [ "fstab" "gpt-auto" ];
      default = "fstab";
      example = "gpt-auto";
      description = ''
        Controls how systemd will interpret the root FS in initrd. See
        {manpage}`kernel-command-line(7)`. NixOS currently does not
        allow specifying the root file system itself this
        way. Instead, the `fstab` value is used in order to interpret
        the root file system specified with the `fileSystems` option.
      '';
    };

    emergencyAccess = mkOption {
      type = with types; oneOf [ bool (nullOr (passwdEntry str)) ];
      description = ''
        Set to true for unauthenticated emergency access, and false for
        no emergency access.

        Can also be set to a hashed super user password to allow
        authenticated access to the emergency mode.
      '';
      default = false;
    };

    initrdBin = mkOption {
      type = types.listOf types.package;
      default = [];
      description = ''
        Packages to include in /bin for the stage 1 emergency shell.
      '';
    };

    additionalUpstreamUnits = mkOption {
      default = [ ];
      type = types.listOf types.str;
      example = [ "debug-shell.service" "systemd-quotacheck.service" ];
      description = ''
        Additional units shipped with systemd that shall be enabled.
      '';
    };

    suppressedUnits = mkOption {
      default = [ ];
      type = types.listOf types.str;
      example = [ "systemd-backlight@.service" ];
      description = ''
        A list of units to skip when generating system systemd configuration directory. This has
        priority over upstream units, {option}`boot.initrd.systemd.units`, and
        {option}`boot.initrd.systemd.additionalUpstreamUnits`. The main purpose of this is to
        prevent a upstream systemd unit from being added to the initrd with any modifications made to it
        by other NixOS modules.
      '';
    };

    units = mkOption {
      description = "Definition of systemd units.";
      default = {};
      visible = "shallow";
      type = systemdUtils.types.units;
    };

    packages = mkOption {
      default = [];
      type = types.listOf types.package;
      example = literalExpression "[ pkgs.systemd-cryptsetup-generator ]";
      description = "Packages providing systemd units and hooks.";
    };

    targets = mkOption {
      default = {};
      visible = "shallow";
      type = systemdUtils.types.initrdTargets;
      description = "Definition of systemd target units.";
    };

    services = mkOption {
      default = {};
      type = systemdUtils.types.initrdServices;
      visible = "shallow";
      description = "Definition of systemd service units.";
    };

    sockets = mkOption {
      default = {};
      type = systemdUtils.types.initrdSockets;
      visible = "shallow";
      description = "Definition of systemd socket units.";
    };

    timers = mkOption {
      default = {};
      type = systemdUtils.types.initrdTimers;
      visible = "shallow";
      description = "Definition of systemd timer units.";
    };

    paths = mkOption {
      default = {};
      type = systemdUtils.types.initrdPaths;
      visible = "shallow";
      description = "Definition of systemd path units.";
    };

    mounts = mkOption {
      default = [];
      type = systemdUtils.types.initrdMounts;
      visible = "shallow";
      description = ''
        Definition of systemd mount units.
        This is a list instead of an attrSet, because systemd mandates the names to be derived from
        the 'where' attribute.
      '';
    };

    automounts = mkOption {
      default = [];
      type = systemdUtils.types.automounts;
      visible = "shallow";
      description = ''
        Definition of systemd automount units.
        This is a list instead of an attrSet, because systemd mandates the names to be derived from
        the 'where' attribute.
      '';
    };

    slices = mkOption {
      default = {};
      type = systemdUtils.types.slices;
      visible = "shallow";
      description = "Definition of slice configurations.";
    };

    enableTpm2 = mkOption {
      default = true;
      type = types.bool;
      description = ''
        Whether to enable TPM2 support in the initrd.
      '';
    };
  };

  config = mkIf (config.boot.initrd.enable && cfg.enable) {
    assertions = [
      {
        assertion = cfg.root == "fstab" -> any (fs: fs.mountPoint == "/") (builtins.attrValues config.fileSystems);
        message = "The ‘fileSystems’ option does not specify your root file system.";
      }
    ] ++ map (name: {
      assertion = lib.attrByPath name (throw "impossible") config.boot.initrd == "";
      message = ''
        systemd stage 1 does not support 'boot.initrd.${lib.concatStringsSep "." name}'. Please
          convert it to analogous systemd units in 'boot.initrd.systemd'.

            Definitions:
        ${lib.concatMapStringsSep "\n" ({ file, ... }: "    - ${file}") (lib.attrByPath name (throw "impossible") options.boot.initrd).definitionsWithLocations}
      '';
    }) [
      [ "preFailCommands" ]
      [ "preDeviceCommands" ]
      [ "preLVMCommands" ]
      [ "postDeviceCommands" ]
      [ "postResumeCommands" ]
      [ "postMountCommands" ]
      [ "extraUdevRulesCommands" ]
      [ "extraUtilsCommands" ]
      [ "extraUtilsCommandsTest" ]
      [ "network" "postCommands" ]
    ];

    system.build = { inherit initialRamdisk; };

    boot.initrd.availableKernelModules = [
      # systemd needs this for some features
      "autofs"
      # systemd-cryptenroll
    ] ++ lib.optional cfg.enableTpm2 "tpm-tis"
    ++ lib.optional (cfg.enableTpm2 && !(pkgs.stdenv.hostPlatform.isRiscV64 || pkgs.stdenv.hostPlatform.isArmv7)) "tpm-crb"
    ++ lib.optional cfg.package.withEfi "efivarfs";

    boot.kernelParams = [
      "root=${config.boot.initrd.systemd.root}"
    ] ++ lib.optional (config.boot.resumeDevice != "") "resume=${config.boot.resumeDevice}"
      # `systemd` mounts root in initrd as read-only unless "rw" is on the kernel command line.
      # For NixOS activation to succeed, we need to have root writable in initrd.
      ++ lib.optional (config.boot.initrd.systemd.root == "gpt-auto") "rw";

    boot.initrd.systemd = {
      # bashInteractive is easier to use and also required by debug-shell.service
      initrdBin = [pkgs.bashInteractive pkgs.coreutils cfg.package.kmod cfg.package];
      extraBin = {
        less = "${pkgs.less}/bin/less";
        mount = "${cfg.package.util-linux}/bin/mount";
        umount = "${cfg.package.util-linux}/bin/umount";
        fsck = "${cfg.package.util-linux}/bin/fsck";
      };

      managerEnvironment.PATH = "/bin:/sbin";

      contents = {
        "/tmp/.keep".text = "systemd requires the /tmp mount point in the initrd cpio archive";
        "/init".source = "${cfg.package}/lib/systemd/systemd";
        "/etc/systemd/system".source = stage1Units;

        "/etc/systemd/system.conf".text = ''
          [Manager]
          DefaultEnvironment=PATH=/bin:/sbin
          ${cfg.extraConfig}
          ManagerEnvironment=${lib.concatStringsSep " " (lib.mapAttrsToList (n: v: "${n}=${lib.escapeShellArg v}") cfg.managerEnvironment)}
        '';

        "/lib".source = "${modulesClosure}/lib";

        "/etc/modules-load.d/nixos.conf".text = concatStringsSep "\n" config.boot.initrd.kernelModules;

        # We can use either ! or * to lock the root account in the
        # console, but some software like OpenSSH won't even allow you
        # to log in with an SSH key if you use ! so we use * instead
        "/etc/shadow".text = "root:${if isBool cfg.emergencyAccess then optionalString (!cfg.emergencyAccess) "*" else cfg.emergencyAccess}:::::::";

        "/bin".source = "${initrdBinEnv}/bin";
        "/sbin".source = "${initrdBinEnv}/sbin";

        "/etc/sysctl.d/nixos.conf".text = "kernel.modprobe = /sbin/modprobe";
        "/etc/modprobe.d/systemd.conf".source = "${cfg.package}/lib/modprobe.d/systemd.conf";
        "/etc/modprobe.d/ubuntu.conf".source = pkgs.runCommand "initrd-kmod-blacklist-ubuntu" { } ''
          ${pkgs.buildPackages.perl}/bin/perl -0pe 's/## file: iwlwifi.conf(.+?)##/##/s;' $src > $out
        '';
        "/etc/modprobe.d/debian.conf".source = pkgs.kmod-debian-aliases;

        "/etc/os-release".source = config.boot.initrd.osRelease;
        "/etc/initrd-release".source = config.boot.initrd.osRelease;

      } // optionalAttrs (config.environment.etc ? "modprobe.d/nixos.conf") {
        "/etc/modprobe.d/nixos.conf".source = config.environment.etc."modprobe.d/nixos.conf".source;
      };

      storePaths = [
        # systemd tooling
        "${cfg.package}/lib/systemd/systemd-executor"
        "${cfg.package}/lib/systemd/systemd-fsck"
        "${cfg.package}/lib/systemd/systemd-hibernate-resume"
        "${cfg.package}/lib/systemd/systemd-journald"
        "${cfg.package}/lib/systemd/systemd-makefs"
        "${cfg.package}/lib/systemd/systemd-modules-load"
        "${cfg.package}/lib/systemd/systemd-remount-fs"
        "${cfg.package}/lib/systemd/systemd-shutdown"
        "${cfg.package}/lib/systemd/systemd-sulogin-shell"
        "${cfg.package}/lib/systemd/systemd-sysctl"
        "${cfg.package}/lib/systemd/systemd-bsod"

        # generators
        "${cfg.package}/lib/systemd/system-generators/systemd-debug-generator"
        "${cfg.package}/lib/systemd/system-generators/systemd-fstab-generator"
        "${cfg.package}/lib/systemd/system-generators/systemd-gpt-auto-generator"
        "${cfg.package}/lib/systemd/system-generators/systemd-hibernate-resume-generator"
        "${cfg.package}/lib/systemd/system-generators/systemd-run-generator"

        # utilities needed by systemd
        "${cfg.package.util-linux}/bin/mount"
        "${cfg.package.util-linux}/bin/umount"
        "${cfg.package.util-linux}/bin/sulogin"

        # required for script services, and some tools like xfs still want the sh symlink
        "${pkgs.bash}/bin"

        # so NSS can look up usernames
        "${pkgs.glibc}/lib/libnss_files.so.2"
      ] ++ optionals (cfg.package.withCryptsetup && cfg.enableTpm2) [
        # tpm2 support
        "${cfg.package}/lib/cryptsetup/libcryptsetup-token-systemd-tpm2.so"
        pkgs.tpm2-tss
      ] ++ optionals cfg.package.withCryptsetup [
        # fido2 support
        "${cfg.package}/lib/cryptsetup/libcryptsetup-token-systemd-fido2.so"
        "${pkgs.libfido2}/lib/libfido2.so.1"
      ] ++ jobScripts;

      targets.initrd.aliases = ["default.target"];
      units =
           mapAttrs' (n: v: nameValuePair "${n}.path"    (pathToUnit    v)) cfg.paths
        // mapAttrs' (n: v: nameValuePair "${n}.service" (serviceToUnit v)) cfg.services
        // mapAttrs' (n: v: nameValuePair "${n}.slice"   (sliceToUnit   v)) cfg.slices
        // mapAttrs' (n: v: nameValuePair "${n}.socket"  (socketToUnit  v)) cfg.sockets
        // mapAttrs' (n: v: nameValuePair "${n}.target"  (targetToUnit  v)) cfg.targets
        // mapAttrs' (n: v: nameValuePair "${n}.timer"   (timerToUnit   v)) cfg.timers
        // listToAttrs (map
                     (v: let n = escapeSystemdPath v.where;
                         in nameValuePair "${n}.mount" (mountToUnit v)) cfg.mounts)
        // listToAttrs (map
                     (v: let n = escapeSystemdPath v.where;
                         in nameValuePair "${n}.automount" (automountToUnit v)) cfg.automounts);

      # make sure all the /dev nodes are set up
      services.systemd-tmpfiles-setup-dev.wantedBy = ["sysinit.target"];

      services.initrd-nixos-activation = {
        after = [ "initrd-fs.target" ];
        requiredBy = [ "initrd.target" ];
        unitConfig.AssertPathExists = "/etc/initrd-release";
        serviceConfig.Type = "oneshot";
        description = "NixOS Activation";

        script = /* bash */ ''
          set -uo pipefail
          export PATH="/bin:${cfg.package.util-linux}/bin"

          # Figure out what closure to boot
          closure=
          for o in $(< /proc/cmdline); do
              case $o in
                  init=*)
                      IFS== read -r -a initParam <<< "$o"
                      closure="''${initParam[1]}"
                      ;;
              esac
          done

          # Sanity check
          if [ -z "''${closure:-}" ]; then
            echo 'No init= parameter on the kernel command line' >&2
            exit 1
          fi

          # Resolve symlinks in the init parameter. We need this for some boot loaders
          # (e.g. boot.loader.generationsDir).
          closure="$(chroot /sysroot ${pkgs.coreutils}/bin/realpath "$closure")"

          # Assume the directory containing the init script is the closure.
          closure="$(dirname "$closure")"

          # If we are not booting a NixOS closure (e.g. init=/bin/sh),
          # we don't know what root to prepare so we don't do anything
          if ! [ -x "/sysroot$(readlink "/sysroot$closure/prepare-root" || echo "$closure/prepare-root")" ]; then
            echo "NEW_INIT=''${initParam[1]}" > /etc/switch-root.conf
            echo "$closure does not look like a NixOS installation - not activating"
            exit 0
          fi
          echo 'NEW_INIT=' > /etc/switch-root.conf


          # We need to propagate /run for things like /run/booted-system
          # and /run/current-system.
          mkdir -p /sysroot/run
          mount --bind /run /sysroot/run

          # Initialize the system
          export IN_NIXOS_SYSTEMD_STAGE1=true
          exec chroot /sysroot $closure/prepare-root
        '';
      };

      # This will either call systemctl with the new init as the last parameter (which
      # is the case when not booting a NixOS system) or with an empty string, causing
      # systemd to bypass its verification code that checks whether the next file is a systemd
      # and using its compiled-in value
      services.initrd-switch-root.serviceConfig = {
        EnvironmentFile = "-/etc/switch-root.conf";
        ExecStart = [
          ""
          ''systemctl --no-block switch-root /sysroot "''${NEW_INIT}"''
        ];
      };

      services.panic-on-fail = {
        wantedBy = ["emergency.target"];
        unitConfig = {
          DefaultDependencies = false;
          ConditionKernelCommandLine = [
            "|boot.panic_on_fail"
            "|stage1panic"
          ];
        };
        script = ''
          echo c > /proc/sysrq-trigger
        '';
        serviceConfig.Type = "oneshot";
      };
    };
  };
}