{
  description = "C3D2 NixOS configurations";

  inputs = {
    # use sandro's fork full with cherry-picked fixes
    nixos.url = "github:SuperSandro2000/nixpkgs/nixos-22.11";
    nixos-mobilizon.url = "github:minijackson/nixpkgs/init-mobilizon";
    nixos-hardware.url = "github:nixos/nixos-hardware";
    nixos-unstable.url = "github:nixos/nixpkgs/nixos-unstable";
    nixos-unstable-simd.url = "github:SuperSandro2000/nixpkgs/nixos-unstable-simd";

    affection-src = {
      url = "git+https://gitea.nek0.eu/nek0/affection";
      inputs = {
        nixpkgs.follows = "nixos";
        flake-utils.follows = "flake-utils";
      };
    };
    bevy-mandelbrot = {
      # url = "github:matelab/bevy_mandelbrot";
      url = "git+https://gitea.c3d2.de/astro/bevy-mandelbrot.git?ref=main";
      inputs = {
        naersk.follows = "naersk";
        nixpkgs.follows = "nixos";
        rust-overlay.follows = "rust-overlay";
      };
    };
    bevy-julia = {
      # url = "github:matelab/bevy_julia";
      url = "git+https://gitea.c3d2.de/astro/bevy-julia.git?ref=main";
      inputs = {
        nixpkgs.follows = "nixos";
        # breaks the build:
        # naersk.follows = "naersk";
        # naersk.inputs.nixpkgs.follows = "nixpkgs";
        rust-overlay.follows = "rust-overlay";
      };
    };
    caveman = {
      url = "git+https://gitea.c3d2.de/astro/caveman.git?ref=main";
      inputs = {
        nixpkgs.follows = "nixos";
        utils.follows = "flake-utils";
        fenix.follows = "fenix";
        fenix.inputs.nixpkgs.follows = "nixpkgs";
        naersk.follows = "naersk";
        naersk.inputs.nixpkgs.follows = "nixpkgs";
      };
    };
    fenix = {
      url = "github:nix-community/fenix";
      inputs.nixpkgs.follows = "nixos";
    };
    flake-utils.url = "github:numtide/flake-utils";
    harmonia = {
      url = "github:helsinki-systems/harmonia";
      flake = false;
    };
    heliwatch = {
      url = "git+https://gitea.c3d2.de/astro/heliwatch.git";
      inputs = {
        fenix.follows = "fenix";
        nixpkgs.follows = "nixos";
        naersk.follows = "naersk";
        utils.follows = "flake-utils";
      };
    };
    hydra-ca.url = "github:mlabs-haskell/hydra/aciceri/ca-derivations";
    microvm = {
      url = "github:astro/microvm.nix";
      inputs = {
        nixpkgs.follows = "nixos";
        flake-utils.follows = "flake-utils";
      };
    };
    naersk = {
      url = "github:nix-community/naersk";
      inputs = {
        nixpkgs.follows = "nixos";
      };
    };
    oparl-scraper = {
      url = "github:offenesdresden/ratsinfo-scraper/oparl";
      flake = false;
    };
    openwrt = {
      url = "git+https://git.openwrt.org/openwrt/openwrt.git?ref=openwrt-21.02";
      flake = false;
    };
    openwrt-imagebuilder = {
      url = "github:astro/nix-openwrt-imagebuilder";
      inputs = {
        nixpkgs.follows = "nixos";
      };
    };
    rust-overlay = {
      url = "github:oxalica/rust-overlay";
      inputs = {
        flake-utils.follows = "flake-utils";
        nixpkgs.follows = "nixos";
      };
    };
    scrapers = {
      url = "git+https://gitea.c3d2.de/astro/scrapers.git";
      flake = false;
    };
    skyflake = {
      url = "github:astro/skyflake";
      inputs = {
        microvm.follows = "microvm";
        nixpkgs.follows = "nixos";
      };
    };
    sshlogd = {
      url = "git+https://gitea.c3d2.de/astro/sshlogd.git?ref=main";
      inputs = {
        utils.follows = "flake-utils";
        naersk.follows = "naersk";
        nixpkgs.follows = "nixos";
        fenix.follows = "fenix";
      };
    };
    secrets = {
      url = "git+ssh://gitea@gitea.c3d2.de/c3d2-admins/secrets.git";
      inputs = {
        nixpkgs.follows = "nixos";
      };
    };
    sops-nix = {
      url = "github:Mic92/sops-nix";
      inputs = {
        nixpkgs.follows = "nixos";
        nixpkgs-22_05.follows = "nixos";
      };
    };
    spacemsg = {
      url = "github:astro/spacemsg";
      flake = false;
    };
    ticker = {
      url = "git+https://gitea.c3d2.de/astro/ticker.git";
      inputs = {
        fenix.follows = "fenix";
        # TODO: build regression in https://github.com/nix-community/naersk/commit/6944160c19cb591eb85bbf9b2f2768a935623ed3
        # naersk.follows = "naersk";
        nixpkgs.follows = "nixos";
        utils.follows = "flake-utils";
      };
    };
    tigger = {
      url = "github:astro/tigger";
      flake = false;
    };
    tracer = {
      # url = "git+https://gitea.nek0.eu/nek0/tracer";
      url = "git+https://gitea.c3d2.de/astro/tracer";
      inputs = {
        affection-src.follows = "affection-src";
        nixpkgs.follows = "nixos";
        flake-utils.follows = "flake-utils";
      };
    };
    yammat = {
      url = "git+https://gitea.c3d2.de/C3D2/yammat.git?ref=nix";
      inputs.nixpkgs.follows = "nixos";
    };
    zentralwerk = {
      url = "git+https://gitea.c3d2.de/zentralwerk/network.git";
      inputs = {
        nixpkgs.follows = "nixos";
        openwrt.follows = "openwrt";
        openwrt-imagebuilder.follows = "openwrt-imagebuilder";
      };
    };
  };

  outputs = inputs@{ self, fenix, harmonia, heliwatch, microvm, naersk, nixos, nixos-hardware, nixos-unstable, nixos-unstable-simd, caveman, oparl-scraper, scrapers, secrets, skyflake, sshlogd, sops-nix, spacemsg, ticker, tigger, yammat, zentralwerk, ... }:
    let
      inherit (nixos) lib;

      extractZwHosts = { hosts4, hosts6, ... }:
        lib.recursiveUpdate (
          builtins.foldl' (result: name:
            lib.recursiveUpdate result {
              "${name}".ip4 = hosts4."${name}";
            }
          ) {} (builtins.attrNames hosts4)
        ) (
          builtins.foldl' (result: ctx:
            builtins.foldl' (result: name:
              lib.recursiveUpdate result {
                "${name}".ip6 = hosts6."${ctx}"."${name}";
              }
            ) result (builtins.attrNames hosts6."${ctx}")
          ) {} (builtins.attrNames hosts6)
        );
      zwHostRegistry = {
        hosts =
          builtins.foldl' (result: net:
            lib.recursiveUpdate result (extractZwHosts zentralwerk.lib.config.site.net."${net}")
          ) {} [ "core" "cluster" "c3d2" "serv" "flpk" "pub" ];
      };
      extraHostRegistry.hosts = import ./host-registry.nix;
      hostRegistry = lib.recursiveUpdate zwHostRegistry extraHostRegistry;

      # Our custom NixOS builder
      nixosSystem' =
        { nixpkgs ? inputs.nixos
        , modules
        , extraArgs ? { }
        , specialArgs ? { }
        , system ? "x86_64-linux"
      }@args:

      { inherit args; } // nixpkgs.lib.nixosSystem {
        inherit specialArgs system;

        modules = [
          ({ ... }: {
            _module.args = extraArgs // {
              inherit hostRegistry inputs zentralwerk;
            };

            nixpkgs = {
              overlays = [ self.overlays ];
            };
          })

          self.nixosModules.c3d2
          ./modules/audio-server.nix
          ./modules/c3d2.nix
          ./modules/stats.nix
          ./modules/pi-sensors.nix
        ] ++ modules;
      };
    in {
      overlays = import ./overlays {
        inherit nixos-unstable;
        inherit (inputs) tracer bevy-mandelbrot bevy-julia;
      };

      legacyPackages = lib.attrsets.mapAttrs (_: pkgs:
        pkgs.appendOverlays [
          fenix.overlays.default
          naersk.overlay
          self.overlays
        ]) nixos.legacyPackages;

      packages = import ./packages.nix { inherit hostRegistry inputs lib microvm secrets self; };

      nixosConfigurations = {
        auth = nixosSystem' {
          modules = [
            self.nixosModules.microvm
            ./hosts/auth
          ];
          # nixpkgs = inputs.nixos-unstable;
        };

        broker = nixosSystem' {
          modules = [
            self.nixosModules.microvm
            ./hosts/broker
          ];
        };

        factorio = nixosSystem' {
          modules = [
            self.nixosModules.microvm
            ./hosts/factorio
          ];
          nixpkgs = inputs.nixos-unstable;
        };

        freifunk = nixosSystem' {
          modules = [
            self.nixosModules.microvm
            ./hosts/freifunk
            {
              nixpkgs.overlays = with secrets.overlays; [
                freifunk ospf
              ];
            }
          ];
        };

        ftp = nixosSystem' {
          modules = [
            self.nixosModules.microvm
            ./hosts/ftp
          ];
        };

        gitea = nixosSystem' {
          modules = [
            self.nixosModules.microvm
            ./hosts/gitea
          ];
          # nixpkgs = inputs.nixos-unstable;
        };

        glotzbert = nixosSystem' {
          modules = [
            ./hosts/glotzbert
            nixos-hardware.nixosModules.common-cpu-intel
            nixos-hardware.nixosModules.common-pc-ssd
            # TODO: migrate away from secrets repo
            secrets.nixosModules.admins
          ];
        };

        hedgedoc = nixosSystem' {
          modules = [
            self.nixosModules.microvm
            ./hosts/hedgedoc
          ];
          # nixpkgs = inputs.nixos-unstable;
        };

        pulsebert = nixosSystem' {
          modules = [
            ./hosts/pulsebert
            # build: outputs.nixosConfigurations.pulsebert.config.system.build.sdImage
            # run: unzstd -cd result/sd-image/nixos-sd-image-*-aarch64-linux.img.zst | pv -br | sudo dd bs=4M of=/dev/sdX
            "${inputs.nixos-unstable}/nixos/modules/installer/sd-card/sd-image-aarch64-new-kernel.nix"
            {
              nixpkgs = {
                hostPlatform = "aarch64-linux";
                # buildPlatform = "x86_64-linux";
              };
            }
          ];
          # nixpkgs = inputs.nixos-unstable;
        };

        radiobert = nixosSystem' {
          modules = [
            ({ ... }:
            {
              nixpkgs.overlays = [ heliwatch.overlay ];
            })
            ./hosts/radiobert
          ];
          system = "aarch64-linux";
        };

        nncp = nixosSystem' {
          modules = [
            self.nixosModules.microvm
            self.nixosModules.nncp
            ./hosts/nncp
          ];
        };

        dacbert = nixosSystem' {
          modules = [
            nixos-hardware.nixosModules.raspberry-pi-4
            self.nixosModules.rpi-netboot
            ./hosts/dacbert
          ];
          system = "aarch64-linux";
        };

        rpi-netboot = nixosSystem' {
          modules = [
            { _module.args = { inherit nixos; }; }
            nixos-hardware.nixosModules.raspberry-pi-4
            self.nixosModules.rpi-netboot
            ./hosts/rpi-netboot
          ];
          system = "aarch64-linux";
        };

        schalter = nixosSystem' {
          modules = [
            "${nixos}/nixos/modules/installer/sd-card/sd-image-raspberrypi.nix"
            ({ lib, ... }: {
              networking.hostName = "schalter";
              hardware.enableRedistributableFirmware = true;
              #networking.wireless.enable = true;
              powerManagement.cpuFreqGovernor = lib.mkDefault "performance";

              boot = {
                loader = {
                  grub.enable = false;
                  raspberryPi = {
                    enable = true;
                    version = 1;
                    uboot.enable = false;
                  };
                  generic-extlinux-compatible.enable = lib.mkForce false;
                };
                # supportedFilesystems = lib.mkForce [ "vfat" "ext4" ];

                tmpOnTmpfs = true;
              };
              nixpkgs.config.packageOverrides = pkgs: {
                makeModulesClosure = x:
                  # prevent kernel install fail due to missing modules
                  pkgs.makeModulesClosure (x // { allowMissing = true; });
              };
              sdImage = {
                compressImage = false;
                imageBaseName = "schalter";
                firmwareSize = 512;
              };

              nixpkgs.crossSystem = nixos.lib.systems.examples.raspberryPi;
            })
          ];
          system = "x86_64-linux";
        };

        matemat = nixosSystem' {
          modules = [
            self.nixosModules.microvm
            ./hosts/matemat
            yammat.nixosModule
            # TODO: migrate away from secrets repo
            secrets.nixosModules.admins
            { nixpkgs.overlays = [ secrets.overlays.matemat ]; }
          ];
        };

        scrape = nixosSystem' {
          modules = [
            self.nixosModules.microvm
            ./hosts/scrape
            {
              nixpkgs.overlays = [ secrets.overlays.scrape ];
              _module.args = { inherit scrapers; };
            }
          ];
        };

        dn42 = nixosSystem' {
          modules = [
            self.nixosModules.microvm
            ./hosts/dn42
            {
              nixpkgs.overlays = [ secrets.overlays.dn42 ];
            }
          ];
        };

        grafana = nixosSystem' {
          modules = [
            self.nixosModules.microvm
            ./hosts/grafana
          ];
          # nixpkgs = nixos-unstable;
        };

        hydra = nixosSystem' {
          modules = [
            self.nixosModules.cluster
            skyflake.nixosModules.default
            (harmonia + "/module.nix")
            ./hosts/hydra
            {
              _module.args = {
                inherit self;
                inherit (inputs) hydra-ca;
              };
            }
          ];
          # nixpkgs = nixos-unstable;
        };

        mucbot = nixosSystem' {
          modules = [
            { _module.args = { inherit tigger; }; }
            "${tigger}/module.nix"
            { nixpkgs.overlays = [ secrets.overlays.mucbot ]; }
            ./hosts/mucbot
            self.nixosModules.cluster-options
          ];
        };

        public-access-proxy = nixosSystem' {
          modules = [
            self.nixosModules.microvm
            ./hosts/public-access-proxy
          ];
        };

        ticker = nixosSystem' {
          modules = [
            self.nixosModules.microvm
            ticker.nixosModules.ticker
            ./hosts/ticker
          ];
        };

        spaceapi = nixosSystem' {
          modules = [
            self.nixosModules.microvm
            "${spacemsg}/spaceapi/module.nix"
            ./hosts/spaceapi
          ];
        };

        stream = nixosSystem' {
          modules = [
            self.nixosModules.cluster-options
            ./hosts/stream
          ];
        };

        mobilizon = nixosSystem' {
          # TODO: pending https://github.com/NixOS/nixpkgs/pull/119132
          nixpkgs = inputs.nixos-mobilizon;
          modules = [
            self.nixosModules.microvm
            ./hosts/mobilizon
          ];
        };

        c3d2-web = nixosSystem' {
          modules = [
            { _module.args = { inherit nixos; }; }
            self.nixosModules.microvm
            ./hosts/c3d2-web
            { nixpkgs.overlays = [ secrets.overlays.c3d2-web ]; }
          ];
        };

        sdrweb = nixosSystem' {
          modules = [
            self.nixosModules.cluster-options
            { nixpkgs.overlays = [ secrets.overlays.mucbot ]; }
            heliwatch.nixosModules.heliwatch
            ./hosts/sdrweb
          ];
          # nixpkgs = nixos-unstable;
        };

        bind = nixosSystem' {
          modules = [
            { nixpkgs.overlays = with secrets.overlays; [ bind ]; }
            self.nixosModules.microvm
            ./hosts/bind
          ];
        };

        jabber = nixosSystem' {
          modules = [
            { nixpkgs.overlays = with secrets.overlays; [ jabber ]; }
            self.nixosModules.microvm
            ./hosts/jabber
          ];
        };

        blogs = nixosSystem' {
          modules = [
            self.nixosModules.plume
            self.nixosModules.microvm
            ./hosts/blogs
          ];
        };

        server8 = nixosSystem' {
          modules = [
            ./hosts/server8
            self.nixosModules.cluster-network
            self.nixosModules.cluster
            skyflake.nixosModules.default
            { _module.args = { inherit self; }; }
          ];
        };

        server9 = nixosSystem' {
          modules = [
            ./hosts/server9
            microvm.nixosModules.host
            self.nixosModules.microvm-host
            self.nixosModules.cluster-network
            self.nixosModules.cluster
            skyflake.nixosModules.default
            { _module.args = { inherit self; }; }
          ];
        };

        server10 = nixosSystem' {
          modules = [
            ./hosts/server10
            microvm.nixosModules.host
            self.nixosModules.microvm-host
            self.nixosModules.cluster-network
            self.nixosModules.cluster
            skyflake.nixosModules.default
            { _module.args = { inherit self; }; }
          ];
        };

        oparl = nixosSystem' {
          modules = [
            self.nixosModules.microvm
            ./hosts/oparl
            {
              _module.args = { inherit oparl-scraper; };
            }
          ];
        };

        leon = nixosSystem' {
          modules = [
            self.nixosModules.cluster-options
            ./hosts/leon
          ];
        };

        leoncloud = nixosSystem' {
          modules = [
            self.nixosModules.cluster-options
            ./hosts/leoncloud
          ];
        };

        nfsroot = nixosSystem' {
          modules = [
            self.nixosModules.microvm
            ./hosts/nfsroot
            {
              _module.args.tftproots = nixos.lib.filterAttrs (name: _:
                builtins.match ".+-tftproot" name != null
              ) self.packages.x86_64-linux;
            }
          ];
        };

        riscbert = nixosSystem' {
          modules = [
            nixos-hardware.nixosModules.starfive-visionfive-v1
            ./hosts/riscbert
            {
              nixpkgs.crossSystem = {
                config = "riscv64-unknown-linux-gnu";
                system = "riscv64-linux";
              };
            }
          ];
          # nixpkgs = nixos-unstable;
          system = "x86_64-linux";
        };

        direkthilfe = nixosSystem' {
          modules = [
            self.nixosModules.microvm
            ./hosts/direkthilfe
          ];
        };

        mediawiki = nixosSystem' {
          modules = [
            self.nixosModules.microvm
            ./hosts/mediawiki
          ];
          # nixpkgs = nixos-unstable;
        };

        gnunet = nixosSystem' {
          modules = [
            self.nixosModules.cluster-options
            ./hosts/gnunet
          ];
          # nixpkgs = nixos-unstable;
        };

        zengel = nixosSystem' {
          modules = [
            self.nixosModules.microvm
            ./hosts/zengel
          ];
        };

        sshlog = nixosSystem' {
          modules = [
            self.nixosModules.cluster-options
            sshlogd.nixosModule
            ./hosts/sshlog
          ];
        };

        network-homepage = nixosSystem' {
          modules = [
            self.nixosModules.microvm
            ./hosts/network-homepage
          ];
        };

        caveman = nixosSystem' {
          modules = [
            self.nixosModules.microvm
            caveman.nixosModule
            ./hosts/caveman
          ];
        };

        owncast = nixosSystem' {
          modules = [
            self.nixosModules.cluster-options
            ./hosts/owncast
          ];
          # nixpkgs = nixos-unstable;
        };

        prometheus = nixosSystem' {
          modules = [
            self.nixosModules.cluster-options
            ./hosts/prometheus
          ];
        };

        mastodon = nixosSystem' {
          modules = [
            self.nixosModules.cluster-options
            ./hosts/mastodon
          ];
        };
      };

      nixosModules = {
        c3d2 = {
          imports = [
            sops-nix.nixosModule
            ./modules/audio-server.nix
            ./modules/autoupdate.nix
            ./modules/backup.nix
            ./modules/c3d2.nix
            ./modules/nncp.nix
            ./modules/logging.nix
            ./modules/stats.nix
          ];
          c3d2.hosts = hostRegistry.hosts;
          c3d2.users = import ./users.nix;
          c3d2.nncp.neigh = import ./modules/nncp-relays.nix;
        };
        cluster = ./modules/cluster;
        cluster-options = ./modules/cluster/deployment-options.nix;
        cluster-network = ./modules/cluster/network.nix;
        microvm.imports = [
          microvm.nixosModules.microvm
          ./modules/microvm.nix
        ];
        microvm-host = ./modules/microvm-host.nix;
        nncp = ./modules/nncp.nix;
        plume = {
          imports = [ ./modules/plume.nix ];
          nixpkgs.overlays = [ fenix.overlays.default naersk.overlay ];
        };
        rpi-netboot = ./modules/rpi-netboot.nix;
      };

      # `nix develop`
      devShell = lib.mapAttrs (system: sopsPkgs:
        with nixos.legacyPackages.${system};
        mkShell {
          sopsPGPKeyDirs = [ "./keys" ];
          nativeBuildInputs = [
            sopsPkgs.sops-import-keys-hook
          ];
        }
      ) sops-nix.packages;

      hydraJobs =
        lib.mapAttrs (_: nixos.lib.hydraJob) (
          let
            getBuildEntryPoint = _: nixosSystem: nixosSystem.config.microvm.declaredRunner or nixosSystem.config.system.build.toplevel;
          in
          lib.mapAttrs getBuildEntryPoint self.nixosConfigurations
          // lib.mapAttrs' (hostname: nixosSystem: lib.nameValuePair
            (hostname + "-simd")
            (getBuildEntryPoint null (nixosSystem' (nixosSystem.args // (with nixosSystem.args; {
              modules = modules ++ [
                {
                  c3d2.simd.enable = lib.mkForce true;
                }
              ];
              nixpkgs = nixos-unstable-simd;
            }))))
          ) self.nixosConfigurations
          // nixos.lib.filterAttrs (name: attr:
            (builtins.match ".+-tftproot" name != null && lib.isDerivation attr)
          ) self.packages.aarch64-linux
        );
    };
}