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

let
  cfg = config.shb.vpn;

  quoteEach = lib.concatMapStrings (x: ''"${x}"'');

  nordvpnConfig =
    {
      name,
      dev,
      authFile,
      remoteServerIP,
      dependentServices ? [ ],
    }:
    ''
      client
      dev ${dev}
      proto tcp
      remote ${remoteServerIP} 443
      resolv-retry infinite
      remote-random
      nobind
      tun-mtu 1500
      tun-mtu-extra 32
      mssfix 1450
      persist-key
      persist-tun
      ping 15
      ping-restart 0
      ping-timer-rem
      reneg-sec 0
      comp-lzo no

      status /tmp/openvpn/${name}.status

      remote-cert-tls server

      auth-user-pass ${authFile}
      verb 3
      pull
      fast-io
      cipher AES-256-CBC
      auth SHA512

      script-security 2
      route-noexec
      route-up ${routeUp name dependentServices}/bin/routeUp.sh
      down ${routeDown name dependentServices}/bin/routeDown.sh

      <ca>
      -----BEGIN CERTIFICATE-----
      MIIFCjCCAvKgAwIBAgIBATANBgkqhkiG9w0BAQ0FADA5MQswCQYDVQQGEwJQQTEQ
      MA4GA1UEChMHTm9yZFZQTjEYMBYGA1UEAxMPTm9yZFZQTiBSb290IENBMB4XDTE2
      MDEwMTAwMDAwMFoXDTM1MTIzMTIzNTk1OVowOTELMAkGA1UEBhMCUEExEDAOBgNV
      BAoTB05vcmRWUE4xGDAWBgNVBAMTD05vcmRWUE4gUm9vdCBDQTCCAiIwDQYJKoZI
      hvcNAQEBBQADggIPADCCAgoCggIBAMkr/BYhyo0F2upsIMXwC6QvkZps3NN2/eQF
      kfQIS1gql0aejsKsEnmY0Kaon8uZCTXPsRH1gQNgg5D2gixdd1mJUvV3dE3y9FJr
      XMoDkXdCGBodvKJyU6lcfEVF6/UxHcbBguZK9UtRHS9eJYm3rpL/5huQMCppX7kU
      eQ8dpCwd3iKITqwd1ZudDqsWaU0vqzC2H55IyaZ/5/TnCk31Q1UP6BksbbuRcwOV
      skEDsm6YoWDnn/IIzGOYnFJRzQH5jTz3j1QBvRIuQuBuvUkfhx1FEwhwZigrcxXu
      MP+QgM54kezgziJUaZcOM2zF3lvrwMvXDMfNeIoJABv9ljw969xQ8czQCU5lMVmA
      37ltv5Ec9U5hZuwk/9QO1Z+d/r6Jx0mlurS8gnCAKJgwa3kyZw6e4FZ8mYL4vpRR
      hPdvRTWCMJkeB4yBHyhxUmTRgJHm6YR3D6hcFAc9cQcTEl/I60tMdz33G6m0O42s
      Qt/+AR3YCY/RusWVBJB/qNS94EtNtj8iaebCQW1jHAhvGmFILVR9lzD0EzWKHkvy
      WEjmUVRgCDd6Ne3eFRNS73gdv/C3l5boYySeu4exkEYVxVRn8DhCxs0MnkMHWFK6
      MyzXCCn+JnWFDYPfDKHvpff/kLDobtPBf+Lbch5wQy9quY27xaj0XwLyjOltpiST
      LWae/Q4vAgMBAAGjHTAbMAwGA1UdEwQFMAMBAf8wCwYDVR0PBAQDAgEGMA0GCSqG
      SIb3DQEBDQUAA4ICAQC9fUL2sZPxIN2mD32VeNySTgZlCEdVmlq471o/bDMP4B8g
      nQesFRtXY2ZCjs50Jm73B2LViL9qlREmI6vE5IC8IsRBJSV4ce1WYxyXro5rmVg/
      k6a10rlsbK/eg//GHoJxDdXDOokLUSnxt7gk3QKpX6eCdh67p0PuWm/7WUJQxH2S
      DxsT9vB/iZriTIEe/ILoOQF0Aqp7AgNCcLcLAmbxXQkXYCCSB35Vp06u+eTWjG0/
      pyS5V14stGtw+fA0DJp5ZJV4eqJ5LqxMlYvEZ/qKTEdoCeaXv2QEmN6dVqjDoTAo
      k0t5u4YRXzEVCfXAC3ocplNdtCA72wjFJcSbfif4BSC8bDACTXtnPC7nD0VndZLp
      +RiNLeiENhk0oTC+UVdSc+n2nJOzkCK0vYu0Ads4JGIB7g8IB3z2t9ICmsWrgnhd
      NdcOe15BincrGA8avQ1cWXsfIKEjbrnEuEk9b5jel6NfHtPKoHc9mDpRdNPISeVa
      wDBM1mJChneHt59Nh8Gah74+TM1jBsw4fhJPvoc7Atcg740JErb904mZfkIEmojC
      VPhBHVQ9LHBAdM8qFI2kRK0IynOmAZhexlP/aT/kpEsEPyaZQlnBn3An1CRz8h0S
      PApL8PytggYKeQmRhl499+6jLxcZ2IegLfqq41dzIjwHwTMplg+1pKIOVojpWA==
      -----END CERTIFICATE-----
      </ca>
      key-direction 1
      <tls-auth>
      #
      # 2048 bit OpenVPN static key
      #
      -----BEGIN OpenVPN Static key V1-----
      e685bdaf659a25a200e2b9e39e51ff03
      0fc72cf1ce07232bd8b2be5e6c670143
      f51e937e670eee09d4f2ea5a6e4e6996
      5db852c275351b86fc4ca892d78ae002
      d6f70d029bd79c4d1c26cf14e9588033
      cf639f8a74809f29f72b9d58f9b8f5fe
      fc7938eade40e9fed6cb92184abb2cc1
      0eb1a296df243b251df0643d53724cdb
      5a92a1d6cb817804c4a9319b57d53be5
      80815bcfcb2df55018cc83fc43bc7ff8
      2d51f9b88364776ee9d12fc85cc7ea5b
      9741c4f598c485316db066d52db4540e
      212e1518a9bd4828219e24b20d88f598
      a196c9de96012090e333519ae18d3509
      9427e7b372d348d352dc4c85e18cd4b9
      3f8a56ddb2e64eb67adfc9b337157ff4
      -----END OpenVPN Static key V1-----
      </tls-auth>
    '';

  routeUp =
    name: dependentServices:
    pkgs.writeShellApplication {
      name = "routeUp.sh";

      runtimeInputs = [
        pkgs.iproute2
        pkgs.systemd
        pkgs.nettools
      ];

      text = ''
        echo "Running route-up..."

        echo "dev=''${dev:?}"
        echo "ifconfig_local=''${ifconfig_local:?}"
        echo "route_vpn_gateway=''${route_vpn_gateway:?}"

        set -x

        ip rule
        ip rule add from "''${ifconfig_local:?}/32" table ${name}
        ip rule add to "''${route_vpn_gateway:?}/32" table ${name}
        ip rule

        ip route list table ${name} || :
        retVal=$?
        if [ $retVal -eq 2 ]; then
          echo "table is empty"
        elif [ $retVal -ne 0 ]; then
          exit 1
        fi
        ip route add default via "''${route_vpn_gateway:?}" dev "''${dev:?}" table ${name}
        ip route flush cache
        ip route list table ${name} || :
        retVal=$?
        if [ $retVal -eq 2 ]; then
          echo "table is empty"
        elif [ $retVal -ne 0 ]; then
          exit 1
        fi

        echo "''${ifconfig_local:?}" > /run/openvpn/${name}/ifconfig_local

        dependencies=(${quoteEach dependentServices})
        for i in "''${dependencies[@]}"; do
            systemctl restart "$i" || :
        done

        echo "Running route-up DONE"
      '';
    };

  routeDown =
    name: dependentServices:
    pkgs.writeShellApplication {
      name = "routeDown.sh";

      runtimeInputs = [
        pkgs.iproute2
        pkgs.systemd
        pkgs.nettools
        pkgs.coreutils
      ];

      text = ''
        echo "Running route-down..."

        echo "dev=''${dev:?}"
        echo "ifconfig_local=''${ifconfig_local:?}"
        echo "route_vpn_gateway=''${route_vpn_gateway:?}"

        set -x

        ip rule
        ip rule del from "''${ifconfig_local:?}/32" table ${name}
        ip rule del to "''${route_vpn_gateway:?}/32" table ${name}
        ip rule

        # This will probably fail because the dev is already gone.
        ip route list table ${name} || :
        retVal=$?
        if [ $retVal -eq 2 ]; then
          echo "table is empty"
        elif [ $retVal -ne 0 ]; then
          exit 1
        fi
        ip route del default via "''${route_vpn_gateway:?}" dev "''${dev:?}" table ${name} || :
        ip route flush cache
        ip route list table ${name} || :
        retVal=$?
        if [ $retVal -eq 2 ]; then
          echo "table is empty"
        elif [ $retVal -ne 0 ]; then
          exit 1
        fi

        rm /run/openvpn/${name}/ifconfig_local

        dependencies=(${quoteEach dependentServices})
        for i in "''${dependencies[@]}"; do
            systemctl stop "$i" || :
        done

        echo "Running route-down DONE"
      '';
    };
in
{
  options =
    let
      instanceOption = lib.types.submodule {
        options = {
          enable = lib.mkEnableOption "OpenVPN config";

          package = lib.mkPackageOption pkgs "openvpn" { };

          provider = lib.mkOption {
            description = "VPN provider, if given uses ready-made configuration.";
            type = lib.types.nullOr (lib.types.enum [ "nordvpn" ]);
            default = null;
          };

          dev = lib.mkOption {
            description = "Name of the interface.";
            type = lib.types.str;
            example = "tun0";
          };

          routingNumber = lib.mkOption {
            description = "Unique number used to route packets.";
            type = lib.types.int;
            example = 10;
          };

          remoteServerIP = lib.mkOption {
            description = "IP of the VPN server to connect to.";
            type = lib.types.str;
          };

          authFile = lib.mkOption {
            description = "Location of file holding authentication secrets for provider.";
            type = lib.types.anything;
          };

          proxyPort = lib.mkOption {
            description = "If not null, sets up a proxy that listens on the given port and sends traffic to the VPN.";
            type = lib.types.nullOr lib.types.int;
            default = null;
          };
        };
      };
    in
    {
      shb.vpn = lib.mkOption {
        description = "OpenVPN instances.";
        default = { };
        type = lib.types.attrsOf instanceOption;
      };
    };

  config = {
    services.openvpn.servers =
      let
        instanceConfig =
          name: c:
          lib.mkIf c.enable {
            ${name} = {
              autoStart = true;

              up = "mkdir -p /run/openvpn/${name}";

              config = nordvpnConfig {
                inherit name;
                inherit (c) dev remoteServerIP authFile;
                dependentServices = lib.optional (c.proxyPort != null) "tinyproxy-${name}.service";
              };
            };
          };
      in
      lib.mkMerge (lib.mapAttrsToList instanceConfig cfg);

    systemd.tmpfiles.rules = map (name: "d /tmp/openvpn/${name}.status 0700 root root") (
      lib.attrNames cfg
    );

    networking.iproute2.enable = true;
    networking.iproute2.rttablesExtraConfig = lib.concatStringsSep "\n" (
      lib.mapAttrsToList (name: c: "${toString c.routingNumber} ${name}") cfg
    );

    shb.tinyproxy =
      let
        instanceConfig =
          name: c:
          lib.mkIf (c.enable && c.proxyPort != null) {
            ${name} = {
              enable = true;
              # package = pkgs.tinyproxy.overrideAttrs (old: {
              #   withDebug = false;
              #   patches = old.patches ++ [
              #     (pkgs.fetchpatch {
              #       name = "";
              #       url = "https://github.com/tinyproxy/tinyproxy/pull/494/commits/2532ba09896352b31f3538d7819daa1fc3f829f1.patch";
              #       sha256 = "sha256-Q0MkHnttW8tH3+hoCt9ACjHjmmZQgF6pC/menIrU0Co=";
              #     })
              #   ];
              # });
              dynamicBindFile = "/run/openvpn/${name}/ifconfig_local";
              settings = {
                Port = c.proxyPort;
                Listen = "127.0.0.1";
                Syslog = "On";
                LogLevel = "Info";
                Allow = [
                  "127.0.0.1"
                  "::1"
                ];
                ViaProxyName = ''"tinyproxy"'';
              };
            };
          };
      in
      lib.mkMerge (lib.mapAttrsToList instanceConfig cfg);
  };
}
