{
  config,
  lib,
  nixpkgs-pacemaker,
  pkgs,
  ...
}: let
  inherit
    (lib)
    attrNames
    attrValues
    concatMapStringsSep
    elemAt
    filterAttrs
    isAttrs
    mkIf
    mkOption
    types
    ;
  inherit (builtins) toFile map listToAttrs;

  pacemakerPath = "services/cluster/pacemaker/default.nix";
  cfg = config.services.pacemaker;
in {
  disabledModules = [pacemakerPath];
  imports = ["${nixpkgs-pacemaker}/nixos/modules/${pacemakerPath}"];

  options.services.pacemaker = {
    resources = mkOption {
      default = {};
      type = with types;
        attrsOf (submodule ({name, ...}: {
          options = {
            enable = mkOption {
              default = true;
              type = types.bool;
            };

            systemdName = mkOption {
              default = name;
              type = types.str;
            };

            # TODO: add assertion to not have same id
            virtualIps = mkOption {
              default = [];
              type = with types;
                listOf (submodule {
                  options = {
                    id = mkOption {
                      type = types.str;
                    };

                    interface = mkOption {
                      default = "eno1";
                      type = types.str;
                    };

                    ip = mkOption {
                      type = types.str;
                    };

                    cidr = mkOption {
                      default = 24;
                      type = types.int;
                    };
                  };
                });
            };

            # TODO: add assertion, needs to be an existing systemdName
            dependsOn = mkOption {
              default = [];
              type = types.listOf types.str;
            };

            # TODO: Add extraResources, extraConstraints ...
          };
        }));
    };
  };

  config = mkIf cfg.enable {
    systemd.services = let
      mkVirtIps = res:
        concatMapStringsSep "\n" (vip: ''
          <primitive class="ocf" id="${res.systemdName}-${vip.id}-vip" provider="heartbeat" type="IPaddr2">
              <instance_attributes id="${res.systemdName}-${vip.id}-vip-attrs">
                  <nvpair
                      id="${res.systemdName}-${vip.id}-vip-attrs-cidr_netmask"
                      name="cidr_netmask"
                      value="${toString vip.cidr}"
                  />
                  <nvpair
                      id="${res.systemdName}-${vip.id}-vip-attrs-ip"
                      name="ip"
                      value="${vip.ip}"
                  />
                  <nvpair
                      id="${res.systemdName}-${vip.id}-vip-attrs-nic"
                      name="nic"
                      value="${vip.interface}"
                  />
              </instance_attributes>
              <operations>
                  <op
                      id="${res.systemdName}-${vip.id}-vip-monitor-interval-30s"
                      interval="30s"
                      name="monitor"
                  />
                  <op
                      id="${res.systemdName}-${vip.id}-vip-start-interval-0s"
                      interval="0s"
                      name="start"
                      timeout="20s"
                  />
                  <op
                      id="${res.systemdName}-${vip.id}-vip-stop-interval-0s"
                      interval="0s"
                      name="stop"
                      timeout="20s"
                  />
              </operations>
          </primitive>
        '')
        res.virtualIps;

      mkSystemdResource = res: ''
        <primitive id="${res.systemdName}" class="systemd" type="${res.systemdName}">
            <operations>
                <op id="stop-${res.systemdName}" name="stop" interval="0" timeout="10s"/>
                <op id="start-${res.systemdName}" name="start" interval="0" timeout="10s"/>
                <op id="monitor-${res.systemdName}" name="monitor" interval="10s" timeout="20s"/>
            </operations>
        </primitive>
      '';

      mkConstraint = res: first: let
        firstName =
          if isAttrs first
          then first.systemdName
          else first;
      in ''
        <rsc_order
            id="order-${res.systemdName}-${firstName}"
            first="${firstName}"
            then="${res.systemdName}"
            kind="Mandatory"
        />
        <rsc_colocation
            id="colocate-${res.systemdName}-${firstName}"
            rsc="${firstName}"
            with-rsc="${res.systemdName}"
            score="INFINITY"
        />
      '';

      mkDependsOn = res: let
        mkConstraint' = first:
          mkConstraint res first;
      in
        concatMapStringsSep "\n" mkConstraint' res.dependsOn;

      mkVipConstraint = res:
        concatMapStringsSep "\n" (
          vip:
            mkConstraint
            res
            "${res.systemdName}-${vip.id}-vip"
        )
        res.virtualIps;

      # If we're updating resources we have to kill constraints to add new resources
      constraintsEmpty = toFile "constraints.xml" ''
        <constraints>
        </constraints>
      '';

      resEnabled = filterAttrs (n: v: v.enable) cfg.resources;

      resWithIp = filterAttrs (n: v: ! isNull v.virtualIps) resEnabled;

      resources = toFile "resources.xml" ''
        <resources>
            ${concatMapStringsSep "\n" mkVirtIps (attrValues resWithIp)}
            ${concatMapStringsSep "\n" mkSystemdResource (attrValues resEnabled)}
        </resources>
      '';

      constraints = toFile "constraints.xml" ''
        <constraints>
            ${concatMapStringsSep "\n" mkVipConstraint (attrValues resWithIp)}
            ${concatMapStringsSep "\n" mkDependsOn (attrValues resEnabled)}
        </constraints>
      '';

      host1 = (elemAt config.services.corosync.nodelist 0).name;
    in
      {
        "pacemaker-setup" = {
          after = ["corosync.service" "pacemaker.service"];

          path = with pkgs; [pacemaker];

          script = ''
            # The config needs to be installed from one node only
            if [ "$(uname -n)" = ${host1} ]; then
                # TODO: setup stonith / fencing
                crm_attribute --type crm_config --name stonith-enabled --update false
                crm_attribute --type crm_config --name no-quorum-policy --delete

                # Install config
                cibadmin --replace --scope constraints --xml-file ${constraintsEmpty}
                cibadmin --replace --scope resources --xml-file ${resources}
                cibadmin --replace --scope constraints --xml-file ${constraints}
            fi
          '';
        };
      }
      # Force all systemd units handled by pacemaker to not start automatically
      // listToAttrs (map (x: {
        name = x;
        value = {
          wantedBy = lib.mkForce [];
        };
      }) (attrNames cfg.resources));

    # FIXME: https://github.com/NixOS/nixpkgs/pull/208298
    nixpkgs.overlays = [
      (final: prev: {
        inherit
          (nixpkgs-pacemaker.legacyPackages.x86_64-linux)
          pacemaker
          ocf-resource-agents
          ;
      })
    ];
  };
}