{
  lib,
  config,
  ...
}:
let
  inherit (lib)
    attrNames
    mapAttrs
    mkOption
    genAttrs
    ;
  inherit (lib.types)
    attrsOf
    attrTag
    deferredModule
    mergeTypes
    nullOr
    submoduleWith
    submodule
    str
    ;
  resource = submoduleWith {
    description = "A deployment resource that can be configured by providers and required by applications";
    modules = [
      {
        options = {
          consumer = mkOption {
            description = "Description how applications can consume the resource";
            type = deferredModule;
          };
          provider = mkOption {
            description = "Description how the hosting provider makes the resource available";
            type = deferredModule;
          };
        };
      }
    ];
  };
  application = submoduleWith {
    description = "A Fediversity application";
    modules = [
      (
        { config, ... }:
        {
          options = {
            module = mkOption {
              description = ''
                A module for configuring the application.
              '';
              type = deferredModule;
            };
            config-mapping = mkOption {
              description = "description of how an application configuration maps to deployment resources";
              # TODO: type = (submodule config.module) -> (attrsOf resource)
            };
          };
        }
      )
    ];
  };
  deployment = submoduleWith {
    description = "A deployment of a configuration of applications to a run-time environment";
    modules = [
      {
        options = {
          # the `applications` option consists of configuration for the above applications
          module = mkOption {
            description = ''
              Configuration to be deployed
            '';
            type = deferredModule;
          };
          runtime-environment = mkOption {
            description = "The run-time environment to deploy to";
            type = runtime-environment;
          };
        };
      }
    ];
  };
  migration = submoduleWith {
    description = "Migration of a Fediversity deployment to a Fediversity run-time environment";
    modules = [
      {
        options = {
          deployment = mkOption {
            description = "Deployment to migrate";
            type = deployment;
          };
          runtime-environment = mkOption {
            description = "Run-time environment to migrate the deployment to";
            type = runtime-environment;
          };
        };
      }
    ];
  };
in
{
  options = {
    providers = mkOption {
      description = "Collection of providers for run-time environments to deploy applications to";
      type = attrTag (genAttrs (attrNames runtime-environment.nestedTypes) (_: provider));
    };
    resources = mkOption {
      description = "Collection of resources for use in Fediversity applications";
      type = attrsOf resource;
    };
    applications = mkOption {
      description = "Collection of (available) Fediversity applications";
      type = attrsOf application;
    };
    deployments = mkOption {
      description = "Deployment of a configuration of applications to a run-time environment";
      type = attrsOf deployment;
    };
    migrations = mkOption {
      description = "Migrations from Fediversity deployments to Fediversity run-time environments";
      type = attrsOf migration;
    };
  };
}