{pkgs, lib, config, ...}:
let
  cfg = config.dysnomia;

  printProperties = properties:
    lib.concatMapStrings (propertyName:
      let
        property = properties.${propertyName};
      in
      if lib.isList property then "${propertyName}=(${lib.concatMapStrings (elem: "\"${toString elem}\" ") (properties.${propertyName})})\n"
      else "${propertyName}=\"${toString property}\"\n"
    ) (builtins.attrNames properties);

  properties = pkgs.stdenv.mkDerivation {
    name = "dysnomia-properties";
    buildCommand = ''
      cat > $out << "EOF"
      ${printProperties cfg.properties}
      EOF
    '';
  };

  containersDir = pkgs.stdenv.mkDerivation {
    name = "dysnomia-containers";
    buildCommand = ''
      mkdir -p $out
      cd $out

      ${lib.concatMapStrings (containerName:
        let
          containerProperties = cfg.containers.${containerName};
        in
        ''
          cat > ${containerName} <<EOF
          ${printProperties containerProperties}
          type=${containerName}
          EOF
        ''
      ) (builtins.attrNames cfg.containers)}
    '';
  };

  linkMutableComponents = {containerName}:
    ''
      mkdir ${containerName}

      ${lib.concatMapStrings (componentName:
        let
          component = cfg.components.${containerName}.${componentName};
        in
        "ln -s ${component} ${containerName}/${componentName}\n"
      ) (builtins.attrNames (cfg.components.${containerName} or {}))}
    '';

  componentsDir = pkgs.stdenv.mkDerivation {
    name = "dysnomia-components";
    buildCommand = ''
      mkdir -p $out
      cd $out

      ${lib.concatMapStrings (containerName:
        linkMutableComponents { inherit containerName; }
      ) (builtins.attrNames cfg.components)}
    '';
  };

  dysnomiaFlags = {
    enableApacheWebApplication = config.services.httpd.enable;
    enableAxis2WebService = config.services.tomcat.axis2.enable;
    enableDockerContainer = config.virtualisation.docker.enable;
    enableEjabberdDump = config.services.ejabberd.enable;
    enableMySQLDatabase = config.services.mysql.enable;
    enablePostgreSQLDatabase = config.services.postgresql.enable;
    enableTomcatWebApplication = config.services.tomcat.enable;
    enableMongoDatabase = config.services.mongodb.enable;
    enableSubversionRepository = config.services.svnserve.enable;
    enableInfluxDatabase = config.services.influxdb.enable;
  };
in
{
  options = {
    dysnomia = {

      enable = lib.mkOption {
        type = lib.types.bool;
        default = false;
        description = "Whether to enable Dysnomia";
      };

      enableAuthentication = lib.mkOption {
        type = lib.types.bool;
        default = false;
        description = "Whether to publish privacy-sensitive authentication credentials";
      };

      package = lib.mkOption {
        type = lib.types.path;
        description = "The Dysnomia package";
      };

      properties = lib.mkOption {
        description = "An attribute set in which each attribute represents a machine property. Optionally, these values can be shell substitutions.";
        default = {};
        type = lib.types.attrs;
      };

      containers = lib.mkOption {
        description = "An attribute set in which each key represents a container and each value an attribute set providing its configuration properties";
        default = {};
        type = lib.types.attrsOf lib.types.attrs;
      };

      components = lib.mkOption {
        description = "An attribute set in which each key represents a container and each value an attribute set in which each key represents a component and each value a derivation constructing its initial state";
        default = {};
        type = lib.types.attrsOf lib.types.attrs;
      };

      extraContainerProperties = lib.mkOption {
        description = "An attribute set providing additional container settings in addition to the default properties";
        default = {};
        type = lib.types.attrs;
      };

      extraContainerPaths = lib.mkOption {
        description = "A list of paths containing additional container configurations that are added to the search folders";
        default = [];
        type = lib.types.listOf lib.types.path;
      };

      extraModulePaths = lib.mkOption {
        description = "A list of paths containing additional modules that are added to the search folders";
        default = [];
        type = lib.types.listOf lib.types.path;
      };

      enableLegacyModules = lib.mkOption {
        type = lib.types.bool;
        default = true;
        description = "Whether to enable Dysnomia legacy process and wrapper modules";
      };
    };
  };

  config = lib.mkIf cfg.enable {

    environment.etc = {
      "dysnomia/containers" = {
        source = containersDir;
      };
      "dysnomia/components" = {
        source = componentsDir;
      };
      "dysnomia/properties" = {
        source = properties;
      };
    };

    environment.variables = {
      DYSNOMIA_STATEDIR = "/var/state/dysnomia-nixos";
      DYSNOMIA_CONTAINERS_PATH = "${lib.concatMapStrings (containerPath: "${containerPath}:") cfg.extraContainerPaths}/etc/dysnomia/containers";
      DYSNOMIA_MODULES_PATH = "${lib.concatMapStrings (modulePath: "${modulePath}:") cfg.extraModulePaths}/etc/dysnomia/modules";
    };

    environment.systemPackages = [ cfg.package ];

    dysnomia.package = pkgs.dysnomia.override (origArgs: dysnomiaFlags // lib.optionalAttrs (cfg.enableLegacyModules) {
      enableLegacy = builtins.trace ''
        WARNING: Dysnomia has been configured to use the legacy 'process' and 'wrapper'
        modules for compatibility reasons! If you rely on these modules, consider
        migrating to better alternatives.

        More information: https://raw.githubusercontent.com/svanderburg/dysnomia/f65a9a84827bcc4024d6b16527098b33b02e4054/README-legacy.md

        If you have migrated already or don't rely on these Dysnomia modules, you can
        disable legacy mode with the following NixOS configuration option:

        dysnomia.enableLegacyModules = false;

        In a future version of Dysnomia (and NixOS) the legacy option will go away!
      '' true;
    });

    dysnomia.properties = {
      hostname = config.networking.hostName;
      inherit (pkgs.stdenv.hostPlatform) system;

      supportedTypes = [
        "echo"
        "fileset"
        "process"
        "wrapper"

        # These are not base modules, but they are still enabled because they work with technology that are always enabled in NixOS
        "systemd-unit"
        "sysvinit-script"
        "nixos-configuration"
      ]
      ++ lib.optional (dysnomiaFlags.enableApacheWebApplication) "apache-webapplication"
      ++ lib.optional (dysnomiaFlags.enableAxis2WebService) "axis2-webservice"
      ++ lib.optional (dysnomiaFlags.enableDockerContainer) "docker-container"
      ++ lib.optional (dysnomiaFlags.enableEjabberdDump) "ejabberd-dump"
      ++ lib.optional (dysnomiaFlags.enableInfluxDatabase) "influx-database"
      ++ lib.optional (dysnomiaFlags.enableMySQLDatabase) "mysql-database"
      ++ lib.optional (dysnomiaFlags.enablePostgreSQLDatabase) "postgresql-database"
      ++ lib.optional (dysnomiaFlags.enableTomcatWebApplication) "tomcat-webapplication"
      ++ lib.optional (dysnomiaFlags.enableMongoDatabase) "mongo-database"
      ++ lib.optional (dysnomiaFlags.enableSubversionRepository) "subversion-repository";
    };

    dysnomia.containers = lib.recursiveUpdate ({
      process = {};
      wrapper = {};
    }
    // lib.optionalAttrs (config.services.httpd.enable) { apache-webapplication = {
      documentRoot = config.services.httpd.virtualHosts.localhost.documentRoot;
    }; }
    // lib.optionalAttrs (config.services.tomcat.axis2.enable) { axis2-webservice = {}; }
    // lib.optionalAttrs (config.services.ejabberd.enable) { ejabberd-dump = {
      ejabberdUser = config.services.ejabberd.user;
    }; }
    // lib.optionalAttrs (config.services.mysql.enable) { mysql-database = {
        mysqlPort = config.services.mysql.settings.mysqld.port;
        mysqlSocket = "/run/mysqld/mysqld.sock";
      } // lib.optionalAttrs cfg.enableAuthentication {
        mysqlUsername = "root";
      };
    }
    // lib.optionalAttrs (config.services.postgresql.enable) { postgresql-database = {
      } // lib.optionalAttrs (cfg.enableAuthentication) {
        postgresqlUsername = "postgres";
      };
    }
    // lib.optionalAttrs (config.services.tomcat.enable) { tomcat-webapplication = {
      tomcatPort = 8080;
    }; }
    // lib.optionalAttrs (config.services.mongodb.enable) { mongo-database = {}; }
    // lib.optionalAttrs (config.services.influxdb.enable) {
      influx-database = {
        influxdbUsername = config.services.influxdb.user;
        influxdbDataDir = "${config.services.influxdb.dataDir}/data";
        influxdbMetaDir = "${config.services.influxdb.dataDir}/meta";
      };
    }
    // lib.optionalAttrs (config.services.svnserve.enable) { subversion-repository = {
      svnBaseDir = config.services.svnserve.svnBaseDir;
    }; }) cfg.extraContainerProperties;

    boot.extraSystemdUnitPaths = [ "/etc/systemd-mutable/system" ];

    system.activationScripts.dysnomia = ''
      mkdir -p /etc/systemd-mutable/system
      if [ ! -f /etc/systemd-mutable/system/dysnomia.target ]
      then
          ( echo "[Unit]"
            echo "Description=Services that are activated and deactivated by Dysnomia"
            echo "After=final.target"
          ) > /etc/systemd-mutable/system/dysnomia.target
      fi
    '';
  };
}