type.nix

{ extracted, lib, pkgs, ... }:

let

  inherit (lib) types mapAttrs mapAttrsToList nameValuePair;
  inherit (lib.modules) evalModules;

  mapListToAttrs = f: lst:
    builtins.listToAttrs (map f lst);

  # Settings module
  settingType = setting: types.submodule ({config, ...}: {
    options = {
      enable = lib.mkOption {
        description = "Enable the \"${setting.name}\" setting";
        type = types.bool;
        default = setting.enabled;
      };
      value = lib.mkOption {
        description = "The value of the \"${setting.name}\" setting";
        type = types.anything;
        default = setting.value;
      };
      flat = lib.mkOption {
        description = "Empty attrset in enable=false, the setting and its value otherwise";
        type = types.attrsOf types.anything;
        readOnly = true;
      };
    };
    config = {
      flat = if config.enable
             then { "${setting.name}" = config.value; }
             else { };
    };
  });
  settingOption = setting:
    nameValuePair setting.name
      (lib.mkOption {
        description = "Control the \"${setting.name}\" setting";
        type = settingType setting;
        default = { };
      });

  # Subsection modules
  subsectionType = name: sub: types.submodule ({config, ...}: {
    options = {
      enable = lib.mkEnableOption "settings for ${name}";
      flatSettings = lib.mkOption {
        description = "Flat attrset of all settings in subsection ${name} enabled";
        type = types.attrsOf types.anything;
        readOnly = true;
      };
    } // mapListToAttrs settingOption sub.settings;
    config = {
      enable = lib.mkDefault true;
      flatSettings =
        if config.enable
        then builtins.foldl' (x: y: x // y) { }
          (map (setting: config."${setting.name}".flat) sub.settings)
        else { };
    };
  });
  subsectionOption = name: sub: lib.mkOption {
    description = "${name}: ${sub.meta.title}\n${sub.meta.description}";
    type = subsectionType name sub;
    default = { };
  };

  # Section module
  sectionType = name: section: let
    subsections = builtins.removeAttrs section [ "meta" ];
  in types.submodule ({config, ...}: {
    options = {
      enable = lib.mkEnableOption "setting for ${name}";
      flatSettings = lib.mkOption {
        description = "Flat attrset of all settings in section ${name} enabled";
        type = types.attrsOf types.anything;
        readOnly = true;
      };
    } // mapAttrs subsectionOption subsections;
    config = {
      flatSettings =
        if config.enable
        then builtins.foldl' (x: y: x // y) { }
          (mapAttrsToList (name: _: config."${name}".flatSettings) subsections)
        else { };
    };
  });
  sectionOption = name: section: lib.mkOption {
    description = "${name}: ${section.meta.title}\n${section.meta.description}";
    type = sectionType name section;
    default = { };
  };

  # Top-level module
  type = types.submodule ({config, ...}: {
    options = {
      enable = lib.mkEnableOption "Arkenfox settings";
      flatSettings = lib.mkOption {
        description = "Flat attrset of all settings enabled";
        type = types.attrsOf types.anything;
        readOnly = true;
      };
    } // mapAttrs sectionOption extracted;
    config = {
      flatSettings =
        if config.enable
        then builtins.foldl' (x: y: x // y) { }
          (mapAttrsToList (name: _: config."${name}".flatSettings) extracted)
        else { };
    };
  });

in type