# SPDX-FileCopyrightText: 2024 Lubin Bailly <lubin.bailly@dgnum.eu>
# SPDX-FileCopyrightText: 2025 Tom Hubrecht <tom.hubrecht@dgnum.eu>
#
# SPDX-License-Identifier: EUPL-1.2

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

let
  inherit (lib)
    attrNames
    concatStringsSep
    escapeXML
    evalModules
    filter
    flip
    getAttr
    hasPrefix
    head
    listToAttrs
    mapAttrsToList
    literalExpression
    mkEnableOption
    mkIf
    mkOption
    nameValuePair
    optionAttrSetToDocList
    optionalString
    pathIsDirectory
    pipe
    removeAttrs
    removePrefix
    removeSuffix
    ;

  inherit (lib.strings)
    sanitizeDerivationName
    ;

  inherit (lib.types)
    attrs
    attrsOf
    deferredModule
    listOf
    nullOr
    path
    submodule
    str
    ;

  mkDocJSON =
    module:
    {
      ignored-modules,
      path-translations,
      paths,
      specialArgs,
      ...
    }:
    let
      # NOTE: A big simplification of nixpkgs' make-options-doc
      # It turns out that we only need the json output, and have
      # no `baseOptionsJSON`, so the transformation done is `id`
      mkOpts = (flip pipe) [
        # Evaluate the modules
        (modules: evalModules { inherit modules specialArgs; })
        # Extract the options
        (getAttr "options")
        # Transform into a list of options
        optionAttrSetToDocList
        # Remove invisible and internal options
        (filter (o: o.visible && !o.internal))
        # Remove extraneous attributes
        (builtins.map (
          o:
          nameValuePair o.name (
            removeAttrs o [
              "name"
              "visible"
              "internal"
            ]
          )
        ))
        # Transform back to an attribute set
        listToAttrs
      ];

      # INFO: Subtract options of the ignored modules from
      #       the complete set of options
      ignored = attrNames (mkOpts ignored-modules);
      options = removeAttrs (mkOpts (paths ++ ignored-modules)) ignored;

      directories = builtins.map (getAttr "base") path-translations;

      mkTranslation =
        path:
        let
          # Get the file associated to the module
          file = if pathIsDirectory path then path + "/default.nix" else path;

          # Get the parent module set
          matching = filter (m: hasPrefix m.base path) path-translations;
          parent = head matching;
          filePath = removePrefix parent.base file;
        in
        if matching == [ ] then
          (throw "${file} is not a descendant of ${module}. Declared parents are: \n  ${concatStringsSep "\n  " directories}")
        else
          {
            name = "<${filePath}>";
            url = "${parent.url}/${filePath}";
          };
    in
    pkgs.runCommand "options-extranix"
      {
        fileName = sanitizeDerivationName "options-${module}.json";
        nativeBuildInputs = [ pkgs.jq ];

        passAsFile = [ "result" ];
        result = builtins.toJSON {
          last_update = "-/-";
          options = mapAttrsToList (
            title:
            {
              default ? {
                text = "";
              },
              description,
              example ? {
                text = "";
              },
              loc,
              readOnly,
              type,
              declarations,
              ...
            }:
            {
              inherit
                loc
                readOnly
                title
                type
                ;

              descriptionHTML = pkgs.runCommandLocal "option-${title}.html" {
                inherit description;
                passAsFile = [ "description" ];

                nativeBuildInputs = [ pkgs.pandoc ];
              } "pandoc -f markdown-raw_html $descriptionPath > $out";

              description = escapeXML description;
              example = escapeXML example.text;
              default = escapeXML default.text;
              declarations = builtins.map mkTranslation declarations;
            }
          ) options;
        };
      }
      ''
        mkdir -p $out
        jq -r '.options[].descriptionHTML | "--rawfile\n" + . + "\n" + .' $resultPath | xargs \
          jq -c '.options |= map(.descriptionHTML as $desc | .descriptionHTML |= $ARGS.named.[$desc])' $resultPath \
          > $out/$fileName
      '';

  website =
    pkgs.runCommand "search-infra"
      {
        inherit (cfg) theme;

        nativeBuildInputs = [ pkgs.hugo ];

        config = builtins.toJSON cfg.settings;
        passAsFile = [ "config" ];

        data = pkgs.symlinkJoin {
          name = "options-data";
          paths = mapAttrsToList mkDocJSON cfg.modules;
        };
      }
      ''
        # Setup the directory structure
        mkdir themes && ln -s $theme themes/options-search
        ln -s $configPath hugo.json
        mkdir static
        ${optionalString (cfg.static != null) "cp -R ${cfg.static} static"}
        ln -s $data static/data

        # Build the website
        hugo -d $out
      '';

  cfg = config.services.extranix;
in

{
  options.services.extranix = {
    enable = mkEnableOption "extranix documentation";

    theme = mkOption {
      type = path;
      description = ''
        Path to a hugo theme for the search website.
      '';
    };

    modules = mkOption {
      type = attrsOf (submodule {
        options = {
          specialArgs = mkOption {
            type = attrs;
            default = { };
            description = ''
              Special arguments to give to evalModules.
            '';
          };

          paths = mkOption {
            type = listOf deferredModule;
            description = ''
              Modules to from which to document options.
            '';
          };

          ignored-modules = mkOption {
            type = listOf deferredModule;
            default = [ ];
            description = ''
              Modules required to make modules of `paths` valid.
            '';
            example = ''
              import "''${infra-modulesPath}/module-list.nix"
            '';
          };

          path-translations = mkOption {
            type = listOf (submodule {
              options = {
                base = mkOption {
                  type = path;
                  description = ''
                    Base path of some module files to be documented.
                  '';
                  apply = v: "${removeSuffix "/" (builtins.toString v)}/";
                };
                url = mkOption {
                  type = str;
                  description = ''
                    Url root to use for files on this path.
                  '';
                  apply = removeSuffix "/";
                };
              };
            });
            description = ''
              Rules to convert file paths to urls in the documentation to indicate where
              the option is declared.
            '';
          };
        };
      });
      description = ''
        Sets of modules to be documented separately. The identifier to give for
        `settings.params.release_current_stable` (which is the default module shown) is the key after
        passing through `sanitizeDerivationName`.
      '';
    };

    host = mkOption {
      type = str;
      description = ''
        Hostname of the service.
      '';
    };

    index = mkOption {
      type = str;
      default = head (attrNames cfg.modules);
      defaultText = literalExpression "head (attrNames config.services.extranix.modules)";
      description = ''
        The main module to show when loading the website.
      '';
      apply = sanitizeDerivationName;
    };

    static = mkOption {
      type = nullOr path;
      default = null;
      description = ''
        Path to extra static files.
      '';
    };

    settings = mkOption {
      inherit (pkgs.formats.json { }) type;

      description = ''
        Settings of the hugo website.
      '';
      example = {
        baseUrl = "https://example.org/";
        title = "Module documentation";
        languageCode = "en-us";
        params = {
          release_current_stable = "Some-Module";
          logo = "logo.png";
          footer_credits_line = ''
            Based on <a href="https://github.com/mipmip/home-manager-option-search">Home Manager Option Search</a>
          '';
          footer_copyright_line = ''
            Made by catvayor for the <a href="https://dgnum.eu">DGNum</a>.
          '';
          main_menu = [
            {
              name = ''Sources'';
              url = "https://git.example.org/";
            }
          ];
        };
      };
    };
  };

  config = mkIf cfg.enable {
    services = {
      extranix.settings = {
        theme = "options-search";
        params = {
          releases = mapAttrsToList (name: _: {
            inherit name;
            value = sanitizeDerivationName name;
          }) cfg.modules;

          release_current_stable = cfg.index;
        };
      };

      nginx = {
        enable = true;
        virtualHosts.${cfg.host}.locations."/".root = website;
      };
    };

    assertions = [
      {
        assertion = cfg.modules != { };
        message = ''
          `services.extranix` can't be enabled without any modules to document.
        '';
      }
    ];
  };
}