with builtins;

rec {
  splitLines = s: filter (x: !isList x) (split "\n" s);

  concatStrings = concatStringsSep "";

  attrsToList =
    a:
    map (name: {
      inherit name;
      value = a.${name};
    }) (builtins.attrNames a);

  replaceStringsRec =
    from: to: string:
    # recursively replace occurrences of `from` with `to` within `string`
    # example:
    #     replaceStringRec "--" "-" "hello-----world"
    #     => "hello-world"
    let
      replaced = replaceStrings [ from ] [ to ] string;
    in
    if replaced == string then string else replaceStringsRec from to replaced;

  squash = replaceStringsRec "\n\n\n" "\n\n";

  trim =
    string:
    # trim trailing spaces and squash non-leading spaces
    let
      trimLine =
        line:
        let
          # separate leading spaces from the rest
          parts = split "(^ *)" line;
          spaces = head (elemAt parts 1);
          rest = elemAt parts 2;
          # drop trailing spaces
          body = head (split " *$" rest);
        in
        spaces + replaceStringsRec "  " " " body;
    in
    concatStringsSep "\n" (map trimLine (splitLines string));

  # FIXME: O(n^2)
  unique = foldl' (acc: e: if elem e acc then acc else acc ++ [ e ]) [ ];

  nameValuePair = name: value: { inherit name value; };

  filterAttrs =
    pred: set:
    listToAttrs (
      concatMap (
        name:
        let
          v = set.${name};
        in
        if pred name v then [ (nameValuePair name v) ] else [ ]
      ) (attrNames set)
    );

  optionalString = cond: string: if cond then string else "";

  showSetting =
    { inlineHTML }:
    name:
    {
      description,
      documentDefault,
      defaultValue,
      aliases,
      value,
      experimentalFeature,
    }:
    let
      result = squash ''
        - ${
          if inlineHTML then ''<span id="conf-${name}">[`${name}`](#conf-${name})</span>'' else ''`${name}`''
        }

        ${indent "  " body}
      '';

      experimentalFeatureNote = optionalString (experimentalFeature != null) ''
        > **Warning**
        > This setting is part of an
        > [experimental feature](@docroot@/contributing/experimental-features.md).

        To change this setting, you need to make sure the corresponding experimental feature,
        [`${experimentalFeature}`](@docroot@/contributing/experimental-features.md#xp-feature-${experimentalFeature}),
        is enabled.
        For example, include the following in [`nix.conf`](#):

        ```
        extra-experimental-features = ${experimentalFeature}
        ${name} = ...
        ```
      '';

      # separate body to cleanly handle indentation
      body = ''
        ${description}

        ${experimentalFeatureNote}

        **Default:** ${showDefault documentDefault defaultValue}

        ${showAliases aliases}
      '';

      showDefault =
        documentDefault: defaultValue:
        if documentDefault then
          # a StringMap value type is specified as a string, but
          # this shows the value type. The empty stringmap is `null` in
          # JSON, but that converts to `{ }` here.
          if defaultValue == "" || defaultValue == [ ] || isAttrs defaultValue then
            "*empty*"
          else if isBool defaultValue then
            if defaultValue then "`true`" else "`false`"
          else
            "`${toString defaultValue}`"
        else
          "*machine-specific*";

      showAliases =
        aliases:
        optionalString (aliases != [ ])
          "**Deprecated alias:** ${(concatStringsSep ", " (map (s: "`${s}`") aliases))}";
    in
    result;

  indent =
    prefix: s: concatStringsSep "\n" (map (x: if x == "" then x else "${prefix}${x}") (splitLines s));

  showSettings =
    args: settingsInfo: concatStrings (attrValues (mapAttrs (showSetting args) settingsInfo));
}