{
  pkgs,
  lib,
  self,
  nixosSystem,
}:
# Options documentation for hyperhive's NixOS module surfaces.
# Closes #616. HTML output added per mara on internal-requests #8.
#
# Three rendering layers:
#   CommonMark — `pkgs.nixosOptionsDoc.optionsCommonMark`. Source of
#                truth; kept as `.md` files in the bundle.
#   HTML       — `pkgs.cmark-gfm` over the CommonMark output, wrapped
#                in a minimal inline-CSS template. Primary surface; the
#                bundle's `index.html` / `host.html` / `agent.html` are
#                what the operator's nginx serves from
#                `hyperhive.darkest.space/options/`.
#
# Three output trees consumed by `flake.nix`:
#   docs-host   — operator-facing host-module options
#                 (`services.hive-c0re.*`, `hyperhive.{domain,forge,matrix}.*`)
#   docs-agent  — per-agent harness options
#                 (`hyperhive.{model,allowedRecipients,extraMcpServers,…}`)
#   docs        — bundled static site (index + host + agent, .html + .md)
#
# All asset paths inside the rendered HTML are relative (e.g.
# `./host.html`) so the bundle can be mounted at any URL prefix
# without rewriting; styles are inline so there's no second-fetch
# request for the operator's browser.
let
  # Evaluate the host module under a stub NixOS system. Stubs satisfy
  # the few hard-required options (filesystems, stateVersion) without
  # actually enabling the hive — we only want the option *declarations*
  # to evaluate, not the config.
  hostEval = nixosSystem {
    system = pkgs.stdenv.hostPlatform.system;
    modules = [
      self.nixosModules.default
      (
        { lib, ... }:
        {
          nixpkgs.overlays = [ self.overlays.default ];
          fileSystems."/" = {
            device = "/dev/null";
            fsType = "tmpfs";
          };
          boot.loader.grub.enable = false;
          system.stateVersion = "25.11";
          # Force-disable every hyperhive subsystem so config evaluation
          # doesn't pull in heavy build inputs (matrix container, forge,
          # etc.). Options are still fully declared either way — that's
          # what nixosOptionsDoc traverses.
          services.hyperhive.enable = lib.mkForce false;
          services.hyperhive.forge.enable = lib.mkForce false;
          services.hyperhive.matrix.enable = lib.mkForce false;
          services.hyperhive.gateway.enable = lib.mkForce false;
        }
      )
    ];
  };

  # Agent options live in the already-evaluated `agent-base` container
  # config. Reusing it avoids re-evaluating the harness module against
  # a fresh stub — the options tree is identical to what a real agent
  # container sees.
  agentEval = self.nixosConfigurations.agent-base;

  # Strip the nix-store prefix from option declaration paths and rewrite
  # them as forge URLs so the rendered docs link back to the source.
  forgeRoot = "https://forge.darkest.space/hyperhive/hyperhive/src/branch/main";
  storePrefix = toString self + "/";
  transformOptions =
    opt:
    opt
    // {
      declarations = map (
        decl:
        let
          declStr = toString decl;
          relPath =
            if lib.hasPrefix storePrefix declStr then
              lib.removePrefix storePrefix declStr
            else
              baseNameOf declStr;
        in
        {
          url = "${forgeRoot}/${relPath}";
          name = relPath;
        }
      ) opt.declarations;
    };

  # Filter an evaluated `options` tree down to a set of top-level
  # subtrees we care about. Anything outside the listed roots is
  # dropped — keeps the rendered docs focused on hyperhive's surface
  # instead of NixOS's 10k+ default options.
  pickSubtrees =
    options: roots:
    let
      pick =
        path:
        if lib.hasAttrByPath path options then
          lib.setAttrByPath path (lib.getAttrFromPath path options)
        else
          { };
    in
    lib.foldl' lib.recursiveUpdate { } (map pick roots);

  # Post-#615, host options live entirely under `services.hyperhive.*`
  # (closes #630). Pre-#615 had a mix of `hyperhive.*` (forge, matrix,
  # domain) and `services.hive-c0re.*` — picking against those roots
  # silently produced an empty options tree on current main, so the
  # rendered host page was just the template chrome with no `<h2>`
  # option headers underneath.
  hostOptions = pickSubtrees hostEval.options [
    [
      "services"
      "hyperhive"
    ]
  ];

  agentOptions = pickSubtrees agentEval.options [
    [ "hyperhive" ]
  ];

  hostDoc = pkgs.nixosOptionsDoc {
    options = hostOptions;
    inherit transformOptions;
  };

  agentDoc = pkgs.nixosOptionsDoc {
    options = agentOptions;
    inherit transformOptions;
  };

  # Plain-markdown page (with a short header). Source of truth; the
  # HTML version is rendered from this.
  mkMarkdownPage =
    name: title: doc:
    pkgs.runCommand "hyperhive-${name}.md" { } ''
      {
        echo "# ${title}"
        echo
        echo "<!-- Auto-generated from the hyperhive flake."
        echo "     Source: nix/docs/default.nix · regenerate with"
        echo "     \`nix build .#${name}\` -->"
        echo
        cat ${doc.optionsCommonMark}
      } > $out
    '';

  # Inline-stylesheet, loaded as plain text from `./style.css` so it's
  # editable with normal CSS tooling (#625). Inlined into every page
  # so the bundle doesn't depend on a second HTTP fetch — keeps the
  # `/options/` mount trivial for nginx (no MIME guessing for separate
  # .css files, no cache-busting needed when this updates).
  styleCSS = builtins.readFile ./style.css;

  # HTML page: CommonMark → cmark-gfm → minimal template with inline
  # CSS + relative-only links. cmark-gfm rather than plain cmark so
  # any future tables / autolinks Just Work without revisiting.
  mkHtmlPage =
    name: title: doc:
    pkgs.runCommand "hyperhive-${name}.html" { nativeBuildInputs = [ pkgs.cmark-gfm ]; } ''
      {
        echo '<!doctype html>'
        echo '<html lang="en">'
        echo '<head>'
        echo '<meta charset="utf-8">'
        echo '<meta name="viewport" content="width=device-width, initial-scale=1">'
        echo '<title>${title}</title>'
        echo '<style>'
        cat ${pkgs.writeText "hyperhive-docs-style.css" styleCSS}
        echo '</style>'
        echo '</head>'
        echo '<body>'
        echo '<nav>'
        echo '<a href="./index.html">index</a>'
        echo '<a href="./host.html">host options</a>'
        echo '<a href="./agent.html">agent options</a>'
        echo '</nav>'
        echo '<main>'
        echo '<h1>${title}</h1>'
        echo '<p><em>Auto-generated from the hyperhive flake. Source: <a href="${forgeRoot}/nix/docs/default.nix">nix/docs/default.nix</a>.</em></p>'
        cmark-gfm ${doc.optionsCommonMark}
        echo '</main>'
        echo '<footer>'
        echo '<p>hyperhive · <a href="${forgeRoot}">source</a></p>'
        echo '</footer>'
        echo '</body>'
        echo '</html>'
      } > $out
    '';

  # Landing page — same template shape as the option pages but
  # hand-authored content (short intro + cross-links). Kept tight; the
  # detail lives on the two option pages.
  indexHTML = pkgs.runCommand "hyperhive-docs-index.html" { } ''
    {
      echo '<!doctype html>'
      echo '<html lang="en">'
      echo '<head>'
      echo '<meta charset="utf-8">'
      echo '<meta name="viewport" content="width=device-width, initial-scale=1">'
      echo '<title>hyperhive — nix options reference</title>'
      echo '<style>'
      cat ${pkgs.writeText "hyperhive-docs-style.css" styleCSS}
      echo '</style>'
      echo '</head>'
      echo '<body>'
      echo '<nav>'
      echo '<a href="./index.html">index</a>'
      echo '<a href="./host.html">host options</a>'
      echo '<a href="./agent.html">agent options</a>'
      echo '</nav>'
      echo '<main>'
      echo '<h1>hyperhive — nix options reference</h1>'
      echo '<p>Auto-generated from the <a href="${forgeRoot}">hyperhive flake</a>. Two reading paths:</p>'
      echo '<h3><a href="./host.html">host options</a></h3>'
      echo '<p>Options exposed by <code>hyperhive.nixosModules.default</code> to operator host configurations: <code>services.hyperhive.{enable,domain,c0re,forge,matrix,gateway}.*</code>.</p>'
      echo '<h3><a href="./agent.html">agent options</a></h3>'
      echo '<p>Per-agent options declared in <code>nix/templates/harness-base.nix</code> and visible from every <code>agent.nix</code>: <code>hyperhive.model</code>, <code>hyperhive.allowedRecipients</code>, <code>hyperhive.extraMcpServers</code>, <code>hyperhive.frontend.*</code>, <code>hyperhive.forge.*</code>, <code>hyperhive.matrix.*</code>, <code>hyperhive.gui.*</code>.</p>'
      echo '<h3>Regenerate</h3>'
      echo '<pre><code>nix build .#docs          # bundled static site (index + host + agent)'
      echo 'nix build .#docs-host     # host page only (HTML)'
      echo 'nix build .#docs-agent    # agent page only (HTML)</code></pre>'
      echo '<p>The bundle also ships <code>.md</code> versions of each page (<code>host.md</code>, <code>agent.md</code>) — same content, source-of-truth shape — alongside the HTML.</p>'
      echo '</main>'
      echo '<footer>'
      echo '<p>hyperhive · <a href="${forgeRoot}">source</a></p>'
      echo '</footer>'
      echo '</body>'
      echo '</html>'
    } > $out
  '';

  hostHTML = mkHtmlPage "docs-host" "hyperhive — host options" hostDoc;
  agentHTML = mkHtmlPage "docs-agent" "hyperhive — per-agent options" agentDoc;
  hostMD = mkMarkdownPage "docs-host" "hyperhive — host options" hostDoc;
  agentMD = mkMarkdownPage "docs-agent" "hyperhive — per-agent options" agentDoc;
in
{
  # Individual page outputs (HTML is the primary surface; the .md
  # source is one `nix build` step away if needed).
  host = hostHTML;
  agent = agentHTML;

  # Bundled static site for nginx to serve at `/options/`. Asset paths
  # are all relative, no root-absolute references, so the prefix can
  # change without rebuild.
  bundle = pkgs.runCommand "hyperhive-options-docs" { } ''
    mkdir -p $out
    cp ${indexHTML} $out/index.html
    cp ${hostHTML} $out/host.html
    cp ${agentHTML} $out/agent.html
    cp ${hostMD} $out/host.md
    cp ${agentMD} $out/agent.md
  '';
}