Ekklesia/apps/api/src/module-display-routes.ts

import type { EkklesiaPrincipal } from "@ekklesia/contracts";
import type { ModuleUiPublicationRegistry, PublishableModuleDisplay } from "@ekklesia/core/modules";
import type { Context, Hono } from "hono";
import {
  type AuthorizationMiddlewareOptions,
  getAuthorizedPrincipal,
  requirePermission,
} from "./authorization-middleware.js";
import { etagMatches } from "./conditional-request.js";
import { createDisplayHostAssets, type DisplayHostAssets } from "./display-host-assets.js";
export {
  MODULE_DISPLAY_DESCRIPTOR_PREFIX,
  MODULE_DISPLAY_PAGE_PREFIX,
  moduleDisplayDescriptorUrl,
  moduleDisplayPageUrl,
} from "./module-display-path.js";
import { moduleDisplayDescriptorUrl, moduleDisplayPageUrl } from "./module-display-path.js";
import { moduleApiBaseUrl } from "./module-http-routes.js";
import { moduleRealtimeBaseUrl } from "./module-realtime-routes.js";
import {
  describeModuleContributions,
  grantedModulePermissionIds,
  type HostModuleContributionDescriptor,
} from "./module-ui-inventory.js";
import { moduleDisplayUiArtifactUrl } from "./module-ui-routes.js";

/** Host-owned namespaces. Neither can collide with module HTTP routes, all of which live under
 * `/api/v1/modules/<module-id>`, and neither string enters the module-facing UI ABI. */
export const DISPLAY_HOST_SCRIPT_PATH = "/assets/ekklesia-display/app.js";
/**
 * Where the display's offline service worker is served (ADR 0043).
 *
 * The path is chosen for its **directory**: a service worker's default scope is the directory it was
 * served from, so `/display/sw.js` controls display pages and nothing else. Serving it from
 * `/assets/…` beside the host script would scope it to `/assets/`, where no page lives, and widening
 * it with `Service-Worker-Allowed` would put the Dashboard under a worker it has no use for.
 *
 * `sw.js` cannot collide with a display page: a display page is registered at the exact literal
 * `/display/<module-id>` for each display-capable module, and `sw.js` is not a valid module id.
 */
export const DISPLAY_SERVICE_WORKER_PATH = "/display/sw.js";

/** The portable facts a browser host needs to mount this module's one display artifact. It mirrors
 * the primary UI descriptor while naming the role explicitly, so a host cannot accidentally load a
 * management artifact into a signage route. No outer Ekklesia route or filesystem path crosses the
 * boundary. */
export interface HostModuleDisplayDescriptor {
  readonly id: string;
  readonly version: string;
  readonly display: { readonly url: string };
  /** The public page a screen opens to mount this display. This is distinct from `display.url`,
   * which is the compiled artifact imported by the platform host. */
  readonly page: { readonly url: string };
  readonly api: { readonly baseUrl: string };
  readonly realtime: { readonly baseUrl: string };
  readonly permissions: readonly string[];
  /** Renderers other modules contributed to capabilities this module provides (ADR 0041) — the
   * mechanism a signage-style display uses to show another module's content without importing it. */
  readonly contributions: readonly HostModuleContributionDescriptor[];
}

/**
 * Who the host resolved as the viewer of this display.
 *
 * The descriptor reports it because the display host must not ask `/api/v1/principal` — that
 * endpoint answers a question about *people*, and a paired device is deliberately anonymous to it
 * (ADR 0036). Reading the viewer from the response that already performed the authorization means
 * the display never has to infer "no human session, so presumably a device", and the two identity
 * classes never have to be told apart by elimination.
 */
export type HostDisplayViewer =
  | { readonly kind: "authenticated"; readonly userId: string }
  | { readonly kind: "device"; readonly deviceId: string };

export interface HostModuleDisplayResource {
  readonly module: HostModuleDisplayDescriptor;
  readonly viewer: HostDisplayViewer;
}

export interface ModuleDisplayRoutesOptions extends AuthorizationMiddlewareOptions {
  /** The same immutable, eligible/running publication registry used for artifact bytes. */
  readonly moduleUi: ModuleUiPublicationRegistry;
  /** Omitted only when the registry contains no display entrypoints. Production reads the exact
   * surface-owned files before binding and supplies their frozen contents here. */
  readonly assets?: DisplayHostAssets;
}

/** A composition error, detected before any display route is registered. Carries no module id,
 * permission id, path, or package location. */
export class ModuleDisplayConfigurationError extends Error {
  constructor() {
    super("The module display host configuration is inconsistent.");
    this.name = "ModuleDisplayConfigurationError";
    this.stack = `${this.name}: ${this.message}`;
    Object.freeze(this);
  }
}

function displayFailure(c: Context): Response {
  c.header("Cache-Control", "no-store");
  return c.json({ code: "AUTHORIZATION_EVALUATION_FAILED" }, 503);
}

/** Copies and validates injected assets before registering any route. Production's loader already
 * creates this exact shape, while this check keeps a test/composition caller from pairing mutable
 * bytes with a stale validator. */
function snapshotAssets(input: DisplayHostAssets): DisplayHostAssets {
  try {
    const snapshot = createDisplayHostAssets(input.html, input.script, input.serviceWorker);
    if (
      snapshot.scriptEtag !== input.scriptEtag ||
      snapshot.serviceWorkerEtag !== input.serviceWorkerEtag
    ) {
      throw new ModuleDisplayConfigurationError();
    }
    return snapshot;
  } catch {
    throw new ModuleDisplayConfigurationError();
  }
}

function describeViewer(principal: EkklesiaPrincipal): HostDisplayViewer | undefined {
  if (principal.kind === "authenticated") {
    return { kind: "authenticated", userId: principal.userId };
  }
  if (principal.kind === "device") {
    return { deviceId: principal.deviceId, kind: "device" };
  }
  // Unreachable behind the permission gate: the display permission is `restricted`, which no
  // anonymous principal satisfies. Stated rather than assumed.
  return undefined;
}

async function describeDisplay(
  options: ModuleDisplayRoutesOptions,
  principal: EkklesiaPrincipal,
  display: PublishableModuleDisplay,
  viewer: HostDisplayViewer,
): Promise<HostModuleDisplayResource> {
  return {
    viewer,
    module: {
      api: { baseUrl: moduleApiBaseUrl(display.moduleId) },
      contributions: describeModuleContributions(options.moduleUi, display.moduleId),
      display: { url: moduleDisplayUiArtifactUrl(display) },
      id: display.moduleId,
      page: { url: moduleDisplayPageUrl(display.moduleId) },
      permissions: await grantedModulePermissionIds(
        options.evaluator,
        principal,
        display.permissions,
      ),
      realtime: { baseUrl: moduleRealtimeBaseUrl(display.moduleId) },
      version: display.version,
    },
  };
}

function mountDisplay(
  app: Hono,
  options: ModuleDisplayRoutesOptions & { readonly assets: DisplayHostAssets },
  display: PublishableModuleDisplay,
): void {
  // The permission comes from an already-validated manifest/publication record. A request selects
  // neither the permission nor the artifact; it can only hit this exact pre-composed route.
  const requireDisplayPermission = requirePermission(options, display.displayPermission);

  /**
   * The page itself is **not** permission-gated, and the descriptor below still is.
   *
   * An unattended screen has no identity until someone pairs it, so a gate here would mean a new
   * television could only ever be told 403 — there would be nowhere for it to display a pairing
   * code, and the only way to adopt one would be to sign a human into it, which is exactly the
   * model this pass exists to remove (ADR 0036).
   *
   * Serving it costs nothing, because it carries nothing: these are the same inert, module-agnostic
   * bytes for every display, with no module id, no data, and one absolute script URL that was
   * already public. Authorization lives entirely in the descriptor — the page can render, and then
   * learns it may show only a pairing code. What this does reveal is that a module with a display
   * exists at that path, which any pairing flow must reveal to the device it is pairing.
   */
  app.get(moduleDisplayPageUrl(display.moduleId), () => {
    return new Response(options.assets.html, {
      headers: {
        "Cache-Control": "no-store",
        "Content-Type": "text/html; charset=utf-8",
        "X-Content-Type-Options": "nosniff",
      },
      status: 200,
    });
  });

  app.get(moduleDisplayDescriptorUrl(display.moduleId), requireDisplayPermission, async (c) => {
    c.header("Cache-Control", "no-store");
    c.header("Vary", "Origin, Cookie");
    try {
      const principal = getAuthorizedPrincipal(c);
      const viewer = describeViewer(principal);
      if (!viewer) {
        return displayFailure(c);
      }
      return c.json(await describeDisplay(options, principal, display, viewer), 200);
    } catch {
      return displayFailure(c);
    }
  });
}

/**
 * Mounts one stable page and one descriptor route per eligible, running display declaration.
 *
 * There is deliberately no display inventory in this pass. A management UI may need one later,
 * but a bookmarked TV needs only its version-independent page URL. Unknown, dashboard-only,
 * disabled, and dependency-blocked modules have no registered route and collapse into the
 * application's ordinary sanitized 404.
 *
 * The page is an inert, module-agnostic shell: its bytes contain no module id and its one absolute
 * script URL cannot be rebased by a deep `/display/<id>` path. The browser reads the validated id
 * from its outer URL, requests the permission-gated descriptor, and only then imports the exact
 * versioned display artifact that the server supplied.
 */
export function mountModuleDisplayRoutes(app: Hono, options: ModuleDisplayRoutesOptions): void {
  const displays = options.moduleUi.listDisplays();
  if (displays.length === 0) {
    return;
  }
  if (!options.assets) {
    throw new ModuleDisplayConfigurationError();
  }
  const assets = snapshotAssets(options.assets);
  for (const display of displays) {
    if (!options.registry.has(display.displayPermission)) {
      throw new ModuleDisplayConfigurationError();
    }
  }

  // One fixed host bundle, never a directory and never a request-selected package file. Like module
  // artifact bytes, fetching this platform code grants no authority; the page and descriptor are
  // where identity and the module-owned display permission are enforced.
  app.get(DISPLAY_HOST_SCRIPT_PATH, (c) => {
    if (etagMatches(c.req.header("if-none-match"), assets.scriptEtag)) {
      return new Response(null, {
        headers: { "Cache-Control": "no-cache", ETag: assets.scriptEtag },
        status: 304,
      });
    }
    return new Response(assets.script, {
      headers: {
        "Cache-Control": "no-cache",
        "Content-Type": "text/javascript; charset=utf-8",
        ETag: assets.scriptEtag,
        "X-Content-Type-Options": "nosniff",
      },
      status: 200,
    });
  });

  /**
   * The worker itself is `no-cache` with a strong validator, exactly like the host script: a browser
   * re-checks it on its own schedule, and the worker deliberately never caches *itself*, which is
   * how a screen avoids being trapped on an obsolete worker.
   *
   * Like the host script and module artifact bytes, fetching this code grants no authority. It
   * caches only public code and never a permission decision, so serving it anonymously withholds
   * nothing the platform was protecting.
   */
  app.get(DISPLAY_SERVICE_WORKER_PATH, (c) => {
    if (etagMatches(c.req.header("if-none-match"), assets.serviceWorkerEtag)) {
      return new Response(null, {
        headers: { "Cache-Control": "no-cache", ETag: assets.serviceWorkerEtag },
        status: 304,
      });
    }
    return new Response(assets.serviceWorker, {
      headers: {
        "Cache-Control": "no-cache",
        "Content-Type": "text/javascript; charset=utf-8",
        ETag: assets.serviceWorkerEtag,
        "X-Content-Type-Options": "nosniff",
      },
      status: 200,
    });
  });

  for (const display of displays) {
    mountDisplay(app, { ...options, assets }, display);
  }
}