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

import type {
  ModuleId,
  ModuleRouteHandlerContext,
  ModuleRuntimeServices,
  RegisteredModuleHttpRoute,
} from "@ekklesia/contracts";
import type { Context, Hono } from "hono";
import {
  type AuthorizationMiddlewareOptions,
  getAuthorizedPrincipal,
  requirePermission,
  requireTrustedOrigin,
} from "./authorization-middleware.js";

const MODULE_ROUTE_PREFIX = "/api/v1/modules";
const STATE_CHANGING_METHODS: ReadonlySet<string> = new Set(["DELETE", "PATCH", "POST", "PUT"]);
const STRIPPED_CORS_RESPONSE_HEADERS = [
  "access-control-allow-credentials",
  "access-control-allow-headers",
  "access-control-allow-methods",
  "access-control-allow-origin",
  "access-control-expose-headers",
  "access-control-max-age",
];

export interface ModuleHttpRoutesOptions extends AuthorizationMiddlewareOptions {
  readonly trustedOrigins: ReadonlySet<string>;
  /** The same frozen services object the started module runtime's `start`/`stop` hooks already
   * received for this API runtime — never a fresh one built per request, and never touched for a
   * denied, trusted-origin-rejected, or `OPTIONS` request, since a handler is only ever invoked
   * after authorization succeeds. */
  readonly services: ModuleRuntimeServices;
}

/** Never carries the offending permission id, route path, module id, or any other configuration
 * detail — a forged or inconsistent route snapshot is a startup-time composition bug, not
 * something to describe in detail to whatever eventually logs it. */
export class ModuleRouteConfigurationError extends Error {
  constructor() {
    super("A published module HTTP route references a permission that is not registered.");
    this.name = "ModuleRouteConfigurationError";
    this.stack = `${this.name}: ${this.message}`;
    Object.freeze(this);
  }
}

/** "/" is the module's own root and maps to the bare module prefix, never a required trailing
 * slash; every other local path appends directly. Root and non-root therefore never collide, and
 * `/api/v1/modules/<module-id>/` (the root path with a trailing slash) is never produced here. */
function moduleRoutePath(moduleId: ModuleId, routePath: string): string {
  return routePath === "/"
    ? `${MODULE_ROUTE_PREFIX}/${moduleId}`
    : `${MODULE_ROUTE_PREFIX}/${moduleId}${routePath}`;
}

function sanitizedModuleHandlerFailure(c: Context): Response {
  c.header("Cache-Control", "no-store");
  return c.json({ code: "MODULE_HANDLER_FAILED" }, 500);
}

/**
 * The one shared `Vary` parsing/canonicalization primitive: splits and trims comma-separated
 * tokens and de-duplicates them case-insensitively — `Vary` lists header *names*, which are
 * themselves case-insensitive, so a module's own `origin` must collapse with a later `Origin`
 * rather than appear as a separate, redundant entry — while preserving first-seen casing and
 * relative order. Never returns early on `*`; callers decide what a `*` token means for their own
 * policy (see `mergedVaryHeader` and `canonicalizeVaryHeader` below, the two callers that build on
 * this instead of re-implementing parsing/dedup independently).
 */
function parseVaryTokens(existingVary: string | null): Map<string, string> {
  const canonicalByLowercase = new Map<string, string>();
  for (const token of (existingVary ?? "").split(",")) {
    const trimmed = token.trim();
    if (trimmed.length === 0) {
      continue;
    }
    const key = trimmed.toLowerCase();
    if (!canonicalByLowercase.has(key)) {
      canonicalByLowercase.set(key, trimmed);
    }
  }
  return canonicalByLowercase;
}

/** A literal `*` (RFC 9110 §12.5.5) must never be combined with any other value; since `*` already
 * means "may vary on anything," a strictly broader signal than any explicit list, its presence
 * collapses the result to `*` alone rather than producing an invalid combination. */
function serializeVaryTokens(tokens: ReadonlyMap<string, string>): string {
  if (tokens.has("*")) {
    return "*";
  }
  return [...tokens.values()].join(", ");
}

/**
 * Used only for a module's own response: always emits the canonical `Origin`/`Cookie` casing
 * regardless of how (or whether) a module already listed them, since every module response is
 * forced to vary on both (see `sanitizeModuleResponse`) — this is a deliberate product policy for
 * module responses specifically, not a generic property every response through the platform's CORS
 * boundary should have forced onto it (an `OPTIONS` preflight, for one, has no `Cookie` concept at
 * all).
 */
export function mergedVaryHeader(existingVary: string | null): string {
  const tokens = parseVaryTokens(existingVary);
  if (tokens.has("*")) {
    return "*";
  }
  tokens.set("origin", "Origin");
  tokens.set("cookie", "Cookie");
  return serializeVaryTokens(tokens);
}

/**
 * Used at the app-level CORS boundary (`apps/api/src/app.ts`), which wraps every response —
 * `OPTIONS` preflights and Core's own routes included, not only module ones — after Hono's own
 * `cors()` has already appended its own `Vary: Origin`. Unlike `mergedVaryHeader`, this never
 * injects a token that was not already present; it only de-duplicates and collapses `*`, since a
 * generic boundary must not assume every response wants `Origin`/`Cookie` forced onto it.
 */
export function canonicalizeVaryHeader(existingVary: string): string {
  return serializeVaryTokens(parseVaryTokens(existingVary));
}

/**
 * The platform owns CORS and caching for every module route: strips any CORS-control header a
 * handler set (defense in depth — the outer `cors()` middleware already computes the authoritative
 * values for the actual response) and forces `Cache-Control: no-store` plus a `Vary` that always
 * includes `Origin` and `Cookie`, since even a public-baseline handler receives an authorized
 * principal and may personalize its response. A separate cache-policy contract is future work;
 * this is the conservative default until then. A module's own legitimate `Vary` values (if any)
 * are preserved alongside the forced ones. Never reads or buffers `response.body` — it is passed
 * through to the new `Response` unread, so a streaming body is neither consumed nor blocked here.
 */
function sanitizeModuleResponse(response: Response): Response {
  const headers = new Headers(response.headers);
  for (const headerName of STRIPPED_CORS_RESPONSE_HEADERS) {
    headers.delete(headerName);
  }
  headers.set("Cache-Control", "no-store");
  headers.set("Vary", mergedVaryHeader(headers.get("Vary")));
  return new Response(response.body, {
    headers,
    status: response.status,
    statusText: response.statusText,
  });
}

/**
 * Mounts `StartedModuleRuntime`'s published, immutable route snapshot into `app`, in publication
 * order — never sorted or mutated, and never invoking a handler while mounting. Every route is
 * protected by the exact same `requirePermission` middleware Core's own routes use, with
 * `route.permission` as the only permission id ever consulted and its baseline coming exclusively
 * from `options.registry`; a state-changing method (`POST`/`PUT`/`PATCH`/`DELETE`) additionally
 * requires `requireTrustedOrigin` before authorization ever runs. `GET` inherits Hono's own
 * implicit `HEAD` handling, which re-enters this exact same middleware chain and strips the
 * response body afterward — there is no separate `HEAD` registration or permission path.
 * `route.handler` is invoked only after authorization succeeds, with the raw Fetch `Request` and a
 * frozen context carrying exactly `moduleId`, `principal`, `params`, and `services` — never a Hono
 * `Context`, authorization store, or configuration; `services.database` is the module's only
 * reachable database surface, and is unreachable to anything short of a successfully authorized
 * handler invocation (a denied request, a rejected trusted-origin check, and `OPTIONS` never reach
 * this handler at all).
 *
 * Because the routes and registry both derive from the same discovered inventory
 * (`prepareStartupModuleInventory`), every registered route permission should already be
 * registered; this loop still checks that invariant explicitly and throws
 * `ModuleRouteConfigurationError` before mounting anything further if it ever does not hold, so a
 * forged or hand-built route snapshot fails app construction instead of silently mounting an
 * unenforceable route. `requirePermission`'s own per-request registry lookup remains the live,
 * defense-in-depth enforcement regardless.
 */
export function mountModuleHttpRoutes(
  app: Hono,
  routes: readonly RegisteredModuleHttpRoute[],
  options: ModuleHttpRoutesOptions,
): void {
  const middlewareOptions: AuthorizationMiddlewareOptions = {
    evaluator: options.evaluator,
    registry: options.registry,
    runtime: options.runtime,
  };
  const requireOrigin = requireTrustedOrigin(options.trustedOrigins);

  for (const route of routes) {
    if (!options.registry.has(route.permission)) {
      throw new ModuleRouteConfigurationError();
    }

    const requireRoutePermission = requirePermission(middlewareOptions, route.permission);
    const path = moduleRoutePath(route.moduleId, route.path);
    const finalHandler = async (c: Context): Promise<Response> => {
      const context: ModuleRouteHandlerContext = Object.freeze({
        moduleId: route.moduleId,
        params: Object.freeze({ ...c.req.param() }),
        principal: getAuthorizedPrincipal(c),
        services: options.services,
      });

      let response: Response;
      try {
        response = await route.handler(c.req.raw, context);
      } catch {
        return sanitizedModuleHandlerFailure(c);
      }
      if (!(response instanceof Response)) {
        return sanitizedModuleHandlerFailure(c);
      }
      return sanitizeModuleResponse(response);
    };

    // Hono's `on()` overloads resolve by literal call arity, not by the runtime length of a spread
    // array — each branch below is therefore a distinct, fixed-arity call rather than one call
    // spreading a variable-length handlers array.
    if (STATE_CHANGING_METHODS.has(route.method)) {
      app.on(route.method, path, requireOrigin, requireRoutePermission, finalHandler);
    } else {
      app.on(route.method, path, requireRoutePermission, finalHandler);
    }
  }
}