import { moduleIdSchema } from "@ekklesia/contracts";
import { isReservedModuleId } from "@ekklesia/core/modules";
import { DASHBOARD_PLATFORM_PAGES } from "@ekklesia/shell/dashboard-routes";
import { Hono } from "hono";
import { etagMatches } from "./conditional-request.js";
import { createDashboardHostAssets, type DashboardHostAssets } from "./dashboard-host-assets.js";

/**
 * The Dashboard's host-owned routes (ADR 0044, ADR 0057). None can collide with anything else the API
 * serves: the page answers at `/`, at the Dashboard's own platform pages (which the shell exports, so
 * this server and the shell's router read one list), and at each installed module's `/<module-id>`.
 * Every one of those first segments is either a reserved platform name or a module id Core accepted,
 * and Core refuses a module id that is a reserved name, so no module page can shadow `/api`,
 * `/assets`, `/display`, or a platform page. The script lives beside, never inside, the display
 * host's `/assets/ekklesia-display/` namespace, and every emailed verification or reset link still
 * lands on `/` with a query (ADR 0038).
 */
export const DASHBOARD_HOST_PAGE_PATH = "/";
export const DASHBOARD_HOST_SCRIPT_PATH = "/assets/ekklesia-dashboard/app.js";
/** The pre-paint appearance script (ADR 0062), beside the application script. */
export const DASHBOARD_HOST_APPEARANCE_SCRIPT_PATH = "/assets/ekklesia-dashboard/appearance.js";

/**
 * Revalidate-always with a strong `ETag`, exactly the module UI and display-host script policy. The
 * shell emits fixed, unhashed file names, so no response here may be cached as `immutable`: a
 * rebuilt Dashboard must reach a browser on its next load, and an unchanged one costs a `304`.
 */
const DASHBOARD_HOST_CACHE_CONTROL = "no-cache";

/**
 * Headers the Dashboard page carries on every answer, including a `304`, so a revalidated cache
 * entry never keeps an older set.
 *
 * The page holds the platform sign-in form, so it refuses to be framed by anyone — `X-Frame-Options`
 * for older browsers, and CSP `frame-ancestors`, the one directive a policy here carries until the
 * full Content-Security-Policy is decided separately. `no-referrer` keeps the page's URL, which can
 * briefly hold an emailed reset token before the shell strips it, out of every request it makes.
 */
const DASHBOARD_PAGE_SECURITY_HEADERS = Object.freeze({
  "Content-Security-Policy": "frame-ancestors 'none'",
  "Referrer-Policy": "no-referrer",
  "X-Content-Type-Options": "nosniff",
  "X-Frame-Options": "DENY",
});

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

/** Copies and validates injected assets before registering any route, as the display host does, so
 * a composition can never pair bytes with a validator computed from different bytes. */
function snapshotAssets(input: DashboardHostAssets): DashboardHostAssets {
  try {
    const snapshot = createDashboardHostAssets(input.html, input.script, input.appearanceScript);
    if (
      snapshot.htmlEtag !== input.htmlEtag ||
      snapshot.scriptEtag !== input.scriptEtag ||
      snapshot.appearanceScriptEtag !== input.appearanceScriptEtag
    ) {
      throw new DashboardHostConfigurationError();
    }
    return snapshot;
  } catch {
    throw new DashboardHostConfigurationError();
  }
}

function fixedAsset(
  ifNoneMatch: string | undefined,
  body: string,
  etag: string,
  contentType: string,
  extraHeaders: Readonly<Record<string, string>>,
): Response {
  if (etagMatches(ifNoneMatch, etag)) {
    return new Response(null, {
      headers: { ...extraHeaders, "Cache-Control": DASHBOARD_HOST_CACHE_CONTROL, ETag: etag },
      status: 304,
    });
  }
  return new Response(body, {
    headers: {
      "X-Content-Type-Options": "nosniff",
      ...extraHeaders,
      "Cache-Control": DASHBOARD_HOST_CACHE_CONTROL,
      "Content-Type": contentType,
      ETag: etag,
    },
    status: 200,
  });
}

export interface DashboardHostRouteOptions {
  /**
   * The id of every module this process discovered that declares a Dashboard UI — enabled or not,
   * since a disabled module's bookmark should open the Dashboard and say the module is unavailable
   * rather than fail as an unknown address. Fixed at startup, like the rest of the module set.
   */
  readonly modulePages: readonly string[];
}

/** Each module page must be a real module id that names no platform namespace, exactly once.
 * Discovery already guarantees this; the routes refuse to compose rather than trust it. */
function validatedModulePages(modulePages: readonly string[]): readonly string[] {
  const seen = new Set<string>();
  for (const moduleId of modulePages) {
    if (
      !moduleIdSchema.safeParse(moduleId).success ||
      isReservedModuleId(moduleId) ||
      DASHBOARD_PLATFORM_PAGES.some((page) => page === moduleId) ||
      seen.has(moduleId)
    ) {
      throw new DashboardHostConfigurationError();
    }
    seen.add(moduleId);
  }
  return [...seen];
}

/**
 * Serves the built Dashboard from the same origin as `/api`, so the identity system keeps its
 * default same-origin shape.
 *
 * Fixed routes over one frozen snapshot: never a static directory, never a path or file name taken
 * from the request, and never the source map. The page answers at `/`, anywhere inside a Dashboard
 * platform page (`/settings/displays/add` as much as `/settings`), and anywhere inside an installed
 * module's page (`/signage/timelines` as much as `/signage`, so the module's own sub-pages need no
 * server change later) — always with the **same** bytes and the same validator, because the path
 * selects a page inside the shell rather than a file here; that is what lets a refreshed or
 * bookmarked deep link stay where it was.
 *
 * A top-level name that is neither — `/definitely-not-a-real-module`, a module that is not
 * installed or has no Dashboard UI, a look-alike such as `/settings-old` — has no route, nor does
 * `/index.html`, `/app.js`, the `.map`, or a traversal spelling: all fall through to the
 * application's ordinary sanitized `404`. Like the display host's code, these bytes grant no
 * authority: the page renders the sign-in form until `/api/v1/principal` says otherwise.
 */
export function createDashboardHostRoutes(
  assets: DashboardHostAssets,
  options: DashboardHostRouteOptions,
): Hono {
  const snapshot = snapshotAssets(assets);
  const modulePages = validatedModulePages(options.modulePages);
  const routes = new Hono();

  const page = (ifNoneMatch: string | undefined): Response =>
    fixedAsset(
      ifNoneMatch,
      snapshot.html,
      snapshot.htmlEtag,
      "text/html; charset=utf-8",
      DASHBOARD_PAGE_SECURITY_HEADERS,
    );

  routes.get(DASHBOARD_HOST_PAGE_PATH, (c) => page(c.req.header("if-none-match")));
  for (const name of [...DASHBOARD_PLATFORM_PAGES, ...modulePages]) {
    routes.get(`/${name}`, (c) => page(c.req.header("if-none-match")));
    routes.get(`/${name}/*`, (c) => page(c.req.header("if-none-match")));
  }

  routes.get(DASHBOARD_HOST_SCRIPT_PATH, (c) =>
    fixedAsset(
      c.req.header("if-none-match"),
      snapshot.script,
      snapshot.scriptEtag,
      "text/javascript; charset=utf-8",
      {},
    ),
  );

  // Same-origin, revalidated like the application script, and carrying nothing but code: the
  // person's cached choice lives in their browser and is read by this script, never served by it.
  routes.get(DASHBOARD_HOST_APPEARANCE_SCRIPT_PATH, (c) =>
    fixedAsset(
      c.req.header("if-none-match"),
      snapshot.appearanceScript,
      snapshot.appearanceScriptEtag,
      "text/javascript; charset=utf-8",
      {},
    ),
  );

  return routes;
}