/**
 * lanternfall — the door. The rules are in `game.ts`, the dungeon in
 * `dungeon.ts` (pure), what happened in `db.ts`; here there is a table of
 * paths and a cookie.
 *
 * A delver belongs to one opaque HttpOnly cookie. It names nobody: the name
 * on the gravestone is derived from the cookie, which is also why a dead
 * delver's successor is somebody new rather than the same person again.
 */

import { randomBytes } from "node:crypto";
import { join } from "node:path";
import * as store from "./db.ts";
import { act, delverFor, isAction, viewFor } from "./game.ts";
import { endPage, gamePage, notFoundPage } from "./pages.ts";

const db = store.open();

const chrome = {
  env: process.env.FORGE_APP_ENV ?? "local",
  pull: process.env.FORGE_APP_PULL,
  commit: (process.env.FORGE_APP_COMMIT ?? "").slice(0, 7),
  ssh: process.env.FORGE_APP_SSH,
};

const HAND = "delver";

function handOf(request: Request): string | undefined {
  for (const part of (request.headers.get("cookie") ?? "").split(";")) {
    const [name, ...rest] = part.trim().split("=");
    if (name === HAND) {
      const value = rest.join("=");
      if (/^[a-f0-9]{32}$/.test(value)) return value;
    }
  }
  return undefined;
}

const newHand = (): string => randomBytes(16).toString("hex");

const handCookie = (hand: string): string =>
  `${HAND}=${hand}; Path=/; Max-Age=31536000; HttpOnly; SameSite=Lax${
    publicOrigin.startsWith("https:") ? "; Secure" : ""
  }`;

// The app's public address is what the forge told us, never the socket's.
const publicOrigin = new URL(process.env.FORGE_APP_URL ?? "http://localhost").origin;

// The security floor every response stands on. The one addition to the
// scaffold's: script-src is still 'self', and the page's only script is a
// file under /static — there is no inline script anywhere.
const SECURITY: Record<string, string> = {
  "content-security-policy":
    "default-src 'self'; style-src 'self' 'unsafe-inline'; img-src 'self' data:; frame-ancestors 'none'; base-uri 'none'; form-action 'self'",
  "x-content-type-options": "nosniff",
  "referrer-policy": "strict-origin-when-cross-origin",
  "permissions-policy": "camera=(), microphone=(), geolocation=()",
  ...(publicOrigin.startsWith("https:")
    ? { "strict-transport-security": "max-age=31536000" }
    : {}),
};

const html = (body: string, status = 200): Response =>
  new Response(body, { status, headers: { "content-type": "text/html; charset=utf-8", ...SECURITY } });

// A browser on another site can make a person's browser POST here; it cannot
// make that request look same-origin. Browsers say where a request came from
// (Sec-Fetch-Site, or Origin); a request that names another site is refused.
const sameOrigin = (request: Request): boolean => {
  const site = request.headers.get("sec-fetch-site");
  if (site !== null) return site === "same-origin" || site === "none";
  const origin = request.headers.get("origin");
  return origin === null || origin === publicOrigin;
};

// A request body is read up to a cap and no further, counting the bytes as
// they arrive. A declared Content-Length is a claim: a chunked request has
// none, and a lie is free. Undefined means "too large" — refuse it. Past the
// cap the rest is drained and dropped so the connection stays usable for
// the next request; past eight times the cap it is cut off instead.
const BODY_MAX = 64 * 1024;
async function readBody(request: Request, max = BODY_MAX): Promise<Uint8Array | undefined> {
  const reader = request.body?.getReader();
  if (reader === undefined) return new Uint8Array();
  const parts: Uint8Array[] = [];
  let size = 0;
  for (;;) {
    const { done, value } = await reader.read();
    if (done) break;
    size += value.byteLength;
    if (size > max) {
      for (;;) {
        const next = await reader.read();
        if (next.done) return undefined;
        size += next.value.byteLength;
        if (size > max * 8) {
          await reader.cancel();
          return undefined;
        }
      }
    }
    parts.push(value);
  }
  const body = new Uint8Array(size);
  let at = 0;
  for (const part of parts) {
    body.set(part, at);
    at += part.byteLength;
  }
  return body;
}

// The form fields of a capped body, decoded the way the browser sent them
// (a plain form or a multipart one), by handing the bytes back to a Request.
async function readForm(request: Request): Promise<FormData | undefined> {
  const body = await readBody(request);
  if (body === undefined) return undefined;
  return new Request(request.url, {
    method: "POST",
    headers: { "content-type": request.headers.get("content-type") ?? "" },
    body,
  }).formData();
}

/** Everything the screen needs for one delver, in one place. */
function screen(hand: string): string {
  const delver = delverFor(db, hand);
  const now = store.turn(db);
  return gamePage(
    chrome,
    delver,
    viewFor(db, delver),
    store.cacheState(db, delver.depth, now),
    store.heard(db, delver.id),
    store.recentGraves(db),
    store.topScores(db),
    store.countSeen(db),
  );
}

export const server = Bun.serve({
  port: Number(process.env.PORT ?? 8080),
  hostname: process.env.HOST ?? "127.0.0.1",
  async fetch(request) {
    const url = new URL(request.url);
    if (request.method === "POST" && !sameOrigin(request))
      return new Response("forbidden", { status: 403 });

    if (request.method === "POST" && url.pathname === "/act") {
      const form = await readForm(request);
      if (form === undefined)
        return new Response("too large", { status: 413, headers: SECURITY });
      const hand = handOf(request) ?? newHand();
      const headers = new Headers({ "set-cookie": handCookie(hand), ...SECURITY });
      const wanted = String(form.get("action") ?? "");
      if (!isAction(wanted)) {
        headers.set("location", "/");
        return new Response(null, { status: 303, headers });
      }
      const result = act(db, hand, wanted);
      // A run that ended gets its own page once; the next action sends
      // somebody new down.
      headers.set("location", result.died ? "/died" : result.climbedOut ? "/out" : "/");
      return new Response(null, { status: 303, headers });
    }

    const reading = request.method === "GET" || request.method === "HEAD";

    if (reading && url.pathname === "/") {
      const seen = handOf(request);
      const hand = seen ?? newHand();
      const full = html(screen(hand));
      const headers = new Headers(full.headers);
      if (seen === undefined) headers.set("set-cookie", handCookie(hand));
      return request.method === "HEAD"
        ? new Response(null, { status: full.status, headers })
        : new Response(await full.text(), { status: full.status, headers });
    }

    if (reading && (url.pathname === "/died" || url.pathname === "/out")) {
      const hand = handOf(request);
      const last = hand === undefined ? null : store.lastDelver(db, hand);
      if (last === null || last.state === "delving") return Response.redirect("/", 303);
      return html(
        endPage(chrome, last, last.state === "returned", store.heard(db, last.id)),
      );
    }

    if (reading && url.pathname.startsWith("/static/") && !url.pathname.includes("..")) {
      const file = Bun.file(join(import.meta.dir, "..", url.pathname.slice(1)));
      if (await file.exists())
        return new Response(file, {
          headers: { "cache-control": "public, max-age=31536000, immutable", ...SECURITY },
        });
    }

    return html(notFoundPage(chrome), 404);
  },
  error(error) {
    console.error(error);
    return html("<h1>Something went wrong</h1>", 500);
  },
});

console.log(
  `lanternfall is open on http://${server.hostname}:${server.port} (${chrome.env}), turn ${store.turn(db)}`,
);