/**
 * Phase 09 Task #82 — PKCE / state / nonce challenge persistence.
 *
 * Stores the tuple { state, nonce, codeVerifier, createdAt } in an
 * HMAC-signed HttpOnly cookie scoped to /auth/admin. The cookie is
 * single-use: `consumeAdminSsoChallenge()` returns the payload and emits a
 * `Set-Cookie` header that clears it.
 *
 * We sign with HMAC-SHA256 over the JSON payload using
 * `CRYPTO_SECRET || SESSION_SECRET` (mirroring the magic-link convention),
 * and we encode payload+signature with URL-safe base64. The payload itself
 * is NOT encrypted — none of the values are user-secret per spec, and
 * encryption would just hide bugs.
 *
 * TTL is 10 minutes which is generous for Authentik UI redirects but short
 * enough that stolen cookies have a tiny replay window. The TTL is checked
 * server-side (cookie Max-Age is best-effort; clients lie).
 */
import { createHmac, randomBytes, timingSafeEqual } from "node:crypto";
import { loadRequiredWebConfig } from "@toolctrl/config";
import { generators } from "openid-client";

export const ADMIN_SSO_CHALLENGE_COOKIE = "admin_sso_challenge";
export const ADMIN_SSO_CHALLENGE_TTL_MS = 10 * 60 * 1000;
const COOKIE_PATH = "/auth/admin";
const PAYLOAD_VERSION = "v1";

export type AdminSsoChallengePayload = {
  readonly state: string;
  readonly nonce: string;
  readonly codeVerifier: string;
  readonly codeChallenge: string;
  /** Epoch milliseconds. */
  readonly createdAt: number;
  /** Optional safe `returnTo` path captured at /auth/admin/login. */
  readonly returnTo?: string;
};

export type ConsumeResult =
  | { readonly ok: true; readonly payload: AdminSsoChallengePayload; readonly clearCookie: string }
  | { readonly ok: false; readonly reason: "missing" | "malformed" | "bad-signature" | "expired" };

export type CreateOptions = {
  readonly returnTo?: string;
  /** Injectable clock for tests. */
  readonly now?: () => number;
  /** Override secret (tests). */
  readonly secret?: string;
};

function getSigningSecret(override?: string): string {
  if (override) return override;
  const { cryptoSecret, sessionSecret } = loadRequiredWebConfig();
  const secret = cryptoSecret || sessionSecret;
  if (!secret) {
    throw new Error("CRYPTO_SECRET or SESSION_SECRET is required for admin-sso challenge cookies.");
  }
  return secret;
}

function base64UrlEncode(buf: Buffer | string): string {
  const b = typeof buf === "string" ? Buffer.from(buf, "utf8") : buf;
  return b.toString("base64").replace(/\+/g, "-").replace(/\//g, "_").replace(/=+$/, "");
}

function base64UrlDecode(value: string): Buffer {
  const pad = value.length % 4 === 0 ? "" : "=".repeat(4 - (value.length % 4));
  const standard = value.replace(/-/g, "+").replace(/_/g, "/") + pad;
  return Buffer.from(standard, "base64");
}

function sign(payload: string, secret: string): string {
  return base64UrlEncode(createHmac("sha256", secret).update(payload).digest());
}

function verifySignature(payload: string, signature: string, secret: string): boolean {
  const expected = sign(payload, secret);
  const a = Buffer.from(signature);
  const b = Buffer.from(expected);
  if (a.length !== b.length) return false;
  return timingSafeEqual(a, b);
}

/**
 * Generate a fresh challenge tuple. Caller is responsible for setting
 * `Set-Cookie` from `cookie` on the redirect response.
 */
export function createAdminSsoChallenge(options: CreateOptions = {}): { payload: AdminSsoChallengePayload; cookie: string } {
  const codeVerifier = generators.codeVerifier();
  const codeChallenge = generators.codeChallenge(codeVerifier);
  const payload: AdminSsoChallengePayload = {
    state: randomBytes(32).toString("hex"),
    nonce: randomBytes(32).toString("hex"),
    codeVerifier,
    codeChallenge,
    createdAt: options.now ? options.now() : Date.now(),
    returnTo: options.returnTo,
  };
  const cookie = serializeAdminSsoChallengeCookie(payload, options.secret);
  return { payload, cookie };
}

export function serializeAdminSsoChallengeCookie(payload: AdminSsoChallengePayload, secretOverride?: string): string {
  const secret = getSigningSecret(secretOverride);
  const body = base64UrlEncode(JSON.stringify({ v: PAYLOAD_VERSION, p: payload }));
  const sig = sign(body, secret);
  const value = `${body}.${sig}`;
  const maxAgeSeconds = Math.ceil(ADMIN_SSO_CHALLENGE_TTL_MS / 1000);
  const attributes = [
    `${ADMIN_SSO_CHALLENGE_COOKIE}=${value}`,
    `Path=${COOKIE_PATH}`,
    "HttpOnly",
    "SameSite=Lax",
    `Max-Age=${maxAgeSeconds}`,
  ];
  if (process.env.NODE_ENV !== "test") {
    attributes.push("Secure");
  }
  return attributes.join("; ");
}

/**
 * Returns a `Set-Cookie` header that clears the challenge cookie.
 */
export function clearAdminSsoChallengeCookie(): string {
  const attributes = [
    `${ADMIN_SSO_CHALLENGE_COOKIE}=`,
    `Path=${COOKIE_PATH}`,
    "HttpOnly",
    "SameSite=Lax",
    "Max-Age=0",
  ];
  if (process.env.NODE_ENV !== "test") {
    attributes.push("Secure");
  }
  return attributes.join("; ");
}

function readCookieValue(request: Request, name: string): string | null {
  const header = request.headers.get("cookie");
  if (!header) return null;
  for (const part of header.split(/;\s*/)) {
    const eq = part.indexOf("=");
    if (eq === -1) continue;
    const key = part.slice(0, eq).trim();
    if (key === name) return part.slice(eq + 1).trim();
  }
  return null;
}

/**
 * Read + verify + invalidate the challenge cookie attached to `request`.
 * Always returns a `clearCookie` header that the caller must include on
 * the redirect response so the cookie cannot be replayed.
 */
export function consumeAdminSsoChallenge(
  request: Request,
  options: { now?: () => number; secret?: string } = {}
): ConsumeResult {
  const value = readCookieValue(request, ADMIN_SSO_CHALLENGE_COOKIE);
  if (!value) return { ok: false, reason: "missing" };
  const dot = value.lastIndexOf(".");
  if (dot <= 0) return { ok: false, reason: "malformed" };
  const body = value.slice(0, dot);
  const sig = value.slice(dot + 1);
  let secret: string;
  try {
    secret = getSigningSecret(options.secret);
  } catch {
    return { ok: false, reason: "malformed" };
  }
  if (!verifySignature(body, sig, secret)) {
    return { ok: false, reason: "bad-signature" };
  }
  let decoded: { v: string; p: AdminSsoChallengePayload };
  try {
    decoded = JSON.parse(base64UrlDecode(body).toString("utf8"));
  } catch {
    return { ok: false, reason: "malformed" };
  }
  if (decoded.v !== PAYLOAD_VERSION || !decoded.p) {
    return { ok: false, reason: "malformed" };
  }
  const now = options.now ? options.now() : Date.now();
  if (typeof decoded.p.createdAt !== "number" || now - decoded.p.createdAt > ADMIN_SSO_CHALLENGE_TTL_MS) {
    return { ok: false, reason: "expired" };
  }
  return { ok: true, payload: decoded.p, clearCookie: clearAdminSsoChallengeCookie() };
}