/**
 * Authenticates the tokens a request carries: session tokens in the
 * `Authorization` header and media tokens in a media URL's query string.
 *
 * @module
 */

import type { Context } from "@oak/oak";
import { verifyJWT, verifyMediaToken } from "./jwt.ts";
import { APIErrorCode } from "../../shared/api.ts";
import { APIException } from "./api-exception.ts";
import type { AuthPayload } from "../model/auth.ts";
import type { Role } from "../../shared/user.ts";
import { getSessionState } from "../services/user-service.ts";

/**
 * Checks a signature-verified token against the live user row: the user must
 * still exist, and the token must not predate their last password change
 * (`users.tokens_valid_after`). Returns the live role, or null to refuse.
 *
 * `iat` has one-second resolution, so a token issued in the same second as the
 * change survives it; one issued after it (the fresh one the change hands back)
 * always does.
 */
function checkTokenOwner(
  userId: string,
  iat: number | undefined,
): { role: Role } | null {
  const state = getSessionState(userId);
  if (!state) return null;
  if (state.tokensValidAfter) {
    const cutoff = Math.floor(
      new Date(state.tokensValidAfter).getTime() / 1000,
    );
    if ((iat ?? 0) < cutoff) return null;
  }
  return { role: state.role };
}

/**
 * Verifies a session token end to end: signature, expiry, a user that still
 * exists and no password change since it was issued. The role comes from the
 * DB, not the token, since tokens last 7 days and roles change under them.
 */
export async function authenticate(
  token: string,
): Promise<AuthPayload | null> {
  const payload = await verifyJWT(token);
  if (!payload) return null;
  const live = checkTokenOwner(payload.userId, payload.iat);
  if (!live) return null;
  return { ...payload, role: live.role };
}

/**
 * Resolves the `?token=` on a media URL to the viewer's user id. Takes a media
 * token, or a session token from a client that predates them.
 */
export async function authenticateMedia(token: string): Promise<string | null> {
  const media = await verifyMediaToken(token);
  if (media) {
    return checkTokenOwner(media.userId, media.iat) ? media.userId : null;
  }
  return (await authenticate(token))?.userId ?? null;
}

/**
 * Returns the user id of an optional Bearer token, or null for an anonymous
 * request.
 *
 * Distinguishes *missing* credentials from *invalid* ones:
 * - No `Authorization: Bearer …` header (or a placeholder value such as the
 *   `Bearer undefined` that the client emits when logged out) → anonymous (null).
 * - A real token that fails verification (expired / bad signature / revoked) →
 *   throws 401, so a stale client session surfaces as an auth error it can react
 *   to, instead of being silently downgraded to anonymous (which yields a
 *   misleading 404 on private resources).
 *
 * @throws {APIException} 401 when a token is present but fails verification.
 */
export async function parseOptionalAuth(ctx: Context): Promise<string | null> {
  const authHeader = ctx.request.headers.get("Authorization");
  if (!authHeader?.startsWith("Bearer ")) return null;

  const token = authHeader.substring(7).trim();
  if (!token || token === "undefined" || token === "null") return null;

  const payload = await authenticate(token);
  if (!payload) {
    throw new APIException(APIErrorCode.UNAUTHORIZED, 401, "Invalid token");
  }
  return payload.userId;
}