import crypto from 'crypto';

/**
 * Issuing and recognising the tokens that open the public intake endpoint.
 *
 * Kept apart from the routes so the rules are pure and testable directly — the
 * same reasoning as `uploadTypes.ts` and `keyByCallerAndEmail`, both of which
 * are exported for their tests because they are where the real decisions live.
 */

// 32 bytes — 256 bits. base64url so the value survives being pasted into a URL,
// a chat message and a QR code without escaping, which is the whole point of a
// link somebody is handed.
const TOKEN_BYTES = 32;

export function generateToken(): string {
  return crypto.randomBytes(TOKEN_BYTES).toString('base64url');
}

/**
 * The digest stored against a link.
 *
 * SHA-256 rather than bcrypt, deliberately, and the reasoning is the opposite
 * of the one that governs passwords. A password hash is slow on purpose,
 * because a human password carries little entropy and has to survive an
 * offline dictionary attack. This is 256 bits from a CSPRNG: there is no
 * dictionary to try, and guessing is not a threat that slowing the hash
 * addresses.
 *
 * Meanwhile the digest is computed on every submission request, and the intake
 * endpoint is unauthenticated. A deliberately slow hash there would be a
 * denial-of-service surface rather than a protection — see #242, where cost-12
 * bcrypt in the test suite was enough to push a request past its timeout under
 * load.
 *
 * No timing-safe comparison is needed. The lookup is an indexed equality match
 * on the digest rather than a byte-by-byte compare of the secret, and an
 * attacker able to mount a timing attack against a 256-bit random value would
 * still need the value.
 */
export function hashToken(token: string): string {
  return crypto.createHash('sha256').update(token).digest('hex');
}