import {
    decryptBox,
    decryptSealed,
    deriveKEK,
    fromBase64,
    toBase64URL,
} from "../crypto/index.js";
import type { AuthorizationResponse } from "./types.js";

export interface UnwrapResult {
    masterKey: Uint8Array;
    secretKey: Uint8Array;
    publicKey: Uint8Array;
    // URL-safe-no-padding base64 of the decrypted token bytes; this is the
    // exact value to put in the X-Auth-Token header on subsequent calls.
    token: string;
}

// Given a successful AuthorizationResponse and the user's password,
// derive the KEK, decrypt the master key, decrypt the secret key, and
// open the sealed auth token. See test/auth/unwrap.test.ts for the
// complete protocol description.
export const unwrapAuth = async (
    response: AuthorizationResponse,
    password: string,
): Promise<UnwrapResult> => {
    if (!response.keyAttributes) {
        throw new Error(
            "unwrapAuth: response.keyAttributes is required (login may be incomplete: TOTP or passkey pending)",
        );
    }
    if (!response.encryptedToken) {
        throw new Error(
            "unwrapAuth: response.encryptedToken is required (login may be incomplete: TOTP or passkey pending)",
        );
    }

    const ka = response.keyAttributes;
    const kek = await deriveKEK(
        password,
        fromBase64(ka.kekSalt),
        ka.opsLimit,
        ka.memLimit,
    );
    const masterKey = decryptBox(
        fromBase64(ka.encryptedKey),
        fromBase64(ka.keyDecryptionNonce),
        kek,
    );
    const secretKey = decryptBox(
        fromBase64(ka.encryptedSecretKey),
        fromBase64(ka.secretKeyDecryptionNonce),
        masterKey,
    );
    const publicKey = fromBase64(ka.publicKey);
    const tokenBytes = decryptSealed(
        fromBase64(response.encryptedToken),
        publicKey,
        secretKey,
    );
    const token = toBase64URL(tokenBytes);

    return { masterKey, secretKey, publicKey, token };
};