import { DerReader } from "../asn1/reader.js";
import { CRYPTO_RSA_CODES, CryptoRsaError } from "../errors/errors.js";
import type { RsaPublicKey } from "./keys.types.js";

/**
 * Parse a DER-encoded PKCS#1 `RSAPublicKey ::= SEQUENCE { modulus INTEGER,
 * publicExponent INTEGER }` per RFC 8017 Appendix A.1.1.
 *
 * Validates that the public exponent is odd and `>= 3`, matching the
 * conformance requirement in the spec delta.
 */
export function parseRsaPublicKeyPkcs1(bytes: Uint8Array): RsaPublicKey {
    const reader = new DerReader(bytes);
    const seq = reader.readSequence();
    const n = seq.readInteger();
    const e = seq.readInteger();
    seq.assertEnd();
    reader.assertEnd();
    return finalisePublicKey(n, e);
}

/**
 * Internal: validate `(n, e)` and compute `bitLength`. Used by SPKI / JWK
 * parsers as well as the PKCS#1 path.
 */
export function finalisePublicKey(n: bigint, e: bigint): RsaPublicKey {
    if (n <= 0n) {
        throw new CryptoRsaError(
            CRYPTO_RSA_CODES.INVALID_KEY,
            "error.crypto-rsa.invalid-key.modulus"
        );
    }
    if (e < 3n) {
        throw new CryptoRsaError(
            CRYPTO_RSA_CODES.INVALID_KEY,
            "error.crypto-rsa.invalid-key.exponent-too-small",
            { context: { e: e.toString() } }
        );
    }
    if ((e & 1n) === 0n) {
        throw new CryptoRsaError(
            CRYPTO_RSA_CODES.INVALID_KEY,
            "error.crypto-rsa.invalid-key.exponent-even"
        );
    }
    const bitLength = n.toString(2).length;
    return { n, e, bitLength };
}