import { HalfCryptoKeyPair } from "encryption/types";

export interface RSASignerI {
    signBinary(data: Uint8Array): Promise<ArrayBuffer>;
    verifyBinary(signature: Uint8Array, data: Uint8Array): Promise<boolean>;
}

export function RSASigner(
    keyPair: CryptoKeyPair | HalfCryptoKeyPair
): RSASignerI {
    const { publicKey, privateKey } = keyPair as CryptoKeyPair;

    const algorithm = RSASigner.getDefaultAlgorithm();

    return {
        async signBinary(data: Uint8Array): Promise<ArrayBuffer> {
            if (!publicKey) {
                throw Error(
                    "Cannot sign data as privateKey has not been supplied."
                );
            }
            return crypto.subtle.sign(algorithm, privateKey, data);
        },
        async verifyBinary(
            signature: Uint8Array,
            data: Uint8Array
        ): Promise<boolean> {
            if (!publicKey) {
                throw Error(
                    "Cannot verify data as publicKey has not been supplied."
                );
            }
            return crypto.subtle.verify(algorithm, publicKey, signature, data);
        }
    };
}

RSASigner.getDefaultAlgorithm = function(): RsaHashedKeyGenParams {
    const hashBitLength = 512;

    return Object.freeze({
        name: "RSA-PSS",
        // RFC 3447 suggests salt lengths are either 0 or the length of the output of the hash function
        saltLength: hashBitLength / 8,
        modulusLength: 2048,
        // From MDN: Unless you have a good reason to use something else, specify 65537 here ([0x01, 0x00, 0x01]).
        publicExponent: new Uint8Array([0x01, 0x00, 0x01]),
        hash: "SHA-" + hashBitLength
    });
};

RSASigner.generateKeyPair = async function(): Promise<CryptoKeyPair> {
    return (await crypto.subtle.generateKey(
        RSASigner.getDefaultAlgorithm(),
        // We need to be able to save this key to the user document, so it needs to be extractable
        true,
        ["sign", "verify"]
    )) as CryptoKeyPair;
};