utils.js

const jwkToPem = require('jwk-to-pem')
const crypto = require('crypto');
const cbor = require('cbor');

const utils = {};

/**
 * Evaluates the sha256 hash of a string
 * @param {string} data
 * @returns {Buffer} sha256 of the input data
 */
utils.sha256 = data => {
    const hash = crypto.createHash('sha256');
    hash.update(data);
    return hash.digest();
}

/**
 * Converts a JWK to a PEM, which is compatible with
 * node's crypto verify methods.
 * @param {any} jwk json web token
 */
utils.jwkToPem = jwk => {
    return jwkToPem(jwk);
}

/**
 * Utility function to convert a DER  to a PEM
 * @param {String} der base64 encoded DER
 * @returns {String} PEM
 */
utils.derToPEM = der => {
    return "-----BEGIN CERTIFICATE-----\n" +
        der +
        "\n-----END CERTIFICATE-----";
}

/**
 * Turns a cert subject string into a map of its fields
 * @param {string} subjectStr cert subject
 * @returns {*} map of subject fields
 */
utils.parseCertSubject = (subjectStr) => {
    return subjectStr
        .slice(1)
        .split("/")
        .map(i=>i.split("="))
        .reduce((a,c)=>{
            a[c[0]] = c[1];
            return a;
        }, {});
}

/**
 * Converts a COSE key to a JWK
 * @param {Buffer} buffer Buffer containing cbor data with COSE key
 * @returns {any} JWK object
 */
utils.coseToJwk = buffer => {
    try {
        let publicKeyJwk = {};
        publicKeyCbor = cbor.decodeAllSync(buffer);
        publicKeyCbor = publicKeyCbor[0]; //first element

        if (publicKeyCbor.get(3) == -7) {
            publicKeyJwk = {
                kty: "EC",
                crv: "P-256",
                x: publicKeyCbor.get(-2).toString('base64'),
                y: publicKeyCbor.get(-3).toString('base64')
            }
        } else if (publicKeyCbor.get(3) == -35) {
            publicKeyJwk = {
                kty: "EC",
                crv: "P-384",
                x: publicKeyCbor.get(-2).toString('base64'),
                y: publicKeyCbor.get(-3).toString('base64')
            }
        } else if (publicKeyCbor.get(3) == -36) {
            publicKeyJwk = {
                kty: "EC",
                crv: "P-521",
                x: publicKeyCbor.get(-2).toString('base64'),
                y: publicKeyCbor.get(-3).toString('base64')
            }
        } else if (publicKeyCbor.get(3) == -257) {
            publicKeyJwk = {
                kty: "RSA",
                n: publicKeyCbor.get(-1).toString('base64'),
                e: publicKeyCbor.get(-2).toString('base64')
            }
        } else if (publicKeyCbor.get(3) == -8) {
            publicKeyJwk = {
                key : {
                    kty: "OKP",
                    crv: "Ed25519",
                    x: publicKeyCbor.get(-2).toString('base64')
                },
                format: 'jwk'
            }
        } else {
            throw new Error("Unknown public key algorithm");
        }

        return publicKeyJwk;
    } catch (e) {
        throw new Error("Could not decode COSE Key");
    }
}

/**
 * Converts a COSE key to hex
 * @param {Buffer} buffer Buffer containing cbor data with COSE key
 * @returns {String} hex encoded
 */
utils.coseToHex = buffer => {
    try {
        publicKeyCbor = cbor.decodeAllSync(buffer);
        publicKeyCbor = publicKeyCbor[0]; //first element

        return cbor.encode(publicKeyCbor).toString('hex').toUpperCase();
    } catch (e) {
        throw new Error("Could not decode COSE Key");
    }
}

/**
 * Returns a default value if the provided string is undefined
 * @param {string} str
 * @param {string} defaultStr
 * @returns {string}
 */
utils.defaultTo = (str, defaultStr) => {
    if (typeof(str) === 'undefined') {
        return defaultStr;
    } else {
        return str;
    }
}

module.exports = utils;