const crypto = require('crypto');
const https  = require('https');

const API_TOKEN  = 'your_apiEuro_token';
const SECRET_KEY = 'you_apiEuro_secretKey';
const DOMAIN     = 'api.euro.pruefster.com';
 
/**
 * Will generate a signature 
 * @param {Object} params
 * @returns signedString for api call 
 */

function gen_Signature(params) {
    const paramsString = Params_Strings(params);
    return crypto.createHmac('sha256', SECRET_KEY).update(paramsString).digest('hex');
}
 
/**
 * Sorts the params alphabetically
 * @param {Object} params
 * @returns sortedString thats needs to be signed
 */

function Params_Strings(params) {
    let string = "";
    const keys = Object.keys(params);
    keys.sort();
    for (let key of keys) {
    let value = typeof(params[key]) == "object" ? JSON.stringify(params[key]) : params[key];
    string += key + "=" + value + "?";
    }
    return Buffer.from(string.slice(0, -1)).toString("utf-8");
}

 
function getExam() {
  // Generating the params:
  // All required and optional params have to be entered inside the params object
  // The only param that get entered inside the 'options.path' is the ':id' or ':exam_id' parameter depending on the api call made, 
  // it is not required inside the params object for the signature.
  
  // For example: getting an exam with the id = 83 would require the following path: '/api/v1/exams/83', any additional parameters
  // have to be entered inside the 'params' object such as the 'timestamp', 'nonce' etc. to be signed. 
  
  const params = {
        nonce:     Math.round(Date.now() / 1000),
        timestamp: Date.now()
        //additonal examdata / studentdata etc.... 
  };
 
  signature = gen_Signature(params);
  params.signature = signature;
 
  const stringifiedParams = JSON.stringify(params);
  
  //New and necessary way to calculate the stringlength via buffer for the content-length in the request header (row: 72)
  const buffStr = Buffer.from(stringifiedParams, 'utf-8');
 
  // path and method are essential for the api call, the path describes the unit that is called inside the Pruefster api,
  // the method describes the specified CRUD function that allows the user of the api to create (POST), read (GET), update (PUT,PATCH) and delete (DELETE)
  // the ressources described inside the documentation.
  
  const options = {
    hostname: DOMAIN,
    path:     '/api/v1/exams/83',
    method:   'GET',
    headers: {
      'Content-Type':   'application/json',
      'Authorization':  'apiEuroToken ' + API_TOKEN,
      'Accept':         'application/json',
      'Content-Length': buffStr.byteLength
    }
  }
 
  const req = https.request(options, (res) => {
    console.log('Status code:', res.statusCode);
 
    res.on('data', (data) => {
      process.stdout.write(data);
    });
  });
 
  req.on('error', error => {
    console.error(error)
  })
 
  req.write(stringifiedParams);
  req.end();
}
 
getExam();