class ApiService {

  getQuestions(userId, onSuccess, onError) {
    this._get('/api/questions' + userId, onSuccess, onError);
  };

  _get(url, onSuccess, onError) {
    fetch(url)
      .then(this._handleResponse(onSuccess, onError))
      .catch((error) => {
        onError({ error: error.message });
      });
  };

  _post(url, requestData, onSuccess, onError) {
    fetch(url, {
      method: 'POST',
      headers: {
        'Accept': 'application/json',
        'Content-Type': 'application/json'
      },
      body: JSON.stringify(requestData)
    })
      .then(this._handleResponse(onSuccess, onError))
      .catch((error) => {
        onError(error);
      });
  };

  _put(url, requestData, onSuccess, onError) {
    fetch(url, {
      method: 'PUT',
      headers: {
        'Accept': 'application/json',
        'Content-Type': 'application/json'
      },
      body: JSON.stringify(requestData)
    }).then(this._handleResponse(onSuccess, onError))
      .catch((error) => {
        onError(error);
      })
  };

  _handleResponse = (onSuccess, onError) => (response) => {
    if (response.status === 200) {
      response.json()
        .then(onSuccess)
    } else if (response.status === 400) {
      // JSON Syntax error
      response.json().then(onError)
    }
    else {
      onError({ "message": "Backend returned status: " + response.status })
    }
  };
}

export default ApiService;