function request(url) {
  var xhr = new XMLHttpRequest();
  xhr.open("POST", url, true);
  xhr.setRequestHeader("Content-Type", "application/json");
  return xhr;
}

function check(id) {
  var checkbox = document.getElementById("task-" + id);
  if (checkbox.checked) {
    var xhr = request("/v1/do");
    xhr.onreadystatechange = function() {
      if (xhr.readyState === 4) {
        data = JSON.parse(xhr.responseText);
        if (data.task) {
          $("#task-" + data.task.id).prop("checked", data.task.done);
        } else {
          console.log(data); // NOTE TEMPORARY (handle errors better!)
        }
      }
    }
    xhr.send(JSON.stringify({api_key: API_KEY, id: id}));
  } else {
    var xhr = request("/v1/undo");
    xhr.onreadystatechange = function() {
      if (xhr.readyState === 4) {
        data = JSON.parse(xhr.responseText);
        if (data.task) {
          $("#task-" + data.task.id).prop("checked", data.task.done);
        } else {
          console.log(data); // NOTE TEMPORARY (handle errors better!)
        }
      }
    }
    xhr.send(JSON.stringify({api_key: API_KEY, id: id}));
  }
}

function new_task() {
  var text = document.getElementById("new-task-input");
  var xhr = request("/v1/new");
  xhr.onreadystatechange = function() {
    if (xhr.readyState === 4) {
      data = JSON.parse(xhr.responseText);
      if (data.task) {
        $("#new-task").before("<li><input type='checkbox' id='task-" + data.task.id + "' onchange='check(" + data.task.id + ")'> " + data.task.content + "</li>");
      } else {
        console.log(data); // NOTE TEMPORARY (handle errors better!)
      }
    }
  }
  xhr.send(JSON.stringify({api_key: API_KEY, content: text.value}));

  return false; // prevent form submission
}

function new_api_key() {
  var xhr = request("/new-api-key");
  xhr.onreadystatechange = function() {
    if (xhr.readyState === 4) {
      data = JSON.parse(xhr.responseText);
      if (data.api_key) {
        $("#new-api-key").before("<li>" + data.api_key.key + "</li>");
      } else {
        console.log(data); // NOTE TEMPORARY (handle errors better!)
      }
    }
  }
  xhr.send(); // NOTE may need to send empty string or empty JSON object
}