function get(url) {
  return new Promise(function (resolve, reject) {
    var req = new XMLHttpRequest();
    req.open('GET', url);

    req.onload = function () {
      if (req.status == 200) {
        resolve(req.response);
      }
      else {
        reject(Error(req.statusText));
      }
    };

    req.onerror = function () {
      reject(Error("Network Error"));
    };

    req.send();
  });
}

function getJSON(url) {
  return get(url).then(JSON.parse)
}

function sortByKey(key, d) {
  return d.slice().sort(function (a, b) {
    return a[key] - b[key]
  }).reverse()
}

function limit(key, m, d) {
  return d.filter(function (d) {
    return d[key].isAfter(m)
  })
}

function sum(a) {
  return a.reduce(function (a, b) {
    return a + b
  }, 0)
}

function one() {
  return 1
}

function trueDefault(d) {
  return d === undefined ? true : d
}

function dictGet(dict, key) {
  var k = key.shift();

  if (!(k in dict)) {
    return null;
    }

  if (key.length == 0) {
    return dict[k];
    }

  return dictGet(dict[k], key)
}

function localStorageTest() {
  var test = 'test';
  try {
    localStorage.setItem(test, test);
    localStorage.removeItem(test);
    return true
  } catch (e) {
    return false
  }
}

function listReplace(s, subst) {
  for (key in subst) {
    var re = new RegExp(key, 'g');
    s = s.replace(re, subst[key])
  }
  return s
}

/* Helpers working with nodes */

function offline(d) {
  return !d.flags.online
}

function online(d) {
  return d.flags.online
}

function has_location(d) {
  return "location" in d.nodeinfo &&
    Math.abs(d.nodeinfo.location.latitude) < 90 &&
    Math.abs(d.nodeinfo.location.longitude) < 180
}

function subtract(a, b) {
  var ids = {};

  b.forEach(function (d) {
    ids[d.nodeinfo.node_id] = true
  });

  return a.filter(function (d) {
    return !(d.nodeinfo.node_id in ids)
  })
}

/* Helpers working with links */

function showDistance(d) {
  if (isNaN(d.distance)) {
    return;
    }

  return d.distance.toFixed(0) + " m"
}

function showTq(d) {
  return (1 / d.tq * 100).toFixed(0) + "%"
}

/* Infobox stuff (XXX: move to module) */

function attributeEntry(el, label, value) {
  if (value === null || value == undefined) {
    return;
    }

  var tr = document.createElement("tr");
  var th = document.createElement("th");
  th.textContent = label;
  tr.appendChild(th);

  var td = document.createElement("td");

  if (typeof value == "function") {
    value(td);
  } else {
    td.appendChild(document.createTextNode(value));
    }

  tr.appendChild(td);

  el.appendChild(tr);

  return td
}

function createIframe(opt, width, height) {
  el = document.createElement("iframe");
  width = typeof width !== 'undefined' ? width : '525px';
  height = typeof height !== 'undefined' ? height : '350px';

  if (opt.src) {
    el.src = opt.src;
  } else {
    el.src = opt;
    }

  if (opt.frameBorder) {
    el.frameBorder = opt.frameBorder;
  } else {
    el.frameBorder = 1;
    }

  if (opt.width) {
    el.width = opt.width;
  } else {
    el.width = width;
    }

  if (opt.height) {
    el.height = opt.height;
  } else {
    el.height = height;
    }

  el.scrolling = "no";
  el.seamless = "seamless";

  return el
}

function showStat(o, subst) {
  var content, caption;
  subst = typeof subst !== 'undefined' ? subst : {};

  if (o.thumbnail) {
    content = document.createElement("img");
    content.src = listReplace(o.thumbnail, subst)
  }

  if (o.caption) {
    caption = listReplace(o.caption, subst);

    if (!content) {
      content = document.createTextNode(caption)
      }
  }

  if (o.iframe) {
    content = createIframe(o.iframe, o.width, o.height);
    if (o.iframe.src) {
      content.src = listReplace(o.iframe.src, subst);
    } else {
      content.src = listReplace(o.iframe, subst)
      }
  }

  var p = document.createElement("p");

  if (o.href) {
    var link = document.createElement("a");
    link.target = "_blank";
    link.href = listReplace(o.href, subst);
    link.appendChild(content);

    if (caption && o.thumbnail) {
      link.title = caption;
    }

    p.appendChild(link)
  } else {
        p.appendChild(content);
    }

  return p
}