(function(mode, cb) {
  var options = {};
  if ("object"==typeof mode) {
    options = mode;
    mode = options.mode;
    if (!mode) throw new Error("Missing mode in setUI({...})");
  }
  var redraw = true;
  if (global.WIDGETS && WIDGETS.back) {
    redraw = false;
    WIDGETS.back.remove(mode && options.back);
  }
  if (Bangle.btnWatches) {
    Bangle.btnWatches.forEach(clearWatch);
    delete Bangle.btnWatches;
  }
  if (Bangle.swipeHandler) {
    Bangle.removeListener("swipe", Bangle.swipeHandler);
    delete Bangle.swipeHandler;
  }
  if (Bangle.touchHandler) {
    Bangle.removeListener("touch", Bangle.touchHandler);
    delete Bangle.touchHandler;
  }
  delete Bangle.uiRedraw;
  delete Bangle.CLOCK;
  if (Bangle.uiRemove) {
    let r = Bangle.uiRemove;
    delete Bangle.uiRemove; // stop recursion if setUI is called inside uiRemove
    r();
  }
  g.reset();// reset graphics state, just in case
  if (!mode) return;
  if (mode=="updown") {
    Bangle.btnWatches = [
      setWatch(function() { cb(-1); }, BTN1, {repeat:1,edge:"falling"}),
      setWatch(function() { cb(1); }, BTN3, {repeat:1,edge:"falling"}),
      setWatch(function() { cb(); }, BTN2, {repeat:1,edge:"falling"})
    ];
  } else if (mode=="leftright") {
    Bangle.btnWatches = [
      setWatch(function() { cb(-1); }, BTN1, {repeat:1,edge:"falling"}),
      setWatch(function() { cb(1); }, BTN3, {repeat:1,edge:"falling"}),
      setWatch(function() { cb(); }, BTN2, {repeat:1,edge:"falling"})
    ];
    Bangle.swipeHandler = d => {cb(d);};
    Bangle.on("swipe", Bangle.swipeHandler);
    Bangle.touchHandler = d => {cb();};
    Bangle.on("touch", Bangle.touchHandler);
  } else if (mode=="clock") {
    Bangle.CLOCK=1;
    Bangle.btnWatches = [
      setWatch(Bangle.showLauncher, BTN2, {repeat:1,edge:"falling"})
    ];
  } else if (mode=="clockupdown") {
    Bangle.CLOCK=1;
    Bangle.btnWatches = [
      setWatch(function() { cb(-1); }, BTN1, {repeat:1,edge:"falling"}),
      setWatch(function() { cb(1); }, BTN3, {repeat:1,edge:"falling"}),
      setWatch(Bangle.showLauncher, BTN2, {repeat:1,edge:"falling"})
    ];
  } else if (mode=="custom") {
    if (options.clock) Bangle.CLOCK=1;
    if (options.touch) {
      Bangle.touchHandler = options.touch;
      Bangle.on("touch", Bangle.touchHandler);
    }
    if (options.swipe) {
      Bangle.swipeHandler = options.swipe;
      Bangle.on("swipe", Bangle.swipeHandler);
    }
    if (options.btn) {
      Bangle.btnWatches = [
        setWatch(function() { options.btn(1); }, BTN1, {repeat:1,edge:"falling"}),
        setWatch(function() { options.btn(2); }, BTN2, {repeat:1,edge:"falling"}),
        setWatch(function() { options.btn(3); }, BTN3, {repeat:1,edge:"falling"})
      ];
    } else if (options.clock) {
      Bangle.btnWatches = [
        setWatch(Bangle.showLauncher, BTN2, {repeat:1,edge:"falling"})
      ];
    }
  } else
    throw new Error("Unknown UI mode "+E.toJS(mode));
  if (options.remove) // handler for removing the UI (intervals/etc)
    Bangle.uiRemove = options.remove;
  if (options.redraw) // handler for redrawing the UI
    Bangle.uiRedraw = options.redraw;
  if (options.back) {
    var touchHandler = (z) => {
      if (z==1) options.back();
    };
    Bangle.on("touch", touchHandler);
    var btnWatch;
    if (Bangle.btnWatches===undefined) // only add back button handler if there's no existing watch on BTN1
      btnWatch = setWatch(function() {
        btnWatch = undefined;
        options.back();
      }, BTN3, {edge:"falling"});
    WIDGETS = Object.assign({back:{
      area:"tl", width:24,
      draw:e=>g.reset().setColor("#f00").drawImage(atob("GBiBAAAYAAH/gAf/4A//8B//+D///D///H/P/n+H/n8P/n4f/vwAP/wAP34f/n8P/n+H/n/P/j///D///B//+A//8Af/4AH/gAAYAA=="),e.x,e.y),
      remove:(noclear)=>{
        if (btnWatch) clearWatch(btnWatch);
        Bangle.removeListener("touch", touchHandler);
        if (!noclear) g.reset().clearRect({x:WIDGETS.back.x, y:WIDGETS.back.y, w:24,h:24});
        delete WIDGETS.back;
        if (!noclear) Bangle.drawWidgets();
      }
    }},global.WIDGETS);
    if (redraw) Bangle.drawWidgets();
  }
})