hackish: real-time random watch face

There's a random clock app, but the way it works is that you have to reload the bootloader manually to actually flush the new random face. That isn't what I want -- I want a real-time random watch face that will show me a different face every time I wake up the display.

This has proven to be rather more difficult than I expected, but I have finally come up with something that, while hackish, is actually functional. I figured I'd share it here instead of making a PR, because I'm pretty sure it would never actually go into the code as-is. Anyway,

The easier of the changes was modifying the settings app to allow a random clock. This was accomplished by simply adding an else case to the existing code:

if (clockApps.length === 0) {
  clockMenu["No Clocks Found"] = () => { };
} else {
  clockMenu[`${settings.clock === " random" ? "* " : ""}[random]`] = () => {
    if (settings.clock !== " random") {
      settings.clock = " random";
      updateSettings();
      showMainMenu();
    }
  };
}

NB: I used " random" because the clockApp is a string name of the application set, and I think adding a leading space ensures that there won't be a collision, but I would appreciate guidance if I'm wrong about that.

The bootloader part was a little more tricky (and I'm still not 100% satisfied, though I'd say it does work about 90% of the way I'd like it to). First off I set about refactoring the code just a bit to make selecting a random clock easier.

const clockApp = (require("Storage").readJSON("setting.js­on",1) || {}).clock;
const evaluateCurrentClockApp = () => {
  const allClockApps = () => (
    require("Storage").list(/\.info$/)
      .map((file) => {
        const app = require("Storage").readJSON(file,1);
        if (app && app.type == "clock") {
          return app;
        }
      })
      .filter((x) => x)
  );
  const clockNotFound = `
    E.showMessage("No Clock Found");
    setWatch(() => {
      Bangle.showLauncher();
    }, BTN2, {repeat:false,edge:"falling"});)
  `;
  const currentClockApp = () => {
    if (" random" === clockApp) {
      const apps = allClockApps();
      return apps.length > 0
        ? require("Storage").read(apps[Math.floor(­Math.random() * apps.length)].src)
        : clockNotFound;
    } else if (clockApp) {
      return require("Storage").read(clockApp);
    }
    // Fallback: first clock app we discover on the system
    const [discoveredApp] = allClockApps().sort((a, b) => a.sortorder - b.sortorder);
    return discoveredApp
      ? require("Storage").read(discoveredApp.sr­c)
      // Fallback: not found
      : clockNotFound;
  };
  delete evaluateCurrentClockApp;
  eval(currentClockApp());
};

Instead of running

      eval(clockApp);
      delete clockApp;

to enter the clock app as before, we just: evaluateCurrentClockApp();.

I was also made aware of the fact that all code in the bootloader persists through the passing of execution to the clock -- that is why delete evaluateCurrentClockApp; is at the end of the function. I think it's pretty crazy that you can delete a function that is currently in calling scope, but it actually works and I verified by trace() in the web IDE that it does indeed clean up the memory.

So this is fairly straightforward, but we end up at the original problem: this runs once when the bootloader is executed, but then the selected "random" clock stays as the watch face unless the bootloader is manually run again (e.g. long press BTN3).

I tried a couple solutions to this problem, but the one that seems the most promising is this: set an LCD power off listener in the bootloader. When the LCD is powered off and the current clock app is set as random, reload the bootloader:

Bangle.on("lcdPower", function onLcdPower(on) {
  if (!on && " random" === clockApp) {
    Bangle.removeListener("lcdPower", onLcdPower);
    load();
  }
});

This actually works fairly well for what it does... the only problem is that reloading the bootloader turns the LCD back on, so you can probably guess what happens next: a never-ending loop of the LCD going off, coming back on with a random clock face, going off, coming back on, etc. Still, I was kinda happy when it happened :)

After this happened, I tried this:

Bangle.setLCDPower(0);
Bangle.on("lcdPower", function onLcdPower(on) {
  if (!on && " random" === clockApp) {
    Bangle.removeListener("lcdPower", onLcdPower);
    load();
  }
});

This actually solves the never-ending wake loop, but it introduces another problem: the LCD screen is off upon initial execution. It's honestly a small price to pay for a true random clock face in my opinion, but I wanted to do better. This is also when I really noticed how after the LCD turns off there is a flicker due to reloading the bootloader, before my LCD power off occurs. Annoying, but acceptable (for me).