BangleApps/apps/ftclock/mkFourTwentyTz.js

let fs = require('fs');
let csv = require('csv');

let countries = {},
    zones = {},
    offsdict = {},
    now = Date.now(); // we need this to find zone's current DST state

function handleWrite(err,bytes) {
 if (err) {
  console.log(`Error writing to file ${err}`);
 }
}

console.log("Generating fourTwentyTz.js...");
fs.createReadStream(__dirname+'/country.csv')
  .pipe(csv.parse())
  .on('data', (r) => {
    countries[r[0]] = r[1];
  })
  .on('end', () => {
    fs.createReadStream(__dirname+'/zone.csv')
      .pipe(csv.parse())
      .on('data', (r) => {
        let parts = r[2].replace('_',' ').split('/');
        let city = parts[parts.length-1];
        let country ='';
        if (parts.length>2) { // e.g. America/North_Dakota/New_Salem
          country = parts[1]; // e.g. North Dakota
        } else {
          country = countries[r[1]]; // e.g. United States
        }
        zones[parseInt(r[0])] = {"name": `${city}, ${country}`};
      })
      .on('end', () => {
        fs.createReadStream(__dirname+'/timezone.csv')
          .pipe(csv.parse())
          .on('data', (r) => {
            code = parseInt(r[0]);
            if (!(code in zones)) return;
            starttime = parseInt(r[2] || "0"); // Bugger. They're feeding us blanks for UTC now
            offs = parseInt(r[3]);
            if (offs<0) {
              offs += 60*60*24;
            }
            zone = zones[code];
            if (starttime<now && (!("starttime" in zone) || zone.starttime<starttime)) {
                zone.starttime = starttime;
                zone.offs = Math.floor(offs/60);
            }
          })
          .on('end', () => {
            for (z in zones) {
              zone = zones[z];
              if (zone.offs%60) continue; // One a dem funky timezones. Ignore.
              zonelist = offsdict[zone.offs] || [];
              zonelist.push(zone.name);
              offsdict[zone.offs] = zonelist;
            }
            fs.open("fourTwentyTz.js","w", (err, fd) => {
              if (err) {
                console.log("Can't open output file");
                return;
              }
              fs.write(fd, "// Generated by mkFourTwentyTz.js\n", handleWrite);
              fs.write(fd, `// ${Date()}\n`, handleWrite);
              fs.write(fd, "// Data source: https://timezonedb.com/files/timezonedb.csv.zip\n", handleWrite);
              fs.write(fd, "exports.timezones = ", handleWrite);
              fs.write(fd, JSON.stringify(offsdict, null, 4), handleWrite);
              console.log('Done.');
            });
          })
      })
  });