// This is deliberately browser-compatible JS, so we avoid fat arrows etc.

var locale = "EN-GB";
var now = getTimeNow();
var nextNewYearUTC = new Date(Date.UTC(getTimeNow().getFullYear()+1, 0, 1));
var secsRemaining = 0;
var nextZone;
var counter = document.getElementById("counter");
var loc = document.getElementById("location");
var time = document.getElementById("localtime");
var untilDate = document.getElementById("until-date");

var countDownSound = new Audio('get-ready.ogg');

// This function returns the current time - or we can adjust it to a
// fake time, if we're testing!
function getTimeNow() {
  var now = new Date();
  var offset = 0; // hours
  
  return new Date(now.valueOf() + offset*3600000);
}

// Convert the next new year time to 'date, hours:mins:secs' in the target timezone
function zoneTime(zone, refTime) {
  return refTime.toLocaleString('EN-US', {
    hour: '2-digit',
    hour12: false,
    minute: '2-digit',
    second: '2-digit',
    year: 'numeric',
    month: 'numeric',
    day: 'numeric',
    timeZone: zone,
  });
}

function zoneOffsetMillis(timestr, baseDate) {
  var v = timestr.split(/[/ :,]+/)
      .map(function(str) { return Number(str); });
  var date = new Date(v[2],v[0]-1,v[1],v[3],v[4],v[5]);
  return date.valueOf() - baseDate.valueOf();
}

// Compile a list of timezones from Intl.supportedValuesOf
var zones = Intl.supportedValuesOf('timeZone')
    .map(function(zone) { return {
      zone: zone,
      offset: zoneOffsetMillis(zoneTime(zone, nextNewYearUTC), nextNewYearUTC)
    }; })
    .sort(function(a,b) { return b.offset - a.offset; });

// Now concoct an index of timezone hour offsets to timezone info.
// Each zone has:
// { abbrevs, offset, hOffset, nydDate }
var zoneIndex = zones
    .reduce((a, v) => {
      var hOffset = v.offset/3600000;
      var zoneInfo = a[hOffset];
      if (zoneInfo)
        zoneInfo.abbrevs.push(v.zone);
      else {
        a[hOffset] = {
          abbrevs: [v.zone],
          offset: v.offset,
          hOffset: hOffset,
          nydDate: new Date(nextNewYearUTC.valueOf() + v.offset),
        };
      }
      return a;
    }, {});
console.debug(nextNewYearUTC, zoneIndex);

// This info is just used to say what cities / countries are in the timezone
var zoneInfo = {
  "-12": {
    country: "small region of U.S.A.",
    city: "Baker Island, Howland Island"
  },
  "-11": {
    country: "American Samoa, Midway Atoll/U.S.A. and 1 more",
    city: "Alofi, Midway, Pago Pago"
  },
  "-10": {
    country: "Cook Islands, small region of U.S.A. and 2 more",
    city: "Honolulu, Rarotonga, Adak, Papeete"
  },
  "-9.5": {
    country: "French Polynesia, Marquesas Islands",
    city: "Taiohae"
  },
  "-9": {
    country: "Alaska/U.S.A. and French Polynesia",
    city: "Anchorage, Fairbanks, Unalaska, Juneau"
  },
  "-8": {
    country: "Pitcairn Islands, regions of U.S.A. Mexico, and Canada",
    city: "Los Angeles, San Francisco, Las Vegas, Seattle"
  },
  "-7": {
    country: "some regions of U.S.A., Mexico, some regions of Canada",
    city: "Calgary, Denver, Edmonton, Phoenix"
  },
  "-6": {
    country: "Belize, regions of U.S.A., Mexico, some regions of Canada and 8 more",
    city: "Mexico City, Chicago, Guatemala, Dallas"
  },
  "-5": {
    country: "regions of U.S.A., regions of Canada and 12 more",
    city: "New York, Washington DC, Detroit, Havana"
  },
  "-4": {
    country: "Venezuela",
    city: "Caracas, Barquisimeto, Maracaibo, Maracay"
  },
  "-3.5": {
    country: "Newfoundland and Labrador/Canada",
    city: "St. John's, Conception Bay South, Corner Brook, Gander"
  },
  "-3": {
    country: "regions of Brazil, Argentina and 7 more",
    city: "Buenos Aires, Santiago, Asuncion, Paramaribo"
  },
  "-2": {
    country: "South Georgia and the South Sandwich Islands",
    city: "Grytviken",
  },
  "-1": {
    country: "Cape Verde, some regions of Greenland and 1 more",
    city: "Praia, Ponta Delgada (Azores), Ittoqqortoormiit, Mindelo"
  },
  "0": {
    country: "United Kingdom and 24 more",
    city: "London, Casablanca, Dublin, Lisbon"
  },
  "1": {
    country: "Germany and 43 more",
    city: "Brussels, Madrid, Paris, Rome"
  },
  "2": {
    country: "Greece and 30 more",
    city: "Cairo, Ankara, Athens, Bucharest"
  },
  "3": {
    country: "Iraq and 20 more",
    city: "Baghdad, Khartoum, Nairobi, Addis Ababa"
  },
  "3.5": {
    country: "Iran",
    city: "Tehran, Rasht, Esfahãn, Bandar-Abbas"
  },
  "4": {
    country: "UAE, parts of Russia, Georgia, Armenia, Mauritius",
    city: "Tblisi, Dubai, Abu Dhabi",
  },
  "4.5": {
    country: "Afghanistan",
    city: "Kabul, Kandahar, Mazari Sharif, Herat"
  },
  "5": {
    country: "Pakistan and 8 more",
    city: "Tashkent, Islamabad, Lahore, Karachi"
  },
  "5.5": {
    country: "India and Sri Lanka",
    city: "New Delhi, Mumbai, Kolkata, Bangalore"
  },
  "5.75": {
    country: "Nepal",
    city: "Kathmandu, Biratnagar, Pokhara"
  },
  "6": {
    country: "Bangladesh, some regions of Russia and 4 more",
    city: "Dhaka, Almaty, Bishkek, Thimphu"
  },
  "6.5": {
    country: "Myanmar and Cocos Islands",
    city: "Yangon, Naypyidaw, Mandalay, Bantam"
  },
  "7": {
    country: "much of Indonesia, Thailand and 7 more",
    city: "Jakarta, Bangkok, Hanoi, Phnom Penh"
  },
  "8": {
    country: "China and 12 more",
    city: "Beijing, Hong Kong, Manila, Singapore"
  },
  "8.75": {
    country: "Western Australia/Australia",
    city: "Eucla"
  },
  "9": {
    country: "Japan and 6 more",
    city: "Tokyo, Seoul, Pyongyang, Dili"
  },
  "9.5": {
    country: "Northern Territory/Australia",
    city: "Darwin, Alice Springs, Uluru"
  },
  "10": {
    country: "Queensland/Australia and 5 more",
    city: "Brisbane, Port Moresby, Guam (Hagåtña), Cairns"
  },
  "10.5": {
    country: "small region of Australia",
    city: "Adelaide, Broken Hill"
  },
  "11": {
    country: "Vanuatu, Solomon Islands, much of Australia and 5 more",
    city: "Melbourne, Sydney, Canberra, Honiara"
  },
  "12": {
    country: "Kiribati, Marshall Islands, Norfolk Island, Tuvalu, Fiji",
    city: "Kingston",
  },
  "13": {
    country: "New Zealand with exceptions and 5 more",
    city: "Auckland, Suva, Wellington, Nukualofa"
  },
  "13.75": {
    country: "Chatham Islands/New Zealand",
    city: "Chatham Islands"
  },
};
console.debug(zoneInfo);

var zoneOrder = Object.keys(zoneIndex)
    .map(Number)
    .sort(function(a,b) { return a-b; });
console.debug(zoneOrder);

function pad(num) {
  return (num<10? "0"+num : ""+num);
}

function counterClass(millisecsRemaining) {
  if (millisecsRemaining > 3600000) return "hours";
  if (millisecsRemaining > 60000) return "minutes";
  if (millisecsRemaining > 10000) return "seconds";
  return "countdown";
}

function timeRemaining(millisecsRemaining) {
  //    var days = Math.floor(millisecsRemaining / millisInDay)
  //    millisecsRemaining -= days * millisInDay

  var hours = Math.floor(millisecsRemaining / 3600000)
  millisecsRemaining -= hours * 3600000
  
  var mins = Math.floor(millisecsRemaining / 60000)
  millisecsRemaining -= mins * 60000
  
  var secs = Math.round(millisecsRemaining / 1000)
  return hours+"h "+pad(mins)+"m "+pad(secs)+"s"
}

var playing = false;
function handleTick(now) {
  console.debug(now, now.getMilliseconds());

  while (!nextZone || zoneIndex[nextZone].nydDate <= now) {
    if (zoneOrder.length == 0) return;

    nextZone = zoneOrder.shift();
    console.debug("next up: zone", nextZone);
  }

  var millisecsRemaining = zoneIndex[nextZone].nydDate.getTime() - now.getTime();

  console.debug("seconds",now.getSeconds());
  if (millisecsRemaining < 2*60*1000) {
    if (!playing) {
      countDownSound.play();
      playing = true;
    }
  }
  else
    // resets the announcement
    playing = false;

  var info = zoneInfo[nextZone];
  var zone = zoneIndex[nextZone];
  
  untilDate.innerHTML = nextNewYearUTC.toLocaleDateString(locale, {
    weekday: "long",
    year: "numeric",
    month: "long",
    day: "numeric",
  });
  counter.innerHTML = timeRemaining(millisecsRemaining);
  loc.innerHTML = info? info.city || info.country : zone.abbrev[0];

  time.innerHTML = zone.nydDate.toLocaleDateString(locale, {
    hour: "2-digit",
    minute: "2-digit",
    second: "2-digit",
  });
  counter.className = counterClass(millisecsRemaining);
}

function ticker() {
  var now = getTimeNow();
  handleTick(now);

  var millis = now.getMilliseconds()
  var millisTilNextSecond = 1000-millis;
  setTimeout(ticker, millisTilNextSecond);
}

ticker();