Traffic by Country in JavaScript

// Twenty countries, sixty days of sessions each, on ONE shared y scale, so
// the long tail reads honestly (flat means small, not "own scale"). The
// column count comes from the container's own width and `minPanelWidth`
// alone: 4 -> 3 -> 2 -> 1 as the container narrows. The chart card has a CSS
// resize handle (bottom-right corner), so drag it: the trellis's single
// ResizeObserver recolumns the live panels without re-creating them.
//
// Why not a top-5 chart with an "other" bucket? Because the tail is where
// the anomalies live: watch New Zealand spike mid-series.
//
// Deterministic walks so the e2e snapshot is stable.
function mulberry32(seed) {
  return function () {
    seed |= 0
    seed = (seed + 0x6d2b79f5) | 0
    var t = Math.imul(seed ^ (seed >>> 15), 1 | seed)
    t = (t + Math.imul(t ^ (t >>> 7), 61 | t)) ^ t
    return ((t ^ (t >>> 14)) >>> 0) / 4294967296
  }
}

var COUNTRIES = [
  { name: 'United States', seed: 5, base: 48000 },
  { name: 'India', seed: 11, base: 30500 },
  { name: 'United Kingdom', seed: 19, base: 22000 },
  { name: 'Germany', seed: 23, base: 18200 },
  { name: 'Brazil', seed: 31, base: 15400 },
  { name: 'France', seed: 37, base: 13100 },
  { name: 'Canada', seed: 43, base: 12000 },
  { name: 'Australia', seed: 47, base: 9600 },
  { name: 'Japan', seed: 59, base: 8100 },
  { name: 'Netherlands', seed: 61, base: 6200 },
  { name: 'Spain', seed: 71, base: 5100 },
  { name: 'Mexico', seed: 79, base: 4300 },
  { name: 'Sweden', seed: 83, base: 3600 },
  { name: 'Poland', seed: 89, base: 3000 },
  { name: 'Singapore', seed: 97, base: 2600 },
  { name: 'South Africa', seed: 101, base: 2200 },
  { name: 'Argentina', seed: 107, base: 1800 },
  { name: 'Ireland', seed: 113, base: 1500 },
  { name: 'Thailand', seed: 127, base: 1200 },
  { name: 'New Zealand', seed: 131, base: 900 },
]

function dailySessions(seed, base, spikeAt) {
  var rand = mulberry32(seed)
  var out = []
  var ts = new Date('01 Jan 2025').getTime()
  var val = base
  for (var i = 0; i < 60; i++) {
    val = Math.max(base * 0.5, val + (rand() - 0.5) * base * 0.12)
    var v = val
    // The anomaly the top-5 chart would never show: a three-day viral spike.
    if (spikeAt && i >= spikeAt && i < spikeAt + 3) {
      v = val + 11000 * (1 - (i - spikeAt) * 0.3)
    }
    out.push([ts, Math.round(v)])
    ts += 86400000
  }
  return out
}

var trafficSeries = COUNTRIES.map(function (c) {
  return {
    name: 'Sessions',
    country: c.name,
    data: dailySessions(c.seed, c.base, c.name === 'New Zealand' ? 34 : 0),
  }
})

var options = {
  series: trafficSeries,
  chart: {
    id: 'trafficTrellis',
    type: 'area',
    animations: {
      enabled: false,
    },
  },
  trellis: {
    by: 'country',
    minPanelWidth: 240,
    panelHeight: 120,
    gap: 12,
  },
  colors: ['#0369A1'],
  stroke: {
    width: 2,
    curve: 'straight',
  },
  fill: {
    type: 'gradient',
    gradient: {
      opacityFrom: 0.35,
      opacityTo: 0.05,
    },
  },
  xaxis: {
    type: 'datetime',
  },
  yaxis: {
    labels: {
      formatter: function (val) {
        return Math.round(val / 1000) + 'k'
      },
    },
  },
  dataLabels: {
    enabled: false,
  },
  tooltip: {
    x: {
      format: 'dd MMM',
    },
  },
}

var chart = new ApexCharts(document.querySelector('#chart'), options)
chart.render()