Switch Slack to dark mode at night

nightOwlForSlack.js

// append this to /Applications/Slack.app/Contents/Resources/app.asar.unpacked/src/static/ssb-interop.js
document.addEventListener('DOMContentLoaded', async function() {
  // supply your location here, use e.g. https://www.latlong.net/ to find it
  const LOCATION = [50.075539, 14.437800]
  const MS_IN_DAY = 24 * 60 * 60 * 1000

  const initTheme = themeCssUrl => new Promise(resolve => $.ajax({
    url: themeCssUrl,
    success: css => {
      const styleJqueryEl = $('<style>').html(css).appendTo('head')
      const styleElement = styleJqueryEl[0]
      styleElement.disabled = true
      resolve(styleElement)
    }
  }))

  const loadTimeInfo = ([latitude, longitude]) => new Promise(resolve => $.ajax({
    // courtesy of https://sunrise-sunset.org/api
    url: `https://api.sunrise-sunset.org/json?lat=${latitude}&lng=${longitude}&formatted=0`,
    success: ({ results: { sunrise, sunset } }) => resolve({
      sunrise: Number(new Date(sunrise)),
      sunset: Number(new Date(sunset)),
      expires: Math.ceil(Date.now() / MS_IN_DAY) * MS_IN_DAY
    })
  }))

  const updateTheme = (styleElement, timeInfo) => {
    const now = Date.now()
    const { sunrise, sunset } = timeInfo
    styleElement.disabled = now >= sunrise && now < sunset
  }

  const darkModeStyle = await initTheme('https://raw.githubusercontent.com/mattiacantalu/Slack-Dark-Mode/master/dark-mode.css')
  let timeInfo = await loadTimeInfo(LOCATION)
  updateTheme(darkModeStyle, timeInfo)
  // can't simply `setTimeout` to the next update time - if the app is sleeping at that time, the call seems to be lost
  window.setInterval(async () => {
    if (Date.now() > timeInfo.expires) {
      timeInfo = await loadTimeInfo(LOCATION)
    }
    updateTheme(darkModeStyle, timeInfo)
  }, 5 * 60 * 1000)
})