Boostnote/browser/main/lib/ThemeManager.js

const chooseTheme = (ui) => {
  if (!ui.enableScheduleTheme) {
    return
  }

  const start = parseInt(ui.scheduleStart)
  const end = parseInt(ui.scheduleEnd)

  const now = new Date()
  const minutes = now.getHours() * 60 + now.getMinutes()

  const isEndAfterStart = end > start
  const isBetweenStartAndEnd = minutes >= start && minutes <= end
  const isBetweenEndAndStart = (minutes >= start || minutes <= end)

  if ((isEndAfterStart && isBetweenStartAndEnd) || (!isEndAfterStart && isBetweenEndAndStart)) {
    if (ui.theme !== ui.scheduledTheme) {
      ui.defaultTheme = ui.theme
      ui.theme = ui.scheduledTheme
      applyTheme(ui.theme)
    }
  } else {
    if (ui.theme !== ui.defaultTheme) {
      ui.theme = ui.defaultTheme
      applyTheme(ui.theme)
    }
  }
}

const applyTheme = (theme) => {
  const supportedThemes = ['dark', 'white', 'solarized-dark', 'monokai', 'dracula']
  if (supportedThemes.indexOf(theme) !== -1) {
    document.body.setAttribute('data-theme', theme)
  } else {
    document.body.setAttribute('data-theme', 'default')
  }
}

module.exports = {
  chooseTheme,
  applyTheme
}