calendar/calendar.js

// calendar.js — Infinite scrolling week-by-week with overlay event rendering
const monthAbbr = ['jan','feb','mar','apr','may','jun','jul','aug','sep','oct','nov','dec']
const DAY_MS = 86400000
const WEEK_MS = 7 * DAY_MS

const isoWeekInfo = date => {
  const d = new Date(Date.UTC(date.getFullYear(), date.getMonth(), date.getDate()))
  const day = d.getUTCDay() || 7
  d.setUTCDate(d.getUTCDate() + 4 - day)
  const year = d.getUTCFullYear()
  const yearStart = new Date(Date.UTC(year, 0, 1))
  const diffDays = Math.floor((d - yearStart) / DAY_MS) + 1
  return { week: Math.ceil(diffDays / 7), year }
}

function toLocalString(date = new Date()) {
  const pad = n => String(Math.floor(Math.abs(n))).padStart(2, '0')
  return `${date.getFullYear()}-${pad(date.getMonth() + 1)}-${pad(date.getDate())}`
}

function fromLocalString(dateString) {
  const [year, month, day] = dateString.split('-').map(Number)
  return new Date(year, month - 1, day)
}

const mondayIndex = d => (d.getDay() + 6) % 7
const pad = n => String(n).padStart(2, '0')

class InfiniteCalendar {
  constructor(config = {}) {
    this.config = {
      select_days: 0,
      min_year: 1900,
      max_year: 2100,
      ...config
    }

    this.weekend = [true, false, false, false, false, false, true]

    // Event storage
    this.events = new Map() // Map of date strings to arrays of events
    this.eventIdCounter = 1

    this.viewport = document.getElementById('calendar-viewport')
    this.content = document.getElementById('calendar-content')
    this.header = document.getElementById('calendar-header')
    this.jogwheelViewport = document.getElementById('jogwheel-viewport')
    this.jogwheelContent = document.getElementById('jogwheel-content')
    this.selectedDateInput = document.getElementById('selected-date')

    this.rowHeight = this.computeRowHeight()
    this.visibleWeeks = new Map()
    this.baseDate = new Date(2024, 0, 1)  // 2024 begins with Monday

    // unified selection state (single or range)
    this.selStart = null
    this.selEnd = null
    this.isDragging = false
    this.dragAnchor = null

    this.init()
  }

  init() {
    this.createHeader()
    this.setupScrollListener()
    this.setupJogwheel()
    this.setupYearScroll()
    this.setupSelectionInput()
    this.setupCurrentDate()
    this.setupInitialView()
  }

  setupInitialView() {
    const minYearDate = new Date(this.config.min_year, 0, 1)
    const maxYearLastDay = new Date(this.config.max_year, 11, 31)
    const lastWeekMonday = new Date(maxYearLastDay)
    lastWeekMonday.setDate(maxYearLastDay.getDate() - mondayIndex(maxYearLastDay))

    this.minVirtualWeek = this.getWeekIndex(minYearDate)
    this.maxVirtualWeek = this.getWeekIndex(lastWeekMonday)
    this.totalVirtualWeeks = this.maxVirtualWeek - this.minVirtualWeek + 1

    this.content.style.height = `${this.totalVirtualWeeks * this.rowHeight}px`
    this.jogwheelContent.style.height = `${(this.totalVirtualWeeks * this.rowHeight) / 10}px`
    const initial = this.config.initial || this.today
    this.navigateTo(fromLocalString(initial))
  }

  setupCurrentDate() {
    const updateDate = () => {
      this.now = new Date()
      const today = toLocalString(this.now)
      if (this.today === today) return
      this.today = today
      for (const cell of this.content.querySelectorAll('.cell.today')) cell.classList.remove('today')
      const cell = this.content.querySelector(`.cell[data-date="${this.today}"]`)
      if (cell) cell.classList.add('today')
      const todayDateElement = document.getElementById('today-date')
      const t = this.now.toLocaleDateString(undefined, { weekday: 'long', month: 'long', day: 'numeric'}).replace(/,? /, "\n")
      todayDateElement.textContent = t.charAt(0).toUpperCase() + t.slice(1)
    }

    const todayDateElement = document.getElementById('today-date')
    todayDateElement.addEventListener('click', () => this.goToToday())
    if (this.config.select_days > 1) this.setupGlobalDragHandlers()
    updateDate()
    setInterval(updateDate, 1000)
  }

  setupYearScroll() {
    let throttled = false
    const handleWheel = e => {
      e.preventDefault()
      e.stopPropagation()
      const currentYear = parseInt(this.yearLabel.textContent)
      const topDisplayIndex = Math.floor(this.viewport.scrollTop / this.rowHeight)
      const currentWeekIndex = topDisplayIndex + this.minVirtualWeek
      const sensitivity = 1/3
      const delta = Math.round(e.deltaY * sensitivity)
      if (!delta) return
      const newYear = Math.max(this.config.min_year, Math.min(this.config.max_year, currentYear + delta))
      if (newYear === currentYear || throttled) return
      throttled = true
      this.navigateToYear(newYear, currentWeekIndex)
      setTimeout(() => throttled = false, 100)
    }
    this.yearLabel.addEventListener('wheel', handleWheel, { passive: false })
  }

  navigateTo(date) {
    const targetWeekIndex = this.getWeekIndex(date) - 3
    return this.scrollToTarget(targetWeekIndex)
  }

  navigateToYear(targetYear, weekIndex) {
    const monday = this.getMondayForVirtualWeek(weekIndex)
    const { week } = isoWeekInfo(monday)
    const jan4 = new Date(targetYear, 0, 4)
    const jan4Monday = new Date(jan4)
    jan4Monday.setDate(jan4.getDate() - mondayIndex(jan4))
    const targetMonday = new Date(jan4Monday)
    targetMonday.setDate(jan4Monday.getDate() + (week - 1) * 7)
    this.scrollToTarget(targetMonday)
  }

  scrollToTarget(target, options = {}) {
    const { smooth = false, forceUpdate = true, allowFloating = false } = options
    let targetWeekIndex
    if (target instanceof Date) {
      if (!this.isDateInAllowedRange(target)) return false
      targetWeekIndex = this.getWeekIndex(target)
    } else if (typeof target === 'number') {
      targetWeekIndex = target
    } else {
      return false
    }

    if (allowFloating) {
      if (targetWeekIndex < this.minVirtualWeek - 0.5 || targetWeekIndex > this.maxVirtualWeek + 0.5) return false
    } else {
      if (targetWeekIndex < this.minVirtualWeek || targetWeekIndex > this.maxVirtualWeek) return false
    }

    const targetScrollTop = (targetWeekIndex - this.minVirtualWeek) * this.rowHeight

    if (smooth) this.viewport.scrollTo({ top: targetScrollTop, behavior: 'smooth' })
    else this.viewport.scrollTop = targetScrollTop

    const mainScrollable = Math.max(0, this.content.scrollHeight - this.viewport.clientHeight)
    const jogScrollable = Math.max(0, this.jogwheelContent.scrollHeight - this.jogwheelViewport.clientHeight)
    const jogwheelTarget = mainScrollable > 0 ? (targetScrollTop / mainScrollable) * jogScrollable : 0

    if (smooth) this.jogwheelViewport.scrollTo({ top: jogwheelTarget, behavior: 'smooth' })
    else this.jogwheelViewport.scrollTop = jogwheelTarget

    if (forceUpdate) this.updateVisibleWeeks()
    return true
  }

  computeRowHeight() {
    const el = document.createElement('div')
    el.style.position = 'absolute'
    el.style.visibility = 'hidden'
    el.style.height = 'var(--cell-h)'
    document.body.appendChild(el)
    const h = el.getBoundingClientRect().height || 64
    el.remove()
    return Math.round(h)
  }

  getLocalizedWeekdayNames() {
    const res = []
    const base = new Date(2025, 0, 6)
    for (let i = 0; i < 7; i++) {
      const d = new Date(base)
      d.setDate(base.getDate() + i)
      res.push(d.toLocaleDateString(undefined, { weekday: 'short' }))
    }
    return res
  }

  getLocalizedMonthName(idx, short = false) {
    const d = new Date(2025, idx, 1)
    return d.toLocaleDateString(undefined, { month: short ? 'short' : 'long' })
  }

  createHeader() {
    this.yearLabel = document.createElement('div')
    this.yearLabel.className = 'year-label'
    this.yearLabel.textContent = isoWeekInfo(new Date()).year
    this.header.appendChild(this.yearLabel)

    const names = this.getLocalizedWeekdayNames()
    names.forEach((name, i) => {
      const c = document.createElement('div')
      c.classList.add('dow')
      const dayIdx = (i + 1) % 7
      if (this.weekend[dayIdx]) c.classList.add('weekend')
      c.textContent = name
      this.header.appendChild(c)
    })

    const spacer = document.createElement('div')
    spacer.className = 'overlay-header-spacer'
    this.header.appendChild(spacer)
  }

  getWeekIndex(date) {
    const monday = new Date(date)
    monday.setDate(date.getDate() - mondayIndex(date))
    return Math.floor((monday - this.baseDate) / WEEK_MS)
  }

  getMondayForVirtualWeek(virtualWeek) {
    const monday = new Date(this.baseDate)
    monday.setDate(monday.getDate() + virtualWeek * 7)
    return monday
  }

  isDateInAllowedRange(date) {
    const y = date.getFullYear()
    return y >= this.config.min_year && y <= this.config.max_year
  }

  setupScrollListener() {
    let t
    this.viewport.addEventListener('scroll', () => {
      this.updateVisibleWeeks()
      clearTimeout(t)
      t = setTimeout(() => this.updateVisibleWeeks(), 8)
    })
  }

  updateVisibleWeeks() {
    const scrollTop = this.viewport.scrollTop
    const viewportH = this.viewport.clientHeight

    this.updateYearLabel(scrollTop)

    const buffer = 10
    const startIdx = Math.floor((scrollTop - buffer * this.rowHeight) / this.rowHeight)
    const endIdx = Math.ceil((scrollTop + viewportH + buffer * this.rowHeight) / this.rowHeight)

    const startVW = Math.max(this.minVirtualWeek, startIdx + this.minVirtualWeek)
    const endVW = Math.min(this.maxVirtualWeek, endIdx + this.minVirtualWeek)

    for (const [vw, el] of this.visibleWeeks) {
      if (vw < startVW || vw > endVW) {
        el.remove()
        this.visibleWeeks.delete(vw)
      }
    }

    for (let vw = startVW; vw <= endVW; vw++) {
      if (this.visibleWeeks.has(vw)) continue
      const weekEl = this.createWeekElement(vw)
      weekEl.style.position = 'absolute'
      weekEl.style.left = '0'
      const displayIndex = vw - this.minVirtualWeek
      weekEl.style.top = `${displayIndex * this.rowHeight}px`
      weekEl.style.width = '100%'
      weekEl.style.height = `${this.rowHeight}px`
      this.content.appendChild(weekEl)
      this.visibleWeeks.set(vw, weekEl)
      this.addEventsToWeek(weekEl, vw)
    }

    this.applySelectionToVisible()
  }

  updateYearLabel(scrollTop) {
    const topDisplayIndex = Math.floor(scrollTop / this.rowHeight)
    const topVW = topDisplayIndex + this.minVirtualWeek
    const monday = this.getMondayForVirtualWeek(topVW)
    const { year } = isoWeekInfo(monday)
    if (this.yearLabel.textContent !== String(year)) this.yearLabel.textContent = year
  }

  createWeekElement(virtualWeek) {
    const weekDiv = document.createElement('div')
    weekDiv.className = 'week-row'
    const monday = this.getMondayForVirtualWeek(virtualWeek)

    const wkLabel = document.createElement('div')
    wkLabel.className = 'week-label'
    wkLabel.textContent = `W${pad(isoWeekInfo(monday).week)}`
    weekDiv.appendChild(wkLabel)

    // days grid container to host cells and overlay
    const daysGrid = document.createElement('div')
    daysGrid.className = 'days-grid'
    daysGrid.style.position = 'relative'
    daysGrid.style.display = 'grid'
    daysGrid.style.gridTemplateColumns = 'repeat(7, 1fr)'
    daysGrid.style.gridAutoRows = '1fr'
    daysGrid.style.height = '100%'
    daysGrid.style.width = '100%'
    weekDiv.appendChild(daysGrid)

    // overlay positioned above cells, same 7-col grid
    const overlay = document.createElement('div')
    overlay.className = 'week-overlay'
    overlay.style.position = 'absolute'
    overlay.style.inset = '0'
    overlay.style.pointerEvents = 'none'
    overlay.style.display = 'grid'
    overlay.style.gridTemplateColumns = 'repeat(7, 1fr)'
    overlay.style.gridAutoRows = '1fr'
    overlay.style.zIndex = '15'
    daysGrid.appendChild(overlay)
    weekDiv._overlay = overlay
    weekDiv._daysGrid = daysGrid

    const cur = new Date(monday)
    let hasFirst = false
    let monthToLabel = null
    let labelYear = null

    for (let i = 0; i < 7; i++) {
      const cell = document.createElement('div')
      cell.className = 'cell'
      const dateStr = toLocalString(cur)
      cell.setAttribute('data-date', dateStr)

      const dow = cur.getDay()
      if (this.weekend[dow]) cell.classList.add('weekend')

      const m = cur.getMonth()
      cell.classList.add(monthAbbr[m])

      const isFirst = cur.getDate() === 1
      if (isFirst) {
        hasFirst = true
        monthToLabel = m
        labelYear = cur.getFullYear()
      }

      const day = document.createElement('h1')
      day.textContent = String(cur.getDate())

      const date = toLocalString(cur)
      cell.dataset.date = date
      if (this.today && date === this.today) cell.classList.add('today')

      if (this.config.select_days > 0) {
        cell.addEventListener('mousedown', e => {
          e.preventDefault()
          e.stopPropagation()
          this.startDrag(dateStr)
        })
        cell.addEventListener('touchstart', e => {
          e.preventDefault()
          e.stopPropagation()
          this.startDrag(dateStr)
        })
        cell.addEventListener('mouseenter', () => {
          if (this.isDragging) this.updateDrag(dateStr)
        })
        cell.addEventListener('mouseup', e => {
          e.stopPropagation()
          if (this.isDragging) this.endDrag(dateStr)
        })
        cell.addEventListener('touchmove', e => {
          if (this.isDragging) {
            e.preventDefault()
            const touch = e.touches[0]
            const elementBelow = document.elementFromPoint(touch.clientX, touch.clientY)
            if (elementBelow && elementBelow.closest('.cell[data-date]')) {
              const cellBelow = elementBelow.closest('.cell[data-date]')
              const touchDateStr = cellBelow.dataset.date
              if (touchDateStr) this.updateDrag(touchDateStr)
            }
          }
        })
        cell.addEventListener('touchend', e => {
          e.stopPropagation()
          if (this.isDragging) this.endDrag(dateStr)
        })
      }

      if (isFirst) {
        cell.classList.add('firstday')
        day.textContent = cur.getMonth() ? monthAbbr[m].slice(0,3).toUpperCase() : cur.getFullYear()
      }

      cell.appendChild(day)
      daysGrid.appendChild(cell)
      cur.setDate(cur.getDate() + 1)
    }

    if (hasFirst && monthToLabel !== null) {
      if (labelYear && labelYear > this.config.max_year) return weekDiv
      const overlayCell = document.createElement('div')
      overlayCell.className = 'month-name-label'

      let weeksSpan = 0
      const d = new Date(cur)
      d.setDate(cur.getDate() - 1)
      for (let i = 0; i < 6; i++) {
        d.setDate(cur.getDate() - 1 + i * 7)
        if (d.getMonth() === monthToLabel) weeksSpan++
      }

      const remainingWeeks = Math.max(1, this.maxVirtualWeek - virtualWeek + 1)
      weeksSpan = Math.max(1, Math.min(weeksSpan, remainingWeeks))

      overlayCell.style.height = `${weeksSpan * this.rowHeight}px`
      overlayCell.style.display = 'flex'
      overlayCell.style.alignItems = 'center'
      overlayCell.style.justifyContent = 'center'
      overlayCell.style.zIndex = '15'
      overlayCell.style.pointerEvents = 'none'

      const label = document.createElement('span')
      const year = String((labelYear ?? monday.getFullYear())).slice(-2)
      label.textContent = `${this.getLocalizedMonthName(monthToLabel)} '${year}`
      overlayCell.appendChild(label)
      weekDiv.appendChild(overlayCell)
      weekDiv.style.zIndex = '18'
    }

    return weekDiv
  }

  setupJogwheel() {
    let lock = null
    const sync = (fromEl, toEl, fromContent, toContent) => {
      if (lock === toEl) return
      lock = fromEl
      const fromScrollable = Math.max(0, fromContent.scrollHeight - fromEl.clientHeight)
      const toScrollable = Math.max(0, toContent.scrollHeight - toEl.clientHeight)
      const ratio = fromScrollable > 0 ? fromEl.scrollTop / fromScrollable : 0
      toEl.scrollTop = ratio * toScrollable
      setTimeout(() => { if (lock === fromEl) lock = null }, 50)
    }

    this.jogwheelViewport.addEventListener('scroll', () =>
      sync(this.jogwheelViewport, this.viewport, this.jogwheelContent, this.content)
    )

    this.viewport.addEventListener('scroll', () =>
      sync(this.viewport, this.jogwheelViewport, this.content, this.jogwheelContent)
    )
  }

  setupSelectionInput() {
    if (this.config.select_days === 0) {
      this.selectedDateInput.style.display = 'none'
    } else {
      this.selectedDateInput.style.display = 'block'
      this.selectedDateInput.classList.add('clean-input')
    }
  }

  goToToday() {
    const top = new Date(this.now)
    top.setDate(top.getDate() - 21)
    this.scrollToTarget(top, { smooth: true })
  }

  // -------- Selection --------

  daysInclusive(aStr, bStr) {
    const a = fromLocalString(aStr)
    const b = fromLocalString(bStr)
    const A = new Date(a.getFullYear(), a.getMonth(), a.getDate()).getTime()
    const B = new Date(b.getFullYear(), b.getMonth(), b.getDate()).getTime()
    return Math.floor(Math.abs(B - A) / DAY_MS) + 1
  }

  addDaysStr(str, n) {
    const d = fromLocalString(str)
    d.setDate(d.getDate() + n)
    return toLocalString(d)
  }

  clampRange(anchorStr, otherStr) {
    if (this.config.select_days <= 1) return [otherStr, otherStr]
    const limit = this.config.select_days
    const forward = fromLocalString(otherStr) >= fromLocalString(anchorStr)
    const span = this.daysInclusive(anchorStr, otherStr)
    if (span <= limit) {
      const a = [anchorStr, otherStr].sort()
      return [a[0], a[1]]
    }
    if (forward) return [anchorStr, this.addDaysStr(anchorStr, limit - 1)]
    return [this.addDaysStr(anchorStr, -(limit - 1)), anchorStr]
  }

  setSelection(aStr, bStr) {
    const [start, end] = this.clampRange(aStr, bStr)
    this.selStart = start
    this.selEnd = end
    this.applySelectionToVisible()
    this.selectedDateInput.value = this.formatDateRange(fromLocalString(start), fromLocalString(end))
  }

  clearSelection() {
    this.selStart = null
    this.selEnd = null
    for (const [, weekEl] of this.visibleWeeks) {
      weekEl.querySelectorAll('.cell.selected').forEach(c => c.classList.remove('selected'))
    }
    this.selectedDateInput.value = ''
  }

  applySelectionToVisible() {
    for (const [, weekEl] of this.visibleWeeks) {
      const cells = weekEl.querySelectorAll('.cell[data-date]')
      for (const cell of cells) {
        if (!this.selStart || !this.selEnd) {
          cell.classList.remove('selected')
          continue
        }
        const ds = cell.dataset.date
        const inRange = ds >= this.selStart && ds <= this.selEnd
        cell.classList.toggle('selected', inRange)
      }
    }
  }

  formatDateRange(startDate, endDate) {
    if (toLocalString(startDate) === toLocalString(endDate)) return toLocalString(startDate)
    const startISO = toLocalString(startDate)
    const endISO = toLocalString(endDate)
    const [sy, sm] = startISO.split('-')
    const [ey, em, ed] = endISO.split('-')
    if (sy === ey && sm === em) return `${startISO}/${ed}`
    if (sy === ey) return `${startISO}/${em}-${ed}`
    return `${startISO}/${endISO}`
  }

  setupGlobalDragHandlers() {
    document.addEventListener('mouseup', () => {
      if (!this.isDragging) return
      this.isDragging = false
      document.body.style.cursor = 'default'
    })
    document.addEventListener('touchend', () => {
      if (!this.isDragging) return
      this.isDragging = false
      document.body.style.cursor = 'default'
    })
    document.addEventListener('touchmove', e => {
      if (!this.isDragging) return
      e.preventDefault()
      const touch = e.touches[0]
      const elementBelow = document.elementFromPoint(touch.clientX, touch.clientY)
      if (elementBelow && elementBelow.closest('.cell[data-date]')) {
        const cellBelow = elementBelow.closest('.cell[data-date]')
        const touchDateStr = cellBelow.dataset.date
        if (touchDateStr) this.updateDrag(touchDateStr)
      }
    }, { passive: false })
    document.addEventListener('selectstart', e => {
      if (this.isDragging) e.preventDefault()
    })
    document.addEventListener('contextmenu', e => {
      if (this.isDragging) e.preventDefault()
    })
  }

  startDrag(dateStr) {
    if (this.config.select_days === 0) return
    this.isDragging = true
    this.dragAnchor = dateStr
    this.setSelection(dateStr, dateStr)
  }

  updateDrag(dateStr) {
    if (!this.isDragging) return
    this.setSelection(this.dragAnchor, dateStr)
    document.body.style.cursor = 'default'
  }

  endDrag(dateStr) {
    if (!this.isDragging) return
    this.isDragging = false
    this.setSelection(this.dragAnchor, dateStr)
    document.body.style.cursor = 'default'
    if (this.selStart && this.selEnd) {
      setTimeout(() => this.promptForEvent(), 100)
    }
  }

  // -------- Event Management (overlay-based) --------

  promptForEvent() {
    const title = prompt('Enter event title:')
    if (!title || title.trim() === '') {
      this.clearSelection()
      return
    }
    this.createEvent({
      title: title.trim(),
      startDate: this.selStart,
      endDate: this.selEnd
    })
    this.clearSelection()
  }

  createEvent(eventData) {
    const event = {
      id: this.eventIdCounter++,
      title: eventData.title,
      startDate: eventData.startDate,
      endDate: eventData.endDate,
      colorId: this.generateEventColorId()
    }

    const startDate = new Date(fromLocalString(event.startDate))
    const endDate = new Date(fromLocalString(event.endDate))

    for (let d = new Date(startDate); d <= endDate; d.setDate(d.getDate() + 1)) {
      const dateStr = toLocalString(d)
      if (!this.events.has(dateStr)) this.events.set(dateStr, [])
      this.events.get(dateStr).push({ ...event, isSpanning: startDate < endDate })
    }

    this.refreshEvents()
  }

  generateEventColorId() {
    // Return a color ID from 0-11 for 12 evenly spaced hues
    return Math.floor(Math.random() * 12)
  }

  refreshEvents() {
    for (const [, weekEl] of this.visibleWeeks) {
      this.addEventsToWeek(weekEl)
    }
  }

  addEventsToWeek(weekEl) {
    const daysGrid = weekEl._daysGrid || weekEl.querySelector('.days-grid')
    const overlay = weekEl._overlay || weekEl.querySelector('.week-overlay')
    if (!daysGrid || !overlay) return

    const cells = Array.from(daysGrid.querySelectorAll('.cell[data-date]'))

    while (overlay.firstChild) overlay.removeChild(overlay.firstChild)

    const weekEvents = new Map()
    for (const cell of cells) {
      const dateStr = cell.dataset.date
      const events = this.events.get(dateStr) || []
      for (const ev of events) {
        if (!weekEvents.has(ev.id)) {
          weekEvents.set(ev.id, {
            ...ev,
            startDateInWeek: dateStr,
            endDateInWeek: dateStr,
            startIdx: cells.indexOf(cell),
            endIdx: cells.indexOf(cell)
          })
        } else {
          const w = weekEvents.get(ev.id)
          w.endDateInWeek = dateStr
          w.endIdx = cells.indexOf(cell)
        }
      }
    }

    const spans = Array.from(weekEvents.values())
      .sort((a, b) => a.startIdx - b.startIdx || (b.endIdx - b.startIdx) - (a.endIdx - a.startIdx))

    const rowsLastEnd = []
    for (const w of spans) {
      let placedRow = 0
      while (placedRow < rowsLastEnd.length && !(w.startIdx > rowsLastEnd[placedRow])) placedRow++
      if (placedRow === rowsLastEnd.length) rowsLastEnd.push(-1)
      rowsLastEnd[placedRow] = w.endIdx
      w._row = placedRow + 1
    }

    overlay.style.gridTemplateRows = `repeat(${Math.max(1, rowsLastEnd.length)}, 1fr)`
    overlay.style.rowGap = '.2em'

    for (const w of spans) this.createOverlaySpan(overlay, w)
  }

  createOverlaySpan(overlay, w) {
    const span = document.createElement('div')
    span.className = `event-span event-color-${w.colorId}`
    span.style.gridColumn = `${w.startIdx + 1} / ${w.endIdx + 2}`
    span.style.gridRow = `${w._row}`
    span.textContent = w.title
    span.title = `${w.title} (${w.startDate === w.endDate ? w.startDate : w.startDate + ' - ' + w.endDate})`
    overlay.appendChild(span)
  }
}

document.addEventListener('DOMContentLoaded', () => {
  new InfiniteCalendar({
    select_days: 14
  })
})