src/components/CalendarGrid.vue

@@ -25,7 +25,8 @@ import {
   getLocalizedWeekdayNames,
   getLocaleWeekendDays,
   getLocaleFirstDay,
-  isoWeekInfo,
+  getISOWeek,
+  getISOWeekYear,
   fromLocalString,
   toLocalString,
   mondayIndex,
@@ -85,7 +86,7 @@ const updateVisibleWeeks = () => {
   const topDisplayIndex = Math.floor(scrollTop / rowHeight.value)
   const topVW = topDisplayIndex + minVirtualWeek.value
   const monday = getMondayForVirtualWeek(topVW)
-  const { year } = isoWeekInfo(monday)
+  const year = getISOWeekYear(monday)
   if (calendarStore.viewYear !== year) {
     calendarStore.setViewYear(year)
   }
@@ -126,7 +127,7 @@ const handleWheel = (e) => {
 
 const navigateToYear = (targetYear, weekIndex) => {
   const monday = getMondayForVirtualWeek(weekIndex)
-  const { week } = isoWeekInfo(monday)
+  const week = getISOWeek(monday)
   const jan4 = new Date(targetYear, 0, 4)
   const jan4Monday = addDays(jan4, -mondayIndex(jan4))
   const targetMonday = addDays(jan4Monday, (week - 1) * 7)

src/components/CalendarHeader.vue

@@ -1,7 +1,12 @@
 <script setup>
 import { computed } from 'vue'
 import { useCalendarStore } from '@/stores/CalendarStore'
-import { getLocalizedWeekdayNames, reorderByFirstDay, isoWeekInfo } from '@/utils/date'
+import {
+  getLocalizedWeekdayNames,
+  reorderByFirstDay,
+  getISOWeek,
+  getISOWeekYear,
+} from '@/utils/date'
 import Numeric from '@/components/Numeric.vue'
 import { addDays } from 'date-fns'
 
@@ -27,7 +32,7 @@ const topVirtualWeek = computed(() => {
 const currentYear = computed(() => {
   const weekStart = addDays(baseDate.value, topVirtualWeek.value * 7)
   const anchor = addDays(weekStart, (4 - weekStart.getDay() + 7) % 7)
-  return isoWeekInfo(anchor).year
+  return getISOWeekYear(anchor)
 })
 
 function virtualWeekOf(d) {
@@ -53,10 +58,10 @@ function changeYear(y) {
   // Anchor Thursday of current calendar week
   const curCalWeekStart = addDays(baseDate.value, vw * 7)
   const curAnchorThu = addDays(curCalWeekStart, (4 - curCalWeekStart.getDay() + 7) % 7)
-  let { week: isoW } = isoWeekInfo(curAnchorThu)
+  let isoW = getISOWeek(curAnchorThu)
   // Build Monday of ISO week
   let weekMon = isoWeekMonday(y, isoW)
-  if (isoWeekInfo(weekMon).year !== y) {
+  if (getISOWeekYear(weekMon) !== y) {
     isoW--
     weekMon = isoWeekMonday(y, isoW)
   }

src/components/CalendarView.vue

@@ -6,7 +6,6 @@ import CalendarWeek from '@/components/CalendarWeek.vue'
 import Jogwheel from '@/components/Jogwheel.vue'
 import SettingsDialog from '@/components/SettingsDialog.vue'
 import {
-  isoWeekInfo,
   getLocalizedMonthName,
   monthAbbr,
   lunarPhaseSymbol,
@@ -17,6 +16,7 @@ import {
   getMondayOfISOWeek,
   getOccurrenceIndex,
   getVirtualOccurrenceEndDate,
+  getISOWeek,
 } from '@/utils/date'
 import { toLocalString, fromLocalString, DEFAULT_TZ } from '@/utils/date'
 import { addDays, differenceInCalendarDays } from 'date-fns'
@@ -134,7 +134,7 @@ function getFirstDayForVirtualWeek(virtualWeek) {
 function createWeek(virtualWeek) {
   const firstDay = getFirstDayForVirtualWeek(virtualWeek)
   const isoAnchor = addDays(firstDay, (4 - firstDay.getDay() + 7) % 7)
-  const weekNumber = isoWeekInfo(isoAnchor).week
+  const weekNumber = getISOWeek(isoAnchor)
   const days = []
   let cur = new Date(firstDay)
   let hasFirst = false

src/components/EventDialog.vue

@@ -4,7 +4,13 @@ import { ref, computed, watch, onMounted, onUnmounted, nextTick } from 'vue'
 import BaseDialog from './BaseDialog.vue'
 import WeekdaySelector from './WeekdaySelector.vue'
 import Numeric from './Numeric.vue'
-import { addDaysStr, getMondayOfISOWeek, fromLocalString, toLocalString, DEFAULT_TZ } from '@/utils/date'
+import {
+  addDaysStr,
+  getMondayOfISOWeek,
+  fromLocalString,
+  toLocalString,
+  DEFAULT_TZ,
+} from '@/utils/date'
 import { addDays, addMonths } from 'date-fns'
 
 const props = defineProps({

src/components/WeekRow.vue

@@ -7,7 +7,11 @@
         <!-- Event spans will be rendered here -->
       </div>
     </div>
-    <div v-if="monthLabel" class="month-name-label" :style="{ height: `${monthLabel.weeksSpan * 64}px` }">
+    <div
+      v-if="monthLabel"
+      class="month-name-label"
+      :style="{ height: `${monthLabel.weeksSpan * 64}px` }"
+    >
       <span>{{ monthLabel.name }} '{{ monthLabel.year }}</span>
     </div>
   </div>
@@ -16,19 +20,23 @@
 <script setup>
 import { computed } from 'vue'
 import DayCell from './DayCell.vue'
-import { isoWeekInfo, toLocalString, getLocalizedMonthName, monthAbbr, DEFAULT_TZ } from '@/utils/date'
+import {
+  toLocalString,
+  getLocalizedMonthName,
+  monthAbbr,
+  DEFAULT_TZ,
+  getISOWeek,
+} from '@/utils/date'
 import { addDays } from 'date-fns'
 
 const props = defineProps({
   week: {
     type: Object,
-    required: true
-  }
+    required: true,
+  },
 })
 
-const weekNumber = computed(() => {
-  return isoWeekInfo(props.week.monday).week
-})
+const weekNumber = computed(() => getISOWeek(props.week.monday))
 
 const days = computed(() => {
   const d = new Date(props.week.monday)
@@ -41,7 +49,7 @@ const days = computed(() => {
       dayOfMonth: d.getDate(),
       month: d.getMonth(),
       isFirstDayOfMonth: d.getDate() === 1,
-      monthClass: monthAbbr[d.getMonth()]
+      monthClass: monthAbbr[d.getMonth()],
     })
     d.setTime(addDays(d, 1).getTime())
   }
@@ -49,7 +57,7 @@ const days = computed(() => {
 })
 
 const monthLabel = computed(() => {
-  const firstDayOfMonth = days.value.find(d => d.isFirstDayOfMonth)
+  const firstDayOfMonth = days.value.find((d) => d.isFirstDayOfMonth)
   if (!firstDayOfMonth) return null
 
   const month = firstDayOfMonth.month
@@ -61,7 +69,7 @@ const monthLabel = computed(() => {
   return {
     name: getLocalizedMonthName(month),
     year: String(year).slice(-2),
-    weeksSpan
+    weeksSpan,
   }
 })
 </script>

src/stores/CalendarStore.js

@@ -593,7 +593,10 @@ export const useCalendarStore = defineStore('calendar', {
       }
 
       snapshot.startDate = newStartStr
-  snapshot.endDate = toLocalString(addDays(fromLocalString(newStartStr, DEFAULT_TZ), finalDurationDays), DEFAULT_TZ)
+      snapshot.endDate = toLocalString(
+        addDays(fromLocalString(newStartStr, DEFAULT_TZ), finalDurationDays),
+        DEFAULT_TZ,
+      )
       // Rotate weekly recurrence pattern when moving (not resizing) so selected weekdays track shift
       if (
         mode === 'move' &&

src/utils/date.js

@@ -1,524 +1,244 @@
-// date-utils.js — Date handling utilities for the calendar (refactored to use date-fns/date-fns-tz)
-import {
-  addDays,
-  differenceInCalendarDays,
-  differenceInCalendarMonths,
-  format,
-  getDate,
-  getDay,
-  getDaysInMonth,
-  getMonth,
-  getYear,
-  isAfter,
-  isBefore,
-  isEqual,
-  parseISO,
-  startOfDay,
-} from 'date-fns'
+// date-utils.js — Restored & clean utilities (date-fns + timezone aware)
+import * as dateFns from 'date-fns'
 import { fromZonedTime, toZonedTime } from 'date-fns-tz'
 
-// We expose a simple alias TZDate for clarity. date-fns by default works with native Date objects.
-// Consumers can pass an optional timeZone; if omitted, local time zone is assumed.
-
 const DEFAULT_TZ = Intl.DateTimeFormat().resolvedOptions().timeZone || 'UTC'
 
-// Helper to create a zoned date (keeps wall-clock components in provided TZ)
+// Re-exported iso helpers (keep the same exported names used elsewhere)
+const getISOWeek = dateFns.getISOWeek
+const getISOWeekYear = dateFns.getISOWeekYear
+
+// Constants
+const monthAbbr = [
+  'jan',
+  'feb',
+  'mar',
+  'apr',
+  'may',
+  'jun',
+  'jul',
+  'aug',
+  'sep',
+  'oct',
+  'nov',
+  'dec',
+]
+
+// Core helpers ------------------------------------------------------------
+/**
+ * Construct a date at local midnight in the specified IANA timezone.
+ * Returns a native Date whose wall-clock components in that zone are (Y, M, D 00:00:00).
+ */
 function makeTZDate(year, monthIndex, day, timeZone = DEFAULT_TZ) {
   const iso = `${String(year).padStart(4, '0')}-${String(monthIndex + 1).padStart(2, '0')}-${String(
-    day
+    day,
   ).padStart(2, '0')}`
-  // Interpret as start of day in target zone
   const utcDate = fromZonedTime(`${iso}T00:00:00`, timeZone)
   return toZonedTime(utcDate, timeZone)
 }
 
-const monthAbbr = ['jan', 'feb', 'mar', 'apr', 'may', 'jun', 'jul', 'aug', 'sep', 'oct', 'nov', 'dec']
-const DAY_MS = 86400000
-const WEEK_MS = 7 * DAY_MS
+/**
+ * Alias constructor for timezone-specific calendar date (semantic sugar over makeTZDate).
+ */
+const TZDate = (year, monthIndex, day, timeZone = DEFAULT_TZ) =>
+  makeTZDate(year, monthIndex, day, timeZone)
 
 /**
- * Get ISO week information for a given date
- * @param {Date} date - The date to get week info for
- * @returns {Object} Object containing week number and year
+ * Construct a UTC-based date/time (wrapper for Date.UTC for consistency).
  */
-const isoWeekInfo = (date) => {
-  // ISO week: Thursday algorithm
-  const d = new Date(Date.UTC(getYear(date), getMonth(date), getDate(date)))
-  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 }
-}
+const UTCDate = (year, monthIndex, day, hour = 0, minute = 0, second = 0, ms = 0) =>
+  new Date(Date.UTC(year, monthIndex, day, hour, minute, second, ms))
 
-/**
- * Convert a Date object to a local date string (YYYY-MM-DD format)
- * @param {Date} date - The date to convert (defaults to new Date())
- * @returns {string} Date string in YYYY-MM-DD format
- */
 function toLocalString(date = new Date(), timeZone = DEFAULT_TZ) {
-  return format(toZonedTime(date, timeZone), 'yyyy-MM-dd')
+  return dateFns.format(toZonedTime(date, timeZone), 'yyyy-MM-dd')
 }
 
-/**
- * Convert a local date string (YYYY-MM-DD) to a Date object
- * @param {string} dateString - Date string in YYYY-MM-DD format
- * @returns {Date} Date object
- */
 function fromLocalString(dateString, timeZone = DEFAULT_TZ) {
-  const parsed = parseISO(dateString)
+  if (!dateString) return makeTZDate(1970, 0, 1, timeZone)
+  const parsed = dateFns.parseISO(dateString)
   const utcDate = fromZonedTime(`${dateString}T00:00:00`, timeZone)
   return toZonedTime(utcDate, timeZone) || parsed
 }
 
-/**
- * Get the Monday of the ISO week for a given date
- * @param {Date} date - The date to get the Monday for
- * @returns {Date} Date object representing the Monday of the ISO week
- */
 function getMondayOfISOWeek(date, timeZone = DEFAULT_TZ) {
-  const d = startOfDay(toZonedTime(date, timeZone))
-  const dayOfWeek = (getDay(d) + 6) % 7
-  return addDays(d, -dayOfWeek)
+  const d = toZonedTime(date, timeZone)
+  const dow = (dateFns.getDay(d) + 6) % 7 // Monday=0
+  return dateFns.addDays(dateFns.startOfDay(d), -dow)
 }
 
-/**
- * Get the index of Monday for a given date (0-6, where Monday = 0)
- * @param {Date} d - The date
- * @returns {number} Monday index (0-6)
- */
-const mondayIndex = (d) => (getDay(d) + 6) % 7
+const mondayIndex = (d) => (dateFns.getDay(d) + 6) % 7
 
-/**
- * Calculate the occurrence index for a repeating weekly event on a specific date
- * @param {Object} event - The event object with repeat info
- * @param {string} dateStr - The date string (YYYY-MM-DD) to check
- * @returns {number|null} The occurrence index (0=base, 1=first repeat) or null if not valid
- */
+// Count how many days in [startDate..endDate] match the boolean `pattern` array
+function countPatternDaysInInterval(startDate, endDate, patternArr) {
+  const days = dateFns.eachDayOfInterval({
+    start: dateFns.startOfDay(startDate),
+    end: dateFns.startOfDay(endDate),
+  })
+  return days.reduce((c, d) => c + (patternArr[dateFns.getDay(d)] ? 1 : 0), 0)
+}
+
+// Recurrence: Weekly ------------------------------------------------------
 function getWeeklyOccurrenceIndex(event, dateStr, timeZone = DEFAULT_TZ) {
-  if (!event.isRepeating || event.repeat !== 'weeks') return null
-
+  if (!event?.isRepeating || event.repeat !== 'weeks') return null
   const pattern = event.repeatWeekdays || []
   if (!pattern.some(Boolean)) return null
 
-  const d = fromLocalString(dateStr, timeZone)
-  const dow = getDay(d)
-  if (!pattern[dow]) return null
-
+  const target = fromLocalString(dateStr, timeZone)
   const baseStart = fromLocalString(event.startDate, timeZone)
+  if (target < baseStart) return null
+
+  const dow = dateFns.getDay(target)
+  if (!pattern[dow]) return null // target not active
+
   const interval = event.repeatInterval || 1
-
-  // Check if date resides in a week block that aligns with interval
   const baseBlockStart = getMondayOfISOWeek(baseStart, timeZone)
-  const currentBlockStart = getMondayOfISOWeek(d, timeZone)
-  const WEEK_MS = 7 * 86400000
-  const blocksDiff = Math.floor((currentBlockStart - baseBlockStart) / WEEK_MS)
+  const currentBlockStart = getMondayOfISOWeek(target, timeZone)
+  // Number of weeks between block starts (each block start is a Monday)
+  const weekDiff = dateFns.differenceInCalendarWeeks(currentBlockStart, baseBlockStart)
+  if (weekDiff < 0 || weekDiff % interval !== 0) return null
 
-  if (blocksDiff < 0 || blocksDiff % interval !== 0) return null
-
-  // For same week as base start, count from base start to target
-  if (isEqual(currentBlockStart, baseBlockStart)) {
-    // Special handling for the first week - only count occurrences on or after base date
-    if (d.getTime() === baseStart.getTime()) {
-      return 0 // Base occurrence is always index 0
+  // Same ISO week as base: count pattern days from baseStart up to target (inclusive)
+  if (weekDiff === 0) {
+    const n = countPatternDaysInInterval(baseStart, target, pattern) - 1
+    return n < 0 || n >= event.repeatCount ? null : n
   }
 
-    if (d < baseStart) {
-      return null // Dates before base start in same week are not valid occurrences
+  const baseWeekEnd = dateFns.addDays(baseBlockStart, 6)
+  // Count pattern days in the first (possibly partial) week from baseStart..baseWeekEnd
+  const firstWeekCount = countPatternDaysInInterval(baseStart, baseWeekEnd, pattern)
+  const alignedWeeksBetween = weekDiff / interval - 1
+  const fullPatternWeekCount = pattern.filter(Boolean).length
+  const middleWeeksCount = alignedWeeksBetween > 0 ? alignedWeeksBetween * fullPatternWeekCount : 0
+  // Count pattern days in the current (possibly partial) week from currentBlockStart..target
+  const currentWeekCount = countPatternDaysInInterval(currentBlockStart, target, pattern)
+  const n = firstWeekCount + middleWeeksCount + currentWeekCount - 1
+  return n >= event.repeatCount ? null : n
 }
 
-  let occurrenceIndex = 0
-	let cursor = new Date(baseStart)
-
-    // Count the base occurrence first
-  if (pattern[getDay(cursor)]) occurrenceIndex++
-
-      // Move to the next day and count until we reach the target
-      cursor = addDays(cursor, 1)
-      while (cursor <= d) {
-        if (pattern[getDay(cursor)]) occurrenceIndex++
-        cursor = addDays(cursor, 1)
-      }
-
-    // Subtract 1 because we want the index, not the count
-    occurrenceIndex--
-
-    // Check against repeat count limit
-    if (event.repeatCount !== 'unlimited') {
-      const limit = parseInt(event.repeatCount, 10)
-      if (isNaN(limit) || occurrenceIndex >= limit) return null
-    }
-
-    return occurrenceIndex
-  }
-
-  // For different weeks, calculate based on complete intervals
-  // Calculate how many pattern days actually occur in the first week (from base start onward)
-  let firstWeekPatternDays = 0
-  let firstWeekCursor = new Date(baseStart)
-  const firstWeekEnd = addDays(new Date(baseBlockStart), 6) // End of first week (Sunday)
-
-  while (firstWeekCursor <= firstWeekEnd) {
-    if (pattern[getDay(firstWeekCursor)]) firstWeekPatternDays++
-    firstWeekCursor = addDays(firstWeekCursor, 1)
-  }
-
-  // For subsequent complete intervals, use the full pattern count
-  const fullWeekdaysPerInterval = pattern.filter(Boolean).length
-  const completeIntervals = blocksDiff / interval
-
-  // First interval uses actual first week count, remaining intervals use full count
-  let occurrenceIndex = firstWeekPatternDays + (completeIntervals - 1) * fullWeekdaysPerInterval
-
-  // Add occurrences from the current week up to the target date
-  cursor = new Date(currentBlockStart)
-  while (cursor < d) {
-    if (pattern[getDay(cursor)]) occurrenceIndex++
-    cursor = addDays(cursor, 1)
-  }
-
-  // Check against repeat count limit
-  if (event.repeatCount !== 'unlimited') {
-    const limit = parseInt(event.repeatCount, 10)
-    if (isNaN(limit) || occurrenceIndex >= limit) return null
-  }
-
-  return occurrenceIndex
-}
-
-/**
- * Calculate the occurrence index for a repeating monthly event on a specific date
- * @param {Object} event - The event object with repeat info
- * @param {string} dateStr - The date string (YYYY-MM-DD) to check
- * @returns {number|null} The occurrence index (0=base, 1=first repeat) or null if not valid
- */
+// Recurrence: Monthly -----------------------------------------------------
 function getMonthlyOccurrenceIndex(event, dateStr, timeZone = DEFAULT_TZ) {
-  if (!event.isRepeating || event.repeat !== 'months') return null
-
+  if (!event?.isRepeating || event.repeat !== 'months') return null
   const baseStart = fromLocalString(event.startDate, timeZone)
   const d = fromLocalString(dateStr, timeZone)
-  const diffMonths = differenceInCalendarMonths(d, baseStart)
-
+  const diffMonths = dateFns.differenceInCalendarMonths(d, baseStart)
   if (diffMonths < 0) return null
-
   const interval = event.repeatInterval || 1
   if (diffMonths % interval !== 0) return null
-
-  // Check day match (clamped for shorter months)
-  const baseDay = getDate(baseStart)
-  const daysInMonth = getDaysInMonth(d)
-  const effectiveDay = Math.min(baseDay, daysInMonth)
-  if (getDate(d) !== effectiveDay) return null
-
-  const occurrenceIndex = diffMonths / interval
-
-  // Check against repeat count limit
-  if (event.repeatCount !== 'unlimited') {
-    const limit = parseInt(event.repeatCount, 10)
-    if (isNaN(limit) || occurrenceIndex >= limit) return null
+  const baseDay = dateFns.getDate(baseStart)
+  const effectiveDay = Math.min(baseDay, dateFns.getDaysInMonth(d))
+  if (dateFns.getDate(d) !== effectiveDay) return null
+  const n = diffMonths / interval
+  return n >= event.repeatCount ? null : n
 }
 
-  return occurrenceIndex
-}
-
-/**
- * Check if a repeating event occurs on a specific date and return occurrence index
- * @param {Object} event - The event object with repeat info
- * @param {string} dateStr - The date string (YYYY-MM-DD) to check
- * @returns {number|null} The occurrence index (0=base, 1=first repeat) or null if not occurring
- */
 function getOccurrenceIndex(event, dateStr, timeZone = DEFAULT_TZ) {
-  if (!event || !event.isRepeating || event.repeat === 'none') return null
+  if (!event?.isRepeating || event.repeat === 'none') return null
   if (dateStr < event.startDate) return null
-
-  if (event.repeat === 'weeks') {
-  return getWeeklyOccurrenceIndex(event, dateStr, timeZone)
-  } else if (event.repeat === 'months') {
-  return getMonthlyOccurrenceIndex(event, dateStr, timeZone)
-  }
-
+  if (event.repeat === 'weeks') return getWeeklyOccurrenceIndex(event, dateStr, timeZone)
+  if (event.repeat === 'months') return getMonthlyOccurrenceIndex(event, dateStr, timeZone)
   return null
 }
 
-/**
- * Calculate the end date for a virtual occurrence of a repeating event
- * @param {Object} event - The base event object
- * @param {string} occurrenceStartDate - The start date of the occurrence (YYYY-MM-DD)
- * @returns {string} The end date of the occurrence (YYYY-MM-DD)
- */
 function getVirtualOccurrenceEndDate(event, occurrenceStartDate, timeZone = DEFAULT_TZ) {
   const baseStart = fromLocalString(event.startDate, timeZone)
   const baseEnd = fromLocalString(event.endDate, timeZone)
-  const spanDays = Math.max(0, differenceInCalendarDays(baseEnd, baseStart))
+  const spanDays = Math.max(0, dateFns.differenceInCalendarDays(baseEnd, baseStart))
   const occurrenceStart = fromLocalString(occurrenceStartDate, timeZone)
-  const occurrenceEnd = addDays(occurrenceStart, spanDays)
-  return toLocalString(occurrenceEnd, timeZone)
+  return toLocalString(dateFns.addDays(occurrenceStart, spanDays), timeZone)
 }
 
-/**
- * Check if a repeating event occurs on or spans through a specific date
- * @param {Object} event - The event object with repeat info
- * @param {string} dateStr - The date string (YYYY-MM-DD) to check
- * @returns {boolean} True if the event occurs on or spans through the date
- */
-function occursOnOrSpansDate(event, dateStr, timeZone = DEFAULT_TZ) {
-  if (!event || !event.isRepeating || event.repeat === 'none') return false
-
-  // Check if this is the base event spanning naturally
-  if (dateStr >= event.startDate && dateStr <= event.endDate) return true
-
-  // For virtual occurrences, we need to check if any occurrence spans through this date
-  const baseStart = fromLocalString(event.startDate, timeZone)
-  const baseEnd = fromLocalString(event.endDate, timeZone)
-  const spanDays = Math.max(0, differenceInCalendarDays(baseEnd, baseStart))
-
-  if (spanDays === 0) {
-    // Single day event - just check if it occurs on this date
-    return getOccurrenceIndex(event, dateStr) !== null
-  }
-
-  // Multi-day event - check if any occurrence's span includes this date
-  const targetDate = fromLocalString(dateStr, timeZone)
-
-  if (event.repeat === 'weeks') {
-  const pattern = event.repeatWeekdays || []
-    if (!pattern.some(Boolean)) return false
-
-  const interval = event.repeatInterval || 1
-  const baseBlockStart = getMondayOfISOWeek(baseStart, timeZone)
-    const WEEK_MS = 7 * 86400000
-
-    // Check a reasonable range of weeks around the target date
-    for (
-      let weekOffset = -Math.ceil(spanDays / 7) - 1;
-      weekOffset <= Math.ceil(spanDays / 7) + 1;
-      weekOffset++
-    ) {
-  const weekStart = addDays(baseBlockStart, weekOffset * 7)
-
-      // Check if this week aligns with the interval
-  const blocksDiff = Math.floor((weekStart - baseBlockStart) / WEEK_MS)
-      if (blocksDiff < 0 || blocksDiff % interval !== 0) continue
-
-      // Check each day in this week
-      for (let day = 0; day < 7; day++) {
-  const candidateStart = addDays(weekStart, day)
-
-        // Skip if before base start
-  if (isBefore(candidateStart, baseStart)) continue
-
-        // Check if this day matches the pattern
-  if (!pattern[getDay(candidateStart)]) continue
-
-        // Check repeat count limit
-  const occIndex = getWeeklyOccurrenceIndex(event, toLocalString(candidateStart, timeZone), timeZone)
-        if (occIndex === null) continue
-
-        // Calculate end date for this occurrence
-  const candidateEnd = addDays(candidateStart, spanDays)
-
-        // Check if target date falls within this occurrence's span
-  if (!isBefore(targetDate, candidateStart) && !isAfter(targetDate, candidateEnd)) {
-          return true
-        }
-      }
-    }
-  } else if (event.repeat === 'months') {
-  const interval = event.repeatInterval || 1
-  const baseDay = getDate(baseStart)
-
-    // Check a reasonable range of months around the target date
-  // targetYear & targetMonth not needed in refactored logic
-  const baseYear = getYear(baseStart)
-  const baseMonth = getMonth(baseStart)
-
-    for (let monthOffset = -spanDays * 2; monthOffset <= spanDays * 2; monthOffset++) {
-      const candidateYear = baseYear + Math.floor((baseMonth + monthOffset) / 12)
-      const candidateMonth = (baseMonth + monthOffset + 12) % 12
-
-      // Check if this month aligns with the interval
-  const diffMonths = (candidateYear - baseYear) * 12 + (candidateMonth - baseMonth)
-      if (diffMonths < 0 || diffMonths % interval !== 0) continue
-
-      // Calculate the actual day (clamped for shorter months)
-  const daysInMonth = getDaysInMonth(new Date(candidateYear, candidateMonth, 1))
-      const effectiveDay = Math.min(baseDay, daysInMonth)
-  const candidateStart = makeTZDate(candidateYear, candidateMonth, effectiveDay)
-
-      // Skip if before base start
-  if (isBefore(candidateStart, baseStart)) continue
-
-      // Check repeat count limit
-  const occIndex = getMonthlyOccurrenceIndex(event, toLocalString(candidateStart, timeZone), timeZone)
-      if (occIndex === null) continue
-
-      // Calculate end date for this occurrence
-  const candidateEnd = addDays(candidateStart, spanDays)
-
-      // Check if target date falls within this occurrence's span
-  if (!isBefore(targetDate, candidateStart) && !isAfter(targetDate, candidateEnd)) {
-        return true
-      }
-    }
-  }
-
-  return false
-} /**
- * Pad a number with leading zeros to make it 2 digits
- * @param {number} n - Number to pad
- * @returns {string} Padded string
- */
+// Utility formatting & localization ---------------------------------------
 const pad = (n) => String(n).padStart(2, '0')
 
-/**
- * Calculate number of days between two date strings (inclusive)
- * @param {string} aStr - First date string (YYYY-MM-DD)
- * @param {string} bStr - Second date string (YYYY-MM-DD)
- * @returns {number} Number of days inclusive
- */
 function daysInclusive(aStr, bStr, timeZone = DEFAULT_TZ) {
   const a = fromLocalString(aStr, timeZone)
   const b = fromLocalString(bStr, timeZone)
-  return Math.abs(differenceInCalendarDays(startOfDay(a), startOfDay(b))) + 1
-}
-
-/**
- * Add days to a date string
- * @param {string} str - Date string in YYYY-MM-DD format
- * @param {number} n - Number of days to add (can be negative)
- * @returns {string} New date string
- */
-function addDaysStr(str, n, timeZone = DEFAULT_TZ) {
-  const d = fromLocalString(str, timeZone)
-  return toLocalString(addDays(d, n), timeZone)
-}
-
-/**
- * Get localized weekday names starting from Monday
- * @returns {Array<string>} Array of localized weekday names
- */
-function getLocalizedWeekdayNames(timeZone = DEFAULT_TZ) {
-  const res = []
-  const base = makeTZDate(2025, 0, 6, timeZone) // Monday
-  for (let i = 0; i < 7; i++) {
-    const d = addDays(base, i)
-    res.push(
-      new Intl.DateTimeFormat(undefined, { weekday: 'short', timeZone }).format(d)
+  return (
+    Math.abs(dateFns.differenceInCalendarDays(dateFns.startOfDay(a), dateFns.startOfDay(b))) + 1
   )
 }
-  return res
+
+function addDaysStr(str, n, timeZone = DEFAULT_TZ) {
+  return toLocalString(dateFns.addDays(fromLocalString(str, timeZone), n), timeZone)
+}
+
+function getLocalizedWeekdayNames(timeZone = DEFAULT_TZ) {
+  const monday = makeTZDate(2025, 0, 6, timeZone) // a Monday
+  return Array.from({ length: 7 }, (_, i) =>
+    new Intl.DateTimeFormat(undefined, { weekday: 'short', timeZone }).format(
+      dateFns.addDays(monday, i),
+    ),
+  )
 }
 
-/**
- * Get the locale's first day of the week (0=Sunday, 1=Monday, etc.)
- * @returns {number} First day of the week (0-6)
- */
 function getLocaleFirstDay() {
-  try {
   return new Intl.Locale(navigator.language).weekInfo.firstDay % 7
-  } catch {
-    return 1 // Default to Monday if locale info not available
-  }
 }
 
-/**
- * Get the locale's weekend days as an array of booleans (Sunday=index 0)
- * @returns {Array<boolean>} Array where true indicates a weekend day
- */
 function getLocaleWeekendDays() {
-  try {
-    const localeWeekend = new Intl.Locale(navigator.language).weekInfo.weekend
-    const dayidx = new Set(localeWeekend)
-    return Array.from({ length: 7 }, (_, i) => dayidx.has(i || 7))
-  } catch {
-    return [true, false, false, false, false, false, true] // Default to Saturday/Sunday weekend
-  }
+  const wk = new Intl.Locale(navigator.language).weekInfo.weekend || [6, 7]
+  const set = new Set(wk.map((d) => d % 7))
+  return Array.from({ length: 7 }, (_, i) => set.has(i))
 }
 
-/**
- * Reorder a 7-element array based on the first day of the week
- * @param {Array} days - Array of 7 elements (Sunday=index 0)
- * @param {number} firstDay - First day of the week (0=Sunday, 1=Monday, etc.)
- * @returns {Array} Reordered array
- */
 function reorderByFirstDay(days, firstDay) {
   return Array.from({ length: 7 }, (_, i) => days[(i + firstDay) % 7])
 }
 
-/**
- * Get localized month name
- * @param {number} idx - Month index (0-11)
- * @param {boolean} short - Whether to return short name
- * @returns {string} Localized month name
- */
 function getLocalizedMonthName(idx, short = false, timeZone = DEFAULT_TZ) {
   const d = makeTZDate(2025, idx, 1, timeZone)
   return new Intl.DateTimeFormat(undefined, { month: short ? 'short' : 'long', timeZone }).format(d)
 }
 
-/**
- * Format a date range for display
- * @param {Date} startDate - Start date
- * @param {Date} endDate - End date
- * @returns {string} Formatted date range string
- */
 function formatDateRange(startDate, endDate, timeZone = DEFAULT_TZ) {
-  if (toLocalString(startDate, timeZone) === toLocalString(endDate, timeZone))
-    return toLocalString(startDate, timeZone)
-  const startISO = toLocalString(startDate, timeZone)
-  const endISO = toLocalString(endDate, timeZone)
-  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}/${endISO}`
+  const a = toLocalString(startDate, timeZone)
+  const b = toLocalString(endDate, timeZone)
+  if (a === b) return a
+  const [ay, am] = a.split('-')
+  const [by, bm, bd] = b.split('-')
+  if (ay === by && am === bm) return `${a}/${bd}`
+  if (ay === by) return `${a}/${bm}-${bd}`
+  return `${a}/${b}`
 }
 
-/**
- * Compute lunar phase symbol for the four main phases on a given date.
- * Returns one of: 🌑 (new), 🌓 (first quarter), 🌕 (full), 🌗 (last quarter), or '' otherwise.
- * Uses an approximate algorithm with a fixed epoch.
- */
 function lunarPhaseSymbol(date) {
-  // Reference new moon: 2000-01-06 18:14 UTC (J2000 era), often used in approximations
-  const ref = Date.UTC(2000, 0, 6, 18, 14, 0)
-  const synodic = 29.530588853 // days
-  // Use UTC noon of given date to reduce timezone edge effects
-  const dUTC = Date.UTC(date.getFullYear(), date.getMonth(), date.getDate(), 12, 0, 0)
-  const daysSince = (dUTC - ref) / DAY_MS
-  const phase = (((daysSince / synodic) % 1) + 1) % 1
+  // Reference new moon (J2000 era) used for approximate phase calculations
+  const ref = UTCDate(2000, 0, 6, 18, 14, 0)
+  const obs = new Date(date)
+  obs.setHours(12, 0, 0, 0)
+  const synodic = 29.530588853 // mean synodic month length in days
+  const daysSince = dateFns.differenceInMinutes(obs, ref) / 60 / 24
+  const phase = (((daysSince / synodic) % 1) + 1) % 1 // normalize to [0,1)
   const phases = [
-    { t: 0.0, s: '🌑' }, // New Moon
+    { t: 0.0, s: '🌑' }, // New
     { t: 0.25, s: '🌓' }, // First Quarter
-    { t: 0.5, s: '🌕' }, // Full Moon
+    { t: 0.5, s: '🌕' }, // Full
     { t: 0.75, s: '🌗' }, // Last Quarter
   ]
-  // threshold in days from exact phase to still count for this date
-  const thresholdDays = 0.5 // ±12 hours
+  const thresholdDays = 0.5 // within ~12h of exact phase
   for (const p of phases) {
     let delta = Math.abs(phase - p.t)
-    if (delta > 0.5) delta = 1 - delta
+    if (delta > 0.5) delta = 1 - delta // wrap shortest arc
     if (delta * synodic <= thresholdDays) return p.s
   }
   return ''
 }
 
-// Export all functions and constants
+// Exports -----------------------------------------------------------------
 export {
+  // constants
   monthAbbr,
-  DAY_MS,
-  WEEK_MS,
-  isoWeekInfo,
+  DEFAULT_TZ,
+  // core tz helpers
+  makeTZDate,
   toLocalString,
   fromLocalString,
+  // recurrence
   getMondayOfISOWeek,
-  getWeeklyOccurrenceIndex,
-  getMonthlyOccurrenceIndex,
+  mondayIndex,
   getOccurrenceIndex,
   getVirtualOccurrenceEndDate,
-  occursOnOrSpansDate,
-  mondayIndex,
+  // formatting & localization
   pad,
   daysInclusive,
   addDaysStr,
@@ -529,6 +249,10 @@ export {
   getLocalizedMonthName,
   formatDateRange,
   lunarPhaseSymbol,
-  makeTZDate,
-  DEFAULT_TZ,
+  // iso helpers re-export
+  getISOWeek,
+  getISOWeekYear,
+  // constructors
+  TZDate,
+  UTCDate,
 }