src/components/CalendarView.vue

@@ -13,6 +13,9 @@ import {
   daysInclusive,
   addDaysStr,
   formatDateRange,
+  getMondayOfISOWeek,
+  getOccurrenceIndex,
+  getVirtualOccurrenceEndDate,
 } from '@/utils/date'
 import { toLocalString, fromLocalString } from '@/utils/date'
 
@@ -153,25 +156,11 @@ function createWeek(virtualWeek) {
   for (let i = 0; i < 7; i++) {
     const dateStr = toLocalString(cur)
     const storedEvents = []
-    const idSet = calendarStore.dates.get(dateStr)
+
-    if (idSet) {
+    // Find all non-repeating events that occur on this date
-      // Support Set or Array; ignore unexpected shapes
+    for (const ev of calendarStore.events.values()) {
-      if (idSet instanceof Set) {
+      if (!ev.isRepeating && dateStr >= ev.startDate && dateStr <= ev.endDate) {
-        idSet.forEach((id) => {
+        storedEvents.push(ev)
-          const ev = calendarStore.events.get(id)
-          if (ev) storedEvents.push(ev)
-        })
-      } else if (Array.isArray(idSet)) {
-        for (const id of idSet) {
-          const ev = calendarStore.events.get(id)
-          if (ev) storedEvents.push(ev)
-        }
-      } else if (typeof idSet === 'object' && idSet !== null) {
-        // If mistakenly hydrated as plain object {id:true,...}
-        for (const id of Object.keys(idSet)) {
-          const ev = calendarStore.events.get(id)
-          if (ev) storedEvents.push(ev)
-        }
       }
     }
     // Build day events starting with stored (base/spanning) then virtual occurrences
@@ -179,56 +168,45 @@ function createWeek(virtualWeek) {
     for (const base of repeatingBases) {
       // Skip if the base itself already on this date (already in storedEvents)
       if (dateStr >= base.startDate && dateStr <= base.endDate) continue
-      if (calendarStore.occursOnDate(base, dateStr)) {
+
-        // Determine sequential occurrence index: base event = 0, first repeat = 1, etc.
+      // Check if any occurrence of this repeating event spans through this date
-        let recurrenceIndex = 0
+      const baseStart = fromLocalString(base.startDate)
-        try {
+      const baseEnd = fromLocalString(base.endDate)
-          if (base.repeat === 'weeks') {
+      const spanDays = Math.max(0, Math.round((baseEnd - baseStart) / (24 * 60 * 60 * 1000)))
-            const pattern = base.repeatWeekdays || []
+      const currentDate = fromLocalString(dateStr)
-            const interval = base.repeatInterval || 1
+
-            const baseStart = new Date(base.startDate + 'T00:00:00')
+      let occurrenceFound = false
-            const baseEnd = new Date(base.endDate + 'T00:00:00')
+
-            const target = new Date(dateStr + 'T00:00:00')
+      // Check dates going backwards to find an occurrence that might span to this date
-            const WEEK_MS = 7 * 86400000
+      for (let offset = 0; offset <= spanDays && !occurrenceFound; offset++) {
-            const baseBlockStart = new Date(baseStart)
+        const candidateStart = new Date(currentDate)
-            baseBlockStart.setDate(baseStart.getDate() - baseStart.getDay())
+        candidateStart.setDate(candidateStart.getDate() - offset)
-            function isAligned(d) {
+        const candidateStartStr = toLocalString(candidateStart)
-              const blk = new Date(d)
+
-              blk.setDate(d.getDate() - d.getDay())
+        const occurrenceIndex = getOccurrenceIndex(base, candidateStartStr)
-              const diff = Math.floor((blk - baseBlockStart) / WEEK_MS)
+        if (occurrenceIndex !== null) {
-              return diff % interval === 0
+          // Calculate the end date of this occurrence
+          const virtualEndDate = getVirtualOccurrenceEndDate(base, candidateStartStr)
+
+          // Check if this occurrence spans through the current date
+          if (dateStr >= candidateStartStr && dateStr <= virtualEndDate) {
+            // Create virtual occurrence (if not already created)
+            const virtualId = base.id + '_v_' + candidateStartStr
+            const alreadyExists = dayEvents.some((ev) => ev.id === virtualId)
+
+            if (!alreadyExists) {
+              dayEvents.push({
+                ...base,
+                id: virtualId,
+                startDate: candidateStartStr,
+                endDate: virtualEndDate,
+                _recurrenceIndex: occurrenceIndex,
+                _baseId: base.id,
+              })
             }
-            // Count valid occurrences after base end and before target
+            occurrenceFound = true
-            let count = 0
-            const cursor = new Date(baseEnd)
-            cursor.setDate(cursor.getDate() + 1)
-            while (cursor < target) {
-              if (pattern[cursor.getDay()] && isAligned(cursor)) count++
-              cursor.setDate(cursor.getDate() + 1)
-            }
-            // Target itself is guaranteed valid (occursOnDate passed), so its index is count+1
-            recurrenceIndex = count + 1
-          } else if (base.repeat === 'months') {
-            const baseStart = new Date(base.startDate + 'T00:00:00')
-            const target = new Date(dateStr + 'T00:00:00')
-            const interval = base.repeatInterval || 1
-            const diffMonths =
-              (target.getFullYear() - baseStart.getFullYear()) * 12 +
-              (target.getMonth() - baseStart.getMonth())
-            // diffMonths should be multiple of interval; sequential index = diffMonths/interval
-            recurrenceIndex = diffMonths / interval
           }
-        } catch {
-          recurrenceIndex = 0
         }
-        dayEvents.push({
-          ...base,
-          id: base.id + '_v_' + dateStr,
-          startDate: dateStr,
-          endDate: dateStr,
-          _recurrenceIndex: recurrenceIndex,
-          _baseId: base.id,
-        })
       }
     }
     const dow = cur.getDay()

src/components/EventDialog.vue

@@ -3,7 +3,7 @@ import { useCalendarStore } from '@/stores/CalendarStore'
 import { ref, computed, watch, onMounted, onUnmounted, nextTick } from 'vue'
 import WeekdaySelector from './WeekdaySelector.vue'
 import Numeric from './Numeric.vue'
-import { addDaysStr } from '@/utils/date'
+import { addDaysStr, getMondayOfISOWeek } from '@/utils/date'
 
 const props = defineProps({
   selection: { type: Object, default: () => ({ startDate: null, dayCount: 0 }) },
@@ -173,11 +173,9 @@ function openEditDialog(payload) {
         // Count valid repeat occurrences (pattern + interval alignment) AFTER the base span
         const interval = event.repeatInterval || 1
         const WEEK_MS = 7 * 86400000
-        const baseBlockStart = new Date(baseStart)
+        const baseBlockStart = getMondayOfISOWeek(baseStart)
-        baseBlockStart.setDate(baseStart.getDate() - baseStart.getDay())
         function isAligned(d) {
-          const blk = new Date(d)
+          const blk = getMondayOfISOWeek(d)
-          blk.setDate(d.getDate() - d.getDay())
           const diff = Math.floor((blk - baseBlockStart) / WEEK_MS)
           return diff % interval === 0
         }

src/stores/CalendarStore.js

@@ -1,5 +1,15 @@
 import { defineStore } from 'pinia'
-import { toLocalString, fromLocalString, getLocaleWeekendDays } from '@/utils/date'
+import {
+  toLocalString,
+  fromLocalString,
+  getLocaleWeekendDays,
+  getMondayOfISOWeek,
+  getOccurrenceIndex,
+  getWeeklyOccurrenceIndex,
+  getMonthlyOccurrenceIndex,
+  getVirtualOccurrenceEndDate,
+  occursOnOrSpansDate,
+} from '@/utils/date'
 
 const MIN_YEAR = 1900
 const MAX_YEAR = 2100
@@ -9,7 +19,6 @@ export const useCalendarStore = defineStore('calendar', {
     today: toLocalString(new Date()),
     now: new Date().toISOString(), // store as ISO string
     events: new Map(), // id -> event object (primary)
-    dates: new Map(), // dateStr -> Set of event ids
     weekend: getLocaleWeekendDays(),
     config: {
       select_days: 1000,
@@ -28,74 +37,7 @@ export const useCalendarStore = defineStore('calendar', {
   actions: {
     // Determine if a repeating event occurs on a specific date (YYYY-MM-DD) without iterating all occurrences.
     occursOnDate(event, dateStr) {
-      if (!event || !event.isRepeating || event.repeat === 'none') return false
+      return getOccurrenceIndex(event, dateStr) !== null
-      // Quick bounds: event cannot occur before its base start
-      if (dateStr < event.startDate) return false
-      // For multi-day spanning events, we treat start date as anchor; UI handles span painting separately.
-      if (event.repeat === 'weeks') {
-        const pattern = event.repeatWeekdays || []
-        if (!pattern.some(Boolean)) return false
-        // Day of week must match
-        const d = fromLocalString(dateStr)
-        const dow = d.getDay()
-        if (!pattern[dow]) return false
-        // Compute week distance blocks respecting interval by counting ISO weeks since anchor Monday of base.
-        const baseStart = fromLocalString(event.startDate)
-        // If date is before base anchor weekday match, ensure anchor alignment
-        // Count days since base start; ensure that number of matching weekdays encountered equals occurrence index < repeatCount
-        // Optimized approach: approximate max occurrences cap first.
-        const interval = event.repeatInterval || 1
-        // Check if date resides in a week block that aligns with interval
-        const baseBlockStart = new Date(baseStart)
-        baseBlockStart.setDate(baseStart.getDate() - baseStart.getDay())
-        const currentBlockStart = new Date(d)
-        currentBlockStart.setDate(d.getDate() - d.getDay())
-        const WEEK_MS = 7 * 86400000
-        const blocksDiff = Math.floor((currentBlockStart - baseBlockStart) / WEEK_MS)
-        if (blocksDiff < 0 || blocksDiff % interval !== 0) return false
-        // Count occurrences up to this date to enforce repeatCount finite limits
-        if (event.repeatCount !== 'unlimited') {
-          const targetTime = d.getTime()
-          let occs = 0
-          const cursor = new Date(baseStart)
-          const limit = parseInt(event.repeatCount, 10)
-          const safetyLimit = Math.min(limit + 1, 10000)
-          while (cursor.getTime() <= targetTime && occs < safetyLimit) {
-            if (pattern[cursor.getDay()]) {
-              if (cursor.getTime() === targetTime) {
-                // This is the occurrence. Validate occs < limit
-                return occs < limit
-              }
-              occs++
-            }
-            cursor.setDate(cursor.getDate() + 1)
-          }
-          return false
-        }
-        return true
-      } else if (event.repeat === 'months') {
-        const baseStart = fromLocalString(event.startDate)
-        const d = fromLocalString(dateStr)
-        const diffMonths =
-          (d.getFullYear() - baseStart.getFullYear()) * 12 + (d.getMonth() - baseStart.getMonth())
-        if (diffMonths < 0) return false
-        const interval = event.repeatInterval || 1
-        if (diffMonths % interval !== 0) return false
-        // Check day match (clamped for shorter months). Base day might exceed target month length.
-        const baseDay = baseStart.getDate()
-        const daysInMonth = new Date(d.getFullYear(), d.getMonth() + 1, 0).getDate()
-        const effectiveDay = Math.min(baseDay, daysInMonth)
-        if (d.getDate() !== effectiveDay) return false
-        if (event.repeatCount !== 'unlimited') {
-          const limit = parseInt(event.repeatCount, 10)
-          if (isNaN(limit)) return false
-          // Base is occurrence 0; diffMonths/interval gives occurrence index
-          const occurrenceIndex = diffMonths / interval
-          return occurrenceIndex < limit
-        }
-        return true
-      }
-      return false
     },
     updateCurrentDate() {
       const d = new Date()
@@ -136,7 +78,6 @@ export const useCalendarStore = defineStore('calendar', {
       }
 
       this.events.set(event.id, { ...event, isSpanning: event.startDate < event.endDate })
-      this._indexEventDates(event.id)
       return event.id
     },
 
@@ -170,14 +111,6 @@ export const useCalendarStore = defineStore('calendar', {
     },
 
     deleteEvent(eventId) {
-      if (!this.events.has(eventId)) return
-      // Remove id from all date sets
-      for (const [dateStr, set] of this.dates) {
-        if (set.has(eventId)) {
-          set.delete(eventId)
-          if (set.size === 0) this.dates.delete(dateStr)
-        }
-      }
       this.events.delete(eventId)
     },
 
@@ -213,11 +146,9 @@ export const useCalendarStore = defineStore('calendar', {
             let found = 0
             let safety = 0
             const WEEK_MS = 7 * 86400000
-            const baseBlockStart = new Date(baseStart)
+            const baseBlockStart = getMondayOfISOWeek(baseStart)
-            baseBlockStart.setDate(baseStart.getDate() - baseStart.getDay())
             function isAligned(d) {
-              const blk = new Date(d)
+              const blk = getMondayOfISOWeek(d)
-              blk.setDate(d.getDate() - d.getDay())
               const diff = Math.floor((blk - baseBlockStart) / WEEK_MS)
               return diff % interval === 0
             }
@@ -236,12 +167,10 @@ export const useCalendarStore = defineStore('calendar', {
 
         // Count occurrences BEFORE target (always include the base occurrence as first)
         const baseStart = new Date(base.startDate + 'T00:00:00')
-        const baseBlockStart = new Date(baseStart)
+        const baseBlockStart = getMondayOfISOWeek(baseStart)
-        baseBlockStart.setDate(baseStart.getDate() - baseStart.getDay())
         const WEEK_MS = 7 * 86400000
         function isAligned(d) {
-          const block = new Date(d)
+          const block = getMondayOfISOWeek(d)
-          block.setDate(d.getDate() - d.getDay())
           const diff = Math.floor((block - baseBlockStart) / WEEK_MS)
           return diff % interval === 0
         }
@@ -473,43 +402,6 @@ export const useCalendarStore = defineStore('calendar', {
       return ev ? { ...ev } : null
     },
 
-    _removeEventFromAllDatesById(eventId) {
-      for (const [dateStr, set] of this.dates) {
-        if (set.has(eventId)) {
-          set.delete(eventId)
-          if (set.size === 0) this.dates.delete(dateStr)
-        }
-      }
-    },
-
-    _addEventToDateRangeWithId(eventId, baseData, startDate, endDate) {
-      // Update base data
-      this.events.set(eventId, {
-        ...baseData,
-        id: eventId,
-        startDate,
-        endDate,
-        isSpanning: startDate < endDate,
-      })
-      this._indexEventDates(eventId)
-    },
-
-    _indexEventDates(eventId) {
-      const ev = this.events.get(eventId)
-      if (!ev) return
-      // remove old date references first
-      for (const [, set] of this.dates) set.delete(eventId)
-      const s = fromLocalString(ev.startDate)
-      const e = fromLocalString(ev.endDate)
-      const cur = new Date(s)
-      while (cur <= e) {
-        const dateStr = toLocalString(cur)
-        if (!this.dates.has(dateStr)) this.dates.set(dateStr, new Set())
-        this.dates.get(dateStr).add(ev.id)
-        cur.setDate(cur.getDate() + 1)
-      }
-    },
-
     // expandRepeats removed: no physical occurrence expansion
 
     // Adjust start/end range of a base event (non-generated) and reindex occurrences
@@ -566,10 +458,13 @@ export const useCalendarStore = defineStore('calendar', {
           snapshot.repeatWeekdays = rotated
         }
       }
-      // Reindex
+      // Update the event directly
-      this._removeEventFromAllDatesById(eventId)
+      this.events.set(eventId, {
-      this._addEventToDateRangeWithId(eventId, snapshot, snapshot.startDate, snapshot.endDate)
+        ...snapshot,
-      // no expansion
+        startDate: snapshot.startDate,
+        endDate: snapshot.endDate,
+        isSpanning: snapshot.startDate < snapshot.endDate,
+      })
     },
 
     // Split a repeating series at a specific occurrence date and move that occurrence (and future) to new range
@@ -596,11 +491,9 @@ export const useCalendarStore = defineStore('calendar', {
         const pattern = base.repeatWeekdays || []
         if (!pattern.some(Boolean)) return
         const WEEK_MS = 7 * 86400000
-        const blockStartBase = new Date(baseStart)
+        const blockStartBase = getMondayOfISOWeek(baseStart)
-        blockStartBase.setDate(blockStartBase.getDate() - blockStartBase.getDay())
         function isAligned(d) {
-          const blk = new Date(d)
+          const blk = getMondayOfISOWeek(d)
-          blk.setDate(d.getDate() - d.getDay())
           const diff = Math.floor((blk - blockStartBase) / WEEK_MS)
           return diff % interval === 0
         }
@@ -694,12 +587,6 @@ export const useCalendarStore = defineStore('calendar', {
       return newId
     },
 
-    _reindexBaseEvent(eventId, snapshot, startDate, endDate) {
-      if (!snapshot) return
-      this._removeEventFromAllDatesById(eventId)
-      this._addEventToDateRangeWithId(eventId, snapshot, startDate, endDate)
-    },
-
     _terminateRepeatSeriesAtIndex(baseId, index) {
       const ev = this.events.get(baseId)
       if (!ev || !ev.isRepeating) return
@@ -713,18 +600,13 @@ export const useCalendarStore = defineStore('calendar', {
 
     // _findEventInAnyList removed (direct map access)
 
-    _addEventToDateRange(event) {
-      this.events.set(event.id, { ...event, isSpanning: event.startDate < event.endDate })
-      this._indexEventDates(event.id)
-    },
-
     // NOTE: legacy dynamic getEventById for synthetic occurrences removed.
   },
   persist: {
     key: 'calendar-store',
     storage: localStorage,
-    // Persist new structures; keep legacy 'events' only for transitional restore if needed
+    // Persist only events map, no dates indexing
-    paths: ['today', 'config', 'events', 'dates'],
+    paths: ['today', 'config', 'events'],
     serializer: {
       serialize(value) {
         return JSON.stringify(value, (_k, v) => {

src/utils/date.js

@@ -51,6 +51,18 @@ function fromLocalString(dateString) {
   return new Date(year, month - 1, day)
 }
 
+/**
+ * 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) {
+  const d = new Date(date)
+  const dayOfWeek = (d.getDay() + 6) % 7 // Convert to Monday=0, Sunday=6
+  d.setDate(d.getDate() - dayOfWeek)
+  return d
+}
+
 /**
  * Get the index of Monday for a given date (0-6, where Monday = 0)
  * @param {Date} d - The date
@@ -59,6 +71,259 @@ function fromLocalString(dateString) {
 const mondayIndex = (d) => (d.getDay() + 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
+ */
+function getWeeklyOccurrenceIndex(event, dateStr) {
+  if (!event.isRepeating || event.repeat !== 'weeks') return null
+
+  const pattern = event.repeatWeekdays || []
+  if (!pattern.some(Boolean)) return null
+
+  const d = fromLocalString(dateStr)
+  const dow = d.getDay()
+  if (!pattern[dow]) return null
+
+  const baseStart = fromLocalString(event.startDate)
+  const interval = event.repeatInterval || 1
+
+  // Check if date resides in a week block that aligns with interval
+  const baseBlockStart = getMondayOfISOWeek(baseStart)
+  const currentBlockStart = getMondayOfISOWeek(d)
+  const WEEK_MS = 7 * 86400000
+  const blocksDiff = Math.floor((currentBlockStart - baseBlockStart) / WEEK_MS)
+
+  if (blocksDiff < 0 || blocksDiff % interval !== 0) return null
+
+  // For same week as base start, count from base start to target
+  if (currentBlockStart.getTime() === baseBlockStart.getTime()) {
+    let occurrenceIndex = 0
+    const cursor = new Date(baseStart)
+    while (cursor < d) {
+      if (pattern[cursor.getDay()]) occurrenceIndex++
+      cursor.setDate(cursor.getDate() + 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
+  }
+
+  // For different weeks, calculate based on complete intervals
+  const weekdaysPerInterval = pattern.filter(Boolean).length
+  const completeIntervals = blocksDiff / interval
+  let occurrenceIndex = completeIntervals * weekdaysPerInterval
+
+  // Add occurrences from the current week up to the target date
+  const cursor = new Date(currentBlockStart)
+  while (cursor < d) {
+    if (pattern[cursor.getDay()]) occurrenceIndex++
+    cursor.setDate(cursor.getDate() + 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
+ */
+function getMonthlyOccurrenceIndex(event, dateStr) {
+  if (!event.isRepeating || event.repeat !== 'months') return null
+
+  const baseStart = fromLocalString(event.startDate)
+  const d = fromLocalString(dateStr)
+  const diffMonths =
+    (d.getFullYear() - baseStart.getFullYear()) * 12 + (d.getMonth() - baseStart.getMonth())
+
+  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 = baseStart.getDate()
+  const daysInMonth = new Date(d.getFullYear(), d.getMonth() + 1, 0).getDate()
+  const effectiveDay = Math.min(baseDay, daysInMonth)
+  if (d.getDate() !== 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
+  }
+
+  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) {
+  if (!event || !event.isRepeating || event.repeat === 'none') return null
+  if (dateStr < event.startDate) return null
+
+  if (event.repeat === 'weeks') {
+    return getWeeklyOccurrenceIndex(event, dateStr)
+  } else if (event.repeat === 'months') {
+    return getMonthlyOccurrenceIndex(event, dateStr)
+  }
+
+  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) {
+  const baseStart = fromLocalString(event.startDate)
+  const baseEnd = fromLocalString(event.endDate)
+  const spanDays = Math.max(0, Math.round((baseEnd - baseStart) / (24 * 60 * 60 * 1000)))
+
+  const occurrenceStart = fromLocalString(occurrenceStartDate)
+  const occurrenceEnd = new Date(occurrenceStart)
+  occurrenceEnd.setDate(occurrenceEnd.getDate() + spanDays)
+
+  return toLocalString(occurrenceEnd)
+}
+
+/**
+ * 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) {
+  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)
+  const baseEnd = fromLocalString(event.endDate)
+  const spanDays = Math.max(0, Math.round((baseEnd - baseStart) / (24 * 60 * 60 * 1000)))
+
+  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)
+
+  if (event.repeat === 'weeks') {
+    const pattern = event.repeatWeekdays || []
+    if (!pattern.some(Boolean)) return false
+
+    const interval = event.repeatInterval || 1
+    const baseBlockStart = getMondayOfISOWeek(baseStart)
+    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 = new Date(baseBlockStart)
+      weekStart.setDate(weekStart.getDate() + 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 = new Date(weekStart)
+        candidateStart.setDate(candidateStart.getDate() + day)
+
+        // Skip if before base start
+        if (candidateStart < baseStart) continue
+
+        // Check if this day matches the pattern
+        if (!pattern[candidateStart.getDay()]) continue
+
+        // Check repeat count limit
+        const occIndex = getWeeklyOccurrenceIndex(event, toLocalString(candidateStart))
+        if (occIndex === null) continue
+
+        // Calculate end date for this occurrence
+        const candidateEnd = new Date(candidateStart)
+        candidateEnd.setDate(candidateEnd.getDate() + spanDays)
+
+        // Check if target date falls within this occurrence's span
+        if (targetDate >= candidateStart && targetDate <= candidateEnd) {
+          return true
+        }
+      }
+    }
+  } else if (event.repeat === 'months') {
+    const interval = event.repeatInterval || 1
+    const baseDay = baseStart.getDate()
+
+    // Check a reasonable range of months around the target date
+    const targetYear = targetDate.getFullYear()
+    const targetMonth = targetDate.getMonth()
+    const baseYear = baseStart.getFullYear()
+    const baseMonth = baseStart.getMonth()
+
+    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 = new Date(candidateYear, candidateMonth + 1, 0).getDate()
+      const effectiveDay = Math.min(baseDay, daysInMonth)
+
+      const candidateStart = new Date(candidateYear, candidateMonth, effectiveDay)
+
+      // Skip if before base start
+      if (candidateStart < baseStart) continue
+
+      // Check repeat count limit
+      const occIndex = getMonthlyOccurrenceIndex(event, toLocalString(candidateStart))
+      if (occIndex === null) continue
+
+      // Calculate end date for this occurrence
+      const candidateEnd = new Date(candidateStart)
+      candidateEnd.setDate(candidateEnd.getDate() + spanDays)
+
+      // Check if target date falls within this occurrence's span
+      if (targetDate >= candidateStart && 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
@@ -207,6 +472,12 @@ export {
   isoWeekInfo,
   toLocalString,
   fromLocalString,
+  getMondayOfISOWeek,
+  getWeeklyOccurrenceIndex,
+  getMonthlyOccurrenceIndex,
+  getOccurrenceIndex,
+  getVirtualOccurrenceEndDate,
+  occursOnOrSpansDate,
   mondayIndex,
   pad,
   daysInclusive,