KI-AGENT: Ergänze wiederholende Termine für Kalender und Plantafel

frontend/utils/eventRecurrence.ts

@@ -0,0 +1,78 @@
+import dayjs from "dayjs"
+
+export const EVENT_REPEAT_INTERVALS = [
+  "Keine Wiederholung",
+  "Täglich",
+  "Wöchentlich",
+  "2-wöchentlich",
+  "Monatlich",
+  "Jährlich"
+] as const
+
+const DEFAULT_REPEAT_INTERVAL = "Keine Wiederholung"
+const MAX_OCCURRENCES = 500
+
+const addInterval = (date: dayjs.Dayjs, repeatInterval: string) => {
+  switch (repeatInterval) {
+    case "Täglich":
+      return date.add(1, "day")
+    case "Wöchentlich":
+      return date.add(1, "week")
+    case "2-wöchentlich":
+      return date.add(2, "week")
+    case "Monatlich":
+      return date.add(1, "month")
+    case "Jährlich":
+      return date.add(1, "year")
+    default:
+      return null
+  }
+}
+
+export const normalizeRepeatInterval = (value?: string | null) =>
+  EVENT_REPEAT_INTERVALS.includes(value as typeof EVENT_REPEAT_INTERVALS[number])
+    ? value as typeof EVENT_REPEAT_INTERVALS[number]
+    : DEFAULT_REPEAT_INTERVAL
+
+export const expandRecurringEvent = <T>(
+  event: {
+    startDate: string | Date
+    endDate?: string | Date | null
+    repeatInterval?: string | null
+  },
+  rangeStart: string | Date,
+  rangeEnd: string | Date,
+  buildOccurrence: (occurrenceStart: dayjs.Dayjs, occurrenceEnd: dayjs.Dayjs | null, occurrenceIndex: number) => T
+) => {
+  const repeatInterval = normalizeRepeatInterval(event.repeatInterval)
+  const baseStart = dayjs(event.startDate)
+  const baseEnd = event.endDate ? dayjs(event.endDate) : null
+  const visibleStart = dayjs(rangeStart)
+  const visibleEnd = dayjs(rangeEnd)
+  const durationMs = baseEnd ? Math.max(baseEnd.diff(baseStart), 0) : 0
+
+  if (repeatInterval === DEFAULT_REPEAT_INTERVAL) {
+    const occurrenceEnd = baseEnd ? baseStart.add(durationMs, "millisecond") : null
+    if (baseStart.isAfter(visibleEnd) || (occurrenceEnd && occurrenceEnd.isBefore(visibleStart))) return []
+    return [buildOccurrence(baseStart, occurrenceEnd, 0)]
+  }
+
+  const occurrences: T[] = []
+  let occurrenceStart = baseStart
+  let occurrenceIndex = 0
+
+  while (occurrenceIndex < MAX_OCCURRENCES && occurrenceStart.isBefore(visibleEnd.add(1, "day"))) {
+    const occurrenceEnd = baseEnd ? occurrenceStart.add(durationMs, "millisecond") : null
+
+    if (!occurrenceStart.isAfter(visibleEnd) && !(occurrenceEnd && occurrenceEnd.isBefore(visibleStart))) {
+      occurrences.push(buildOccurrence(occurrenceStart, occurrenceEnd, occurrenceIndex))
+    }
+
+    const nextStart = addInterval(occurrenceStart, repeatInterval)
+    if (!nextStart || nextStart.isSame(occurrenceStart)) break
+    occurrenceStart = nextStart
+    occurrenceIndex += 1
+  }
+
+  return occurrences
+}