feat: support custom task recurrence

frontend/src/lib/task-utils.ts

@@ -104,6 +104,46 @@ export function moveItemWithinScope<T extends { id: string; parent_id?: string |
   return items.map((item) => (item.parent_id ?? null) === (source.parent_id ?? null) ? reorderedIterator.next().value! : item)
 }
 
+export type TaskRepeatConfig = {
+  frequency: 'daily' | 'weekly' | 'monthly' | 'yearly'
+  interval: number
+  weekdays?: string[]
+  monthDays?: number[]
+  endMode: 'never' | 'date' | 'count'
+  count?: number
+  until?: string
+}
+
+export function buildTaskRrule(config: TaskRepeatConfig) {
+  const interval = Math.floor(Number(config.interval))
+  if (!Number.isFinite(interval) || interval < 1) throw new Error('重复间隔至少为 1')
+  if (config.frequency === 'weekly' && !config.weekdays?.length) throw new Error('至少选择一个重复日期')
+  if (config.frequency === 'monthly' && (!config.monthDays?.length || config.monthDays.some((day) => day < 1 || day > 31))) throw new Error('请输入 1 到 31 的每月日期')
+  if (config.endMode === 'count' && (!config.count || config.count < 1)) throw new Error('重复次数至少为 1')
+  if (config.endMode === 'date' && !config.until) throw new Error('请选择结束日期')
+  const parts = [`FREQ=${config.frequency.toUpperCase()}`]
+  if (interval > 1) parts.push(`INTERVAL=${interval}`)
+  if (config.frequency === 'weekly' && config.weekdays?.length) parts.push(`BYDAY=${config.weekdays.join(',')}`)
+  if (config.frequency === 'monthly' && config.monthDays?.length) parts.push(`BYMONTHDAY=${config.monthDays.join(',')}`)
+  if (config.endMode === 'count') parts.push(`COUNT=${Math.max(1, Math.floor(config.count ?? 1))}`)
+  if (config.endMode === 'date' && config.until) parts.push(`UNTIL=${config.until}T23:59:59`)
+  return parts.join(';')
+}
+
+export function parseTaskRrule(rrule = ''): TaskRepeatConfig {
+  const parts = Object.fromEntries(rrule.split(';').filter(Boolean).map((part) => part.split('=', 2)))
+  const frequency = (parts.FREQ?.toLowerCase() || 'daily') as TaskRepeatConfig['frequency']
+  return {
+    frequency,
+    interval: Math.max(1, Number(parts.INTERVAL ?? 1)),
+    weekdays: parts.BYDAY?.split(',').filter(Boolean) ?? [],
+    monthDays: parts.BYMONTHDAY?.split(',').map(Number).filter(Number.isFinite) ?? [],
+    endMode: parts.COUNT ? 'count' : parts.UNTIL ? 'date' : 'never',
+    count: parts.COUNT ? Number(parts.COUNT) : 1,
+    until: parts.UNTIL?.slice(0, 10) ?? '',
+  }
+}
+
 export function toDateTimeLocal(value: string | null | undefined) {
   if (!value) return ''
   const date = new Date(value)