feat: support custom task recurrence

frontend/src/lib/task-utils.test.ts

@@ -1,5 +1,5 @@
 import { describe, expect, it } from 'vitest'
-import { filterTasks, groupTaskTree, moveItemWithinScope, renderMarkdown, toDateTimeLocal } from './task-utils'
+import { buildTaskRrule, filterTasks, groupTaskTree, moveItemWithinScope, parseTaskRrule, renderMarkdown, toDateTimeLocal } from './task-utils'
 
 type SearchTask = {
   id: string
@@ -38,6 +38,15 @@ describe('task utilities', () => {
     expect(moveItemWithinScope(rows, 'a1', 'b', 'before')).toEqual(rows)
   })
 
+  it('builds and parses custom repeat rules like TickTick', () => {
+    expect(buildTaskRrule({ frequency: 'weekly', interval: 2, weekdays: ['MO', 'WE', 'FR'], endMode: 'never' })).toBe('FREQ=WEEKLY;INTERVAL=2;BYDAY=MO,WE,FR')
+    expect(buildTaskRrule({ frequency: 'monthly', interval: 1, monthDays: [1, 15, 31], endMode: 'count', count: 10 })).toBe('FREQ=MONTHLY;BYMONTHDAY=1,15,31;COUNT=10')
+    expect(buildTaskRrule({ frequency: 'yearly', interval: 1, weekdays: [], monthDays: [], endMode: 'date', count: 10, until: '2027-12-31' })).toBe('FREQ=YEARLY;UNTIL=2027-12-31T23:59:59')
+    expect(parseTaskRrule('FREQ=WEEKLY;INTERVAL=2;BYDAY=MO,WE;COUNT=8')).toEqual({ frequency: 'weekly', interval: 2, weekdays: ['MO', 'WE'], monthDays: [], endMode: 'count', count: 8, until: '' })
+    expect(() => buildTaskRrule({ frequency: 'weekly', interval: 2, weekdays: [], monthDays: [], endMode: 'never', count: 10, until: '' })).toThrow('至少选择一个重复日期')
+    expect(() => buildTaskRrule({ frequency: 'daily', interval: 0, weekdays: [], monthDays: [], endMode: 'never', count: 10, until: '' })).toThrow('重复间隔至少为 1')
+  })
+
   it('renders safe basic markdown and strips unsafe html', () => {
     const html = renderMarkdown('# Plan\n**bold** [link](https://example.com)\n<script>alert(1)</script>')
     expect(html).toContain('<h1>Plan</h1>')