feat: implement serializeICS with round-trip support

test/ical-io.test.js

@@ -3,6 +3,7 @@ import { readFileSync } from 'node:fs'
 import { fileURLToPath } from 'node:url'
 import { dirname, join } from 'node:path'
 import { parseICS } from '../src/lib/ical-io.js'
+import { serializeICS } from '../src/lib/ical-io.js'
 
 const __dirname = dirname(fileURLToPath(import.meta.url))
 const GOLDEN = readFileSync(join(__dirname, 'golden-org.ics'), 'utf-8')
@@ -48,3 +49,60 @@ describe('parseICS', () => {
     expect(events[60].uid).toBe('uid60')
   })
 })
+
+describe('serializeICS round-trip', () => {
+  it('round-trips: parse(serialize(parse(x))) equals parse(x)', () => {
+    const original = parseICS(GOLDEN)
+    const text = serializeICS(original)
+    const reparsed = parseICS(text)
+
+    expect(reparsed.events).toHaveLength(original.events.length)
+    // Spot-check first event
+    const e0 = reparsed.events[0]
+    expect(e0.summary).toBe(original.events[0].summary)
+    expect(e0.dtstartDate).toBe(original.events[0].dtstartDate)
+    expect(e0.dtstartTime).toBe(original.events[0].dtstartTime)
+    expect(e0.tzid).toBe(original.events[0].tzid)
+    expect(e0._raw.dtstamp).toBe(original.events[0]._raw.dtstamp)
+  })
+
+  it('preserves VTIMEZONE in output', () => {
+    const { meta } = parseICS(serializeICS(parseICS(GOLDEN)))
+    expect(meta.vtimezones).toHaveLength(1)
+  })
+
+  it('serializes a manually-built recurring event', () => {
+    const ev = {
+      uid: 'test-1',
+      summary: 'Test Event',
+      location: 'Room A',
+      description: 'Desc',
+      dtstartDate: '2026-07-27',
+      dtstartTime: '09:00',
+      dtendTime: '10:30',
+      tzid: 'UTC',
+      rrule: { freq: 'WEEKLY', interval: 1, byday: 'MO', untilDate: '2026-10-19' },
+      exdates: ['2026-09-21'],
+      _raw: { dtstamp: '20260711T085008Z' },
+    }
+    const text = serializeICS({
+      meta: {
+        prodid: '-//Test//EN', version: '2.0', calscale: 'GREGORIAN',
+        method: null, xWrCalname: null, xWrTimezone: null, vtimezones: [],
+      },
+      events: [ev],
+    })
+    expect(text).toContain('BEGIN:VEVENT')
+    expect(text).toContain('SUMMARY:Test Event')
+    expect(text).toContain('RRULE:FREQ=WEEKLY')
+    expect(text).toContain('BYDAY=MO')
+    expect(text).toContain('EXDATE')
+    expect(text).toContain('DTSTART:20260727T090000Z')
+
+    // Re-parse and verify
+    const reparsed = parseICS(text)
+    expect(reparsed.events[0].rrule.freq).toBe('WEEKLY')
+    expect(reparsed.events[0].rrule.byday).toBe('MO')
+    expect(reparsed.events[0].exdates).toContain('2026-09-21')
+  })
+})