Add iCal download composable with RFC 5545 VEVENT generation

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/composables/__tests__/useIcalDownload.spec.ts

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+import { describe, it, expect } from 'vitest'
+import { generateIcs } from '../useIcalDownload'
+
+describe('generateIcs', () => {
+  const baseEvent = {
+    eventToken: '550e8400-e29b-41d4-a716-446655440000',
+    title: 'Sommerfest am See',
+    dateTime: '2026-07-15T18:00:00+02:00',
+    location: 'Stadtpark Berlin',
+    description: 'Bring your own drinks',
+  }
+
+  it('generates valid VCALENDAR wrapper', () => {
+    const ics = generateIcs(baseEvent)
+    expect(ics).toMatch(/^BEGIN:VCALENDAR\r\n/)
+    expect(ics).toMatch(/\r\nEND:VCALENDAR\r\n$/)
+  })
+
+  it('includes VERSION and PRODID', () => {
+    const ics = generateIcs(baseEvent)
+    expect(ics).toContain('VERSION:2.0\r\n')
+    expect(ics).toContain('PRODID:-//fete//EN\r\n')
+  })
+
+  it('generates valid VEVENT block', () => {
+    const ics = generateIcs(baseEvent)
+    expect(ics).toContain('BEGIN:VEVENT\r\n')
+    expect(ics).toContain('END:VEVENT\r\n')
+  })
+
+  it('sets UID from eventToken', () => {
+    const ics = generateIcs(baseEvent)
+    expect(ics).toContain('UID:550e8400-e29b-41d4-a716-446655440000@fete\r\n')
+  })
+
+  it('sets DTSTART in UTC format', () => {
+    const ics = generateIcs(baseEvent)
+    expect(ics).toContain('DTSTART:20260715T160000Z\r\n')
+  })
+
+  it('does NOT include DTEND or DURATION', () => {
+    const ics = generateIcs(baseEvent)
+    expect(ics).not.toContain('DTEND')
+    expect(ics).not.toContain('DURATION')
+  })
+
+  it('sets SUMMARY from title', () => {
+    const ics = generateIcs(baseEvent)
+    expect(ics).toContain('SUMMARY:Sommerfest am See\r\n')
+  })
+
+  it('sets LOCATION when present', () => {
+    const ics = generateIcs(baseEvent)
+    expect(ics).toContain('LOCATION:Stadtpark Berlin\r\n')
+  })
+
+  it('sets DESCRIPTION when present', () => {
+    const ics = generateIcs(baseEvent)
+    expect(ics).toContain('DESCRIPTION:Bring your own drinks\r\n')
+  })
+
+  it('omits LOCATION when not provided', () => {
+    const { location: _location, ...noLocation } = baseEvent
+    const ics = generateIcs(noLocation)
+    expect(ics).not.toContain('LOCATION')
+  })
+
+  it('omits DESCRIPTION when not provided', () => {
+    const { description: _description, ...noDesc } = baseEvent
+    const ics = generateIcs(noDesc)
+    expect(ics).not.toContain('DESCRIPTION')
+  })
+
+  it('includes SEQUENCE:0', () => {
+    const ics = generateIcs(baseEvent)
+    expect(ics).toContain('SEQUENCE:0\r\n')
+  })
+
+  it('includes DTSTAMP in UTC format', () => {
+    const ics = generateIcs(baseEvent)
+    expect(ics).toMatch(/DTSTAMP:\d{8}T\d{6}Z\r\n/)
+  })
+
+  it('escapes commas in text fields', () => {
+    const ics = generateIcs({ ...baseEvent, title: 'Hello, World' })
+    expect(ics).toContain('SUMMARY:Hello\\, World\r\n')
+  })
+
+  it('escapes semicolons in text fields', () => {
+    const ics = generateIcs({ ...baseEvent, description: 'foo; bar' })
+    expect(ics).toContain('DESCRIPTION:foo\\; bar\r\n')
+  })
+
+  it('escapes backslashes in text fields', () => {
+    const ics = generateIcs({ ...baseEvent, title: 'path\\to' })
+    expect(ics).toContain('SUMMARY:path\\\\to\r\n')
+  })
+
+  it('escapes newlines in text fields', () => {
+    const ics = generateIcs({ ...baseEvent, description: 'line1\nline2' })
+    expect(ics).toContain('DESCRIPTION:line1\\nline2\r\n')
+  })
+
+  it('produces deterministic output for the same input', () => {
+    const ics1 = generateIcs(baseEvent)
+    const ics2 = generateIcs(baseEvent)
+    // DTSTAMP changes with time, so strip it for comparison
+    const strip = (s: string) => s.replace(/DTSTAMP:\d{8}T\d{6}Z\r\n/, '')
+    expect(strip(ics1)).toBe(strip(ics2))
+  })
+
+  it('uses CRLF line endings throughout', () => {
+    const ics = generateIcs(baseEvent)
+    const lines = ics.split('\r\n')
+    // Every "line" split by CRLF should not contain a bare LF
+    for (const line of lines) {
+      expect(line).not.toContain('\n')
+    }
+  })
+})

frontend/src/composables/useIcalDownload.ts

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+import { slugify } from '@/utils/slugify'
+
+export interface IcalEvent {
+  eventToken: string
+  title: string
+  dateTime: string
+  location?: string
+  description?: string
+}
+
+function escapeText(value: string): string {
+  return value
+    .replace(/\\/g, '\\\\')
+    .replace(/;/g, '\\;')
+    .replace(/,/g, '\\,')
+    .replace(/\n/g, '\\n')
+}
+
+function toUtcString(isoDateTime: string): string {
+  const d = new Date(isoDateTime)
+  const pad = (n: number) => String(n).padStart(2, '0')
+  return (
+    `${d.getUTCFullYear()}${pad(d.getUTCMonth() + 1)}${pad(d.getUTCDate())}` +
+    `T${pad(d.getUTCHours())}${pad(d.getUTCMinutes())}${pad(d.getUTCSeconds())}Z`
+  )
+}
+
+export function generateIcs(event: IcalEvent): string {
+  const lines: string[] = [
+    'BEGIN:VCALENDAR',
+    'VERSION:2.0',
+    'PRODID:-//fete//EN',
+    'BEGIN:VEVENT',
+    `UID:${event.eventToken}@fete`,
+    `DTSTAMP:${toUtcString(new Date().toISOString())}`,
+    `DTSTART:${toUtcString(event.dateTime)}`,
+    `SUMMARY:${escapeText(event.title)}`,
+    'SEQUENCE:0',
+  ]
+
+  if (event.location) {
+    lines.push(`LOCATION:${escapeText(event.location)}`)
+  }
+
+  if (event.description) {
+    lines.push(`DESCRIPTION:${escapeText(event.description)}`)
+  }
+
+  lines.push('END:VEVENT', 'END:VCALENDAR', '')
+
+  return lines.join('\r\n')
+}
+
+export function useIcalDownload() {
+  function download(event: IcalEvent) {
+    const ics = generateIcs(event)
+    const blob = new Blob([ics], { type: 'text/calendar;charset=utf-8' })
+    const url = URL.createObjectURL(blob)
+
+    const filename = `${slugify(event.title) || 'event'}.ics`
+    const link = document.createElement('a')
+    link.href = url
+    link.download = filename
+    document.body.appendChild(link)
+    link.click()
+    document.body.removeChild(link)
+    URL.revokeObjectURL(url)
+  }
+
+  return { download }
+}