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 }
}