// Generates a robots.txt. Two modes:
//   'new'  — full file (user has no robots.txt at all)
//   'diff' — only the bot blocks the user is missing
import { AI_BOTS } from './extract.js'

function botBlock(bot) {
  return `User-agent: ${bot}\nAllow: /\nAllow: /llms.txt\n`
}

export function generateRobotsTxt(siteData) {
  const { url = '', existingRobots = '', existingAiBots = [] } = siteData
  const hasRobots = existingRobots.trim().length > 0
  const sitemap = url ? `${url.replace(/\/$/, '')}/sitemap.xml` : '[Bitte ergänzen: https://deine-domain.de/sitemap.xml]'

  if (!hasRobots) {
    const header =
`# robots.txt — generated by VISIGINE
# ${url || 'https://deine-domain.de'}

User-agent: *
Allow: /

# AI search engines and language model crawlers
`
    const blocks = AI_BOTS.map(botBlock).join('\n')
    return {
      content: `${header}${blocks}\nSitemap: ${sitemap}\n`,
      mode: 'new',
    }
  }

  const missing = AI_BOTS.filter((b) => !existingAiBots.includes(b))
  if (missing.length === 0) {
    return {
      content: '# Deine robots.txt deckt bereits alle relevanten KI-Bots ab. Keine Änderungen nötig.\n',
      mode: 'diff',
    }
  }

  const header =
`# Folgende Blöcke zu deiner bestehenden robots.txt hinzufügen
# (am Ende der Datei, vor der Sitemap-Zeile falls vorhanden)

`
  return {
    content: header + missing.map(botBlock).join('\n'),
    mode: 'diff',
  }
}