import { NextRequest, NextResponse } from 'next/server'
import { getGoogleOAuthCredentials, readIntegrationMeta, writeIntegrationMeta } from '@/lib/integrations/google-integration-tokens'

export async function GET(req: NextRequest) {
  const url = new URL(req.url)
  const code = url.searchParams.get('code')
  const userId = url.searchParams.get('state')
  const error = url.searchParams.get('error')

  if (error || !code || !userId) {
    return NextResponse.redirect(`${url.origin}/settings/integrations?error=gmail_auth_failed`)
  }

  const { clientId, clientSecret } = getGoogleOAuthCredentials()
  const tokenRes = await fetch('https://oauth2.googleapis.com/token', {
    method: 'POST',
    headers: { 'Content-Type': 'application/x-www-form-urlencoded' },
    body: new URLSearchParams({
      client_id: clientId,
      client_secret: clientSecret,
      code,
      redirect_uri: `${url.origin}/api/integrations/gmail/callback`,
      grant_type: 'authorization_code',
    }),
  })

  const tokenData = await tokenRes.json()
  if (!tokenData.access_token) {
    return NextResponse.redirect(`${url.origin}/settings/integrations?error=gmail_token_failed`)
  }

  const meta = await readIntegrationMeta(userId)
  meta.gmailAccessToken = tokenData.access_token
  if (tokenData.refresh_token) meta.gmailRefreshToken = tokenData.refresh_token
  await writeIntegrationMeta(userId, meta)

  return NextResponse.redirect(`${url.origin}/settings/integrations?connected=gmail`)
}