/**
 * GET /api/integrations/calendar/callback
 * Google OAuth callback — exchanges code for tokens and persists them.
 */

import { NextRequest, NextResponse } from 'next/server'
import prisma from '@/lib/prisma'

const GOOGLE_TOKEN_URL = 'https://oauth2.googleapis.com/token'

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=calendar_auth_failed`,
    )
  }

  const clientId = process.env.GOOGLE_CALENDAR_CLIENT_ID || process.env.AUTH_GOOGLE_ID || ''
  const clientSecret = process.env.GOOGLE_CALENDAR_CLIENT_SECRET || process.env.AUTH_GOOGLE_SECRET || ''
  const redirectUri = `${url.origin}/api/integrations/calendar/callback`

  const tokenRes = await fetch(GOOGLE_TOKEN_URL, {
    method: 'POST',
    headers: { 'Content-Type': 'application/x-www-form-urlencoded' },
    body: new URLSearchParams({
      client_id: clientId,
      client_secret: clientSecret,
      code,
      redirect_uri: redirectUri,
      grant_type: 'authorization_code',
    }),
  })

  const tokenData = await tokenRes.json()

  if (!tokenData.access_token) {
    return NextResponse.redirect(
      `${url.origin}/settings/integrations?error=calendar_token_failed`,
    )
  }

  // Persist tokens in UserAISettings.integrationTokens
  const aiSettings = await prisma.userAISettings.findUnique({
    where: { userId },
    select: { integrationTokens: true },
  })
  const meta =
    typeof aiSettings?.integrationTokens === 'string'
      ? JSON.parse(aiSettings.integrationTokens)
      : (aiSettings?.integrationTokens as Record<string, unknown> | null) ?? {}

  meta.calendarAccessToken = tokenData.access_token
  if (tokenData.refresh_token) {
    meta.calendarRefreshToken = tokenData.refresh_token
  }

  await prisma.userAISettings.upsert({
    where: { userId },
    update: { integrationTokens: JSON.stringify(meta) },
    create: { userId, integrationTokens: JSON.stringify(meta) },
  })

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