/**
 * Next.js Middleware - i18n + Hydration 防護
 * ==========================================
 * Phase D #17: 修復 i18n 語系切換 Hydration 當機
 *
 * 問題: Client/Server 渲染語系落差導致 Hydration Mismatch
 * 解法: 強制綁定 NEXT_LOCALE Cookie，確保一致性
 *
 * 版本: v1.1
 * 建立: 2026-03-31 (台北時區)
 * 建立者: Claude Code
 *
 * @see QA Report 3.1 節 - i18n 語系切換報錯
 */

import createMiddleware from 'next-intl/middleware'
import { NextResponse, type NextRequest } from 'next/server'
import { routing } from './i18n/routing'

// 建立 next-intl middleware
const intlMiddleware = createMiddleware(routing)

/**
 * 強制綁定 NEXT_LOCALE Cookie
 *
 * 確保 Server/Client 語系一致，避免 Hydration Mismatch
 */
export default function middleware(request: NextRequest) {
  // 先執行 next-intl middleware
  const response = intlMiddleware(request)

  // 從 URL 路徑提取當前語系
  const pathname = request.nextUrl.pathname
  const localeFromPath = routing.locales.find(
    (locale) => pathname.startsWith(`/${locale}/`) || pathname === `/${locale}`
  )

  // 決定最終語系 (優先使用路徑中的語系)
  const finalLocale = localeFromPath || routing.defaultLocale

  // 🎯 Phase D #17: 強制設定 NEXT_LOCALE cookie
  // 確保 Client-side Hydration 時使用相同語系
  if (response instanceof NextResponse) {
    const existingLocale = request.cookies.get('NEXT_LOCALE')?.value

    // 只有當 cookie 不存在或不一致時才設定
    if (existingLocale !== finalLocale) {
      response.cookies.set('NEXT_LOCALE', finalLocale, {
        path: '/',
        maxAge: 60 * 60 * 24 * 365, // 1 年
        sameSite: 'lax',
      })
    }
  }

  return response
}

export const config = {
  // 匹配所有路徑，除了以下例外:
  // - api 路由
  // - _next 靜態檔案
  // - 靜態資源 (images, fonts, etc.)
  matcher: ['/((?!api|_next|_vercel|.*\\..*).*)'],
}