import { ref, onMounted, onServerPrefetch, Ref } from 'vue'
import { getCurrentInstance } from 'vue'
import type { SSRContext } from './ssrContext'
import { resolveSSRContext } from './ssrContext'

// 全局数据缓存，用于 SSR 数据共享
const globalCache = new Map<string, any>()

// SSR 上下文类型从 ssrContext.ts 引入

// useFetch 的配置选项
interface UseFetchOptions<T = any> {
  key?: string
  server?: boolean
  default?: () => any
  transform?: (data: any) => T
  onError?: (error: Error) => void
}

// useFetch 返回值类型
interface UseFetchReturn<T> {
  data: Ref<T | null>
  error: Ref<Error | null>
  pending: Ref<boolean>
  refresh: () => Promise<void>
  execute: () => Promise<void>
}

/**
 * SSR 兼容的 useFetch hook
 * 支持服务端预取和客户端水合
 */
export function useFetch<T = any>(
  url: string | (() => string) | (() => Promise<string>),
  options: UseFetchOptions<T> = {}
): UseFetchReturn<T> {
  const {
    key,
    server = true,
    default: defaultValue,
    transform,
    onError
  } = options

  // 生成缓存键
  const cacheKey = key || (typeof url === 'string' ? url : `fetch-${Date.now()}`)
  
  // 响应式状态
  const data = ref<T | null>(null)
  const error = ref<Error | null>(null)
  const pending = ref(false)

  // 获取当前组件实例
  const instance = getCurrentInstance()
  
  // 获取 SSR 上下文
  const getSSRContext = (): SSRContext | null => resolveSSRContext(instance)

  // 获取缓存
  const getCache = () => {
    const ssrContext = getSSRContext()
    return ssrContext?.cache || globalCache
  }

  // 设置缓存
  const setCache = (key: string, value: any) => {
    const cache = getCache()
    cache.set(key, value)
  }

  // 获取缓存数据
  const getCachedData = () => {
    const cache = getCache()
    return cache.get(cacheKey)
  }

  // 执行 fetch 请求
  const execute = async (): Promise<void> => {
    try {
      pending.value = true
      error.value = null

      // 获取 URL
      const fetchUrl = typeof url === 'function' ? await url() : url

      // 仅在服务端注入 Cookie，客户端浏览器会自动携带
      let requestInit: RequestInit | undefined
      if (typeof window === 'undefined') {
        const ssrContext = getSSRContext()
        const cookieHeader = ssrContext?.cookies
          ? Object.entries(ssrContext.cookies)
              .filter(([k, v]) => k && v != null)
              .map(([k, v]) => `${k}=${String(v)}`)
              .join('; ')
          : undefined
        if (cookieHeader) {
          requestInit = { headers: { Cookie: cookieHeader } }
        }
      }

      // 执行请求
      const response = await fetch(fetchUrl, requestInit)
      
      if (!response.ok) {
        throw new Error(`HTTP ${response.status}: ${response.statusText}`)
      }

      let result = await response.json()

      // 应用转换函数
      if (transform) {
        result = transform(result)
      }

      data.value = result
      setCache(cacheKey, result)

      // 收集服务端返回的 Set-Cookie，回传到最终响应头
      if (typeof window === 'undefined') {
        const ssrContext = getSSRContext()
        if (ssrContext) {
          const setCookieValues: string[] = []
          const anyHeaders: any = response.headers as any
          // undici 扩展：getSetCookie()
          if (typeof anyHeaders?.getSetCookie === 'function') {
            try {
              const arr = anyHeaders.getSetCookie()
              if (Array.isArray(arr)) setCookieValues.push(...arr)
            } catch {}
          }
          // node-fetch/raw headers API
          if (typeof anyHeaders?.raw === 'function') {
            try {
              const raw = anyHeaders.raw()
              const arr = raw?.['set-cookie']
              if (Array.isArray(arr)) setCookieValues.push(...arr)
            } catch {}
          }
          // 兜底：单值
          const single = response.headers.get('set-cookie')
          if (single) setCookieValues.push(single)

          if (setCookieValues.length) {
            if (!Array.isArray(ssrContext.setCookies)) ssrContext.setCookies = []
            ssrContext.setCookies.push(...setCookieValues)
          }
        }
      }

    } catch (err) {
      const fetchError = err instanceof Error ? err : new Error(String(err))
      error.value = fetchError
      
      if (onError) {
        onError(fetchError)
      }

      // 设置默认值
      if (defaultValue) {
        data.value = typeof defaultValue === 'function' ? defaultValue() : defaultValue
      }
    } finally {
      pending.value = false
    }
  }

  // 刷新数据
  const refresh = async (): Promise<void> => {
    // 清除缓存
    const cache = getCache()
    cache.delete(cacheKey)
    await execute()
  }

  // 服务端预取
  if (server && typeof window === 'undefined') {
    onServerPrefetch(async () => {
      // 检查是否已有缓存数据
      const cachedData = getCachedData()
      if (cachedData !== undefined) {
        data.value = cachedData
        return
      }

      // 执行预取
      await execute()
    })
  }

  // 立即检查缓存数据（服务端和客户端都需要）
  const cachedData = getCachedData()
  if (cachedData !== undefined) {
    data.value = cachedData
    console.log(`[useFetch] 从缓存加载数据: ${cacheKey}`, cachedData)
  } else {
    console.log(`[useFetch] 缓存中无数据: ${cacheKey}`)
  }

  // 客户端水合
  if (typeof window !== 'undefined') {
    onMounted(async () => {
      // 如果已经有缓存数据，不需要再次请求
      if (cachedData !== undefined) {
        return
      }

      // 如果没有预取数据，则执行请求
      await execute()
    })
  }

  return {
    data: data as Ref<T | null>,
    error: error as Ref<Error | null>,
    pending: pending as Ref<boolean>,
    refresh,
    execute
  }
}