'use client'

import { Suspense } from 'react'
import { useEffect, useRef, useState } from 'react'
import { useSearchParams } from 'next/navigation'
import { Stack, Text, Loader } from '@mantine/core'

const SSO_STATE_STORAGE_KEY = 'sso_login_state'

function CallbackContent() {
  const searchParams = useSearchParams()
  const [error, setError] = useState<string | null>(null)
  const callbackStarted = useRef(false)

  useEffect(() => {
    if (callbackStarted.current) return

    const code = searchParams.get('sso_code')
    const state = searchParams.get('state')
    const expectedState = window.sessionStorage.getItem(SSO_STATE_STORAGE_KEY)

    if (!code) {
      setError('缺少 sso_code 参数')
      return
    }
    if (!state || !expectedState || state !== expectedState) {
      window.sessionStorage.removeItem(SSO_STATE_STORAGE_KEY)
      setError('state 无效或已过期，请重新登录')
      return
    }

    callbackStarted.current = true
    window.sessionStorage.removeItem(SSO_STATE_STORAGE_KEY)

    // 用 code 调用本应用的 /api/callback 换取用户信息
    fetch('/api/callback', {
      method: 'POST',
      headers: { 'Content-Type': 'application/json' },
      body: JSON.stringify({ code }),
    })
      .then(async (res) => {
        if (!res.ok) {
          const data = await res.json()
          throw new Error(data.error || '认证失败')
        }
        // 成功 -> 跳转到首页
        window.location.href = '/'
      })
      .catch((err) => {
        setError(err instanceof Error ? err.message : '认证失败')
      })
  }, [searchParams])

  if (error) {
    return (
      <Stack align="center" justify="center" h="100vh" gap="md">
        <Text size="lg" c="red">认证失败</Text>
        <Text size="sm" c="dimmed">{error}</Text>
        <Text
          size="sm"
          c="brand"
          style={{ cursor: 'pointer' }}
          onClick={() => (window.location.href = '/')}>
          返回首页重试
        </Text>
      </Stack>
    )
  }

  return (
    <Stack align="center" justify="center" h="100vh" gap="md">
      <Loader size="lg" />
      <Text size="sm" c="dimmed">正在验证 SSO 登录...</Text>
    </Stack>
  )
}

export default function CallbackPage() {
  return (
    <Suspense
      fallback={
        <Stack align="center" justify="center" h="100vh" gap="md">
          <Loader size="lg" />
          <Text size="sm" c="dimmed">正在验证 SSO 登录...</Text>
        </Stack>
      }>
      <CallbackContent />
    </Suspense>
  )
}