import { useState } from 'react'
import { Send, Trash2, Loader2 } from 'lucide-react'

const DEFAULT_MODEL = 'nvidia/nemotron-3-ultra-550b-a55b:free'
const TIMEOUT_MS = 180000

/** 解析一筆 SSE 行：回傳 { delta } / { error } / { done } / null */
function parseSseLine(line) {
  const payload = line.trim()
  if (!payload.startsWith('data:')) return null
  const raw = payload.slice(5).trim()
  if (raw === '[DONE]') return { done: true }
  let data
  try { data = JSON.parse(raw) } catch { return null }
  if (data.error) return { error: data.error.message || 'API 回傳錯誤' }
  return { delta: data.choices?.[0]?.delta?.content }
}

/** 把內容接到最後一則 assistant 訊息（還沒有就新增一則） */
function withLastAssistant(prev, content, append) {
  const last = prev[prev.length - 1]
  if (last && last.role === 'assistant') {
    return [...prev.slice(0, -1), { role: 'assistant', content: append ? last.content + content : content }]
  }
  return [...prev, { role: 'assistant', content }]
}

async function readErrorMessage(res) {
  try {
    const data = await res.json()
    return data?.error?.message || data?.error?.data?.message || data?.message || '無錯誤訊息'
  } catch {
    try { return (await res.text()).slice(0, 300) || '無錯誤訊息' }
    catch { return '無錯誤訊息' }
  }
}

export default function ChatInterface({ apiConfig, onChange }) {
  const [messages, setMessages] = useState([])
  const [input, setInput] = useState('')
  const [loading, setLoading] = useState(false)

  const setField = (field, value) => onChange({ ...apiConfig, [field]: value })

  const clearChat = () => {
    if (!loading) setMessages([])
  }

  const sendMessage = async () => {
    const text = input.trim()
    if (!text || loading) return
    if (!apiConfig.apiKey?.trim()) return alert('請輸入 API Key')

    // 送完整對話歷史，不只最新一則
    const next = [...messages, { role: 'user', content: text }, { role: 'assistant', content: '' }]
    setMessages(next)
    setInput('')
    setLoading(true)

    const controller = new AbortController()
    const timer = setTimeout(() => controller.abort(), TIMEOUT_MS)

    try {
      const base = String(apiConfig.supplier).replace(/\/+$/, '')
      const res = await fetch(`${base}/chat/completions`, {
        method: 'POST',
        signal: controller.signal,
        headers: {
          Authorization: `Bearer ${apiConfig.apiKey.trim()}`,
          'Content-Type': 'application/json',
          'HTTP-Referer': window.location.origin,
          'X-Title': 'Agent Studio',
        },
        body: JSON.stringify({
          model: apiConfig.model || DEFAULT_MODEL,
          messages: next.filter((m) => m.content !== ''),
          stream: true,
        }),
      })

      if (!res.ok) {
        const detail = await readErrorMessage(res)
        setMessages((prev) => withLastAssistant(prev, `⚠️ API 錯誤 ${res.status}：${detail}`, false))
        return
      }
      if (!res.body) {
        setMessages((prev) => withLastAssistant(prev, '⚠️ 回應不含可讀取的串流', false))
        return
      }

      const reader = res.body.getReader()
      const decoder = new TextDecoder()
      let buffer = ''
      let gotAny = false

      for (;;) {
        const { value, done } = await reader.read()
        if (done) break
        buffer += decoder.decode(value, { stream: true })
        const lines = buffer.split('\n')
        buffer = lines.pop() // 最後一行可能還沒送完，留到下一次
        for (const line of lines) {
          const event = parseSseLine(line)
          if (!event) continue
          if (event.done) continue
          if (event.error) throw new Error(event.error)
          if (event.delta) {
            gotAny = true
            setMessages((prev) => withLastAssistant(prev, event.delta, true))
          }
        }
      }

      if (!gotAny) {
        setMessages((prev) => withLastAssistant(prev, '⚠️ 模型沒有回傳任何內容', false))
      }
    } catch (e) {
      const message =
        e.name === 'AbortError' ? `請求逾時（超過 ${TIMEOUT_MS / 1000} 秒）` : e.message
      setMessages((prev) => withLastAssistant(prev, `⚠️ ${message}`, false))
    } finally {
      clearTimeout(timer)
      setLoading(false)
    }
  }

  const keyState = apiConfig.apiKey?.trim()
    ? <span className="text-emerald-400 text-xs">Key 已設定</span>
    : <span className="text-red-400 text-xs">尚未設定 Key</span>

  return (
    <div className="flex flex-col h-[80vh] border border-edge rounded-3xl overflow-hidden bg-panel">
      <div className="p-4 border-b border-edge flex items-center gap-3 flex-wrap bg-app">
        <input
          type="text"
          value={apiConfig.supplier}
          onChange={(e) => setField('supplier', e.target.value)}
          placeholder="API URL"
          className="bg-field px-4 py-2 rounded-xl w-64 focus:outline-none"
        />
        <input
          type="password"
          value={apiConfig.apiKey}
          onChange={(e) => setField('apiKey', e.target.value)}
          placeholder="API Key"
          className="bg-field px-4 py-2 rounded-xl w-52 focus:outline-none"
        />
        <input
          type="text"
          value={apiConfig.model}
          onChange={(e) => setField('model', e.target.value)}
          placeholder="Model"
          className="bg-field px-4 py-2 rounded-xl w-60 focus:outline-none"
        />
        {keyState}
        <div className="flex-1" />
        <button
          onClick={clearChat}
          disabled={loading || messages.length === 0}
          className="flex items-center gap-2 px-4 py-2 bg-field rounded-xl disabled:opacity-40"
          title="清空對話"
        >
          <Trash2 className="w-4 h-4" /> 清空
        </button>
        <button
          onClick={sendMessage}
          disabled={loading || !input.trim()}
          className="flex items-center gap-2 bg-blue-600 hover:bg-blue-700 px-6 py-2 rounded-2xl disabled:opacity-50"
        >
          {loading ? <Loader2 className="w-4 h-4 animate-spin" /> : <Send className="w-4 h-4" />}
          {loading ? '思考中...' : '發送'}
        </button>
      </div>

      <div className="flex-1 overflow-y-auto p-4 space-y-4">
        {messages.length === 0 && (
          <div className="h-full flex items-center justify-center text-muted text-sm">
            輸入訊息開始對話。API 設定與 Agent 頁共用。
          </div>
        )}
        {messages.map((msg, i) => (
          <div key={i} className={`flex ${msg.role === 'user' ? 'justify-end' : 'justify-start'}`}>
            <div
              className={`max-w-[75%] px-5 py-3 rounded-3xl whitespace-pre-wrap break-words ${
                msg.role === 'user' ? 'bg-blue-600' : msg.content.startsWith('⚠️') ? 'bg-red-900/60 text-red-200' : 'bg-field'
              }`}
            >
              {msg.content || (msg.role === 'assistant' && loading ? '…' : '')}
            </div>
          </div>
        ))}
      </div>

      <div className="p-4 border-t border-edge">
        <input
          value={input}
          onChange={(e) => setInput(e.target.value)}
          onKeyDown={(e) => {
            if (e.key === 'Enter' && !e.shiftKey) {
              e.preventDefault()
              sendMessage()
            }
          }}
          placeholder="輸入訊息..."
          className="w-full bg-field px-6 py-3 rounded-3xl focus:outline-none"
        />
      </div>
    </div>
  )
}