'use client'

/**
 * ThinkingStreamTest - Tracer Bullet 測試元件 (企業級強化版)
 *
 * 修復項目:
 * 1. Buffer 累積 - 防止 TCP 封包切斷 JSON
 * 2. AbortController - 防止 Memory Leak
 * 3. Zustand 整合 - 符合 ADR-004
 * 4. Nothing.tech 美學 - 符合 ADR-002
 */

import { useCallback, useRef, useEffect } from 'react'
import { cn } from '@/lib/utils'
import { useAgentStore } from '@/stores/agent.store'

interface StreamThinkingStep {
  type: 'thinking' | 'result'
  content: string
}

const API_BASE_URL = process.env.NEXT_PUBLIC_API_URL || 'http://localhost:8000/v1'

export function ThinkingStreamTest() {
  // ADR-004: 使用 Zustand 全域狀態
  const {
    status,
    thinkingStream,
    setStatus,
    appendThinking,
    clearThinking,
  } = useAgentStore()

  const isStreaming = status === 'thinking'

  // 防線 1: AbortController 用於中斷連線
  const abortControllerRef = useRef<AbortController | null>(null)

  // 防線 2: 組件卸載時自動清理
  useEffect(() => {
    return () => {
      abortControllerRef.current?.abort()
    }
  }, [])

  const startStream = useCallback(async () => {
    // 中斷前一次未完成的請求
    abortControllerRef.current?.abort()
    abortControllerRef.current = new AbortController()

    // 重置狀態 (透過 Zustand)
    clearThinking()
    setStatus('thinking')

    try {
      const response = await fetch(`${API_BASE_URL}/agent/thinking`, {
        signal: abortControllerRef.current.signal,
      })

      if (!response.ok) {
        throw new Error(`HTTP ${response.status}: ${response.statusText}`)
      }

      const reader = response.body?.getReader()
      if (!reader) {
        throw new Error('無法建立串流通道')
      }

      const decoder = new TextDecoder()
      let buffer = '' // 防線 3: 字串緩衝區，防止 JSON 被切斷

      // eslint-disable-next-line no-constant-condition -- SSE stream read loop
      while (true) {
        const { done, value } = await reader.read()
        if (done) break

        buffer += decoder.decode(value, { stream: true })

        // SSE 規範: 事件之間以 \n\n 分隔
        const events = buffer.split('\n\n')

        // 保留最後一個可能不完整的片段
        buffer = events.pop() || ''

        for (const event of events) {
          if (event.startsWith('data: ')) {
            const data = event.slice(6).trim()

            // 結束標記
            if (data === '[DONE]') {
              setStatus('idle')
              return
            }

            // 安全解析 JSON
            try {
              const step = JSON.parse(data) as StreamThinkingStep
              // 派發到 Zustand (ADR-004)
              appendThinking({
                type: step.type === 'result' ? 'result' : 'thinking',
                content: step.content,
                timestamp: new Date(),
              })
            } catch (e) {
              console.warn('JSON 解析錯誤，跳過片段:', data)
            }
          }
        }
      }
    } catch (err: unknown) {
      if (err instanceof Error && err.name === 'AbortError') {
        console.log('串流已手動中斷')
      } else {
        const message = err instanceof Error ? err.message : '未知錯誤'
        appendThinking({
          type: 'error',
          content: message,
          timestamp: new Date(),
        })
      }
    } finally {
      setStatus('idle')
    }
  }, [setStatus, appendThinking, clearThinking])

  return (
    <div className="glass-panel p-6 max-w-2xl w-full space-y-4">
      {/* Header - Nothing.tech 風格 */}
      <div className="flex items-center justify-between border-b border-nothing-gray-800 pb-4">
        <h2 className="font-display text-display-sm">AWOOOI Terminal</h2>
        <span className="font-body text-xs text-nothing-gray-500">
          v0.1.0 | SSE
        </span>
      </div>

      {/* Control Button */}
      <button
        onClick={startStream}
        disabled={isStreaming}
        className={cn(
          'w-full py-3 px-4 rounded-button font-body text-sm transition-all border',
          isStreaming
            ? 'bg-nothing-gray-800 text-nothing-gray-500 border-nothing-gray-700 cursor-not-allowed'
            : 'bg-nothing-white text-nothing-black border-transparent hover:bg-nothing-gray-200'
        )}
      >
        {isStreaming ? '>_ EXECUTING...' : 'INITIATE SYNC'}
      </button>

      {/* Terminal Output */}
      <div className="bg-nothing-gray-900 rounded-card p-4 min-h-[200px] max-h-[300px] overflow-y-auto">
        {thinkingStream.length === 0 && !isStreaming && (
          <div className="font-body text-sm text-nothing-gray-600">
            {'>'} Waiting for command...
          </div>
        )}

        {thinkingStream.map((step, index) => (
          <div
            key={index}
            className={cn(
              'font-body text-sm py-0.5 animate-fade-in',
              step.type === 'result' && 'text-status-healthy',
              step.type === 'thinking' && 'text-nothing-gray-500',
              step.type === 'error' && 'text-status-critical'
            )}
          >
            [{step.type.toUpperCase()}] {step.content}
          </div>
        ))}

        {/* Cursor 動畫 */}
        {isStreaming && (
          <div className="flex items-center gap-1 mt-1">
            <span className="font-body text-sm text-nothing-gray-500">{'>'}</span>
            <span className="w-2 h-4 bg-nothing-white animate-pulse" />
          </div>
        )}
      </div>

      {/* Connection Info */}
      <div className="pt-2 border-t border-nothing-gray-800">
        <p className="font-body text-xs text-nothing-gray-600">
          ENDPOINT: {API_BASE_URL}/agent/thinking
        </p>
      </div>
    </div>
  )
}
