import { Readable } from 'stream';

const providers = {
  deepseek: {
    id: 'deepseek',
    name: 'DeepSeek',
    description: '深度求索',
    apiUrl: process.env.DEEPSEEK_API_URL || 'https://api.deepseek.com/chat/completions',
    apiKey: process.env.DEEPSEEK_API_KEY || '',
    model: process.env.DEEPSEEK_MODEL || 'deepseek-chat'
  },
  qianfan: {
    id: 'qianfan',
    name: '千帆大模型',
    description: '百度文心一言',
    apiUrl: process.env.QIANFAN_API_URL || 'https://qianfan.baidubce.com/v2/chat/completions',
    apiKey: process.env.QIANFAN_API_KEY || '',
    appId: process.env.QIANFAN_APP_ID || '',
    model: process.env.QIANFAN_MODEL || 'ernie-4.0-8k'
  },
  openai: {
    id: 'openai',
    name: 'OpenAI',
    description: 'GPT 系列',
    apiUrl: process.env.OPENAI_API_URL || 'https://api.openai.com/v1/chat/completions',
    apiKey: process.env.OPENAI_API_KEY || '',
    model: process.env.OPENAI_MODEL || 'gpt-4o'
  },
  claude: {
    id: 'claude',
    name: 'Claude',
    description: 'Anthropic Claude',
    apiUrl: process.env.CLAUDE_API_URL || 'https://api.anthropic.com/v1/messages',
    apiKey: process.env.CLAUDE_API_KEY || '',
    model: process.env.CLAUDE_MODEL || 'claude-3-5-sonnet'
  },
  custom: {
    id: 'custom',
    name: '自定义',
    description: '自定义 API 端点',
    apiUrl: process.env.CUSTOM_API_URL || '',
    apiKey: process.env.CUSTOM_API_KEY || '',
    model: process.env.CUSTOM_MODEL || ''
  }
};

export const getProviderSummary = () => {
  return Object.values(providers).map(provider => ({
    id: provider.id,
    name: provider.name,
    description: provider.description,
    model: provider.model,
    enabled: Boolean(provider.apiKey)
  }));
};

const buildHeaders = (provider) => {
  const headers = {
    'Content-Type': 'application/json'
  };

  if (provider.apiKey) {
    headers['Authorization'] = provider.apiKey.trim().startsWith('Bearer ')
      ? provider.apiKey.trim()
      : `Bearer ${provider.apiKey.trim()}`;
  }

  if (provider.appId) {
    headers['appid'] = provider.appId;
  }

  return headers;
};

export const streamChat = async ({
  providerId,
  model,
  appId,
  messages,
  options,
  res
}) => {
  const provider = providers[providerId];

  if (!provider) {
    res.status(400).json({ success: false, error: '未知模型服务商' });
    return;
  }

  if (!provider.apiKey) {
    res.status(400).json({ success: false, error: '模型服务商未配置 API Key' });
    return;
  }

  if (!provider.apiUrl) {
    res.status(400).json({ success: false, error: '模型服务商未配置 API 地址' });
    return;
  }

  const payload = {
    model: model || provider.model,
    messages,
    ...options,
    stream: true
  };

  const headers = buildHeaders({ ...provider, appId: appId || provider.appId });

  console.log('LLM 代理: 发起请求', { providerId, model: payload.model, apiUrl: provider.apiUrl });

  let response;
  try {
    response = await fetch(provider.apiUrl, {
      method: 'POST',
      headers,
      body: JSON.stringify(payload)
    });
  } catch (fetchError) {
    console.error('LLM 代理: Fetch 错误', fetchError);
    if (!res.headersSent) {
      res.status(500).json({ success: false, error: fetchError.message || '网络请求失败' });
    }
    return;
  }

  if (!response.ok) {
    const errorText = await response.text();
    console.error('LLM 代理: 上游响应错误', response.status, errorText);
    res.status(500).json({ success: false, error: errorText || `上游请求失败: ${response.status}` });
    return;
  }

  console.log('LLM 代理: 开始流式响应');
  res.status(200);
  res.setHeader('Content-Type', 'text/event-stream; charset=utf-8');
  res.setHeader('Cache-Control', 'no-cache');
  res.setHeader('Connection', 'keep-alive');
  res.flushHeaders();

  const readable = Readable.fromWeb(response.body);
  readable.on('data', (chunk) => {
    res.write(chunk);
  });
  readable.on('end', () => {
    console.log('LLM 代理: 流式响应完成');
    res.end();
  });
  readable.on('error', (error) => {
    console.error('LLM 流式代理错误:', error);
    res.end();
  });
};