import { TextDecoder } from 'util';
import { renderChunk } from './output.js';

const API_URL = 'https://api.deepseek.com/chat/completions';

export async function streamChat({ model, apiKey, prompt, userInput }) {
  const body = {
    model,
    messages: [
      { role: 'system', content: prompt },
      { role: 'user', content: userInput },
    ],
    stream: true,
  };

  const res = await fetch(API_URL, {
    method: 'POST',
    headers: {
      'Content-Type': 'application/json',
      Authorization: `Bearer ${apiKey}`,
    },
    body: JSON.stringify(body),
  });

  if (!res.ok) {
    const t = await res.text().catch(() => '');
    throw new Error(`请求失败 ${res.status}: ${t}`);
  }

  process.stdout.write(`发送中 (模型: ${model})...\n`);

  const decoder = new TextDecoder();
  const reader = res.body.getReader();
  let buffer = '';
  let sawReason = false;
  let sawContent = false;
  const enableReason = model === 'deepseek-reasoner';

  while (true) {
    const { value, done } = await reader.read();
    if (done) break;
    buffer += decoder.decode(value, { stream: true });
    const lines = buffer.split(/\r?\n/);
    buffer = lines.pop(); // keep incomplete line
    for (const line of lines) {
      if (!line.startsWith('data: ')) continue;
      const data = line.slice(6);
      if (data === '[DONE]') {
        process.stdout.write('\n');
        return;
      }
      let delta;
      try {
        delta = JSON.parse(data)?.choices?.[0]?.delta || {};
      } catch {
        continue;
      }
      const rc = delta.reasoning_content || '';
      const ct = delta.content || '';

      if (enableReason && rc) {
        if (!sawReason) {
          process.stdout.write('思考：\n');
          sawReason = true;
        }
        process.stdout.write(renderChunk(rc));
      }

      if (ct) {
        if (!sawContent) {
          if (sawReason) process.stdout.write('\n\n');
          process.stdout.write('回复：\n');
          sawContent = true;
        }
        process.stdout.write(renderChunk(ct));
      }
    }
  }
  // flush possible remaining buffered text (unlikely but safe)
  if (buffer.trim()) {
    try {
      const delta = JSON.parse(buffer)?.choices?.[0]?.delta || {};
      const ct = delta.content || '';
      if (ct) process.stdout.write(ct);
    } catch {
      // ignore malformed tail
    }
  }
  process.stdout.write('\n');
}