const Anthropic = require('@anthropic-ai/sdk');
const OpenAI = require('openai');

/**
 * Normalize Anthropic + OpenAI-compatible streams into one AsyncIterable.
 * Yields: { token, done, fullText } events.
 * Handles errors gracefully — emits error event, doesn't crash.
 *
 * Usage:
 *   for await (const chunk of streamCompletion(model, messages, systemPrompt)) {
 *     // chunk = { token: string, done: boolean, fullText: string }
 *   }
 */
async function* streamCompletion(model, messages, systemPrompt) {
  if (!model || !model.provider) {
    yield { token: '', done: true, fullText: '', error: 'Model or provider not specified' };
    return;
  }

  try {
    if (model.provider === 'anthropic') {
      yield* streamAnthropic(model, messages, systemPrompt);
    } else if (model.provider === 'openai') {
      yield* streamOpenAI(model, messages, systemPrompt);
    } else {
      yield { token: '', done: true, fullText: '', error: `Unknown provider: ${model.provider}` };
    }
  } catch (err) {
    console.error('[llm] streamCompletion error:', err.message);
    yield { token: '', done: true, fullText: '', error: err.message };
  }
}

async function* streamAnthropic(model, messages, systemPrompt) {
  const client = new Anthropic({
    apiKey: model.api_key || process.env.ANTHROPIC_API_KEY,
  });

  const stream = await client.messages.create({
    model: model.name,
    max_tokens: 4096,
    system: systemPrompt || undefined,
    messages: messages.map(m => ({ role: m.role, content: m.content })),
    stream: true,
  });

  let fullText = '';

  for await (const event of stream) {
    if (event.type === 'content_block_delta' && event.delta?.type === 'text_delta') {
      const token = event.delta.text || '';
      fullText += token;
      yield { token, done: false, fullText };
    }
  }

  yield { token: '', done: true, fullText };
}

async function* streamOpenAI(model, messages, systemPrompt) {
  const client = new OpenAI({
    apiKey: model.api_key || process.env.OPENAI_API_KEY,
    baseURL: model.api_base,
  });

  const openaiMessages = [];
  if (systemPrompt) {
    openaiMessages.push({ role: 'system', content: systemPrompt });
  }
  openaiMessages.push(...messages.map(m => ({ role: m.role, content: m.content })));

  const stream = await client.chat.completions.create({
    model: model.name,
    messages: openaiMessages,
    stream: true,
  });

  let fullText = '';

  for await (const chunk of stream) {
    const token = chunk.choices?.[0]?.delta?.content || '';
    if (token) {
      fullText += token;
      yield { token, done: false, fullText };
    }
  }

  yield { token: '', done: true, fullText };
}

module.exports = { streamCompletion };