// Streaming Chat Completion (Fetch API - Cloudflare Workers)
// Server-Sent Events (SSE) parsing for edge runtimes

interface Env {
  OPENAI_API_KEY: string;
}

export default {
  async fetch(request: Request, env: Env): Promise<Response> {
    if (request.method !== 'POST') {
      return new Response('Method not allowed', { status: 405 });
    }

    const { message } = await request.json() as { message: string };

    // Call OpenAI with streaming
    const response = await fetch('https://api.openai.com/v1/chat/completions', {
      method: 'POST',
      headers: {
        'Authorization': `Bearer ${env.OPENAI_API_KEY}`,
        'Content-Type': 'application/json',
      },
      body: JSON.stringify({
        model: 'gpt-5',
        messages: [
          { role: 'user', content: message }
        ],
        stream: true,
      }),
    });

    // Create a transformed stream for the client
    const { readable, writable } = new TransformStream();
    const writer = writable.getWriter();
    const encoder = new TextEncoder();

    // Process SSE stream
    (async () => {
      const reader = response.body?.getReader();
      const decoder = new TextDecoder();

      try {
        while (true) {
          const { done, value } = await reader!.read();
          if (done) break;

          const chunk = decoder.decode(value);
          const lines = chunk.split('\n').filter(line => line.trim() !== '');

          for (const line of lines) {
            if (line.startsWith('data: ')) {
              const data = line.slice(6);

              if (data === '[DONE]') {
                await writer.write(encoder.encode('data: [DONE]\n\n'));
                break;
              }

              try {
                const json = JSON.parse(data);
                const content = json.choices[0]?.delta?.content || '';

                if (content) {
                  // Forward to client
                  await writer.write(encoder.encode(`data: ${JSON.stringify({ content })}\n\n`));
                }
              } catch (e) {
                // Skip invalid JSON
              }
            }
          }
        }
      } finally {
        await writer.close();
      }
    })();

    return new Response(readable, {
      headers: {
        'Content-Type': 'text/event-stream',
        'Cache-Control': 'no-cache',
        'Connection': 'keep-alive',
      },
    });
  },
};