export default async (req, context) => {
  if (req.method === 'OPTIONS') {
    return new Response(null, {
      headers: {
        'Access-Control-Allow-Origin': '*',
        'Access-Control-Allow-Methods': 'POST, OPTIONS',
        'Access-Control-Allow-Headers': 'Content-Type',
      },
    });
  }

  try {
    const { prompt, context: ctx, systemPrompt } = await req.json();
    const apiKey = process.env.GEMINI_API_KEY || 'AIzaSyDZn7tv1D3n2zuns8uaXIqp_z1FZTeVyKI';

    const system = systemPrompt || 'You are an expert agile and enterprise coaching assistant for Falah Consulting. Be concise, practical, and outcome-focused.';
    const fullPrompt = ctx ? `Context: ${ctx}\n\n${prompt}` : prompt;

    const geminiRes = await fetch(
      `https://generativelanguage.googleapis.com/v1beta/models/gemini-1.5-flash:generateContent?key=${apiKey}`,
      {
        method: 'POST',
        headers: { 'Content-Type': 'application/json' },
        body: JSON.stringify({
          systemInstruction: { parts: [{ text: system }] },
          contents: [{ role: 'user', parts: [{ text: fullPrompt }] }],
          generationConfig: { temperature: 0.7, maxOutputTokens: 1024 },
        }),
      }
    );

    if (!geminiRes.ok) {
      const err = await geminiRes.json();
      throw new Error(err?.error?.message || `Gemini HTTP ${geminiRes.status}`);
    }

    const data = await geminiRes.json();
    const text = data?.candidates?.[0]?.content?.parts?.[0]?.text ?? '';

    return new Response(JSON.stringify({ text }), {
      status: 200,
      headers: {
        'Content-Type': 'application/json',
        'Access-Control-Allow-Origin': '*',
      },
    });
  } catch (err) {
    return new Response(JSON.stringify({ error: err.message }), {
      status: 500,
      headers: { 'Content-Type': 'application/json' },
    });
  }
};

export const config = { path: '/api/gemini' };