import { GoogleGenAI } from '@google/genai';
import { ChatMessage, PersonaMode } from '@/types/chat';
import { SYSTEM_PROMPT, MODE_MODIFIERS } from './prompts';

const apiKey = process.env.GEMINI_API_KEY;

export function getGeminiClient() {
  if (!apiKey) {
    throw new Error('GEMINI_API_KEY is not defined in your environment variables.');
  }
  return new GoogleGenAI({ apiKey });
}

export async function streamSchopenhauerReply(
  messages: ChatMessage[],
  mode: PersonaMode
) {
  const ai = getGeminiClient();
  const systemInstruction = `${SYSTEM_PROMPT}\n\n${MODE_MODIFIERS[mode]}`;

  // Map our messages to Gemini API format.
  // Gemini expects: { role: 'user' | 'model', parts: [{ text: string }] }
  // We limit the history to the last 16 messages for performance.
  const historyLimit = 16;
  const recentMessages = messages.slice(-historyLimit);

  const contents = recentMessages.map((msg) => ({
    role: msg.role === 'assistant' ? 'model' : 'user',
    parts: [{ text: msg.content }],
  }));

  const modelCandidates = [
    process.env.GEMINI_MODEL || 'gemini-3.1-flash',
    'gemini-2.5-flash',
    'gemini-1.5-flash',
  ];

  let lastError: any = null;
  for (const modelName of modelCandidates) {
    try {
      const responseStream = await ai.models.generateContentStream({
        model: modelName,
        contents,
        config: {
          systemInstruction,
          temperature: 0.7,
        },
      });
      return { responseStream, modelUsed: modelName };
    } catch (err) {
      console.warn(`Failed to start stream with model ${modelName}:`, err);
      lastError = err;
    }
  }
  throw lastError || new Error('All Gemini model candidates failed to initialize.');
}