import { ServiceUnavailableException } from '@nestjs/common';
import { ConfigService } from '@nestjs/config';

export type AiProviderConfig = {
  apiKey: string;
  baseUrl: string;
  model: string;
};

export function resolveAiProvider(config: ConfigService): AiProviderConfig {
  const configured = config.get<string>('AI_PROVIDER')?.trim().toLowerCase();
  const groqKey = config.get<string>('GROQ_API_KEY')?.trim();
  const openAiKey = config.get<string>('OPENAI_API_KEY')?.trim();

  const useGroq =
    configured === 'groq' || (!configured && !!groqKey) || (!openAiKey && !!groqKey);

  if (useGroq) {
    if (!groqKey) {
      throw new ServiceUnavailableException(
        'AI is not configured. Set GROQ_API_KEY on the server.',
      );
    }

    return {
      apiKey: groqKey,
      baseUrl: 'https://api.groq.com/openai/v1',
      model: config.get<string>('GROQ_MODEL')?.trim() || 'llama-3.3-70b-versatile',
    };
  }

  if (!openAiKey) {
    throw new ServiceUnavailableException(
      'AI is not configured. Set GROQ_API_KEY or OPENAI_API_KEY on the server.',
    );
  }

  return {
    apiKey: openAiKey,
    baseUrl: 'https://api.openai.com/v1',
    model: config.get<string>('OPENAI_MODEL')?.trim() || 'gpt-4.1-nano',
  };
}

function supportsCustomTemperature(model: string): boolean {
  // gpt-5 / o-series chat models only accept the API default temperature.
  const id = model.trim().toLowerCase();
  return !(
    id.startsWith('gpt-5') ||
    id.startsWith('o1') ||
    id.startsWith('o3') ||
    id.startsWith('o4')
  );
}

export async function requestAiJsonCompletion(
  provider: AiProviderConfig,
  systemPrompt: string,
  userPrompt: string,
  temperature = 0.4,
): Promise<string> {
  const body: Record<string, unknown> = {
    model: provider.model,
    response_format: { type: 'json_object' },
    messages: [
      { role: 'system', content: systemPrompt },
      { role: 'user', content: userPrompt },
    ],
  };

  if (supportsCustomTemperature(provider.model)) {
    body.temperature = temperature;
  }

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

  if (!response.ok) {
    const detail = await response.text();
    throw new Error(`AI provider error (${response.status}): ${detail.slice(0, 240)}`);
  }

  const payload = (await response.json()) as {
    choices?: { message?: { content?: string } }[];
  };

  const content = payload.choices?.[0]?.message?.content;
  if (!content) {
    throw new Error('AI returned an empty response');
  }

  return content;
}