Curio/src/app/api/surprise/route.ts

import { NextRequest, NextResponse } from 'next/server';
import { generateObject } from 'ai';
import { z } from 'zod';
import { prompts } from '@/lib/llm/prompts';
import { llmClient } from '@/lib/llm/client';
import { withSafety } from '@/lib/llm/safety';
import { traceLLMCall } from '@/lib/observability';
import { getColdStartRatelimit } from '@/lib/ratelimit';

const TopicSchema = z.object({
  topic: z
    .string()
    .min(8)
    .max(300)
    .describe('A natural-language learning intent phrased as the learner would type it.'),
});

const LOCALE_NAMES: Record<string, string> = {
  en: 'English', fr: 'French', es: 'Spanish', de: 'German',
  pt: 'Portuguese', it: 'Italian', nl: 'Dutch', ja: 'Japanese',
  zh: 'Chinese', ar: 'Arabic', ru: 'Russian', ko: 'Korean',
};

// Domain nudge diversifies suggestions across calls — the model otherwise
// gravitates to a handful of crowd-pleasers.
const DOMAINS = [
  'physics', 'biology', 'economics', 'history', 'computer science', 'chemistry',
  'astronomy', 'linguistics', 'mathematics', 'neuroscience', 'music', 'geology',
  'everyday objects', 'the human body', 'engineering', 'art history',
];

/**
 * GET /api/surprise — AI-chosen learning topic ("Spark something").
 *
 * Returns a single fresh learning intent the client then feeds into the normal
 * /api/intent flow. Rate-limited on the cold-start limiter (it spends a model call).
 * All LLM access via llmClient.generator (invariant #1); prompt from registry (#2).
 */
export async function GET(req: NextRequest): Promise<NextResponse> {
  const limiter = getColdStartRatelimit();
  if (limiter) {
    const ip = req.headers.get('x-forwarded-for')?.split(',')[0]?.trim() ?? 'anonymous';
    const { success } = await limiter.limit(ip);
    if (!success) {
      return NextResponse.json({ error: 'Too many requests' }, { status: 429 });
    }
  }

  const locale = req.cookies.get('NEXT_LOCALE')?.value ?? 'en';
  const localeName = LOCALE_NAMES[locale] ?? 'English';
  const domain = DOMAINS[Math.floor(Math.random() * DOMAINS.length)];

  const systemPrompt = withSafety(prompts.SUGGEST_TOPIC.template);
  const userPrompt = `Suggest one learning intent. Lean toward ${domain} this time, but only if a genuinely intriguing question fits. Phrase the topic in ${localeName}.`;

  try {
    const start = Date.now();
    type TopicResult = { object: { topic: string }; usage: { promptTokens?: number; completionTokens?: number } | undefined };
    let genResult!: TopicResult;
    try {
      genResult = await generateObject({
        model: llmClient.generator,
        schema: TopicSchema,
        system: systemPrompt,
        prompt: userPrompt,
        temperature: 1,
        maxTokens: 512,
      });
    } catch (genErr) {
      const raw = (genErr as Record<string, unknown>)?.text;
      if (typeof raw === 'string') {
        const { repairTruncatedJson } = await import('@/lib/llm/repair');
        const parsed = TopicSchema.parse(JSON.parse(repairTruncatedJson(raw)));
        genResult = { object: parsed, usage: (genErr as Record<string, unknown>)?.usage as TopicResult['usage'] };
      } else {
        throw genErr;
      }
    }
    const { object, usage } = genResult;
    void traceLLMCall({
      name: 'suggest-topic',
      role: 'generator',
      model: process.env.LLM_GENERATOR_MODEL ?? 'unknown',
      input: userPrompt,
      output: object,
      latencyMs: Date.now() - start,
      usage: { promptTokens: usage?.promptTokens, completionTokens: usage?.completionTokens },
      metadata: { domain, locale },
    });

    return NextResponse.json({ topic: object.topic });
  } catch (err) {
    console.error('[GET /api/surprise]', err);
    return NextResponse.json({ error: 'Failed to suggest a topic' }, { status: 500 });
  }
}