// Learner voice playback — POST /api/tts
//
// Synthesizes an answer into audio with a content-addressed cache: the same
// text+voice+provider always maps to the same file, so repeated answers (and
// repeated learners asking the same thing) cost one synthesis. Falls back to
// browser speech synthesis client-side when this endpoint is unavailable.
//
// Provider resolution mirrors `/api/generate/tts` (server-configured provider
// wins, client key ignored for managed providers). Default provider:
// `QA_TTS_PROVIDER` env, else the first server-configured TTS provider.

import { promises as fs } from 'fs';
import path from 'path';
import { createHash } from 'crypto';
import { type NextRequest } from 'next/server';
import { apiError, API_ERROR_CODES } from '@/lib/server/api-response';
import { generateTTS } from '@/lib/audio/tts-providers';
import { recordGenerationUsage } from '@/lib/server/usage-storage';
import {
  isServerConfiguredProvider,
  isServerTTSProviderDisabled,
  resolveTTSApiKey,
  resolveTTSBaseUrl,
  resolveTTSModel,
} from '@/lib/server/provider-config';
import type { TTSProviderId } from '@/lib/audio/types';
import { createLogger } from '@/lib/logger';
import { createSlidingWindowLimiter, clientIp } from '@/lib/qa/rate-limit';
import { providerAccessApiError } from '@/lib/server/provider-access-response';

const log = createLogger('QA TTS API');

export const maxDuration = 60;

const TTS_MAX_REQUESTS_PER_MIN = Number(process.env.TTS_RATE_LIMIT_PER_MIN ?? 30);
const ttsLimiter = createSlidingWindowLimiter({
  windowMs: 60_000,
  max: TTS_MAX_REQUESTS_PER_MIN,
});

const TTS_MAX_TEXT_CHARS = 2000;
const TTS_CACHE_DIR = process.env.TTS_CACHE_DIR ?? path.join(process.cwd(), 'data', 'tts-cache');

const KNOWN_TTS_PROVIDERS: TTSProviderId[] = [
  'openai-tts',
  'azure-tts',
  'glm-tts',
  'qwen-tts',
  'voxcpm-tts',
];

/** Resolve the default TTS provider: env override, else first configured. */
function resolveQaTtsProvider(): TTSProviderId | undefined {
  const configured = process.env.QA_TTS_PROVIDER;
  if (configured) return configured as TTSProviderId;
  return KNOWN_TTS_PROVIDERS.find((id) => isServerConfiguredProvider('tts', id));
}

interface TtsCacheKey {
  providerId: string;
  voice: string;
  text: string;
}

function ttsCacheKey(input: TtsCacheKey): string {
  return createHash('sha256')
    .update(`${input.providerId}|${input.voice}|${input.text}`)
    .digest('hex');
}

function ttsCachePath(key: string, format: string): string {
  return path.join(TTS_CACHE_DIR, `${key}.${format}`);
}

export async function POST(req: NextRequest) {
  try {
    const body = (await req.json()) as { text?: string; voice?: string; providerId?: string };
    const text = typeof body.text === 'string' ? body.text.trim() : '';
    if (!text || text.length > TTS_MAX_TEXT_CHARS) {
      return apiError(
        API_ERROR_CODES.MISSING_REQUIRED_FIELD,
        400,
        `text is required (1..${TTS_MAX_TEXT_CHARS} chars)`,
      );
    }

    const ip = clientIp(req);
    const limit = ttsLimiter.check(ip);
    if (!limit.allowed) {
      return apiError(
        API_ERROR_CODES.RATE_LIMITED,
        429,
        `TTS rate limit exceeded; retry in ${Math.ceil(limit.retryAfterMs / 1000)}s`,
      );
    }

    // Provider resolution: explicit (server-validated) or the server default.
    const providerId =
      (typeof body.providerId === 'string' && body.providerId) || resolveQaTtsProvider();
    if (!providerId) {
      return apiError(
        API_ERROR_CODES.PROVIDER_DISABLED,
        503,
        'No TTS provider configured; set QA_TTS_PROVIDER or configure a TTS provider server-side',
      );
    }
    if (isServerTTSProviderDisabled(providerId)) {
      return apiError(API_ERROR_CODES.PROVIDER_DISABLED, 403, 'This TTS provider is disabled');
    }

    const voice =
      typeof body.voice === 'string' && body.voice.trim() ? body.voice.trim() : 'default';
    const apiKey = resolveTTSApiKey(providerId);
    const baseUrl = resolveTTSBaseUrl(providerId);
    const config = {
      providerId: providerId as TTSProviderId,
      modelId: resolveTTSModel(providerId),
      voice,
      speed: 1.0,
      apiKey,
      baseUrl,
    };

    // Content-addressed cache: hit → stream the file, miss → synthesize + write.
    const cacheKey = ttsCacheKey({ providerId, voice, text });
    const cacheFile = ttsCachePath(cacheKey, 'mp3');
    try {
      const cached = await fs.readFile(cacheFile);
      return cachedAudioResponse(cached, 'audio/mpeg', cacheFile);
    } catch {
      // cache miss → synthesize below
    }

    const { audio, format } = await generateTTS(config, text);
    void recordGenerationUsage({
      kind: 'tts',
      unit: 'character',
      providerId,
      modelId: config.modelId,
      quantity: text.length,
    });

    const mime = format === 'wav' ? 'audio/wav' : 'audio/mpeg';
    await fs.mkdir(TTS_CACHE_DIR, { recursive: true }).catch(() => undefined);
    await fs.writeFile(cacheFile, audio).catch((error) => {
      log.warn('TTS cache write failed (serving uncached):', error);
    });
    return cachedAudioResponse(audio, mime, cacheFile);
  } catch (error) {
    log.error('QA TTS failed:', error);
    const providerAccessError = providerAccessApiError(error);
    if (providerAccessError) return providerAccessError;

    return apiError(
      API_ERROR_CODES.INTERNAL_ERROR,
      500,
      'TTS synthesis failed',
      error instanceof Error ? error.message : undefined,
    );
  }
}

function cachedAudioResponse(
  bytes: Uint8Array | Buffer,
  mime: string,
  cacheFile: string,
): Response {
  return new Response(bytes as unknown as BodyInit, {
    headers: {
      'Content-Type': mime,
      'Content-Length': String(bytes.byteLength),
      // Content-addressed → cacheable forever by intermediaries and the client.
      'Cache-Control': 'public, max-age=31536000, immutable',
      ETag: `"${path.basename(cacheFile)}"`,
    },
  });
}