/**
 * Translation Service using DeepL API
 * Sovereign translation service for Tractatus multilingual submissions
 * Based on proven family-history implementation
 */

const axios = require('axios');
const crypto = require('crypto');
const NodeCache = require('node-cache');
const logger = require('../utils/logger.util');

class TranslationService {
  constructor() {
    // DeepL API configuration
    this.apiUrl = process.env.DEEPL_API_URL || 'https://api-free.deepl.com/v2';
    this.apiKey = process.env.DEEPL_API_KEY;

    // Cache translations for 24 hours to reduce API calls
    this.cache = new NodeCache({ stdTTL: 86400 });

    // Supported language pairs (as per Tractatus SubmissionTracking schema)
    this.supportedLanguages = {
      'en': 'English',
      'fr': 'French',
      'de': 'German',
      'es': 'Spanish',
      'pt': 'Portuguese',
      'zh': 'Chinese',
      'ja': 'Japanese',
      'ar': 'Arabic',
      'mi': 'Te Reo Māori (not supported by DeepL - fallback to EN)',
      'it': 'Italian',
      'nl': 'Dutch',
      'pl': 'Polish',
      'ru': 'Russian'
    };

    // Track service availability
    this.isAvailable = false;
    this.lastHealthCheck = null;

    // Check service availability on startup
    this.checkAvailability();
  }

  /**
   * Check if DeepL service is available
   */
  async checkAvailability() {
    try {
      if (!this.apiKey || this.apiKey === 'your-deepl-api-key-here') {
        logger.warn('[Translation] DeepL API key not configured');
        logger.warn('[Translation] Set DEEPL_API_KEY in .env file');
        this.isAvailable = false;
        return false;
      }

      // Test with a simple translation
      const response = await axios.post(`${this.apiUrl}/translate`,
        `auth_key=${encodeURIComponent(this.apiKey)}&text=${encodeURIComponent('test')}&target_lang=FR`,
        {
          headers: {
            'Content-Type': 'application/x-www-form-urlencoded'
          },
          timeout: 5000
        }
      );

      this.isAvailable = true;
      this.lastHealthCheck = new Date();

      logger.info('✅ DeepL translation service available');
      return true;
    } catch (error) {
      this.isAvailable = false;
      logger.warn(`[Translation] DeepL service not available: ${error.message}`);
      if (error.response?.status === 403) {
        logger.error('[Translation] Invalid DeepL API key');
      }
      return false;
    }
  }

  /**
   * Generate cache key for translation
   */
  getCacheKey(text, sourceLang, targetLang) {
    const hash = crypto.createHash('md5')
      .update(`${sourceLang}:${targetLang}:${text}`)
      .digest('hex');
    return `trans_${hash}`;
  }

  /**
   * Translate text between languages
   * @param {string} text - Text to translate
   * @param {string} sourceLang - Source language code (e.g., 'en')
   * @param {string} targetLang - Target language code (e.g., 'fr')
   * @param {Object} options - Additional options
   * @returns {Object} Translation result
   */
  async translate(text, sourceLang, targetLang, options = {}) {
    // Quick validation
    if (!text || sourceLang === targetLang) {
      return {
        translatedText: text,
        cached: false,
        sourceLang,
        targetLang
      };
    }

    // Check service availability (with periodic recheck)
    if (!this.isAvailable ||
        !this.lastHealthCheck ||
        Date.now() - this.lastHealthCheck > 300000) { // 5 minutes
      await this.checkAvailability();
    }

    if (!this.isAvailable) {
      logger.error('[Translation] DeepL service not available');
      return {
        translatedText: text,
        cached: false,
        sourceLang,
        targetLang,
        error: true,
        errorMessage: 'DeepL translation service not available. Please check DEEPL_API_KEY.'
      };
    }

    // Check cache first
    const cacheKey = this.getCacheKey(text, sourceLang, targetLang);
    const cached = this.cache.get(cacheKey);
    if (cached && !options.skipCache) {
      return {
        translatedText: cached,
        cached: true,
        sourceLang,
        targetLang
      };
    }

    try {
      // Prepare parameters for DeepL API
      const params = new URLSearchParams();
      params.append('auth_key', this.apiKey);
      params.append('text', text);
      params.append('target_lang', targetLang.toUpperCase());

      // Only add source_lang if not auto-detecting
      if (sourceLang && sourceLang !== 'auto') {
        params.append('source_lang', sourceLang.toUpperCase());
      }

      // Add HTML handling if needed
      if (options.format === 'html') {
        params.append('tag_handling', 'html');
        params.append('preserve_formatting', '1');
      }

      // Add formality setting (more formal for publications)
      if (options.formality) {
        params.append('formality', options.formality); // 'default', 'more', or 'less'
      } else {
        params.append('formality', 'more'); // Default to formal for submissions
      }

      // Make translation request
      const response = await axios.post(`${this.apiUrl}/translate`, params.toString(), {
        headers: {
          'Content-Type': 'application/x-www-form-urlencoded'
        },
        timeout: 30000 // 30 second timeout
      });

      const translation = response.data.translations[0];
      const translatedText = translation.text;
      const detectedLang = translation.detected_source_language;

      // Cache the result
      if (translatedText && !options.skipCache) {
        this.cache.set(cacheKey, translatedText);
      }

      logger.info(`[Translation] ${sourceLang} → ${targetLang}: ${text.substring(0, 50)}... (${translatedText.length} chars)`);

      return {
        translatedText,
        cached: false,
        sourceLang: detectedLang ? detectedLang.toLowerCase() : sourceLang,
        targetLang,
        detectedLang: detectedLang ? detectedLang.toLowerCase() : null
      };

    } catch (error) {
      logger.error('[Translation] DeepL API error:', error.message);
      if (error.response) {
        logger.error('[Translation] Response status:', error.response.status);
        logger.error('[Translation] Response data:', error.response.data);
      }

      // Return original text with error flag
      return {
        translatedText: text,
        error: true,
        errorMessage: `Translation failed: ${error.message}`,
        cached: false,
        sourceLang,
        targetLang
      };
    }
  }

  /**
   * Translate multiple texts in batch
   * @param {Array} texts - Array of texts to translate
   * @param {string} sourceLang - Source language
   * @param {string} targetLang - Target language
   * @returns {Array} Array of translation results
   */
  async translateBatch(texts, sourceLang, targetLang) {
    if (!Array.isArray(texts) || texts.length === 0) {
      return [];
    }

    // DeepL supports up to 50 texts per request
    const batchSize = 50;
    const results = [];

    for (let i = 0; i < texts.length; i += batchSize) {
      const batch = texts.slice(i, i + batchSize);

      try {
        // Prepare parameters
        const params = new URLSearchParams();
        params.append('auth_key', this.apiKey);

        // Add each text as a separate parameter
        batch.forEach(text => params.append('text', text));

        params.append('target_lang', targetLang.toUpperCase());
        if (sourceLang && sourceLang !== 'auto') {
          params.append('source_lang', sourceLang.toUpperCase());
        }
        params.append('formality', 'more'); // Formal for submissions

        const response = await axios.post(`${this.apiUrl}/translate`, params.toString(), {
          headers: {
            'Content-Type': 'application/x-www-form-urlencoded'
          },
          timeout: 60000 // 60 seconds for batch
        });

        const translations = response.data.translations.map(t => ({
          translatedText: t.text,
          detectedLang: t.detected_source_language ? t.detected_source_language.toLowerCase() : null,
          cached: false,
          sourceLang: t.detected_source_language ? t.detected_source_language.toLowerCase() : sourceLang,
          targetLang
        }));

        results.push(...translations);
      } catch (error) {
        logger.error('[Translation] Batch translation error:', error.message);
        // Return original texts for failed batch
        results.push(...batch.map(text => ({
          translatedText: text,
          error: true,
          errorMessage: error.message,
          cached: false,
          sourceLang,
          targetLang
        })));
      }

      // Small delay between batches to respect rate limits
      if (i + batchSize < texts.length) {
        await new Promise(resolve => setTimeout(resolve, 100));
      }
    }

    return results;
  }

  /**
   * Get DeepL API usage statistics
   */
  async getUsageStats() {
    if (!this.isAvailable) {
      return { error: 'Service not available' };
    }

    try {
      const response = await axios.get(`${this.apiUrl}/usage`, {
        params: { auth_key: this.apiKey },
        timeout: 5000
      });

      return {
        characterCount: response.data.character_count,
        characterLimit: response.data.character_limit,
        percentageUsed: ((response.data.character_count / response.data.character_limit) * 100).toFixed(2)
      };
    } catch (error) {
      logger.error('[Translation] Usage check error:', error.message);
      return { error: error.message };
    }
  }

  /**
   * Get cache statistics
   */
  getCacheStats() {
    return {
      keys: this.cache.keys().length,
      hits: this.cache.getStats().hits,
      misses: this.cache.getStats().misses
    };
  }

  /**
   * Clear translation cache
   */
  clearCache() {
    this.cache.flushAll();
    logger.info('[Translation] Cache cleared');
  }

  /**
   * Get service status
   */
  getStatus() {
    return {
      available: this.isAvailable,
      lastHealthCheck: this.lastHealthCheck,
      apiUrl: this.apiUrl,
      cacheStats: this.getCacheStats(),
      supportedLanguages: this.supportedLanguages,
      service: 'DeepL',
      apiKeyConfigured: !!(this.apiKey && this.apiKey !== 'your-deepl-api-key-here')
    };
  }
}

// Create singleton instance
let instance = null;

module.exports = {
  getInstance: () => {
    if (!instance) {
      instance = new TranslationService();
    }
    return instance;
  },
  TranslationService
};