const fs = require('fs');
const path = require('path');

class CsvLogger {
  /**
   * @param {string} logDir - Directory where log files will be saved
   * @param {string[]} headers - CSV header row
   * @param {number} maxFileAgeDays - How many days log files should be kept
   */
  constructor(logDir, headers = ['timestamp', 'level', 'message'], maxFileAgeDays = 30) {
    this.logDir = logDir;
    this.headers = headers;
    this.maxFileAgeDays = maxFileAgeDays;
    this.timestamp = null

    if (!fs.existsSync(logDir)) {
      fs.mkdirSync(logDir, { recursive: true });
    }

    // Cleanup old log files once on startup
    this.deleteOldLogFiles().catch(console.error);
  }

  /**
   * Writes a new log entry to today's CSV file
   * @param {string} level - Log level (e.g., 'info', 'error')
   * @param {string} message - Log message
   * @param {string[]} extraFields - Optional additional fields
   */
  log(level, message, extraFields = []) {
    const timestamp = new Date().toISOString();
    const filePath = this.getLogFilePath();

    this.ensureFileWithHeaders(filePath);

    const row = [timestamp, level, message, ...extraFields]
      .map(this.escapeCsv)
      .join(',') + '\n';

    fs.appendFileSync(filePath, row, (err) => {
      if (err) {
        console.error('Failed to write to log file:', err);
      }
    });
  }

  /**
   * Constructs the log file path for today
   */
  getLogFilePath() {
    const today = new Date().toISOString().split('T')[0]; // YYYY-MM-DD
    let filename = "logs.csv"
    
     if (this.timestamp == null) {      
      filename =  `logs_${today}.csv`
    } else {
      filename =  `${this.timestamp}_logs.csv`
    }
    return path.join(this.logDir, filename);
  }

  /**
   * Ensures headers are written if file doesn't exist
   */
  ensureFileWithHeaders(filePath) {
    if (!fs.existsSync(filePath)) {
      const headerRow = this.headers.join(',') + '\n';
      fs.writeFileSync(filePath, headerRow);
    }
  }

  /**
   * Escapes a value for safe CSV output
   */
  escapeCsv(value) {
    if (value == null) return '';
    const str = String(value);
    return /[",\n]/.test(str) ? `"${str.replace(/"/g, '""')}"` : str;
  }

  /**
   * Deletes log files older than maxFileAgeDays
   */
  async deleteOldLogFiles() {
    const files = await fs.promises.readdir(this.logDir);

    const now = Date.now();
    const maxAgeMs = this.maxFileAgeDays * 24 * 60 * 60 * 1000;

    for (const file of files) {
      const filePath = path.join(this.logDir, file);
      if (!/^logs_\d{4}-\d{2}-\d{2}\.csv$/.test(file)) continue;

      try {
        const stats = await fs.promises.stat(filePath);
        const age = now - stats.mtimeMs;

        if (age > maxAgeMs) {
          await fs.promises.unlink(filePath);
          console.log(`Deleted old log file: ${file}`);
        }
      } catch (err) {
        console.warn(`Could not process file ${file}: ${err.message}`);
      }
    }
  }
}

module.exports = CsvLogger;