txnbot - rewrite and lint (#53)

resolves #46

Co-authored-by: johba <johba@harb.eth>
Reviewed-on: https://codeberg.org/johba/harb/pulls/53

services/txnBot/src/logger.ts

@@ -0,0 +1,56 @@
+import fs from 'fs';
+import path from 'path';
+import { fileURLToPath } from 'url';
+
+const __filename = fileURLToPath(import.meta.url);
+const __dirname = path.dirname(__filename);
+
+type LogLevel = 'info' | 'warn' | 'error';
+
+interface LogEntry {
+  timestamp: string;
+  level: LogLevel;
+  message: string;
+  data?: unknown;
+}
+
+export class Logger {
+  private logFilePath: string;
+
+  constructor(logFileName = 'txnbot.log') {
+    this.logFilePath = path.resolve(__dirname, '..', logFileName);
+  }
+
+  private writeLog(level: LogLevel, message: string, data?: unknown): void {
+    const logEntry: LogEntry = {
+      timestamp: new Date().toISOString(),
+      level,
+      message,
+      ...(data !== undefined && { data }),
+    };
+
+    const logLine = JSON.stringify(logEntry) + '\n';
+
+    try {
+      fs.appendFileSync(this.logFilePath, logLine, 'utf8');
+    } catch (error) {
+      // Fallback to stderr if file write fails
+      process.stderr.write(`Failed to write log: ${error}\n`);
+      process.stderr.write(logLine);
+    }
+  }
+
+  info(message: string, data?: unknown): void {
+    this.writeLog('info', message, data);
+  }
+
+  warn(message: string, data?: unknown): void {
+    this.writeLog('warn', message, data);
+  }
+
+  error(message: string, data?: unknown): void {
+    this.writeLog('error', message, data);
+  }
+}
+
+export const logger = new Logger();