chore: establish learning module baseline

OpenMAIC/lib/logger.ts

@@ -0,0 +1,52 @@
+const LOG_LEVELS = { debug: 0, info: 1, warn: 2, error: 3 } as const;
+type LogLevel = keyof typeof LOG_LEVELS;
+
+function getMinLevel(): LogLevel {
+  const env = (process.env.LOG_LEVEL ?? 'info').toLowerCase();
+  return env in LOG_LEVELS ? (env as LogLevel) : 'info';
+}
+
+function isJsonFormat(): boolean {
+  return process.env.LOG_FORMAT === 'json';
+}
+
+function formatLine(level: LogLevel, tag: string, args: unknown[]): string {
+  const timestamp = new Date().toISOString();
+  const upperLevel = level.toUpperCase();
+  const msg = args
+    .map((a) =>
+      a instanceof Error ? (a.stack ?? a.message) : typeof a === 'string' ? a : JSON.stringify(a),
+    )
+    .join(' ');
+
+  if (isJsonFormat()) {
+    return JSON.stringify({ timestamp, level: upperLevel, tag, message: msg });
+  }
+  return `[${timestamp}] [${upperLevel}] [${tag}] ${msg}`;
+}
+
+export function createLogger(tag: string) {
+  const emit = (level: LogLevel, args: unknown[]) => {
+    if (LOG_LEVELS[level] < LOG_LEVELS[getMinLevel()]) return;
+
+    const line = formatLine(level, tag, args);
+
+    // Console output
+    const fn =
+      level === 'debug'
+        ? console.debug
+        : level === 'warn'
+          ? console.warn
+          : level === 'error'
+            ? console.error
+            : console.log;
+    fn(line);
+  };
+
+  return {
+    debug: (...args: unknown[]) => emit('debug', args),
+    info: (...args: unknown[]) => emit('info', args),
+    warn: (...args: unknown[]) => emit('warn', args),
+    error: (...args: unknown[]) => emit('error', args),
+  };
+}