Scaffold monorepo dev setup

packages/observability/src/logger.ts

@@ -0,0 +1,54 @@
+export type LogLevel = "debug" | "info" | "warn" | "error";
+
+export type LogContext = Record<string, unknown>;
+
+export type LogRecord = LogContext & {
+  level: LogLevel;
+  service: string;
+  msg: string;
+  ts: string;
+};
+
+export type LoggerFn = (msg: string, context?: LogContext) => void;
+
+export type Logger = {
+  debug: LoggerFn;
+  info: LoggerFn;
+  warn: LoggerFn;
+  error: LoggerFn;
+};
+
+export type LoggerOptions = {
+  service: string;
+  now?: () => string;
+  sink?: (record: LogRecord) => void;
+};
+
+const defaultSink = (record: LogRecord) => {
+  console.log(JSON.stringify(record));
+};
+
+export const createLogger = ({
+  service,
+  now = () => new Date().toISOString(),
+  sink = defaultSink
+}: LoggerOptions): Logger => {
+  const write = (level: LogLevel, msg: string, context?: LogContext) => {
+    const record: LogRecord = {
+      level,
+      service,
+      msg,
+      ts: now(),
+      ...(context ?? {})
+    };
+
+    sink(record);
+  };
+
+  return {
+    debug: (msg, context) => write("debug", msg, context),
+    info: (msg, context) => write("info", msg, context),
+    warn: (msg, context) => write("warn", msg, context),
+    error: (msg, context) => write("error", msg, context)
+  };
+};