feat(api): add common logging types & default impls

- add ILogger interface, LogLevel enum
- add NULL_LOGGER & ConsoleLogger

packages/api/src/api.ts

@@ -327,6 +327,15 @@ export type TypedArray =
  */
 export type Watch<T> = (id: string, oldState: T, newState: T) => void;
 
+export const enum LogLevel {
+    FINE,
+    DEBUG,
+    INFO,
+    WARN,
+    SEVERE,
+    NONE
+}
+
 /**
  * @param K key type
  * @param V value type
@@ -566,6 +575,14 @@ export interface ILength {
     readonly length: number;
 }
 
+export interface ILogger {
+    fine(...args: any[]): void;
+    debug(...args: any[]): void;
+    info(...args: any[]): void;
+    warn(...args: any[]): void;
+    severe(...args: any[]): void;
+}
+
 /**
  * Generic interface for types supporting metadata. Implementations MUST
  * exclude metadata from any comparisons, equality checks & hashing.

packages/api/src/index.ts

@@ -1,6 +1,7 @@
 export * from "./api";
 
 export * from "./assert";
+export * from "./logger";
 export * from "./mixin";
 
 export * from "./decorators/configurable";

packages/api/src/logger.ts

@@ -0,0 +1,43 @@
+import { ILogger, LogLevel } from "./api";
+
+export const NULL_LOGGER: ILogger = {
+    fine() {},
+    debug() {},
+    info() {},
+    warn() {},
+    severe() {}
+};
+
+export class ConsoleLogger implements ILogger {
+    id: string;
+    level: LogLevel;
+
+    constructor(id: string, level = LogLevel.FINE) {
+        this.id = id;
+        this.level = level;
+    }
+
+    fine(...args: any[]): void {
+        this.level <= LogLevel.FINE && this.log("FINE", args);
+    }
+
+    debug(...args: any[]): void {
+        this.level <= LogLevel.DEBUG && this.log("DEBUG", args);
+    }
+
+    info(...args: any[]): void {
+        this.level <= LogLevel.INFO && this.log("INFO", args);
+    }
+
+    warn(...args: any[]): void {
+        this.level <= LogLevel.WARN && this.log("WARN", args);
+    }
+
+    severe(...args: any[]): void {
+        this.level <= LogLevel.SEVERE && this.log("SEVERE", args);
+    }
+
+    protected log(level: string, args: any[]) {
+        console.info(`[${level}][${this.id}]`, ...args);
+    }
+}