Refactor logger

src/core/logger.ts

@@ -1,26 +1,78 @@
-import util from 'util';
-
-type LogType = 'info' | 'debug' | 'warn' | 'error';
+import { format } from 'util';
 
 /**
- * Logger for all of Squeebot. Use this instead of console.log/warn/error!
+ * Log level
+ */
+export enum LogLevel {
+  INFO,
+  WARN,
+  ERROR,
+  DEBUG,
+}
+
+export type LogListener = (
+  ltype: LogLevel,
+  ...data: any[]
+) => void | Promise<void>;
+
+export type ConsoleFunction = (...data: any[]) => void;
+export type ConsoleLogFunction = ConsoleFunction;
+export type ConsoleWarnFunction = ConsoleFunction;
+export type ConsoleErrorFunction = ConsoleFunction;
+
+/**
+ * Logger for all of Squeebot. Use this instead of console.log/warn/error in your plugins!
  */
 export class Logger {
-  private console = [console.log, console.warn, console.error];
+  /**
+   * The `console.*` functions used for logging convenience.
+   *
+   * Defaults to `console.log`, `console.warn`, `console.error`.
+   *
+   * Can really be anything that accepts the input for `node:util.format`.
+   */
+  public console: [
+    ConsoleLogFunction,
+    ConsoleWarnFunction,
+    ConsoleErrorFunction
+  ] = [console.log, console.warn, console.error];
 
-  constructor(
-    public timestamp = 'dd/mm/yy HH:MM:ss'
-  ) {}
+  /**
+   * External Logger log event listeners.
+   */
+  protected listeners: LogListener[] = [];
 
-  public dateFmt(date: Date) {
-    return date.toISOString()
-      .replace(/T/, ' ')
-      .replace(/\..+/, '');
+  constructor(public timestamp = 'dd/mm/yy HH:MM:ss') {}
+
+  public formatDate(date: Date): string {
+    return date.toISOString().replace(/T/, ' ').replace(/\..+/, '');
   }
 
   /**
-   * Set node.js readline consideration
+   * Add a logger listener, useful for redirecting logger output somewhere else.
+   * Will not await any Promises but it will catch unhandled rejections - please do not depend on this.
+   * @param fn Log listener
+   */
+  public listen(fn: LogListener): void {
+    this.listeners.push(fn);
+  }
+
+  /**
+   * Remove a logger listener.
+   * @param fn Log listener
+   * @returns nothing
+   */
+  public unlisten(fn: LogListener): void {
+    const inx = this.listeners.indexOf(fn);
+    if (inx === -1) return;
+    this.listeners.splice(inx, 1);
+  }
+
+  /**
+   * Set node.js readline consideration.
    * @param rl Readline instance
+   * @see Logger.console - the array modified by this function
+   * @see Logger.resetConsole - the "undo" to this function
    */
   public setReadline(rl: any): void {
     for (const index in this.console) {
@@ -34,32 +86,41 @@ export class Logger {
   }
 
   /**
-   * Write out to log
-   * @param ltype Logger level
-   * @param data Data to log
+   * Reset output consoles to default. Useful for dynamically detaching readline.
+   * @see Logger.console
    */
-  private write(ltype: LogType, ...data: any[]): void {
+  public resetConsole() {
+    this.console = [console.log, console.warn, console.error];
+  }
+
+  /**
+   * Write out to log
+   * @param logLevel Logger level
+   * @param data Data to log. Will be sent to `node:util.format`
+   * @see util.format
+   */
+  public write(logLevel: LogLevel, ...data: any[]): void {
     const message = [];
-    let cfunc = this.console[0];
+    let outputFunction = this.console[0];
 
     if (this.timestamp) {
-      message.push(`[${this.dateFmt(new Date())}]`);
+      message.push(`[${this.formatDate(new Date())}]`);
     }
 
-    switch (ltype) {
-    case 'info':
+    switch (logLevel) {
+    case LogLevel.INFO:
       message.push('[ INFO]');
       break;
-    case 'debug':
+    case LogLevel.DEBUG:
       message.push('[DEBUG]');
       break;
-    case 'warn':
+    case LogLevel.WARN:
       message.push('[ WARN]');
-      cfunc = this.console[1];
+      outputFunction = this.console[1];
       break;
-    case 'error':
+    case LogLevel.ERROR:
       message.push('[ERROR]');
-      cfunc = this.console[2];
+      outputFunction = this.console[2];
       break;
     }
 
@@ -67,10 +128,13 @@ export class Logger {
     let final = data[0];
     if (data.length > 1) {
       const fargs = data.slice(1);
-      final = util.format(data[0], ...fargs);
+      final = format(data[0], ...fargs);
     }
     message.push(final);
-    cfunc(...message);
+
+    // Notify listeners and output
+    this.notify(logLevel, ...message);
+    outputFunction(...message);
   }
 
   /**
@@ -79,7 +143,7 @@ export class Logger {
    * See `console.log` for more information.
    */
   public log(...data: any[]): void {
-    this.write('info', ...data);
+    this.write(LogLevel.INFO, ...data);
   }
 
   /**
@@ -88,7 +152,7 @@ export class Logger {
    * See `console.warn` for more information.
    */
   public warn(...data: any[]): void {
-    this.write('warn', ...data);
+    this.write(LogLevel.WARN, ...data);
   }
 
   /**
@@ -97,7 +161,7 @@ export class Logger {
    * See `console.log` for more information.
    */
   public info(...data: any[]): void {
-    this.write('info', ...data);
+    this.write(LogLevel.INFO, ...data);
   }
 
   /**
@@ -106,7 +170,7 @@ export class Logger {
    * See `console.error` for more information.
    */
   public error(...data: any[]): void {
-    this.write('error', ...data);
+    this.write(LogLevel.ERROR, ...data);
   }
 
   /**
@@ -115,7 +179,34 @@ export class Logger {
    * See `console.log` for more information.
    */
   public debug(...data: any[]): void {
-    this.write('debug', ...data);
+    this.write(LogLevel.DEBUG, ...data);
+  }
+
+  /**
+   * Notify logger listeners about new lines. Catches uncaught errors.
+   * @param level Log level
+   * @param data Log data
+   */
+  protected notify(level: LogLevel, ...data: any): void {
+    for (const listener of this.listeners) {
+      try {
+        const resp = listener.call(null, level, ...data);
+        // Catch Promise errors
+        if (resp instanceof Promise) {
+          resp.catch((err) =>
+            process.stderr.write(
+              `A Logger listener threw an unhandled rejection: ${err.stack}\r\n`
+            )
+          );
+        }
+      } catch (err) {
+        process.stderr.write(
+          `A Logger listener threw an unhandled error: ${
+            (err as Error).stack
+          }\r\n`
+        );
+      }
+    }
   }
 }