refactor: Make Logger an interface.

src/logging/LazyLoggerFactory.ts

@@ -1,27 +1,10 @@
-import { Logger } from './Logger';
-import type { BasicLogger } from './Logger';
+import { WrappingLogger } from './Logger';
+import type { Logger } from './Logger';
 import type { LoggerFactory } from './LoggerFactory';
 import type { LogLevel } from './LogLevel';
 
 /**
- * Wraps around another {@link Logger} that can be set lazily.
- */
-class WrappingLogger extends Logger {
-  public logger: BasicLogger;
-
-  public constructor(logger: BasicLogger) {
-    super();
-    this.logger = logger;
-  }
-
-  public log(level: LogLevel, message: string): Logger {
-    this.logger.log(level, message);
-    return this;
-  }
-}
-
-/**
- * Temporary {@link LoggerFactory} that creates buffered {@link WrappingLogger}s
+ * Temporary {@link LoggerFactory} that buffers log messages in memory
  * until the {@link TemporaryLoggerFactory#switch} method is called.
  */
 class TemporaryLoggerFactory implements LoggerFactory {

src/logging/Logger.ts

@@ -5,7 +5,7 @@ import type { LogLevel } from './LogLevel';
  *
  * @see getLoggerFor on how to instantiate loggers.
  */
-export type BasicLogger = {
+export interface SimpleLogger {
   /**
    * Log the given message at the given level.
    * If the internal level is higher than the given level, the message may be voided.
@@ -13,15 +13,15 @@ export type BasicLogger = {
    * @param message - The message to log.
    * @param meta - Optional metadata to include in the log message.
    */
-  log: (level: LogLevel, message: string) => BasicLogger;
-};
+  log: (level: LogLevel, message: string) => SimpleLogger;
+}
 
 /**
  * Logs messages, with convenience methods to log on a specific level.
  *
  * @see getLoggerFor on how to instantiate loggers.
  */
-export abstract class Logger implements BasicLogger {
+export interface Logger extends SimpleLogger {
   /**
    * Log the given message at the given level.
    * If the internal level is higher than the given level, the message may be voided.
@@ -29,59 +29,97 @@ export abstract class Logger implements BasicLogger {
    * @param message - The message to log.
    * @param meta - Optional metadata to include in the log message.
    */
-  public abstract log(level: LogLevel, message: string): Logger;
+  log: (level: LogLevel, message: string) => Logger;
 
   /**
    * Log a message at the 'error' level.
    * @param message - The message to log.
    * @param meta - Optional metadata to include in the log message.
    */
-  public error(message: string): Logger {
-    return this.log('error', message);
-  }
+  error: (message: string) => Logger;
 
   /**
    * Log a message at the 'warn' level.
    * @param message - The message to log.
    * @param meta - Optional metadata to include in the log message.
    */
-  public warn(message: string): Logger {
-    return this.log('warn', message);
-  }
+  warn: (message: string) => Logger;
 
   /**
    * Log a message at the 'info' level.
    * @param message - The message to log.
    * @param meta - Optional metadata to include in the log message.
    */
-  public info(message: string): Logger {
-    return this.log('info', message);
-  }
+  info: (message: string) => Logger;
 
   /**
    * Log a message at the 'verbose' level.
    * @param message - The message to log.
    * @param meta - Optional metadata to include in the log message.
    */
-  public verbose(message: string): Logger {
-    return this.log('verbose', message);
-  }
+  verbose: (message: string) => Logger;
 
   /**
    * Log a message at the 'debug' level.
    * @param message - The message to log.
    * @param meta - Optional metadata to include in the log message.
    */
-  public debug(message: string): Logger {
-    return this.log('debug', message);
-  }
+  debug: (message: string) => Logger;
 
   /**
    * Log a message at the 'silly' level.
    * @param message - The message to log.
    * @param meta - Optional metadata to include in the log message.
    */
+  silly: (message: string) => Logger;
+}
+
+/**
+ * Base class that implements all additional {@link BaseLogger} methods,
+ * leaving only the implementation of {@link SimpleLogger}.
+ */
+export abstract class BaseLogger implements Logger {
+  public abstract log(level: LogLevel, message: string): Logger;
+
+  public error(message: string): Logger {
+    return this.log('error', message);
+  }
+
+  public warn(message: string): Logger {
+    return this.log('warn', message);
+  }
+
+  public info(message: string): Logger {
+    return this.log('info', message);
+  }
+
+  public verbose(message: string): Logger {
+    return this.log('verbose', message);
+  }
+
+  public debug(message: string): Logger {
+    return this.log('debug', message);
+  }
+
   public silly(message: string): Logger {
     return this.log('silly', message);
   }
 }
+
+/**
+ * Implements {@link BaseLogger} around a {@link SimpleLogger},
+ * which can be swapped out a runtime.
+ */
+export class WrappingLogger extends BaseLogger {
+  public logger: SimpleLogger;
+
+  public constructor(logger: SimpleLogger) {
+    super();
+    this.logger = logger;
+  }
+
+  public log(level: LogLevel, message: string): this {
+    this.logger.log(level, message);
+    return this;
+  }
+}

src/logging/VoidLogger.ts

@@ -1,12 +1,12 @@
-import { Logger } from './Logger';
+import { BaseLogger } from './Logger';
 import type { LogLevel } from './LogLevel';
 
 /**
  * A logger that does nothing on a log message.
  */
-export class VoidLogger extends Logger {
+export class VoidLogger extends BaseLogger {
   // eslint-disable-next-line @typescript-eslint/no-unused-vars
-  public log(level: LogLevel, message: string, meta?: any): Logger {
+  public log(level: LogLevel, message: string, meta?: any): this {
     // Do nothing
     return this;
   }

src/logging/VoidLoggerFactory.ts

@@ -1,4 +1,3 @@
-import type { Logger } from './Logger';
 import type { LoggerFactory } from './LoggerFactory';
 import { VoidLogger } from './VoidLogger';
 
@@ -9,7 +8,7 @@ export class VoidLoggerFactory implements LoggerFactory {
   private readonly logger = new VoidLogger();
 
   // eslint-disable-next-line @typescript-eslint/no-unused-vars
-  public createLogger(label: string): Logger {
+  public createLogger(label: string): VoidLogger {
     return this.logger;
   }
 }

src/logging/WinstonLogger.ts

@@ -1,11 +1,11 @@
 import type { Logger as WinstonInnerLogger } from 'winston';
-import { Logger } from './Logger';
+import { BaseLogger } from './Logger';
 import type { LogLevel } from './LogLevel';
 
 /**
  * A WinstonLogger implements the {@link Logger} interface using a given winston logger.
  */
-export class WinstonLogger extends Logger {
+export class WinstonLogger extends BaseLogger {
   private readonly logger: WinstonInnerLogger;
 
   public constructor(logger: WinstonInnerLogger) {

test/unit/logging/Logger.test.ts

@@ -1,44 +1,95 @@
-import { Logger } from '../../../src/logging/Logger';
+import { BaseLogger, WrappingLogger } from '../../../src/logging/Logger';
+import type { SimpleLogger } from '../../../src/logging/Logger';
 
 describe('Logger', (): void => {
-  let logger: Logger;
-  beforeEach(async(): Promise<void> => {
-    logger = new (Logger as any)();
-    logger.log = jest.fn();
+  describe('a BaseLogger', (): void => {
+    let logger: BaseLogger;
+
+    beforeEach(async(): Promise<void> => {
+      logger = new (BaseLogger as any)();
+      logger.log = jest.fn();
+    });
+
+    it('delegates error to log.', async(): Promise<void> => {
+      logger.error('my message');
+      expect(logger.log).toHaveBeenCalledTimes(1);
+      expect(logger.log).toHaveBeenCalledWith('error', 'my message');
+    });
+
+    it('warn delegates to log.', async(): Promise<void> => {
+      logger.warn('my message');
+      expect(logger.log).toHaveBeenCalledTimes(1);
+      expect(logger.log).toHaveBeenCalledWith('warn', 'my message');
+    });
+
+    it('info delegates to log.', async(): Promise<void> => {
+      logger.info('my message');
+      expect(logger.log).toHaveBeenCalledTimes(1);
+      expect(logger.log).toHaveBeenCalledWith('info', 'my message');
+    });
+
+    it('verbose delegates to log.', async(): Promise<void> => {
+      logger.verbose('my message');
+      expect(logger.log).toHaveBeenCalledTimes(1);
+      expect(logger.log).toHaveBeenCalledWith('verbose', 'my message');
+    });
+
+    it('debug delegates to log.', async(): Promise<void> => {
+      logger.debug('my message');
+      expect(logger.log).toHaveBeenCalledTimes(1);
+      expect(logger.log).toHaveBeenCalledWith('debug', 'my message');
+    });
+
+    it('silly delegates to log.', async(): Promise<void> => {
+      logger.silly('my message');
+      expect(logger.log).toHaveBeenCalledTimes(1);
+      expect(logger.log).toHaveBeenCalledWith('silly', 'my message');
+    });
   });
 
-  it('Error delegates to log.', async(): Promise<void> => {
-    logger.error('my message');
-    expect(logger.log).toHaveBeenCalledTimes(1);
-    expect(logger.log).toHaveBeenCalledWith('error', 'my message');
-  });
+  describe('a WrappingLogger', (): void => {
+    let logger: SimpleLogger;
+    let wrapper: WrappingLogger;
 
-  it('Warn delegates to log.', async(): Promise<void> => {
-    logger.warn('my message');
-    expect(logger.log).toHaveBeenCalledTimes(1);
-    expect(logger.log).toHaveBeenCalledWith('warn', 'my message');
-  });
+    beforeEach(async(): Promise<void> => {
+      logger = { log: jest.fn() };
+      wrapper = new WrappingLogger(logger);
+    });
 
-  it('Info delegates to log.', async(): Promise<void> => {
-    logger.info('my message');
-    expect(logger.log).toHaveBeenCalledTimes(1);
-    expect(logger.log).toHaveBeenCalledWith('info', 'my message');
-  });
-  it('Verbose delegates to log.', async(): Promise<void> => {
-    logger.verbose('my message');
-    expect(logger.log).toHaveBeenCalledTimes(1);
-    expect(logger.log).toHaveBeenCalledWith('verbose', 'my message');
-  });
+    it('error delegates to the internal logger.', async(): Promise<void> => {
+      wrapper.error('my message');
+      expect(logger.log).toHaveBeenCalledTimes(1);
+      expect(logger.log).toHaveBeenCalledWith('error', 'my message');
+    });
 
-  it('Debug delegates to log.', async(): Promise<void> => {
-    logger.debug('my message');
-    expect(logger.log).toHaveBeenCalledTimes(1);
-    expect(logger.log).toHaveBeenCalledWith('debug', 'my message');
-  });
+    it('warn delegates to the internal logger.', async(): Promise<void> => {
+      wrapper.warn('my message');
+      expect(logger.log).toHaveBeenCalledTimes(1);
+      expect(logger.log).toHaveBeenCalledWith('warn', 'my message');
+    });
 
-  it('Silly delegates to log.', async(): Promise<void> => {
-    logger.silly('my message');
-    expect(logger.log).toHaveBeenCalledTimes(1);
-    expect(logger.log).toHaveBeenCalledWith('silly', 'my message');
+    it('info delegates to the internal logger.', async(): Promise<void> => {
+      wrapper.info('my message');
+      expect(logger.log).toHaveBeenCalledTimes(1);
+      expect(logger.log).toHaveBeenCalledWith('info', 'my message');
+    });
+
+    it('verbose delegates to the internal logger.', async(): Promise<void> => {
+      wrapper.verbose('my message');
+      expect(logger.log).toHaveBeenCalledTimes(1);
+      expect(logger.log).toHaveBeenCalledWith('verbose', 'my message');
+    });
+
+    it('debug delegates to the internal logger.', async(): Promise<void> => {
+      wrapper.debug('my message');
+      expect(logger.log).toHaveBeenCalledTimes(1);
+      expect(logger.log).toHaveBeenCalledWith('debug', 'my message');
+    });
+
+    it('silly delegates to the internal logger.', async(): Promise<void> => {
+      wrapper.silly('my message');
+      expect(logger.log).toHaveBeenCalledTimes(1);
+      expect(logger.log).toHaveBeenCalledWith('silly', 'my message');
+    });
   });
 });