This logger sends messages in batches using beacon API.

example.ts

const logger = new Logger('https://api.example.com/logs');
logger.log('Log message');
logger.info('Info message');
logger.warn('Warn message');
logger.error('Error message');

logger.test.ts

import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
import { Logger } from './logger'; // Предполагаем, что Logger экспортирован из файла logger.ts

describe('Logger', () => {
  let logger: Logger;
  let mockBeacon: ReturnType<typeof vi.fn>;

  beforeEach(() => {
    vi.useFakeTimers();
    mockBeacon = vi.fn().mockReturnValue(true);
    Object.defineProperty(navigator, 'sendBeacon', {
      value: mockBeacon,
      configurable: true,
    });
    logger = new Logger('https://api.example.com/logs', 3, 5000);
  });

  afterEach(() => {
    vi.useRealTimers();
    vi.restoreAllMocks();
  });

  it('should create log entries correctly', () => {
    const spy = vi.spyOn(logger as any, 'addToQueue');
    logger.log('Test log');
    expect(spy).toHaveBeenCalledWith(expect.objectContaining({
      level: 'log',
      message: 'Test log',
    }));
  });

  it('should flush logs when batch size is reached', () => {
    logger.log('Log 1');
    logger.log('Log 2');
    logger.log('Log 3');
    expect(mockBeacon).toHaveBeenCalledTimes(1);
    expect(mockBeacon).toHaveBeenCalledWith(
      'https://api.example.com/logs',
      expect.any(Blob)
    );
  });

  it('should flush logs after max wait time', () => {
    logger.log('Log 1');
    logger.log('Log 2');
    vi.advanceTimersByTime(5000);
    expect(mockBeacon).toHaveBeenCalledTimes(1);
  });

  it('should flush remaining logs on beforeunload', () => {
    logger.log('Log 1');
    logger.log('Log 2');
    window.dispatchEvent(new Event('beforeunload'));
    expect(mockBeacon).toHaveBeenCalledTimes(1);
  });

  it('should not flush if queue is empty', () => {
    (logger as any).flush();
    expect(mockBeacon).not.toHaveBeenCalled();
  });

  it('should log to console as well', () => {
    const consoleSpy = vi.spyOn(console, 'log');
    logger.log('Console log');
    expect(consoleSpy).toHaveBeenCalledWith('Console log');
  });
});

logger.ts

interface LogEntry {
  level: 'log' | 'info' | 'warn' | 'error';
  message: string;
  timestamp: number;
}

class Logger {
  private logQueue: LogEntry[] = [];
  private readonly batchSize: number;
  private readonly maxWaitTime: number;
  private timer: ReturnType<typeof setTimeout> | null = null;
  private readonly endpoint: string;

  constructor(endpoint: string, batchSize: number = 10, maxWaitTime: number = 5000) {
    this.endpoint = endpoint;
    this.batchSize = batchSize;
    this.maxWaitTime = maxWaitTime;

    window.addEventListener('beforeunload', this.flush.bind(this));
  }

  private createLogEntry(level: LogEntry['level'], message: string): LogEntry {
    return {
      level,
      message,
      timestamp: Date.now(),
    };
  }

  private addToQueue(entry: LogEntry): void {
    this.logQueue.push(entry);
    if (this.logQueue.length >= this.batchSize) {
      this.flush();
    } else if (!this.timer) {
      this.timer = setTimeout(() => this.flush(), this.maxWaitTime);
    }
  }

  private flush(): void {
    if (this.logQueue.length === 0) return;

    if (this.timer) {
      clearTimeout(this.timer);
      this.timer = null;
    }

    const logsToSend = this.logQueue.splice(0, this.batchSize);
    const blob = new Blob([JSON.stringify(logsToSend)], { type: 'application/json' });
    navigator.sendBeacon(this.endpoint, blob);
  }

  log(message: string): void {
    this.addToQueue(this.createLogEntry('log', message));
    console.log(message);
  }

  info(message: string): void {
    this.addToQueue(this.createLogEntry('info', message));
    console.info(message);
  }

  warn(message: string): void {
    this.addToQueue(this.createLogEntry('warn', message));
    console.warn(message);
  }

  error(message: string): void {
    this.addToQueue(this.createLogEntry('error', message));
    console.error(message);
  }
}