import { beforeEach, describe, expect, it, vi } from 'vitest';

// Mock PerformanceMonitor class for testing
class MockPerformanceMonitor {
  constructor() {
    this.startTime = Date.now();
    this.marks = new Map();
  }

  /**
   * Mark a performance measurement
   * @param {string} name - Name of the mark
   */
  mark(name) {
    if (this.marks.has(name)) {
      console.warn(`Mark with name ${name} already exists.`);
    }
    this.marks.set(name, Date.now() - this.startTime);
  }

  getMetrics() {
    return Object.fromEntries(this.marks.entries());
  }
}

describe('Performance Monitoring', () => {
  /** @type {MockPerformanceMonitor} */
  let monitor;

  beforeEach(() => {
    monitor = new MockPerformanceMonitor();
  });

  describe('PerformanceMonitor Class', () => {
    it('should initialize with start time', () => {
      expect(monitor.startTime).toBeDefined();
      expect(typeof monitor.startTime).toBe('number');
    });

    it('should create timing marks', () => {
      monitor.mark('test-mark');

      const metrics = monitor.getMetrics();
      expect(metrics).toHaveProperty('test-mark');
      expect(typeof metrics['test-mark']).toBe('number');
    });

    it('should handle multiple marks', () => {
      monitor.mark('mark1');
      monitor.mark('mark2');
      monitor.mark('mark3');

      const metrics = monitor.getMetrics();
      expect(Object.keys(metrics)).toHaveLength(3);
      expect(metrics).toHaveProperty('mark1');
      expect(metrics).toHaveProperty('mark2');
      expect(metrics).toHaveProperty('mark3');
    });

    it('should warn on duplicate mark names', () => {
      // Mock console.warn for this test
      const originalWarn = console.warn;
      const mockWarn = vi.fn();
      console.warn = mockWarn;

      monitor.mark('duplicate');
      monitor.mark('duplicate');

      expect(mockWarn).toHaveBeenCalledWith('Mark with name duplicate already exists.');

      // Restore original console.warn
      console.warn = originalWarn;
    });

    it('should return metrics as plain object', () => {
      monitor.mark('test');

      const metrics = monitor.getMetrics();
      expect(metrics).toBeTypeOf('object');
      expect(Array.isArray(metrics)).toBe(false);
    });

    it('should track elapsed time correctly', async () => {
      monitor.mark('start');

      // Wait a small amount of time
      await new Promise(resolve => setTimeout(resolve, 10));

      monitor.mark('end');

      const metrics = monitor.getMetrics();
      expect(metrics.end).toBeGreaterThan(metrics.start);
    });
  });

  describe('Performance Metrics Validation', () => {
    it('should produce serializable metrics', () => {
      monitor.mark('request-start');
      monitor.mark('proxy-start');
      monitor.mark('proxy-end');
      monitor.mark('request-end');

      const metrics = monitor.getMetrics();

      expect(() => JSON.stringify(metrics)).not.toThrow();
    });

    it('should have reasonable timing values', () => {
      monitor.mark('test-mark');

      const metrics = monitor.getMetrics();
      const timing = metrics['test-mark'];

      // Should be a positive number and reasonable (less than 1 second for this test)
      expect(timing).toBeGreaterThanOrEqual(0);
      expect(timing).toBeLessThan(1000);
    });

    it('should maintain chronological order', async () => {
      monitor.mark('first');
      await new Promise(resolve => setTimeout(resolve, 5));
      monitor.mark('second');
      await new Promise(resolve => setTimeout(resolve, 5));
      monitor.mark('third');

      const metrics = monitor.getMetrics();

      expect(metrics.first).toBeLessThan(metrics.second);
      expect(metrics.second).toBeLessThan(metrics.third);
    });
  });

  describe('Common Performance Scenarios', () => {
    it('should track request lifecycle', () => {
      // Simulate typical request flow
      monitor.mark('request-received');
      monitor.mark('validation-complete');
      monitor.mark('proxy-start');
      monitor.mark('proxy-response');
      monitor.mark('response-sent');

      const metrics = monitor.getMetrics();

      expect(metrics).toHaveProperty('request-received');
      expect(metrics).toHaveProperty('validation-complete');
      expect(metrics).toHaveProperty('proxy-start');
      expect(metrics).toHaveProperty('proxy-response');
      expect(metrics).toHaveProperty('response-sent');
    });

    it('should track cache operations', () => {
      monitor.mark('cache-check-start');
      monitor.mark('cache-miss');
      monitor.mark('upstream-request');
      monitor.mark('cache-store');

      const metrics = monitor.getMetrics();

      expect(metrics).toHaveProperty('cache-check-start');
      expect(metrics).toHaveProperty('cache-miss');
      expect(metrics).toHaveProperty('upstream-request');
      expect(metrics).toHaveProperty('cache-store');
    });

    it('should track error scenarios', () => {
      monitor.mark('request-start');
      monitor.mark('error-occurred');
      monitor.mark('error-handled');

      const metrics = monitor.getMetrics();

      expect(metrics).toHaveProperty('request-start');
      expect(metrics).toHaveProperty('error-occurred');
      expect(metrics).toHaveProperty('error-handled');
    });
  });

  describe('Performance Thresholds', () => {
    it('should identify slow operations', () => {
      monitor.mark('operation-start');

      // Simulate slow operation
      const slowTiming = 5000; // 5 seconds
      monitor.marks.set('operation-end', slowTiming);

      const metrics = monitor.getMetrics();
      const operationTime = metrics['operation-end'] - (metrics['operation-start'] || 0);

      // Should identify as slow (> 1 second)
      expect(operationTime).toBeGreaterThan(1000);
    });

    it('should identify fast operations', () => {
      monitor.mark('fast-operation');

      const metrics = monitor.getMetrics();
      const timing = metrics['fast-operation'];

      // Should be fast (< 100ms for this test)
      expect(timing).toBeLessThan(100);
    });
  });

  describe('Memory and Resource Usage', () => {
    it('should not leak memory with many marks', () => {
      const initialSize = monitor.marks.size;

      // Add many marks
      for (let i = 0; i < 1000; i++) {
        monitor.mark(`mark-${i}`);
      }

      expect(monitor.marks.size).toBe(initialSize + 1000);

      // Clear marks (if such method existed)
      monitor.marks.clear();
      expect(monitor.marks.size).toBe(0);
    });

    it('should handle concurrent mark operations', () => {
      const promises = [];

      for (let i = 0; i < 10; i++) {
        promises.push(
          new Promise((/** @type {(value?: unknown) => void} */ resolve) => {
            setTimeout(() => {
              monitor.mark(`concurrent-${i}`);
              resolve();
            }, Math.random() * 10);
          })
        );
      }

      return Promise.all(promises).then(() => {
        const metrics = monitor.getMetrics();
        expect(Object.keys(metrics)).toHaveLength(10);
      });
    });
  });
});