import { describe, it, expect } from 'vitest';
import { FilterMetrics } from '../src/llm/metrics.js';

describe('FilterMetrics', () => {
  it('starts with zeroed stats', () => {
    const m = new FilterMetrics();
    const stats = m.getStats();
    expect(stats.totalTokensProcessed).toBe(0);
    expect(stats.tokensSaved).toBe(0);
    expect(stats.cacheHits).toBe(0);
    expect(stats.cacheMisses).toBe(0);
    expect(stats.filterCount).toBe(0);
    expect(stats.averageFilterLatencyMs).toBe(0);
  });

  it('records filter operations and accumulates tokens', () => {
    const m = new FilterMetrics();
    m.recordFilter(500, 200, 50);
    m.recordFilter(300, 100, 30);

    const stats = m.getStats();
    expect(stats.totalTokensProcessed).toBe(800);
    expect(stats.tokensSaved).toBe(500); // (500-200) + (300-100)
    expect(stats.filterCount).toBe(2);
    expect(stats.averageFilterLatencyMs).toBe(40); // (50+30)/2
  });

  it('does not allow negative token savings', () => {
    const m = new FilterMetrics();
    // Filtered output is larger than original (edge case)
    m.recordFilter(100, 200, 10);

    const stats = m.getStats();
    expect(stats.totalTokensProcessed).toBe(100);
    expect(stats.tokensSaved).toBe(0); // clamped to 0
  });

  it('records cache hits and misses independently', () => {
    const m = new FilterMetrics();
    m.recordCacheHit();
    m.recordCacheHit();
    m.recordCacheMiss();

    const stats = m.getStats();
    expect(stats.cacheHits).toBe(2);
    expect(stats.cacheMisses).toBe(1);
  });

  it('computes average latency correctly', () => {
    const m = new FilterMetrics();
    m.recordFilter(100, 50, 10);
    m.recordFilter(100, 50, 20);
    m.recordFilter(100, 50, 30);

    expect(m.getStats().averageFilterLatencyMs).toBe(20);
  });

  it('returns 0 average latency when no filter operations', () => {
    const m = new FilterMetrics();
    // Only cache operations, no filter calls
    m.recordCacheHit();
    expect(m.getStats().averageFilterLatencyMs).toBe(0);
  });

  it('resets all metrics to zero', () => {
    const m = new FilterMetrics();
    m.recordFilter(500, 200, 50);
    m.recordCacheHit();
    m.recordCacheMiss();

    m.reset();
    const stats = m.getStats();
    expect(stats.totalTokensProcessed).toBe(0);
    expect(stats.tokensSaved).toBe(0);
    expect(stats.cacheHits).toBe(0);
    expect(stats.cacheMisses).toBe(0);
    expect(stats.filterCount).toBe(0);
    expect(stats.averageFilterLatencyMs).toBe(0);
  });

  it('returns independent snapshots', () => {
    const m = new FilterMetrics();
    m.recordFilter(100, 50, 10);
    const snap1 = m.getStats();

    m.recordFilter(200, 100, 20);
    const snap2 = m.getStats();

    // snap1 should not have been mutated
    expect(snap1.totalTokensProcessed).toBe(100);
    expect(snap2.totalTokensProcessed).toBe(300);
  });
});