loadr/lib/metrics.go

package lib

import (
	"encoding/csv"
	"fmt"
	"math"
	"net/http"
	"os"
	"path/filepath"
	"sort"
	"strings"
	"time"
)

// Global metrics instance to track performance during load testing
var metrics = PerformanceMetrics{
	MinLatency:       time.Duration(math.MaxInt64),
	ResponseCounters: make(map[int]int32),
	RequestLatencies: make([]RequestMetric, 0),
}

// UpdateMetrics records metrics for each individual request
// Parameters:
//   - duration: time taken to complete the request
//   - resp: HTTP response from the request
//   - second: elapsed seconds since the start of the test
func UpdateMetrics(duration time.Duration, resp *http.Response, second int) {
	metrics.Mu.Lock()
	defer metrics.Mu.Unlock()

	// Create and store individual request metric
	metric := RequestMetric{
		Timestamp:  time.Now(),
		Duration:   duration,
		StatusCode: resp.StatusCode,
		Verb:       resp.Request.Method,
	}
	metrics.RequestLatencies = append(metrics.RequestLatencies, metric)

	// Update aggregate metrics
	metrics.TotalRequests++
	metrics.TotalLatency += duration

	// Update max/min latencies
	if duration > metrics.MaxLatency {
		metrics.MaxLatency = duration
	}
	if duration < metrics.MinLatency {
		metrics.MinLatency = duration
	}

	// Track successful responses
	if resp.StatusCode == http.StatusOK {
		metrics.TotalResponses++
		metrics.ResponseCounters[second]++
	}
}

// calculatePercentile calculates the nth percentile of latencies
// Parameters:
//   - latencies: sorted slice of request durations
//   - percentile: desired percentile (e.g., 50 for p50, 95 for p95)
//
// Returns: the duration at the specified percentile
func calculatePercentile(latencies []time.Duration, percentile float64) time.Duration {
	if len(latencies) == 0 {
		return 0
	}

	index := int(math.Ceil((percentile/100.0)*float64(len(latencies)))) - 1
	if index < 0 {
		index = 0
	}
	return latencies[index]
}

// CalculateAndPrintMetrics generates and saves comprehensive test results
// Parameters:
//   - startTime: when the load test began
//   - requestsPerSecond: target request rate
//   - endpoint: URL being tested
//   - patterns: request patterns used in the test
func CalculateAndPrintMetrics(startTime time.Time, requestsPerSecond float64, endpoint string, patterns []RequestPattern) {
	// Small delay to ensure all metrics are captured
	time.Sleep(100 * time.Millisecond)

	metrics.Mu.Lock()
	defer metrics.Mu.Unlock()

	// Prepare latencies for percentile calculations
	latencies := make([]time.Duration, len(metrics.RequestLatencies))
	for i, metric := range metrics.RequestLatencies {
		latencies[i] = metric.Duration
	}
	sort.Slice(latencies, func(i, j int) bool {
		return latencies[i] < latencies[j]
	})

	// Calculate various percentiles
	p50 := calculatePercentile(latencies, 50)
	p95 := calculatePercentile(latencies, 95)
	p99 := calculatePercentile(latencies, 99)

	// Calculate average latency
	averageLatency := time.Duration(0)
	if metrics.TotalRequests > 0 {
		averageLatency = metrics.TotalLatency / time.Duration(metrics.TotalRequests)
	}

	// Calculate total duration and responses
	totalDuration := time.Since(startTime).Seconds()
	totalResponses := int32(0)
	for _, count := range metrics.ResponseCounters {
		totalResponses += count
	}

	// Reset min latency if unused
	if metrics.MinLatency == time.Duration(math.MaxInt64) {
		metrics.MinLatency = 0
	}

	// Build detailed results string
	results := fmt.Sprintf("Load Test Report\n=============\n\n")
	results += fmt.Sprintf("Endpoint: %s\n", endpoint)
	results += fmt.Sprintf("Pattern: ")

	// Format request patterns
	for i, p := range patterns {
		if i > 0 {
			results += " → "
		}
		if p.Percentage > 0 && p.Percentage < 100 {
			results += fmt.Sprintf("%.0f%%%s", p.Percentage, strings.ToLower(p.Verb[:1]))
		} else {
			results += fmt.Sprintf("%d%s", p.Sequence, strings.ToLower(p.Verb[:1]))
		}
	}
	results += "\n\n"

	// Add performance metrics
	results += fmt.Sprintf("Performance Metrics\n")
	results += fmt.Sprintf("-----------------\n")
	results += fmt.Sprintf("Total Requests Sent: %d\n", metrics.TotalRequests)
	results += fmt.Sprintf("Total Responses Received: %d\n", totalResponses)
	results += fmt.Sprintf("Average Latency: %s\n", averageLatency)
	results += fmt.Sprintf("Max Latency: %s\n", metrics.MaxLatency)
	results += fmt.Sprintf("Min Latency: %s\n", metrics.MinLatency)
	results += fmt.Sprintf("Requests/sec (Target): %.2f\n", requestsPerSecond)
	results += fmt.Sprintf("Requests/sec (Actual): %.2f\n", float64(metrics.TotalRequests)/totalDuration)
	results += fmt.Sprintf("Responses/sec: %.2f\n", float64(totalResponses)/totalDuration)

	// Add percentile information
	results += fmt.Sprintf("\nLatency Percentiles\n")
	results += fmt.Sprintf("-----------------\n")
	results += fmt.Sprintf("50th percentile (p50): %s\n", p50)
	results += fmt.Sprintf("95th percentile (p95): %s\n", p95)
	results += fmt.Sprintf("99th percentile (p99): %s\n", p99)

	fmt.Println(results)
	saveReport(results)
	saveDetailedMetrics()
}

// saveDetailedMetrics writes per-request metrics to a CSV file
// The CSV includes timestamp, duration, status code, and request type for each request
func saveDetailedMetrics() {
	resultsDir := ".reports"
	os.MkdirAll(resultsDir, os.ModePerm)

	csvFile := filepath.Join(resultsDir, fmt.Sprintf("detailed_metrics_%d.csv", time.Now().Unix()))
	file, err := os.Create(csvFile)
	if err != nil {
		fmt.Println("Error creating CSV file:", err)
		return
	}
	defer file.Close()

	writer := csv.NewWriter(file)
	defer writer.Flush()

	// Write CSV header
	writer.Write([]string{
		"Timestamp",
		"Duration (ms)",
		"Status Code",
		"Request Type",
	})

	// Write individual request metrics
	for _, metric := range metrics.RequestLatencies {
		writer.Write([]string{
			metric.Timestamp.Format(time.RFC3339),
			fmt.Sprintf("%.2f", float64(metric.Duration.Milliseconds())),
			fmt.Sprintf("%d", metric.StatusCode),
			metric.Verb,
		})
	}

	fmt.Println("Detailed metrics saved:", csvFile)
}

// saveReport writes the summary report to a text file
// Parameters:
//   - results: formatted string containing the complete test results
func saveReport(results string) {
	resultsDir := ".reports"
	os.MkdirAll(resultsDir, os.ModePerm)

	resultsFile := filepath.Join(resultsDir, fmt.Sprintf("summary_%d.txt", time.Now().Unix()))

	if err := os.WriteFile(resultsFile, []byte(results), 0644); err != nil {
		fmt.Println("Error saving report:", err)
		return
	}

	fmt.Println("Summary report saved:", resultsFile)
}