honeyDueAPI/internal/monitoring/middleware.go

package monitoring

import (
	"sort"
	"sync"
	"time"

	"github.com/gin-gonic/gin"
)

// HTTPStatsCollector collects HTTP request metrics
type HTTPStatsCollector struct {
	mu           sync.RWMutex
	requests     map[string]int64         // endpoint -> count
	totalLatency map[string]time.Duration // endpoint -> total latency
	errors       map[string]int64         // endpoint -> error count
	byStatus     map[int]int64            // status code -> count
	latencies    []latencySample          // recent latency samples for P95
	startTime    time.Time
	lastReset    time.Time
}

type latencySample struct {
	endpoint  string
	latency   time.Duration
	timestamp time.Time
}

const (
	maxLatencySamples = 1000
	maxEndpoints      = 200          // Cap unique endpoints tracked
	statsResetPeriod  = 1 * time.Hour // Reset stats periodically to prevent unbounded growth
)

// NewHTTPStatsCollector creates a new HTTP stats collector
func NewHTTPStatsCollector() *HTTPStatsCollector {
	now := time.Now()
	return &HTTPStatsCollector{
		requests:     make(map[string]int64),
		totalLatency: make(map[string]time.Duration),
		errors:       make(map[string]int64),
		byStatus:     make(map[int]int64),
		latencies:    make([]latencySample, 0, maxLatencySamples),
		startTime:    now,
		lastReset:    now,
	}
}

// Record records a single HTTP request
func (c *HTTPStatsCollector) Record(endpoint string, latency time.Duration, status int) {
	c.mu.Lock()
	defer c.mu.Unlock()

	// Periodically reset to prevent unbounded memory growth
	if time.Since(c.lastReset) > statsResetPeriod {
		c.resetLocked()
	}

	// Check if we've hit the endpoint limit and this is a new endpoint
	if _, exists := c.requests[endpoint]; !exists && len(c.requests) >= maxEndpoints {
		// Use a catch-all bucket for overflow endpoints
		endpoint = "OTHER"
	}

	c.requests[endpoint]++
	c.totalLatency[endpoint] += latency
	c.byStatus[status]++

	if status >= 400 {
		c.errors[endpoint]++
	}

	// Store latency sample
	c.latencies = append(c.latencies, latencySample{
		endpoint:  endpoint,
		latency:   latency,
		timestamp: time.Now(),
	})

	// Keep only recent samples
	if len(c.latencies) > maxLatencySamples {
		c.latencies = c.latencies[len(c.latencies)-maxLatencySamples:]
	}
}

// resetLocked resets stats while holding the lock
func (c *HTTPStatsCollector) resetLocked() {
	c.requests = make(map[string]int64)
	c.totalLatency = make(map[string]time.Duration)
	c.errors = make(map[string]int64)
	c.byStatus = make(map[int]int64)
	c.latencies = make([]latencySample, 0, maxLatencySamples)
	c.lastReset = time.Now()
	// Keep startTime for uptime calculation
}

// GetStats returns the current HTTP statistics
func (c *HTTPStatsCollector) GetStats() HTTPStats {
	c.mu.RLock()
	defer c.mu.RUnlock()

	stats := HTTPStats{
		ByEndpoint:   make(map[string]EndpointStats),
		ByStatusCode: make(map[int]int64),
	}

	var totalRequests int64
	var totalErrors int64
	var totalLatency time.Duration

	for endpoint, count := range c.requests {
		avgLatency := c.totalLatency[endpoint] / time.Duration(count)
		errCount := c.errors[endpoint]
		errRate := float64(0)
		if count > 0 {
			errRate = float64(errCount) / float64(count)
		}

		stats.ByEndpoint[endpoint] = EndpointStats{
			Count:        count,
			AvgLatencyMs: float64(avgLatency.Milliseconds()),
			ErrorRate:    errRate,
			P95LatencyMs: c.calculateP95(endpoint),
		}

		totalRequests += count
		totalErrors += errCount
		totalLatency += c.totalLatency[endpoint]
	}

	// Copy status code counts
	for status, count := range c.byStatus {
		stats.ByStatusCode[status] = count
	}

	stats.RequestsTotal = totalRequests
	if totalRequests > 0 {
		stats.AvgLatencyMs = float64(totalLatency.Milliseconds()) / float64(totalRequests)
		stats.ErrorRate = float64(totalErrors) / float64(totalRequests)
	}

	uptime := time.Since(c.startTime).Minutes()
	if uptime > 0 {
		stats.RequestsPerMinute = float64(totalRequests) / uptime
	}

	return stats
}

// calculateP95 calculates the 95th percentile latency for an endpoint
// Must be called with read lock held
func (c *HTTPStatsCollector) calculateP95(endpoint string) float64 {
	var endpointLatencies []time.Duration

	for _, sample := range c.latencies {
		if sample.endpoint == endpoint {
			endpointLatencies = append(endpointLatencies, sample.latency)
		}
	}

	if len(endpointLatencies) == 0 {
		return 0
	}

	// Sort latencies
	sort.Slice(endpointLatencies, func(i, j int) bool {
		return endpointLatencies[i] < endpointLatencies[j]
	})

	// Calculate P95 index
	p95Index := int(float64(len(endpointLatencies)) * 0.95)
	if p95Index >= len(endpointLatencies) {
		p95Index = len(endpointLatencies) - 1
	}

	return float64(endpointLatencies[p95Index].Milliseconds())
}

// Reset clears all collected stats
func (c *HTTPStatsCollector) Reset() {
	c.mu.Lock()
	defer c.mu.Unlock()

	c.requests = make(map[string]int64)
	c.totalLatency = make(map[string]time.Duration)
	c.errors = make(map[string]int64)
	c.byStatus = make(map[int]int64)
	c.latencies = make([]latencySample, 0, maxLatencySamples)
	c.startTime = time.Now()
}

// MetricsMiddleware returns a Gin middleware that collects request metrics
func MetricsMiddleware(collector *HTTPStatsCollector) gin.HandlerFunc {
	return func(c *gin.Context) {
		start := time.Now()

		// Process request
		c.Next()

		// Calculate latency
		latency := time.Since(start)

		// Get endpoint pattern (use route path, fallback to actual path)
		endpoint := c.FullPath()
		if endpoint == "" {
			endpoint = c.Request.URL.Path
		}

		// Combine method with path for unique endpoint identification
		endpoint = c.Request.Method + " " + endpoint

		// Record metrics
		collector.Record(endpoint, latency, c.Writer.Status())
	}
}