lbc/web/stats.go

package web

import (
	"encoding/json"
	"net/http"
	"path/filepath"
	"strconv"
	"sync"

	"github.com/gorilla/mux"
)

// Stats implement a statistics counter for hits to the FizzBuzz endpoint.
type Stats struct {
	sync.Mutex
	hits    map[string]int
	maxKey  string
	maxHits int
}

// Incr records a hit in a way that supports reporting in O(1) time and space.
func (s *Stats) Incr(int1, int2, limit int, str1, str2 string) {
	s.Lock()
	defer s.Unlock()
	key := filepath.Join(strconv.Itoa(int1), strconv.Itoa(int2), strconv.Itoa(limit), str1, str2)
	s.hits[key]++
	if s.hits[key] <= s.maxHits {
		return
	}
	s.maxHits = s.hits[key]
	s.maxKey = key
}

// MarshalJSON implements [json.Marshaler].
func (s *Stats) MarshalJSON() ([]byte, error) {
	raw := map[string]any{
		"key":  s.maxKey,
		"hits": s.maxHits,
	}
	return json.Marshal(raw)
}

// Handler provides the statistics endpoint.
func (s *Stats) Handler() http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set(CT, JSON)
		enc := json.NewEncoder(w)
		enc.SetEscapeHTML(true)
		enc.SetIndent("", "  ")
		enc.Encode(s)
	}
}

// Middleware provides the statistics middleware.
func (s *Stats) Middleware() mux.MiddlewareFunc {
	return func(h http.Handler) http.Handler {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			int1, int2, limit, str1, str2, status := argsFromRequest(r)
			if status >= http.StatusBadRequest {
				http.Error(w, http.StatusText(http.StatusNotFound), http.StatusNotFound)
				return
			}
			s.Incr(int1, int2, limit, str1, str2)
			h.ServeHTTP(w, r)
		})
	}
}

func NewStats() *Stats {
	return &Stats{hits: make(map[string]int)}
}