package health

import (
	"context"
	"encoding/json"
	"fmt"
	"log/slog"
	"net/http"
	"strings"
	"time"
)

type Server struct {
	address string
	server  *http.Server
	metrics func() any
}

func NewServer(address string, metrics func() any) *Server {
	if address == "" {
		return nil
	}

	mux := http.NewServeMux()
	mux.HandleFunc("/healthz", func(w http.ResponseWriter, _ *http.Request) {
		writeJSON(w, http.StatusOK, map[string]string{"status": "ok"})
	})
	mux.HandleFunc("/readyz", func(w http.ResponseWriter, _ *http.Request) {
		writeJSON(w, http.StatusOK, map[string]string{"status": "ready"})
	})
	mux.HandleFunc("/metrics", func(w http.ResponseWriter, _ *http.Request) {
		if metrics == nil {
			writeJSON(w, http.StatusOK, map[string]string{"status": "metrics_unavailable"})
			return
		}

		w.Header().Set("Content-Type", "text/plain; version=0.0.4")
		_, _ = w.Write([]byte(formatMetrics(metrics())))
	})

	return &Server{
		address: address,
		metrics: metrics,
		server: &http.Server{
			Addr:              address,
			Handler:           mux,
			ReadHeaderTimeout: 5 * time.Second,
		},
	}
}

func (server *Server) Start() {
	if server == nil {
		return
	}

	go func() {
		slog.Info("health server started", "address", server.address)
		if err := server.server.ListenAndServe(); err != nil && err != http.ErrServerClosed {
			slog.Error("health server stopped with error", "error", err)
		}
	}()
}

func (server *Server) Shutdown(ctx context.Context) error {
	if server == nil {
		return nil
	}
	return server.server.Shutdown(ctx)
}

func writeJSON(w http.ResponseWriter, status int, value any) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(status)
	_ = json.NewEncoder(w).Encode(value)
}

func formatMetrics(snapshot any) string {
	encoded, err := json.Marshal(snapshot)
	if err != nil {
		return "mqqt_scrubber_metrics_encode_error 1\n"
	}

	var fields map[string]uint64
	if err := json.Unmarshal(encoded, &fields); err != nil {
		return "mqqt_scrubber_metrics_decode_error 1\n"
	}

	var builder strings.Builder
	for key, value := range fields {
		builder.WriteString(fmt.Sprintf("mqqt_scrubber_%s %d\n", key, value))
	}
	return builder.String()
}