package httpserver

import (
	"context"
	"encoding/json"
	"errors"
	"log/slog"
	"net/http"
	"sync/atomic"
	"time"
)

// Server 提供 /health 和 /ready HTTP 探针。
type Server struct {
	appName         string
	addr            string
	shutdownTimeout time.Duration
	logger          *slog.Logger
	drainHook       DrainHook
	ready           atomic.Bool
}

// DrainHook 在服务摘除 readiness 后执行，例如注销注册中心节点。
type DrainHook interface {
	OnDeregister(context.Context) error
}

// New 创建探针 HTTP 服务。
func New(appName string, addr string, shutdownTimeout time.Duration, logger *slog.Logger, drainHook DrainHook) *Server {
	server := &Server{
		appName:         appName,
		addr:            addr,
		shutdownTimeout: shutdownTimeout,
		logger:          logger,
		drainHook:       drainHook,
	}
	server.ready.Store(true)
	return server
}

// Run 启动 HTTP 服务并在退出时优雅关闭。
func (s *Server) Run(ctx context.Context) error {
	mux := http.NewServeMux()
	mux.HandleFunc("/health", s.handleHealth)
	mux.HandleFunc("/heath", s.handleHealth)
	mux.HandleFunc("/ready", s.handleReady)

	httpServer := &http.Server{
		Addr:              s.addr,
		Handler:           mux,
		ReadHeaderTimeout: 5 * time.Second,
	}

	go func() {
		<-ctx.Done()
		s.ready.Store(false)
		shutdownCtx, cancel := context.WithTimeout(context.Background(), s.shutdownTimeout)
		defer cancel()
		if s.drainHook != nil {
			if err := s.drainHook.OnDeregister(shutdownCtx); err != nil {
				s.logger.Error("run deregister hook failed", "error", err)
			}
		}
		_ = httpServer.Shutdown(shutdownCtx)
	}()

	s.logger.Info("pay http server started", "addr", s.addr)

	err := httpServer.ListenAndServe()
	if errors.Is(err, http.ErrServerClosed) {
		return nil
	}
	return err
}

func (s *Server) handleHealth(w http.ResponseWriter, _ *http.Request) {
	writeJSON(w, http.StatusOK, map[string]string{
		"status":  "ok",
		"service": s.appName,
	})
}

func (s *Server) handleReady(w http.ResponseWriter, _ *http.Request) {
	if !s.ready.Load() {
		writeJSON(w, http.StatusServiceUnavailable, map[string]string{
			"code":    "not_ready",
			"message": "service is shutting down",
		})
		return
	}

	writeJSON(w, http.StatusOK, map[string]string{
		"status":  "ready",
		"service": s.appName,
	})
}

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