// 一个最小的 Go HTTP 服务，用来演示多阶段构建、健康检查和优雅退出。
package main

import (
	"context"
	"errors"
	"log"
	"net/http"
	"os"
	"os/signal"
	"syscall"
	"time"
)

func newMux() *http.ServeMux {
	mux := http.NewServeMux()
	mux.HandleFunc("GET /healthz", func(w http.ResponseWriter, r *http.Request) {
		w.Write([]byte("ok"))
	})
	mux.HandleFunc("GET /api/hello", func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("Content-Type", "application/json")
		w.Write([]byte(`{"message":"hello from container"}`))
	})
	return mux
}

func main() {
	addr := ":" + getenv("PORT", "8080")
	srv := &http.Server{Addr: addr, Handler: newMux(), ReadHeaderTimeout: 5 * time.Second}

	// 容器停止时 Docker 先发 SIGTERM，等待一段时间（默认 10 秒）后才 SIGKILL
	ctx, stop := signal.NotifyContext(context.Background(), syscall.SIGINT, syscall.SIGTERM)
	defer stop()
	go func() {
		log.Printf("listening on %s", addr)
		if err := srv.ListenAndServe(); err != nil && !errors.Is(err, http.ErrServerClosed) {
			log.Fatal(err)
		}
	}()
	<-ctx.Done()
	shutdownCtx, cancel := context.WithTimeout(context.Background(), 8*time.Second)
	defer cancel()
	if err := srv.Shutdown(shutdownCtx); err != nil { // 不再接新请求，等正在处理的请求完成
		log.Printf("shutdown: %v", err)
	}
	log.Println("bye")
}

func getenv(k, def string) string {
	if v := os.Getenv(k); v != "" {
		return v
	}
	return def
}