main.go

package main

import (
	"encoding/json"
	"html/template"
	"log"
	"net/http"

	"greeting-app/internal/userservice"
)

var tmpl *template.Template

func main() {
	var err error
	tmpl, err = template.ParseFiles("templates/index.html")
	if err != nil {
		log.Fatalf("failed to parse templates: %v", err)
	}

	svc, err := userservice.New("data/users.json")
	if err != nil {
		log.Fatalf("failed to load user service: %v", err)
	}

	http.HandleFunc("/", indexHandler)
	http.HandleFunc("/api/greet", greetHandler(svc))

	log.Println("Server listening on :8080")
	if err := http.ListenAndServe("127.0.0.1:8080", nil); err != nil {
		log.Fatalf("server error: %v", err)
	}
}

func indexHandler(w http.ResponseWriter, r *http.Request) {
	if err := tmpl.Execute(w, nil); err != nil {
		http.Error(w, "template error", http.StatusInternalServerError)
	}
}

type GreetRequest struct {
	UserID string `json:"userId"`
}

type GreetResponse struct {
	Message string `json:"message"`
	Error   string `json:"error,omitempty"`
}

func greetHandler(svc *userservice.Service) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		if r.Method != http.MethodPost {
			http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
			return
		}

		var req GreetRequest
		if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
			w.Header().Set("Content-Type", "application/json")
			w.WriteHeader(http.StatusBadRequest)
			json.NewEncoder(w).Encode(GreetResponse{Error: "invalid request body"})
			return
		}

		if req.UserID == "" {
			w.Header().Set("Content-Type", "application/json")
			w.WriteHeader(http.StatusBadRequest)
			json.NewEncoder(w).Encode(GreetResponse{Error: "user_id is required"})
			return
		}

		name, err := svc.GetUserName(req.UserID)
		if err != nil {
			w.Header().Set("Content-Type", "application/json")
			w.WriteHeader(http.StatusNotFound)
			json.NewEncoder(w).Encode(GreetResponse{Error: "user not found"})
			return
		}

		w.Header().Set("Content-Type", "application/json")
		json.NewEncoder(w).Encode(GreetResponse{Message: "Hello " + name})
	}
}