feat(story-1.3): add user registration API with Argon2 password hashing

internal/handler/auth.go

@@ -0,0 +1,58 @@
+// Package handler contains HTTP handlers for the REST API.
+package handler
+
+import (
+	"encoding/json"
+	"errors"
+	"net/http"
+
+	"github.com/michael/flowreader/internal/service"
+)
+
+// AuthHandler handles authentication-related HTTP requests.
+type AuthHandler struct {
+	authService *service.AuthService
+}
+
+// NewAuthHandler creates a new authentication handler.
+func NewAuthHandler(authService *service.AuthService) *AuthHandler {
+	return &AuthHandler{authService: authService}
+}
+
+// Register handles POST /api/v1/auth/register
+func (h *AuthHandler) Register(w http.ResponseWriter, r *http.Request) {
+	var req service.RegisterRequest
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		respondError(w, http.StatusBadRequest, "Invalid request body")
+		return
+	}
+
+	resp, err := h.authService.Register(req)
+	if err != nil {
+		switch {
+		case errors.Is(err, service.ErrInvalidEmail):
+			respondError(w, http.StatusBadRequest, "Invalid email format")
+		case errors.Is(err, service.ErrPasswordTooShort):
+			respondError(w, http.StatusBadRequest, "Password must be at least 8 characters")
+		case errors.Is(err, service.ErrEmailAlreadyExists):
+			respondError(w, http.StatusConflict, "Email already registered")
+		default:
+			respondError(w, http.StatusInternalServerError, "Registration failed")
+		}
+		return
+	}
+
+	respondJSON(w, http.StatusCreated, resp)
+}
+
+// respondJSON writes a JSON response.
+func respondJSON(w http.ResponseWriter, status int, data interface{}) {
+	w.Header().Set("Content-Type", "application/json")
+	w.WriteHeader(status)
+	json.NewEncoder(w).Encode(data)
+}
+
+// respondError writes an error response.
+func respondError(w http.ResponseWriter, status int, message string) {
+	respondJSON(w, status, map[string]string{"error": message})
+}