Implement endpoints with Services Dependency Injection.

**Note: This implementation is not in minimalAPI way and not optimized, expected to be changed soon.**

Add: `UserService` and its interface `IUserService`.

Fix: `UserEndpoint` is now in instance class style with DI to work.

Fix: change main program to work with above design.

OptixServe.Api/Endpoints/UserEndpoint.cs

@@ -1,4 +1,5 @@
 using System.Text.Json.Serialization;
+using OptixServe.Core.Services;
 using OptixServe.Api.Dtos;
 
 namespace OptixServe.Api.Endpoints;
@@ -8,25 +9,37 @@ namespace OptixServe.Api.Endpoints;
 [JsonSerializable(typeof(IEnumerable<UserDto>))]
 public partial class UserJsonContext : JsonSerializerContext { }
 
-public static class UserEndpoint
+public class UserEndpoint
 {
-    public static IEnumerable<UserDto> GetUsers()
+    private readonly IUserService _userService;
+
+    // 通过构造函数注入依赖
+    public UserEndpoint(IUserService userService)
     {
-        return [
-            new() {Id="1234", UserName = "xxx"},
-            new() {Id="5678", UserName = "yyy"},
-        ];
+        _userService = userService;
     }
 
     public static void Register(WebApplication app)
     {
         var group = app.MapGroup("/users");
 
-        group.MapGet("/", GetAllUsers);
+        group.MapGet("/", (UserEndpoint endpoint) => endpoint.GetAllUsers());
+        group.MapGet("/{id}", (string id, UserEndpoint endpoint) => endpoint.GetUserById(id));
     }
 
-    public static IResult GetAllUsers()
+    public IResult GetAllUsers()
     {
-        return Results.Ok(GetUsers());
+        var users = _userService.GetUsers()
+            .Select(u => new UserDto { Id = u.Id, UserName = u.UserName });
+        return Results.Ok(users);
+    }
+
+    public IResult GetUserById(string id)
+    {
+        var user = _userService.GetUserById(id);
+        if (user == null)
+            return Results.NotFound();
+
+        return Results.Ok(new UserDto { Id = user.Id, UserName = user.UserName });
     }
 }