From a4a75188bd17e31b39a02511bbd6d628bab5c909 Mon Sep 17 00:00:00 2001
From: crupest <crupest@outlook.com>
Date: Sun, 25 Apr 2021 21:20:04 +0800
Subject: ...

---
 BackEnd/Timeline/Services/User/BasicUserService.cs | 94 ++++++++++++++++++++++
 1 file changed, 94 insertions(+)
 create mode 100644 BackEnd/Timeline/Services/User/BasicUserService.cs

(limited to 'BackEnd/Timeline/Services/User/BasicUserService.cs')

diff --git a/BackEnd/Timeline/Services/User/BasicUserService.cs b/BackEnd/Timeline/Services/User/BasicUserService.cs
new file mode 100644
index 00000000..a3763ef6
--- /dev/null
+++ b/BackEnd/Timeline/Services/User/BasicUserService.cs
@@ -0,0 +1,94 @@
+using Microsoft.EntityFrameworkCore;
+using System;
+using System.Linq;
+using System.Threading.Tasks;
+using Timeline.Entities;
+using Timeline.Models.Validation;
+
+namespace Timeline.Services.User
+{
+    /// <summary>
+    /// This service provide some basic user features, which should be used internally for other services.
+    /// </summary>
+    public interface IBasicUserService
+    {
+        /// <summary>
+        /// Check if a user exists.
+        /// </summary>
+        /// <param name="id">The id of the user.</param>
+        /// <returns>True if exists. Otherwise false.</returns>
+        Task<bool> CheckUserExistence(long id);
+
+        /// <summary>
+        /// Get the user id of given username.
+        /// </summary>
+        /// <param name="username">Username of the user.</param>
+        /// <returns>The id of the user.</returns>
+        /// <exception cref="ArgumentNullException">Thrown when <paramref name="username"/> is null.</exception>
+        /// <exception cref="ArgumentException">Thrown when <paramref name="username"/> is of bad format.</exception>
+        /// <exception cref="UserNotExistException">Thrown when the user with given username does not exist.</exception>
+        Task<long> GetUserIdByUsername(string username);
+
+        /// <summary>
+        /// Get the username modified time of a user.
+        /// </summary>
+        /// <param name="userId">User id.</param>
+        /// <returns>The time.</returns>
+        /// <exception cref="UserNotExistException">Thrown when user does not exist.</exception>
+        Task<DateTime> GetUsernameLastModifiedTime(long userId);
+    }
+
+    public class BasicUserService : IBasicUserService
+    {
+        private readonly DatabaseContext _database;
+
+        private readonly UsernameValidator _usernameValidator = new UsernameValidator();
+
+        public BasicUserService(DatabaseContext database)
+        {
+            _database = database;
+        }
+
+        public async Task<bool> CheckUserExistence(long id)
+        {
+            return await _database.Users.AnyAsync(u => u.Id == id);
+        }
+
+        public async Task<long> GetUserIdByUsername(string username)
+        {
+            if (username == null)
+                throw new ArgumentNullException(nameof(username));
+
+            if (!_usernameValidator.Validate(username, out var message))
+                throw new ArgumentException(message);
+
+            var entity = await _database.Users.Where(user => user.Username == username).Select(u => new { u.Id }).SingleOrDefaultAsync();
+
+            if (entity == null)
+                throw new UserNotExistException(username);
+
+            return entity.Id;
+        }
+
+        public async Task<DateTime> GetUsernameLastModifiedTime(long userId)
+        {
+            var entity = await _database.Users.Where(u => u.Id == userId).Select(u => new { u.UsernameChangeTime }).SingleOrDefaultAsync();
+
+            if (entity is null)
+                throw new UserNotExistException(userId);
+
+            return entity.UsernameChangeTime;
+        }
+    }
+
+    public static class BasicUserServiceExtensions
+    {
+        public static async Task ThrowIfUserNotExist(this IBasicUserService service, long userId)
+        {
+            if (!await service.CheckUserExistence(userId))
+            {
+                throw new UserNotExistException(userId);
+            }
+        }
+    }
+}
-- 
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