1 files changed, 36 insertions, 0 deletions
diff --git a/BackEnd/Timeline/Services/User/IBasicUserService.cs b/BackEnd/Timeline/Services/User/IBasicUserService.cs
new file mode 100644
index 00000000..0e30d733
--- /dev/null
+++ b/BackEnd/Timeline/Services/User/IBasicUserService.cs
@@ -0,0 +1,36 @@
+using System;
+using System.Threading.Tasks;
+
+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> CheckUserExistenceAsync(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> GetUserIdByUsernameAsync(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> GetUsernameLastModifiedTimeAsync(long userId);
+    }
+}