feat: extract channel management to IChannelService and implement CRUD operations

src/EchoHub.Core/Contracts/IChannelService.cs

@@ -0,0 +1,22 @@
+using EchoHub.Core.DTOs;
+
+namespace EchoHub.Core.Contracts;
+
+public interface IChannelService
+{
+    // Channel CRUD
+    Task<PaginatedResponse<ChannelDto>> GetChannelsAsync(Guid userId, int offset, int limit);
+    Task<ChannelOperationResult> CreateChannelAsync(Guid creatorUserId, string name, string? topic, bool isPublic);
+    Task<ChannelOperationResult> UpdateTopicAsync(Guid callerUserId, string channelName, string? topic);
+    Task<ChannelOperationResult> DeleteChannelAsync(Guid callerUserId, string channelName);
+
+    // Channel queries
+    Task<(string? Topic, bool Exists)> GetChannelTopicAsync(string channelName);
+    Task<List<ChannelListItem>> GetChannelListAsync();
+    Task<ChannelDto?> GetChannelByNameAsync(string channelName);
+
+    // Membership
+    Task<(bool Success, string? Error)> EnsureChannelMembershipAsync(Guid userId, string channelName);
+}
+
+public record ChannelListItem(string Name, string? Topic, int OnlineCount);

src/EchoHub.Core/Contracts/IChatService.cs

@@ -25,12 +25,8 @@ public interface IChatService
     Task BroadcastMessageAsync(string channelName, MessageDto message);
     Task BroadcastChannelUpdatedAsync(ChannelDto channel, string? channelName = null);
 
-    // Query operations (used by IRC gateway for WHOIS, TOPIC, LIST, AUTH)
+    // Query operations (used by IRC gateway for WHOIS, AUTH)
     Task<UserProfileDto?> GetUserProfileAsync(string username);
-    Task<(string? Topic, bool Exists)> GetChannelTopicAsync(string channelName);
-    Task<List<ChannelListItem>> GetChannelListAsync();
     Task<List<string>> GetChannelsForUserAsync(string username);
     Task<(Guid UserId, string Username)?> AuthenticateUserAsync(string username, string password);
 }
-
-public record ChannelListItem(string Name, string? Topic, int OnlineCount);

src/EchoHub.Core/DTOs/CommonDtos.cs

@@ -3,3 +3,20 @@ namespace EchoHub.Core.DTOs;
 public record ErrorResponse(string Error, string? Detail = null);
 
 public record PaginatedResponse<T>(List<T> Items, int Total, int Offset, int Limit);
+
+public enum ChannelError
+{
+    ValidationFailed,
+    AlreadyExists,
+    NotFound,
+    Forbidden,
+    Protected
+}
+
+public record ChannelOperationResult(ChannelDto? Channel, ChannelError? Error, string? ErrorMessage)
+{
+    public bool IsSuccess => Error is null;
+
+    public static ChannelOperationResult Success(ChannelDto channel) => new(channel, null, null);
+    public static ChannelOperationResult Fail(ChannelError error, string message) => new(null, error, message);
+}