Initial import of the CBDDC codebase with docs and tests. Add a .NET-focused gitignore to keep generated artifacts out of source control.

src/ZB.MOM.WW.CBDDC.Network/Leadership/ILeaderElectionService.cs

@@ -0,0 +1,65 @@
+using System;
+using System.Threading.Tasks;
+
+namespace ZB.MOM.WW.CBDDC.Network.Leadership;
+
+/// <summary>
+/// Event arguments for leadership change events.
+/// </summary>
+public class LeadershipChangedEventArgs : EventArgs
+{
+    /// <summary>
+    /// Gets the NodeId of the current cloud gateway (leader).
+    /// Null if no leader is elected.
+    /// </summary>
+    public string? CurrentGatewayNodeId { get; }
+
+    /// <summary>
+    /// Gets whether the local node is now the cloud gateway.
+    /// </summary>
+    public bool IsLocalNodeGateway { get; }
+
+    /// <summary>
+    /// Initializes a new instance of the LeadershipChangedEventArgs class.
+    /// </summary>
+    /// <param name="currentGatewayNodeId">The NodeId of the current gateway node, or <see langword="null"/> when none is elected.</param>
+    /// <param name="isLocalNodeGateway">A value indicating whether the local node is the gateway.</param>
+    public LeadershipChangedEventArgs(string? currentGatewayNodeId, bool isLocalNodeGateway)
+    {
+        CurrentGatewayNodeId = currentGatewayNodeId;
+        IsLocalNodeGateway = isLocalNodeGateway;
+    }
+}
+
+/// <summary>
+/// Service for managing leader election in a distributed cluster.
+/// Uses the Bully algorithm where the node with the lexicographically smallest NodeId becomes the leader.
+/// Only the leader (Cloud Gateway) synchronizes with remote cloud nodes.
+/// </summary>
+public interface ILeaderElectionService
+{
+    /// <summary>
+    /// Gets whether the local node is currently the cloud gateway (leader).
+    /// </summary>
+    bool IsCloudGateway { get; }
+
+    /// <summary>
+    /// Gets the NodeId of the current cloud gateway, or null if no gateway is elected.
+    /// </summary>
+    string? CurrentGatewayNodeId { get; }
+
+    /// <summary>
+    /// Event raised when leadership changes.
+    /// </summary>
+    event EventHandler<LeadershipChangedEventArgs>? LeadershipChanged;
+
+    /// <summary>
+    /// Starts the leader election service.
+    /// </summary>
+    Task Start();
+
+    /// <summary>
+    /// Stops the leader election service.
+    /// </summary>
+    Task Stop();
+}