Introduce notification hub pool

src/Core/NotificationHub/NotificationHubPool.cs

@@ -0,0 +1,58 @@
+using Bit.Core.Settings;
+using Bit.Core.Utilities;
+using Microsoft.Azure.NotificationHubs;
+using Microsoft.Extensions.Logging;
+
+namespace Bit.Core.NotificationHub;
+
+public class NotificationHubPool : INotificationHubPool
+{
+    private List<NotificationHubConnection> _connections { get; }
+    private readonly IEnumerable<INotificationHubClient> _clients;
+    private readonly ILogger<NotificationHubPool> _logger;
+    public NotificationHubPool(ILogger<NotificationHubPool> logger, GlobalSettings globalSettings)
+    {
+        _logger = logger;
+        _connections = filterInvalidHubs(globalSettings.NotificationHubPool.NotificationHubSettings);
+        _clients = _connections.Select(c => c.HubClient);
+    }
+
+    private List<NotificationHubConnection> filterInvalidHubs(IEnumerable<GlobalSettings.NotificationHubSettings> hubs)
+    {
+        List<NotificationHubConnection> result = new();
+        foreach (var hub in hubs)
+        {
+            var connection = NotificationHubConnection.From(hub);
+            if (!connection.IsValid)
+            {
+                _logger.LogWarning("Invalid notification hub settings: {0}", hub.HubName ?? "hub name missing");
+                continue;
+            }
+            result.Add(connection);
+        }
+
+        return result;
+    }
+
+
+    /// <summary>
+    /// Gets the NotificationHubClient for the given comb ID.
+    /// </summary>
+    /// <param name="comb"></param>
+    /// <returns></returns>
+    /// <exception cref="InvalidOperationException"></exception>
+    public NotificationHubClient ClientFor(Guid comb)
+    {
+        var possibleConnections = _connections.Where(c => c.RegistrationEnabled(comb)).ToArray();
+        if (possibleConnections.Length == 0)
+        {
+            throw new InvalidOperationException($"No valid notification hubs are available for the given comb ({comb}).\n" +
+                $"The comb's datetime is {CoreHelpers.DateFromComb(comb)}." +
+                $"Hub start and end times are configured as follows:\n" +
+                string.Join("\n", _connections.Select(c => $"Hub {c.HubName} - Start: {c.RegistrationStartDate}, End: {c.RegistrationEndDate}")));
+        }
+        return possibleConnections[CoreHelpers.BinForComb(comb, possibleConnections.Length)].HubClient;
+    }
+
+    public INotificationHubProxy AllClients { get { return new NotificationHubClientProxy(_clients); } }
+}