Shard notification hub (#4450)

* Allow for binning of comb IDs by date and value

* Introduce notification hub pool

* Replace device type sharding with comb + range sharding

* Fix proxy interface

* Use enumerable services for multiServiceNotificationHub

* Fix push interface usage

* Fix push notification service dependencies

* Fix push notification keys

* Fixup documentation

* Remove deprecated settings

* Fix tests

* PascalCase method names

* Remove unused request model properties

* Remove unused setting

* Improve DateFromComb precision

* Prefer readonly service enumerable

* Pascal case template holes

* Name TryParse methods TryParse

* Apply suggestions from code review

Co-authored-by: Justin Baur <19896123+justindbaur@users.noreply.github.com>

* AllClients is a set of clients and must be deduplicated

* Fix registration start time

* Add logging to initialization of a notification hub

* more logging

* Add lower level logging for hub settings

* Log when connection is resolved

* Improve log message

* Log pushes to notification hub

* temporarily elevate log messages for visibility

* Log in multi-service when relaying to another push service

* Revert to more reasonable logging free of user information

* Fixup merge

Deleting user was extracted to a command in #4803, this updates that work to use just the device ids as I did elsewhere in abd67e8ec

* Do not use bouncy castle exception types

* Add required services for logging

---------

Co-authored-by: Justin Baur <19896123+justindbaur@users.noreply.github.com>
Co-authored-by: bnagawiecki <107435978+bnagawiecki@users.noreply.github.com>

src/Core/NotificationHub/NotificationHubConnection.cs

@@ -0,0 +1,128 @@
+using Bit.Core.Settings;
+using Bit.Core.Utilities;
+using Microsoft.Azure.NotificationHubs;
+
+class NotificationHubConnection
+{
+    public string HubName { get; init; }
+    public string ConnectionString { get; init; }
+    public bool EnableSendTracing { get; init; }
+    private NotificationHubClient _hubClient;
+    /// <summary>
+    /// Gets the NotificationHubClient for this connection.
+    /// 
+    /// If the client is null, it will be initialized.
+    /// 
+    /// <throws>Exception</throws> if the connection is invalid.
+    /// </summary>
+    public NotificationHubClient HubClient
+    {
+        get
+        {
+            if (_hubClient == null)
+            {
+                if (!IsValid)
+                {
+                    throw new Exception("Invalid notification hub settings");
+                }
+                Init();
+            }
+            return _hubClient;
+        }
+        private set
+        {
+            _hubClient = value;
+        }
+    }
+    /// <summary>
+    /// Gets the start date for registration.
+    /// 
+    /// If null, registration is always disabled.
+    /// </summary>
+    public DateTime? RegistrationStartDate { get; init; }
+    /// <summary>
+    /// Gets the end date for registration.
+    /// 
+    /// If null, registration has no end date.
+    /// </summary>
+    public DateTime? RegistrationEndDate { get; init; }
+    /// <summary>
+    /// Gets whether all data needed to generate a connection to Notification Hub is present.
+    /// </summary>
+    public bool IsValid
+    {
+        get
+        {
+            {
+                var invalid = string.IsNullOrWhiteSpace(HubName) || string.IsNullOrWhiteSpace(ConnectionString);
+                return !invalid;
+            }
+        }
+    }
+
+    public string LogString
+    {
+        get
+        {
+            return $"HubName: {HubName}, EnableSendTracing: {EnableSendTracing}, RegistrationStartDate: {RegistrationStartDate}, RegistrationEndDate: {RegistrationEndDate}";
+        }
+    }
+
+    /// <summary>
+    /// Gets whether registration is enabled for the given comb ID.
+    /// This is based off of the generation time encoded in the comb ID.
+    /// </summary>
+    /// <param name="comb"></param>
+    /// <returns></returns>
+    public bool RegistrationEnabled(Guid comb)
+    {
+        var combTime = CoreHelpers.DateFromComb(comb);
+        return RegistrationEnabled(combTime);
+    }
+
+    /// <summary>
+    /// Gets whether registration is enabled for the given time.
+    /// </summary>
+    /// <param name="queryTime">The time to check</param>
+    /// <returns></returns>
+    public bool RegistrationEnabled(DateTime queryTime)
+    {
+        if (queryTime >= RegistrationEndDate || RegistrationStartDate == null)
+        {
+            return false;
+        }
+
+        return RegistrationStartDate < queryTime;
+    }
+
+    private NotificationHubConnection() { }
+
+    /// <summary>
+    /// Creates a new NotificationHubConnection from the given settings.
+    /// </summary>
+    /// <param name="settings"></param>
+    /// <returns></returns>
+    public static NotificationHubConnection From(GlobalSettings.NotificationHubSettings settings)
+    {
+        return new()
+        {
+            HubName = settings.HubName,
+            ConnectionString = settings.ConnectionString,
+            EnableSendTracing = settings.EnableSendTracing,
+            // Comb time is not precise enough for millisecond accuracy
+            RegistrationStartDate = settings.RegistrationStartDate.HasValue ? Truncate(settings.RegistrationStartDate.Value, TimeSpan.FromMilliseconds(10)) : null,
+            RegistrationEndDate = settings.RegistrationEndDate
+        };
+    }
+
+    private NotificationHubConnection Init()
+    {
+        HubClient = NotificationHubClient.CreateClientFromConnectionString(ConnectionString, HubName, EnableSendTracing);
+        return this;
+    }
+
+    private static DateTime Truncate(DateTime dateTime, TimeSpan resolution)
+    {
+        return dateTime.AddTicks(-(dateTime.Ticks % resolution.Ticks));
+    }
+}