First commit that builds.

code/MessengerBroker/Handlers/DataHandler.cs

@@ -0,0 +1,81 @@
+using MessengerApi.Db;
+using MessengerBroker.Db;
+using Microsoft.EntityFrameworkCore;
+
+namespace MessengerBroker.Handlers
+{
+    public class DataHandler
+    {
+        private readonly Settings _settings;
+
+        public Task<Tuple<MessengerApi.Db.Entities.User[], MessengerApi.Db.Entities.UserRoute[]>> GetLocalUsersAndRoutes()
+        {
+            var foreignUserIds = (Guid[])null;
+            using(var broCtx = new BrokerDbContext(this._settings.MessengerBrokerDbConnectionString))
+            {
+                foreignUserIds = broCtx.Users.Select(x => x.Id).ToArray();
+            }
+
+            using (var apiCtx = new MessengerDbContext(this._settings.MessengerApiDbConnectionString))
+            {
+                var localUsers = apiCtx.Users
+                    .Where(x => !foreignUserIds.Any(f => f == x.Id))
+                    .ToArray();
+                var localRoutes = apiCtx.UserRoutes
+                    .Include(x => x.From)
+                    .Include(x => x.To)
+                    .Where(x => localUsers.Any(l => l.Id == x.From.Id) && localUsers.Any(l => l.Id == x.To.Id))
+                    .ToArray();
+
+                return Task.FromResult(new Tuple<MessengerApi.Db.Entities.User[], MessengerApi.Db.Entities.UserRoute[]>(
+                    localUsers,
+                    localRoutes));
+            }
+        }
+
+        private Task<MessengerApi.Db.Entities.User[]> GetForeignUsers(Guid brokerId)
+        {
+            var foreignUserIds = (Guid[])null;
+            using (var broCtx = new BrokerDbContext(this._settings.MessengerBrokerDbConnectionString))
+            {
+                foreignUserIds = broCtx.Users.Where(x=>x.BrokerId == brokerId).Select(x => x.Id).ToArray();
+            }
+
+            using (var apiCtx = new MessengerDbContext(this._settings.MessengerApiDbConnectionString))
+            {
+                var localUsers = apiCtx.Users
+                    .Where(x => !foreignUserIds.Any(f => f == x.Id))
+                    .ToArray();
+
+                return Task.FromResult(localUsers);
+            }
+        }
+
+        public async Task<MessengerApi.Db.Entities.Message[]> GetMessages(Guid brokerId, DateTime sinceUtc)
+        {
+            var userIds = (Guid[])null;
+
+            if(brokerId == this._settings.BrokerId)
+            {
+                // Our messages.
+                var users = await this.GetLocalUsersAndRoutes();
+                userIds = users.Item1.Select(x => x.Id).ToArray();
+            }
+            else
+            {
+                var users = await this.GetForeignUsers(brokerId);
+                userIds = users.Select(x => x.Id).ToArray();
+            }
+
+            using (var apiCtx = new MessengerDbContext(this._settings.MessengerApiDbConnectionString))
+            {
+                var messages = apiCtx.Messages
+                    .Include(x => x.From).Include(x => x.To)
+                    .Where(x => x.CreatedUtc >= sinceUtc && userIds.Contains(x.From.Id))
+                    .ToArray();
+
+                return messages;
+            }
+        }
+    }
+}