Added offline queue management (#23)

* Offline DbContext and operations queue injection code.

* (#20) Tests for updating queue when the DbContext is changed.

src/CommunityToolkit.Datasync.Client/CommunityToolkit.Datasync.Client.csproj

@@ -15,15 +15,12 @@
 
   <ItemGroup>
     <PackageReference Include="Microsoft.Extensions.Http" Version="8.0.0" />
+    <PackageReference Include="Microsoft.Azure.Core.Spatial" Version="1.1.0" />
+    <PackageReference Include="Microsoft.EntityFrameworkCore" Version="8.0.4" />
+    <PackageReference Include="Microsoft.EntityFrameworkCore.Sqlite" Version="8.0.4" />
   </ItemGroup>
 
   <ItemGroup>
     <ProjectReference Include="..\CommunityToolkit.Datasync.Server.Abstractions\CommunityToolkit.Datasync.Server.Abstractions.csproj" />
   </ItemGroup>
-
-  <ItemGroup>
-    <Reference Include="Microsoft.Azure.Core.Spatial">
-      <HintPath>..\..\..\..\..\..\..\Nuget\microsoft.azure.core.spatial\1.1.0\lib\netstandard2.0\Microsoft.Azure.Core.Spatial.dll</HintPath>
-    </Reference>
-  </ItemGroup>
 </Project>

src/CommunityToolkit.Datasync.Client/Offline/DatasyncTableInformation.cs

@@ -0,0 +1,30 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.ComponentModel.DataAnnotations;
+using System.ComponentModel.DataAnnotations.Schema;
+
+namespace CommunityToolkit.Datasync.Client.Offline;
+
+/// <summary>
+/// To support incremental sync, every synchronization event is recorded in the <see cref="OfflineDbContext"/>
+/// together with the last time that the synchronization happened.  This information is used to determine what
+/// parameters to add to the query to get only the changes since the last sync.
+/// </summary>
+[Table("__datasync_tableinfo")]
+public sealed class DatasyncTableInformation
+{
+    /// <summary>
+    /// The unique ID for the query.  This is generated from the table name
+    /// and query when not provided.
+    /// </summary>
+    [Key]
+    public string QueryId { get; set; } = string.Empty;
+
+    /// <summary>
+    /// The number of ticks when the last synchronization happened (or 0L if never synchronized).
+    /// </summary>
+    [Required]
+    public long LastSynchronization { get; set; } = 0L;
+}

src/CommunityToolkit.Datasync.Client/Offline/IOperationsQueueManager.cs

@@ -0,0 +1,38 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using Microsoft.EntityFrameworkCore.ChangeTracking;
+using System.Text.Json;
+
+namespace CommunityToolkit.Datasync.Client.Offline;
+
+/// <summary>
+/// Definition of the operations queue manager.  This is the set of methods used to
+/// maintain the queue of operations that need to be synchronized with the remote service.
+/// </summary>
+internal interface IOperationsQueueManager
+{
+    /// <summary>
+    /// The <see cref="JsonSerializerOptions"/> to use for serializing and deserializing data.
+    /// </summary>
+    JsonSerializerOptions JsonSerializerOptions { get; }
+
+    /// <summary>
+    /// Creates a new Create/Insert/Add operation for the given state change.
+    /// </summary>
+    /// <param name="entry">The entry being processed.</param>
+    void AddCreateOperation(EntityEntry entry);
+
+    /// <summary>
+    /// Creates a new Delete operation for the given state change.
+    /// </summary>
+    /// <param name="entry">The entry being processed.</param>
+    void AddDeleteOperation(EntityEntry entry);
+
+    /// <summary>
+    /// Creates a new Modify/Update operation for the given state change.
+    /// </summary>
+    /// <param name="entry">The entry being processed.</param>
+    void AddUpdateOperation(EntityEntry entry);
+}

src/CommunityToolkit.Datasync.Client/Offline/OfflineClientEntity.cs

@@ -0,0 +1,31 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+namespace CommunityToolkit.Datasync.Client;
+
+/// <summary>
+/// The base class for entities that are stored in an offline database.
+/// </summary>
+public abstract class OfflineClientEntity
+{
+    /// <summary>
+    /// The globally unique ID for the entity.
+    /// </summary>
+    public string Id { get; set; }
+
+    /// <summary>
+    /// The date/time that the entity was last updated on the server.
+    /// </summary>
+    public DateTimeOffset UpdatedAt { get; set; } = DateTimeOffset.MinValue;
+
+    /// <summary>
+    /// The version of the entity on the server.
+    /// </summary>
+    public string Version { get; set; } = string.Empty;
+
+    /// <summary>
+    /// If <c>true</c>, the entity is deleted on the server.
+    /// </summary>
+    public bool Deleted { get; set; }
+}

src/CommunityToolkit.Datasync.Client/Offline/OfflineDatasetException.cs

@@ -0,0 +1,29 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Diagnostics.CodeAnalysis;
+
+namespace CommunityToolkit.Datasync.Client;
+
+/// <summary>
+/// A base exception class for all the exceptions thrown by the offline dataset processing.
+/// </summary>
+[ExcludeFromCodeCoverage(Justification = "Standard exception class")]
+public class OfflineDatasetException : ApplicationException
+{
+    /// <inheritdoc />
+    public OfflineDatasetException() : base()
+    {
+    }
+
+    /// <inheritdoc />
+    public OfflineDatasetException(string message) : base(message)
+    {
+    }
+
+    /// <inheritdoc />
+    public OfflineDatasetException(string message, Exception innerException) : base(message, innerException)
+    {
+    }
+}

src/CommunityToolkit.Datasync.Client/Offline/OfflineDbContext.cs

@@ -0,0 +1,151 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using CommunityToolkit.Datasync.Client.Offline;
+using CommunityToolkit.Datasync.Server;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.ChangeTracking;
+using System.Diagnostics.CodeAnalysis;
+using System.Text.Json;
+
+namespace CommunityToolkit.Datasync.Client;
+
+/// <summary>
+/// The <see cref="OfflineDbContext"/> class is a base class for a <see cref="DbContext"/> that is
+/// used to store offline data that is later synchronized to a remote datasync service.
+/// </summary>
+public abstract class OfflineDbContext : DbContext
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="OfflineDbContext"/> class.  The <see cref="OnConfiguring(DbContextOptionsBuilder)"/>
+    /// method will be called to configure the database (and other options) to be used for this context.
+    /// </summary>
+    [ExcludeFromCodeCoverage(Justification = "Standard entry point that is part of DbContext")]
+    protected OfflineDbContext() : base()
+    {
+    }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="OfflineDbContext"/> class. The <see cref="OnConfiguring(DbContextOptionsBuilder)"/>
+    /// method will still be called to configure the database to be used for this context.
+    /// </summary>
+    /// <param name="options">The options to use in configuring the <see cref="OfflineDbContext"/>.</param>
+    protected OfflineDbContext(DbContextOptions options) : base(options)
+    {
+    }
+
+    /// <summary>
+    /// The list of entities that are awaiting synchronization.
+    /// </summary>
+    public DbSet<OfflineQueueEntity> DatasyncOperationsQueue => Set<OfflineQueueEntity>();
+
+    /// <summary>
+    /// The metadata storage for each table synchronization set.
+    /// </summary>
+    public DbSet<DatasyncTableInformation> DatasyncTableMetadata => Set<DatasyncTableInformation>();
+
+    /// <summary>
+    /// The <see cref="JsonSerializerOptions"/> to use for serializing and deserializing entities.
+    /// </summary>
+    public JsonSerializerOptions JsonSerializerOptions { get; set; }
+
+    /// <summary>
+    /// Used to manage the operations queue internally.
+    /// </summary>
+    internal IOperationsQueueManager OperationsQueueManager { get; set; }
+
+    /// <inheritdoc />
+    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
+    {
+        base.OnConfiguring(optionsBuilder);
+        JsonSerializerOptions ??= new DatasyncServiceOptions().JsonSerializerOptions;
+        OperationsQueueManager ??= new OperationsQueueManager(this);
+    }
+
+    /// <inheritdoc />
+    protected override void OnModelCreating(ModelBuilder modelBuilder)
+    {
+        modelBuilder.Entity<OfflineQueueEntity>(entity =>
+        {
+            entity.HasKey(e => e.Id);
+            entity.HasIndex(e => e.EntityName);
+            entity.HasIndex(e => e.EntityId);
+        });
+
+        modelBuilder.Entity<DatasyncTableInformation>(entity =>
+        {
+            entity.HasKey(e => e.QueryId);
+            entity.Property(e => e.LastSynchronization).IsRequired().HasDefaultValue(0L);
+        });
+
+        base.OnModelCreating(modelBuilder);
+    }
+
+    /// <inheritdoc />
+    public virtual new int SaveChanges() => SaveChanges(true);
+
+    /// <inheritdoc />
+    public virtual new int SaveChanges(bool acceptAllChangesOnSuccess)
+    {
+        StoreChangesInOperationsQueue();
+        return base.SaveChanges(acceptAllChangesOnSuccess);
+    }
+
+    /// <inheritdoc />
+    public virtual new Task<int> SaveChangesAsync(CancellationToken cancellationToken = default) => SaveChangesAsync(true, cancellationToken);
+
+    /// <inheritdoc />
+    public virtual new Task<int> SaveChangesAsync(bool acceptAllChangesOnSuccess, CancellationToken cancellationToken = default)
+    {
+        StoreChangesInOperationsQueue();
+        return base.SaveChangesAsync(acceptAllChangesOnSuccess, cancellationToken);
+    }
+
+    /// <summary>
+    /// When <see cref="SaveChanges(bool)"/> or the async equivalent is called, this method looks through the changes
+    /// to see if any should be pushed to the service.  An <see cref="OfflineQueueEntity"/> is created for each change.
+    /// </summary>
+    /// <remarks>
+    /// Every offline-capable entity must be derived from OfflineClientData and have a <see cref="DbSet{TEntity}"/> that
+    /// is using the entity.
+    /// </remarks>
+    internal void StoreChangesInOperationsQueue()
+    {
+        ChangeTracker.DetectChanges();
+        List<EntityEntry> changedEntities = ChangeTracker.Entries().Where(t => t.State is EntityState.Added or EntityState.Deleted or EntityState.Modified).ToList();
+        foreach (EntityEntry entry in changedEntities)
+        {
+            StoreChangeInOperationsQueue(entry);
+        }
+    }
+
+    /// <summary>
+    /// When <see cref="SaveChanges(bool)"/> or the async equivalent is called, this method is used to add the entry via
+    /// the operations queue manager.  An <see cref="OfflineQueueEntity"/> is created for each change.
+    /// </summary>
+    /// <remarks>
+    /// Every offline-capable entity must be derived from OfflineClientData and have a <see cref="DbSet{TEntity}"/> that
+    /// is using the entity.
+    /// </remarks>
+    internal void StoreChangeInOperationsQueue(EntityEntry entry)
+    {
+        if (entry.Entity is OfflineClientEntity)
+        {
+            switch (entry.State)
+            {
+                case EntityState.Added:
+                    OperationsQueueManager.AddCreateOperation(entry);
+                    break;
+                case EntityState.Deleted:
+                    OperationsQueueManager.AddDeleteOperation(entry);
+                    break;
+                case EntityState.Modified:
+                    OperationsQueueManager.AddUpdateOperation(entry);
+                    break;
+                default:
+                    throw new InvalidOperationException("Unknown entity state");
+            }
+        }
+    }
+}

src/CommunityToolkit.Datasync.Client/Offline/OfflineQueueEntity.cs

@@ -0,0 +1,75 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using Microsoft.EntityFrameworkCore;
+using System.ComponentModel.DataAnnotations;
+using System.ComponentModel.DataAnnotations.Schema;
+
+namespace CommunityToolkit.Datasync.Client.Offline;
+
+/// <summary>
+/// The potential change types that can be recorded in the <see cref="OfflineQueueEntity"/>.
+/// </summary>
+public enum EntityChangeType
+{
+    /// <summary>
+    /// The change type is unknown (and hence skipped - this is always an error).
+    /// </summary>
+    Unknown,
+
+    /// <summary>
+    /// The entity is being added.
+    /// </summary>
+    Add,
+
+    /// <summary>
+    /// The entity is to be deleted.
+    /// </summary>
+    Delete,
+
+    /// <summary>
+    /// The entity is being updated.
+    /// </summary>
+    Update
+}
+
+/// <summary>
+/// When an entity is modified while offline, the changes are stored in the <see cref="OfflineDbContext"/>
+/// in an operations queue.  This entity is used to record what changes are pending push to the server.
+/// </summary>
+[Table("__datasync_opsqueue")]
+[Index(nameof(EntityName))]
+public sealed class OfflineQueueEntity
+{
+    /// <summary>
+    /// The globally unique ID for the change.
+    /// </summary>
+    [Key]
+    public string Id { get; set; } = Guid.NewGuid().ToString("N");
+
+    /// <summary>
+    /// The type of the change (Add,  Delete, or Update).
+    /// </summary>
+    public EntityChangeType ChangeType { get; set; } = EntityChangeType.Unknown;
+
+    /// <summary>
+    /// The name of the entity or table that is being modified.
+    /// </summary>
+    public string EntityName { get; set; } = string.Empty;
+
+    /// <summary>
+    /// The ID of the entity that is being modified.
+    /// </summary>
+    public string EntityId { get; set; } = string.Empty;
+
+    /// <summary>
+    /// The replacement version of the entity that is being modified.
+    /// </summary>
+    public string ReplacementJsonEntityData { get; set; } = string.Empty;
+
+    /// <summary>
+    /// The original version of the entity that is being modified.
+    /// </summary>
+    public string OriginalJsonEntityEntity { get; set; } = string.Empty;
+}