Add Mediator pattern via request objects

Author: jviau

src/Abstractions/ActivityRequest.cs

@@ -0,0 +1,82 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+namespace Microsoft.DurableTask;
+
+/// <summary>
+/// Represents the base request to run a <see cref="ITaskActivity" />.
+/// </summary>
+public interface IBaseActivityRequest
+{
+    /// <summary>
+    /// Gets the <see cref="TaskName" /> representing the <see cref="ITaskActivity" /> to run.
+    /// </summary>
+    /// <returns>A <see cref="TaskName" />.</returns>
+    /// <remarks>
+    /// This is a function instead of a property so it is excluded in serialization without needing to use a
+    /// serialization library specific attribute to exclude it.
+    /// </remarks>
+    TaskName GetTaskName();
+}
+
+/// <summary>
+/// Represents a request to run a <see cref="ITaskActivity" /> which returns <typeparamref name="TResult" />.
+/// </summary>
+/// <typeparam name="TResult">The result of the orchestrator that is to be ran.</typeparam>
+public interface IActivityRequest<out TResult> : IBaseActivityRequest
+{
+}
+
+/// <summary>
+/// Represents a request to run a <see cref="ITaskActivity" /> which has no return.
+/// </summary>
+public interface IActivityRequest : IActivityRequest<Unit>
+{
+}
+
+/// <summary>
+/// Helpers for creating activity requests.
+/// </summary>
+public static class ActivityRequest
+{
+    /// <summary>
+    /// Gets an <see cref="IActivityRequest{TResult}" /> which has an explicitly provided input.
+    /// </summary>
+    /// <remarks>
+    /// This is useful when you want to use an existing type for input (like <see cref="string" />) and not derive an
+    /// entirely new type.
+    /// </remarks>
+    /// <typeparam name="TResult">The result type of the activity.</typeparam>
+    /// <param name="name">The name of the activity to run.</param>
+    /// <param name="input">The input for the activity.</param>
+    /// <returns>A request that can be used to enqueue an activity.</returns>
+    public static IActivityRequest<TResult> Create<TResult>(TaskName name, object? input = null)
+        => new Request<TResult>(name, input);
+
+    /// <summary>
+    /// Represents an activity request where the input is not the request itself.
+    /// </summary>
+    /// <typeparam name="TResult">The result type.</typeparam>
+    class Request<TResult> : IActivityRequest<TResult>, IProvidesInput
+    {
+        readonly TaskName name;
+        readonly object? input;
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="Request{TResult}"/> class.
+        /// </summary>
+        /// <param name="name">The task name.</param>
+        /// <param name="input">The input.</param>
+        public Request(TaskName name, object? input)
+        {
+            this.name = name;
+            this.input = input;
+        }
+
+        /// <inheritdoc/>
+        public object? GetInput() => this.input;
+
+        /// <inheritdoc/>
+        public TaskName GetTaskName() => this.name;
+    }
+}

src/Abstractions/IProvidesInput.cs

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+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+namespace Microsoft.DurableTask;
+
+/// <summary>
+/// Contract for providing input to an orchestration or activity.
+/// </summary>
+interface IProvidesInput
+{
+    /// <summary>
+    /// Gets the input for the orchestration or activity.
+    /// </summary>
+    /// <returns>The input value.</returns>
+    /// <remarks>
+    /// This is a method and not a property to ensure it is not included in serialization.
+    /// </remarks>
+    object? GetInput();
+}

src/Abstractions/Mediator/IOrchestrationRequest.cs

@@ -0,0 +1,82 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+namespace Microsoft.DurableTask;
+
+/// <summary>
+/// Represents the base request to run a <see cref="ITaskOrchestrator" />.
+/// </summary>
+public interface IBaseOrchestrationRequest
+{
+    /// <summary>
+    /// Gets the <see cref="TaskName" /> representing the <see cref="ITaskOrchestrator" /> to run.
+    /// </summary>
+    /// <returns>A <see cref="TaskName" />.</returns>
+    /// <remarks>
+    /// This is a function instead of a property so it is excluded in serialization without needing to use a
+    /// serialization library specific attribute to exclude it.
+    /// </remarks>
+    TaskName GetTaskName();
+}
+
+/// <summary>
+/// Represents a request to run a <see cref="ITaskOrchestrator" /> which returns <typeparamref name="TResult" />.
+/// </summary>
+/// <typeparam name="TResult">The result of the orchestrator that is to be ran.</typeparam>
+public interface IOrchestrationRequest<out TResult> : IBaseOrchestrationRequest
+{
+}
+
+/// <summary>
+/// Represents a request to run a <see cref="ITaskOrchestrator" /> which has no return.
+/// </summary>
+public interface IOrchestrationRequest : IOrchestrationRequest<Unit>
+{
+}
+
+/// <summary>
+/// Helpers for creating orchestration requests.
+/// </summary>
+public static class OrchestrationRequest
+{
+    /// <summary>
+    /// Gets an <see cref="IOrchestrationRequest{TResult}" /> which has an explicitly provided input.
+    /// </summary>
+    /// <remarks>
+    /// This is useful when you want to use an existing type for input (like <see cref="string" />) and not derive an
+    /// entirely new type.
+    /// </remarks>
+    /// <typeparam name="TResult">The result type of the orchestration.</typeparam>
+    /// <param name="name">The name of the orchestration to run.</param>
+    /// <param name="input">The input for the orchestration.</param>
+    /// <returns>A request that can be used to enqueue an orchestration.</returns>
+    public static IOrchestrationRequest<TResult> Create<TResult>(TaskName name, object? input = null)
+        => new Request<TResult>(name, input);
+
+    /// <summary>
+    /// Represents an orchestration request where the input is not the request itself.
+    /// </summary>
+    /// <typeparam name="TResult">The result type.</typeparam>
+    class Request<TResult> : IOrchestrationRequest<TResult>, IProvidesInput
+    {
+        readonly TaskName name;
+        readonly object? input;
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="Request{TResult}"/> class.
+        /// </summary>
+        /// <param name="name">The task name.</param>
+        /// <param name="input">The input.</param>
+        public Request(TaskName name, object? input)
+        {
+            this.name = name;
+            this.input = input;
+        }
+
+        /// <inheritdoc/>
+        public object? GetInput() => this.input;
+
+        /// <inheritdoc/>
+        public TaskName GetTaskName() => this.name;
+    }
+}