Basic functioning workflow engine

.editorconfig

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.gitignore

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+#Ignore thumbnails created by Windows
+Thumbs.db
+
+#Ignore files built by Visual Studio
+*.obj
+*.exe
+*.pdb
+*.user
+*.aps
+*.pch
+*.vspscc
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+[Dd]ebug*/
+*.lib
+*.sbr
+obj/
+[Rr]elease*/
+_ReSharper*/
+[Tt]est[Rr]esult*
+.vs/
+
+#Nuget packages folder
+packages/
+
+#Ignore git-related files
+*.orig
+
+#Rider
+.idea

Flowsharp.sln

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src/Flowsharp.Abstractions/Activities/Activity.cs

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+using System.Collections.Generic;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
+using Flowsharp.ActivityResults;
+using Flowsharp.Models;
+using Microsoft.Extensions.Localization;
+
+namespace Flowsharp.Activities
+{
+    public abstract class Activity : IActivity
+    {
+        public virtual string Name => GetType().Name;
+
+        public Task ProvideMetadataAsync(ActivityMetadataContext context, CancellationToken cancellationToken)
+        {
+            ProvideMetadata(context);
+            return Task.CompletedTask;
+        }
+
+        public virtual Task<bool> CanExecuteAsync(WorkflowExecutionContext workflowContext, ActivityExecutionContext activityContext, CancellationToken cancellationToken)
+        {
+            return Task.FromResult(true);
+        }
+
+        public virtual Task<ActivityExecutionResult> ExecuteAsync(WorkflowExecutionContext workflowContext, ActivityExecutionContext activityContext, CancellationToken cancellationToken)
+        {
+            return Task.FromResult(Execute(workflowContext, activityContext));
+        }
+
+        public virtual Task<ActivityExecutionResult> ResumeAsync(WorkflowExecutionContext workflowContext, ActivityExecutionContext activityContext, CancellationToken cancellationToken)
+        {
+            return Task.FromResult(Resume(workflowContext, activityContext));
+        }
+
+        public virtual IEnumerable<Outcome> GetOutcomes(WorkflowExecutionContext workflowContext, ActivityExecutionContext activityContext)
+        {
+            return Enumerable.Empty<Outcome>();
+        }
+
+        public virtual Task OnActivityExecutedAsync(WorkflowExecutionContext workflowContext, ActivityExecutionContext activityContext, CancellationToken cancellationToken)
+        {
+            OnActivityExecuted(workflowContext, activityContext);
+            return Task.CompletedTask;
+        }
+
+        public virtual Task OnActivityExecutingAsync(WorkflowExecutionContext workflowContext, ActivityExecutionContext activityContext, CancellationToken cancellationToken)
+        {
+            OnActivityExecuting(workflowContext, activityContext);
+            return  Task.CompletedTask;    
+        }
+
+        public virtual Task ReceiveInputAsync(WorkflowExecutionContext workflowContext, IDictionary<string, object> input, CancellationToken cancellationToken)
+        {
+            ReceiveInput(workflowContext, input);
+            return Task.CompletedTask;
+        }
+
+        public virtual Task WorkflowResumedAsync(WorkflowExecutionContext workflowContext, CancellationToken cancellationToken)
+        {
+            WorkflowResumed(workflowContext);
+            return Task.CompletedTask;
+        }
+
+        public virtual Task WorkflowResumingAsync(WorkflowExecutionContext workflowContext, CancellationToken cancellationToken)
+        {
+            WorkflowResuming(workflowContext);
+            return Task.CompletedTask;
+        }
+
+        public virtual Task WorkflowStartedAsync(WorkflowExecutionContext workflowContext, CancellationToken cancellationToken)
+        {
+            WorkflowStarted(workflowContext);
+            return Task.CompletedTask;
+        }
+
+        public virtual Task WorkflowStartingAsync(WorkflowExecutionContext workflowContext, CancellationToken cancellationToken)
+        {
+            WorkflowStarting(workflowContext);
+            return Task.CompletedTask;
+        }
+
+        protected virtual void ProvideMetadata(ActivityMetadataContext context)
+        {
+        }
+
+        protected virtual ActivityExecutionResult Execute(WorkflowExecutionContext workflowContext, ActivityExecutionContext activityContext)
+        {
+            return Noop();
+        }
+
+        protected virtual ActivityExecutionResult Resume(WorkflowExecutionContext workflowContext, ActivityExecutionContext activityContext)
+        {
+            return Noop();
+        }
+
+        protected virtual void OnActivityExecuted(WorkflowExecutionContext workflowContext, ActivityExecutionContext activityContext) {}
+        protected virtual void OnActivityExecuting(WorkflowExecutionContext workflowContext, ActivityExecutionContext activityContext) {}
+        protected virtual void ReceiveInput(WorkflowExecutionContext workflowContext, IDictionary<string, object> input) {}
+        protected virtual void WorkflowResumed(WorkflowExecutionContext workflowContext) {}
+        protected virtual void WorkflowResuming(WorkflowExecutionContext workflowContext) {}
+        protected virtual void WorkflowStarted(WorkflowExecutionContext workflowContext) {}
+        protected virtual void WorkflowStarting(WorkflowExecutionContext workflowContext) {}
+
+        protected IEnumerable<Outcome> Outcomes(params LocalizedString[] names)
+        {
+            return names.Select(x => new Outcome(x));
+        }
+
+        protected IEnumerable<Outcome> Outcomes(IEnumerable<LocalizedString> names)
+        {
+            return names.Select(x => new Outcome(x));
+        }
+
+        protected ActivityExecutionResult Outcomes(params string[] names)
+        {
+            return Outcomes((IEnumerable<string>)names);
+        }
+
+        protected ActivityExecutionResult Outcomes(IEnumerable<string> names)
+        {
+            return new OutcomeResult(names);
+        }
+
+        protected ActivityExecutionResult Halt()
+        {
+            return new HaltResult();
+        }
+
+        protected ActivityExecutionResult Noop()
+        {
+            return new NoopResult();
+        }
+    }
+}

src/Flowsharp.Abstractions/Activities/IActivity.cs

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+using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
+using Flowsharp.ActivityResults;
+using Flowsharp.Models;
+
+namespace Flowsharp.Activities
+{
+    public interface IActivity
+    {
+        /// <summary>
+        /// The system name of the activity.
+        /// </summary>
+        /// <remarks>The Name is used to identify a given activity type and must be unique.</remarks>
+        string Name { get; }
+
+        /// <summary>
+        /// Provides metadata about the specified activity.
+        /// </summary>
+        Task ProvideMetadataAsync(ActivityMetadataContext context, CancellationToken cancellationToken);
+
+        /// <summary>
+        /// Returns a list of possible outcomes when the activity is executed.
+        /// </summary>
+        IEnumerable<Outcome> GetOutcomes(WorkflowExecutionContext workflowContext, ActivityExecutionContext activityContext);
+
+        /// <summary>
+        /// Returns a value of whether the specified activity can execute.
+        /// </summary>
+        Task<bool> CanExecuteAsync(WorkflowExecutionContext workflowContext, ActivityExecutionContext activityContext, CancellationToken cancellationToken);
+
+        /// <summary>
+        /// Executes the specified activity.
+        /// </summary>
+        Task<ActivityExecutionResult> ExecuteAsync(WorkflowExecutionContext workflowContext, ActivityExecutionContext activityContext, CancellationToken cancellationToken);
+
+        /// <summary>
+        /// Resumes the specified activity.
+        /// </summary>
+        Task<ActivityExecutionResult> ResumeAsync(WorkflowExecutionContext workflowContext, ActivityExecutionContext activityContext, CancellationToken cancellationToken);
+
+        /// <summary>
+        /// Executes before a workflow starts or resumes, giving activities an opportunity to read and store any values of interest.
+        /// </summary>
+        Task ReceiveInputAsync(WorkflowExecutionContext workflowContext, IDictionary<string, object> input, CancellationToken cancellationToken);
+
+        /// <summary>
+        /// Executes when a workflow is about to start.
+        /// </summary>
+        Task WorkflowStartingAsync(WorkflowExecutionContext workflowContext, CancellationToken cancellationToken);
+
+        /// <summary>
+        /// Executes when a workflow has started.
+        /// </summary>
+        Task WorkflowStartedAsync(WorkflowExecutionContext context, CancellationToken cancellationToken);
+
+        /// <summary>
+        /// Executes when a workflow is about to be resumed.
+        /// </summary>
+        Task WorkflowResumingAsync(WorkflowExecutionContext context, CancellationToken cancellationToken);
+
+        /// <summary>
+        /// Executes when a workflow is resumed.
+        /// </summary>
+        Task WorkflowResumedAsync(WorkflowExecutionContext context, CancellationToken cancellationToken);
+
+        /// <summary>
+        /// Executes when an activity is about to be executed.
+        /// </summary>
+        /// <param name="workflowContext">The workflow execution context.</param>
+        /// <param name="activityContext">The activity context containing the activity that is the subject of the event.</param>
+        /// <param name="cancellationToken">The cancellation token.</param>
+        Task OnActivityExecutingAsync(WorkflowExecutionContext workflowContext, ActivityExecutionContext activityContext, CancellationToken cancellationToken = default(CancellationToken));
+
+        /// <summary>
+        /// Called on each activity when an activity has been executed.
+        /// </summary>
+        /// <param name="workflowContext">The workflow execution context.</param>
+        /// <param name="activityContext">The activity context containing the activity that is the subject of the event.</param>
+        /// <param name="cancellationToken">The cancellation token.</param>
+        Task OnActivityExecutedAsync(WorkflowExecutionContext workflowContext, ActivityExecutionContext activityContext, CancellationToken cancellationToken);
+    }
+}

src/Flowsharp.Abstractions/ActivityProviders/TypedActivityProvider.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
+using Flowsharp.Activities;
+using Flowsharp.Descriptors;
+using Flowsharp.Services;
+
+namespace Flowsharp.ActivityProviders
+{
+    /// <summary>
+    /// Provides activities based on <see cref="IActivity"/> implementations that have been registered with the service container.
+    /// </summary>
+    public class TypedActivityProvider : IActivityProvider
+    {
+        private readonly Func<IEnumerable<IActivity>> _activitiesFactory;
+
+        public TypedActivityProvider(Func<IEnumerable<IActivity>> activitiesFactory)
+        {
+            _activitiesFactory = activitiesFactory;
+        }
+
+        public Task<IEnumerable<ActivityDescriptor>> GetActivityDescriptorsAsync(CancellationToken cancellationToken)
+        {
+            return Task.FromResult(_activitiesFactory().Select(ToDescriptor));
+        }
+
+        private ActivityDescriptor ToDescriptor(IActivity activity)
+        {
+            return new ActivityDescriptor
+            {
+                Name =  activity.Name,
+                GetMetadataAsync = activity.ProvideMetadataAsync,
+                CanExecuteAsync = activity.CanExecuteAsync,
+                GetOutcomes = activity.GetOutcomes,
+                ExecuteActivityAsync = activity.ExecuteAsync,
+                ResumeActivityAsync = activity.ResumeAsync,
+                ReceiveInputAsync = activity.ReceiveInputAsync,
+                WorkflowResumedAsync = activity.WorkflowResumedAsync,
+                WorkflowResumingAsync = activity.WorkflowResumingAsync,
+                WorkflowStartedAsync = activity.WorkflowStartedAsync,
+                WorkflowStartingAsync = activity.WorkflowStartingAsync,
+                OnActivityExecutedAsync = activity.OnActivityExecutedAsync,
+                OnActivityExecutingAsync = activity.OnActivityExecutingAsync
+            };
+        }
+    }
+}