Connected.Common.Types/Common.Types/TaxRates/TaxRateOps.cs

using System.Collections.Immutable;
using Connected.Entities;
using Connected.Entities.Storage;
using Connected.Notifications.Events;
using Connected.ServiceModel;
using Connected.Services;

namespace Common.Types.TaxRates;

internal class TaxRateOps
{
	/// <summary>
	/// Queries all <see cref="ITaxRate"/> records.
	/// </summary>
	internal sealed class Query : ServiceFunction<QueryArgs, ImmutableList<ITaxRate>?>
	{
		/// <summary>
		/// Creates a new instance of the <see cref="Query"/> class.
		/// </summary>
		/// <param name="cache">The cache where the records are stored.</param>
		public Query(ITaxRateCache cache, IStorageProvider storage)
		{
			Cache = cache;
			Storage = storage;
		}

		private ITaxRateCache Cache { get; }
		public IStorageProvider Storage { get; }

		protected override async Task<ImmutableList<ITaxRate>?> OnInvoke()
		{
			var r = await (from dc in Storage.Open<TaxRate>() select dc).WithArguments(Arguments).AsEntities<ITaxRate>();
			/*
			 * We simply return all records that exist in the system.
			 */
			return await (from dc in Cache select dc).WithArguments(Arguments).AsEntities<ITaxRate>();
		}
	}

	/// <summary>
	/// Returns <see cref="ITaxRate"/> with the specified id or null
	/// if the record for the specified id does not exist.
	/// </summary>
	internal sealed class Select : ServiceFunction<PrimaryKeyArgs<int>, ITaxRate?>
	{
		public Select(ITaxRateCache cache)
		{
			Cache = cache;
		}

		private ITaxRateCache Cache { get; }

		protected override async Task<ITaxRate?> OnInvoke()
		{
			/*
			 * Filter cache by the id.
			 */

			return await (from dc in Cache where dc.Id == Arguments.Id select dc).AsEntity();
		}
	}
	/// <summary>
	/// Returns <see cref="ITaxRate"/> with the specified name and rate or null if
	/// the record with the specified arguments does not exist.
	/// </summary>
	internal sealed class SelectByRate : ServiceFunction<TaxRateArgs, ITaxRate?>
	{
		public SelectByRate(ITaxRateCache cache)
		{
			Cache = cache;
		}

		private ITaxRateCache Cache { get; }
		protected override async Task<ITaxRate?> OnInvoke()
		{
			return await (from dc in Cache
						  where string.Equals(dc.Name, Arguments.Name, StringComparison.OrdinalIgnoreCase) && dc.Rate == Arguments.Rate
						  select dc).AsEntity();
		}
	}
	/// <summary>
	/// Returns List of <see cref="ITaxRate"/> for the specified set of ids. Use this method when joining data
	/// to other entities.
	/// </summary>
	internal sealed class Lookup : ServiceFunction<PrimaryKeyListArgs<int>, ImmutableList<ITaxRate>?>
	{
		public Lookup(ITaxRateCache cache)
		{
			Cache = cache;
		}

		private ITaxRateCache Cache { get; }
		protected override async Task<ImmutableList<ITaxRate>?> OnInvoke()
		{
			/*
			 * Use simple linq join for the specified set of ids.
			 */
			return await (from dc in Cache where Arguments.IdList.Contains(dc.Id) select dc).AsEntities<ITaxRate>();
		}
	}
	/// <summary>
	/// Inserts a new <see cref="ITaxRate"/> and returns its Id.
	/// </summary>
	internal sealed class Insert : ServiceFunction<InsertTaxRateArgs, int>
	{
		public Insert(ITaxRateService taxRateService, IStorageProvider storage, IEventService events, ITaxRateCache cache)
		{
			TaxRateService = taxRateService;
			Storage = storage;
			Events = events;
			Cache = cache;
		}
		private ITaxRateService TaxRateService { get; }
		private IStorageProvider Storage { get; }
		private IEventService Events { get; }
		private ITaxRateCache Cache { get; }

		protected override async Task<int> OnInvoke()
		{
			/*
			 * First, create a new entity from the passed arguments and mark its state as new. This will
			 * signal the DatabaseContext to perform an insert operation when calling the Update.
			 */
			var entity = Arguments.AsEntity<TaxRate>(State.New);
			/*
			 * Call update on the DatabaseContext. This call will return a new ITaxRate of the inserted
			 * entity.
			 */
			return (await Storage.Open<TaxRate>().Update(entity)).Id;
		}

		protected override async Task OnCommitted()
		{
			/*
			 * At this stage, the transaction has been commited which means
			 * record is definitely permanently stored in the database.
			 * We are making a simple call to the cache to refresh the item with the
			 * new id. Cache will query a database for new record and will store it 
			 * in memory.
			 */
			await Cache.Refresh(Result);
			/*
			 * Now trigger the inserted event which will notify all components hooked in the
			 * same process, out of process scale out instances and clients (wasm).
			 */
			await Events.Enqueue(this, TaxRateService, ServiceEvents.Inserted, Result);
		}
	}
	/// <summary>
	/// Permanently deletes a <see cref="ITaxRate"/> from the system.
	/// </summary>
	/// <remarks>
	/// This method gets called after all <see cref="Server.Data.DataProtection.IDataProtectionMiddleware{TArgs}"/>
	/// middleware passed successfuly.
	/// </remarks>
	internal sealed class Delete : ServiceAction<PrimaryKeyArgs<int>>
	{
		public Delete(ITaxRateService taxRateService, IStorageProvider storage, ITaxRateCache cache, IEventService events)
		{
			TaxRateService = taxRateService;
			Storage = storage;
			Cache = cache;
			Events = events;
		}

		private ITaxRateService TaxRateService { get; }
		private IStorageProvider Storage { get; }
		private ITaxRateCache Cache { get; }
		private IEventService Events { get; }

		protected override async Task OnInvoke()
		{
			/*
			 * we don't need a reference to a record here because delete uses only
			 * an id. The overhead would only occur in cases if the record wouldn't exist
			 * but this is not the job of the operation. The Validators should theoretically 
			 * reject such an operation.
			 */
			await Storage.Open<TaxRate>().Update(new TaxRate { Id = Arguments.Id, State = State.Deleted });
		}

		protected override async Task OnCommitted()
		{
			/*
			 * Once all the transactions have been commited remove the non existing record
			 * from the cache.
			 */
			await Cache.Remove(Arguments.Id);
			/*
			 * And notify audience about the event.
			 */
			await Events.Enqueue(this, TaxRateService, ServiceEvents.Deleted, Arguments.Id);
		}
	}
	/// <summary>
	/// Updates the <see cref="ITaxRate"/> entity.
	/// </summary>
	internal sealed class Update : ServiceAction<UpdateTaxRateArgs>
	{
		public Update(ITaxRateService taxRateService, IStorageProvider storage, ITaxRateCache cache, IEventService events)
		{
			TaxRateService = taxRateService;
			Storage = storage;
			Cache = cache;
			Events = events;
		}

		private IStorageProvider Storage { get; }
		private ITaxRateCache Cache { get; }
		private IEventService Events { get; }
		private ITaxRateService TaxRateService { get; }

		protected override async Task OnInvoke()
		{
			/*
			 * TaxRate is concurrency entity which means the platform takes care of
			 * data consistency. Data consistency means we can't overwrite updates made
			 * by others.
			 * Updating Concurrency entity thus requires a bit more logic. We must use a retry logic 
			 * in case of Concurrency failure. We'll call Update method with reload lambda function.
			 */
			var entity = SetState(await Load());

			await Storage.Open<TaxRate>().Update(entity, Arguments, async () =>
			{
				/*
				 * The concurrency exception occured.
				 * Refresh the entry from the cache. This will load a new version from 
				 * a database.
				 */
				await Cache.Refresh(Arguments.Id);

				return SetState(await Load());
			});
		}

		private async Task<TaxRate?> Load() => await (from dc in Cache where dc.Id == Arguments.Id select dc).AsEntity();

		protected override async Task OnCommitted()
		{
			/*
			 * Once the update is complete refresh the cache because the database assigned a new timestamp
			 * to an entity and any sunsequent update would fail anyway.
			 */
			await Cache.Refresh(Arguments.Id);
			/*
			 * Now trigger the distributed event notifying the update has completed. 
			 */
			await Events.Enqueue(this, TaxRateService, ServiceEvents.Updated, Arguments.Id);
		}
	}
}