using Common.Distributed;
using Connected;
using Connected.Interop;
using Connected.ServiceModel;
using Connected.Threading;

namespace Common.Documents;
internal sealed class DocumentLocker<TDocument, TPrimaryKey> : IDocumentLocker<TDocument, TPrimaryKey>
	where TDocument : IDocument<TPrimaryKey>
	where TPrimaryKey : notnull

{
	public event EventHandler? Expired;
	public DocumentLocker(IDistributedLockService locking)
	{
		Locking = locking;
		Cancel = new();
	}

	private bool IsDisposed { get; set; }
	public Guid Key { get; private set; }
	private IDistributedLockService Locking { get; }

	public TimeSpan LockTimeout { get; set; } = TimeSpan.FromSeconds(2);
	public TimeSpan Timeout { get; set; } = TimeSpan.FromMilliseconds(1500);
	public TimeSpan Lifetime { get; set; } = TimeSpan.FromSeconds(30);
	private CancellationTokenSource Cancel { get; }
	public async Task Lock(TDocument document)
	{
		var id = TypeConversion.Convert<string>(document.Id);

		if (string.IsNullOrEmpty(id))
			throw new NullReferenceException(nameof(document.Id));
		/*
		 * Obtain the lock on the document to ensure no other process
		 * will change it while we are updating the stock. If the lock
		 * could not be obtained the exception will be thrown.
		 */
		Key = await Locking.Lock(new DistributedLockArgs
		{
			Duration = LockTimeout,
			Entity = typeof(TDocument).Name,
			EntityId = id
		});
		/*
		 * Make sure we don't get outdated by using the scheduled
		 * task which will ping the lock before it expires.
		 */
		using var timeout = new ScheduledTask(async () =>
		{
			await Locking.Ping(new DistributedLockPingArgs
			{
				Id = Key,
				Duration = LockTimeout
			});
		}, async () =>
		{
			await Unlock();

			Expired?.Invoke(this, EventArgs.Empty);
		}, Timeout, Lifetime, Cancel.Token);

		timeout.Start();
	}

	public async Task Unlock()
	{
		/*
		 * Finally release the lock on the document so it becomes
		 * updatable again.
		 */
		await Locking.Unlock(new PrimaryKeyArgs<Guid> { Id = Key });
	}

	private void Dispose(bool disposing)
	{
		if (!IsDisposed)
		{
			if (disposing)
			{
				AsyncUtils.RunSync(Unlock);

				Cancel.Cancel();
				Cancel.Dispose();
			}

			IsDisposed = true;
		}
	}

	public void Dispose()
	{
		Dispose(true);
		GC.SuppressFinalize(this);
	}
}