using System.Collections;
using System.Linq.Expressions;

namespace Connected.Expressions.Query;

internal sealed class EntityQuery<TEntity> : IQueryable<TEntity>, IAsyncEnumerable<TEntity>, IOrderedQueryable<TEntity>
{
	public EntityQuery(IQueryProvider provider, Expression expression)
	{
		Provider = provider;
		Expression = expression;
	}

	public Type ElementType => typeof(TEntity);

	public Expression Expression { get; }

	public IQueryProvider Provider { get; }

	public async IAsyncEnumerator<TEntity> GetAsyncEnumerator(CancellationToken cancellationToken = default)
	{
		var result = Provider.Execute(Expression);

		if (result is IEnumerable en)
		{
			var enumerator = en.GetEnumerator();

			while (enumerator.MoveNext())
			{
				await Task.CompletedTask;

				yield return (TEntity)enumerator.Current;
			}
		}
	}

	public IEnumerator<TEntity> GetEnumerator()
	{
		return ((IEnumerable<TEntity>)Provider.Execute(Expression)).GetEnumerator();
	}

	IEnumerator IEnumerable.GetEnumerator()
	{
		return ((IEnumerable)Provider.Execute(Expression)).GetEnumerator();
	}
}