// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.

using System.Linq;
using System.Runtime.CompilerServices;

namespace System.Web.Http
{
    /// <summary>
    /// Represents an <see cref="IQueryable"/> containing zero or one entities. Use together with an
    /// <c>[EnableQuery]</c> from the System.Web.Http.OData or System.Web.OData namespace.
    /// </summary>
    [TypeForwardedFrom("System.Web.Http.OData, Version=5.1.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35")]
    public abstract class SingleResult
    {
        /// <summary>
        /// Initializes a new instance of the <see cref="SingleResult"/> class.
        /// </summary>
        /// <param name="queryable">The <see cref="IQueryable"/> containing zero or one entities.</param>
        protected SingleResult(IQueryable queryable)
        {
            if (queryable == null)
            {
                throw Error.ArgumentNull("queryable");
            }

            Queryable = queryable;
        }

        /// <summary>
        /// The <see cref="IQueryable"/> containing zero or one entities.
        /// </summary>
        public IQueryable Queryable { get; private set; }

        /// <summary>
        /// Creates a <see cref="SingleResult{T}"/> from an <see cref="IQueryable{T}"/>. A helper method to instantiate
        /// a <see cref="SingleResult{T}"/> object without having to explicitly specify the type
        /// <typeparamref name="T"/>.
        /// </summary>
        /// <typeparam name="T">The type of the data in the data source.</typeparam>
        /// <param name="queryable">The <see cref="IQueryable{T}"/> containing zero or one entities.</param>
        /// <returns>The created <see cref="SingleResult{T}"/>.</returns>
        public static SingleResult<T> Create<T>(IQueryable<T> queryable)
        {
            return new SingleResult<T>(queryable);
        }
    }
}