// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc.Core;
using Microsoft.AspNetCore.Mvc.Infrastructure;

namespace Microsoft.AspNetCore.Mvc
{
    /// <summary>
    /// A type that wraps either an <typeparamref name="TValue"/> instance or an <see cref="ActionResult"/>.
    /// </summary>
    /// <typeparam name="TValue">The type of the result.</typeparam>
    public sealed class ActionResult<TValue> : IConvertToActionResult
    {
        private const int DefaultStatusCode = StatusCodes.Status200OK;

        /// <summary>
        /// Initializes a new instance of <see cref="ActionResult{TValue}"/> using the specified <paramref name="value"/>.
        /// </summary>
        /// <param name="value">The value.</param>
        public ActionResult(TValue value)
        {
            if (typeof(IActionResult).IsAssignableFrom(typeof(TValue)))
            {
                var error = Resources.FormatInvalidTypeTForActionResultOfT(typeof(TValue), "ActionResult<T>");
                throw new ArgumentException(error);
            }

            Value = value;
        }

        /// <summary>
        /// Initializes a new instance of <see cref="ActionResult{TValue}"/> using the specified <see cref="ActionResult"/>.
        /// </summary>
        /// <param name="result">The <see cref="ActionResult"/>.</param>
        public ActionResult(ActionResult result)
        {
            if (typeof(IActionResult).IsAssignableFrom(typeof(TValue)))
            {
                var error = Resources.FormatInvalidTypeTForActionResultOfT(typeof(TValue), "ActionResult<T>");
                throw new ArgumentException(error);
            }

            Result = result ?? throw new ArgumentNullException(nameof(result));
        }

        /// <summary>
        /// Gets the <see cref="ActionResult"/>.
        /// </summary>
        public ActionResult? Result { get; }

        /// <summary>
        /// Gets the value.
        /// </summary>
        public TValue? Value { get; }

        /// <summary>
        /// Implicitly converts the specified <paramref name="value"/> to an <see cref="ActionResult{TValue}"/>.
        /// </summary>
        /// <param name="value">The value to convert.</param>
        public static implicit operator ActionResult<TValue>(TValue value)
        {
            return new ActionResult<TValue>(value);
        }

        /// <summary>
        /// Implicitly converts the specified <paramref name="result"/> to an <see cref="ActionResult{TValue}"/>.
        /// </summary>
        /// <param name="result">The <see cref="ActionResult"/>.</param>
        public static implicit operator ActionResult<TValue>(ActionResult result)
        {
            return new ActionResult<TValue>(result);
        }

        IActionResult IConvertToActionResult.Convert()
        {
            if (Result != null)
            {
                return Result;
            }

            int statusCode;
            if (Value is ProblemDetails problemDetails && problemDetails.Status != null)
            {
                statusCode = problemDetails.Status.Value;
            }
            else
            {
                statusCode = DefaultStatusCode;
            }

            return new ObjectResult(Value)
            {
                DeclaredType = typeof(TValue),
                StatusCode = statusCode
            };
        }
    }
}
