// Copyright (c) Microsoft Corporation. All rights reserved. See License.txt in the project root for license information.

namespace System.Web.Mvc
{
    public class HttpPostedFileBaseModelBinder : IModelBinder
    {
        public object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
        {
            if (controllerContext == null)
            {
                throw new ArgumentNullException("controllerContext");
            }
            if (bindingContext == null)
            {
                throw new ArgumentNullException("bindingContext");
            }

            HttpPostedFileBase theFile = controllerContext.HttpContext.Request.Files[bindingContext.ModelName];
            return ChooseFileOrNull(theFile);
        }

        // helper that returns the original file if there was content uploaded, null if empty
        internal static HttpPostedFileBase ChooseFileOrNull(HttpPostedFileBase rawFile)
        {
            // case 1: there was no <input type="file" ... /> element in the post
            if (rawFile == null)
            {
                return null;
            }

            // case 2: there was an <input type="file" ... /> element in the post, but it was left blank
            if (rawFile.ContentLength == 0 && String.IsNullOrEmpty(rawFile.FileName))
            {
                return null;
            }

            // case 3: the file was posted
            return rawFile;
        }
    }
}
