Umbraco-CMS/src/Umbraco.Web.Common/ModelBinders/ContentModelBinder.cs

using System;
using System.Text;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc.ModelBinding;
using Umbraco.Cms.Core;
using Umbraco.Cms.Core.Events;
using Umbraco.Cms.Core.Models;
using Umbraco.Cms.Core.Models.PublishedContent;
using Umbraco.Cms.Web.Common.Routing;
using Umbraco.Extensions;

namespace Umbraco.Cms.Web.Common.ModelBinders
{

    /// <summary>
    /// Maps view models, supporting mapping to and from any <see cref="IPublishedContent"/> or <see cref="IContentModel"/>.
    /// </summary>
    public class ContentModelBinder : IModelBinder
    {
        private readonly IEventAggregator _eventAggregator;

        /// <summary>
        /// Initializes a new instance of the <see cref="ContentModelBinder"/> class.
        /// </summary>
        public ContentModelBinder(IEventAggregator eventAggregator) => _eventAggregator = eventAggregator;

        /// <inheritdoc/>
        public Task BindModelAsync(ModelBindingContext bindingContext)
        {
            // Although this model binder is built to work both ways between IPublishedContent and IContentModel in reality
            // only IPublishedContent will ever exist in the request so when this model binder is used as an IModelBinder
            // in the aspnet pipeline it will really only support converting from IPublishedContent which is contained
            // in the UmbracoRouteValues --> IContentModel
            UmbracoRouteValues umbracoRouteValues = bindingContext.HttpContext.Features.Get<UmbracoRouteValues>();
            if (umbracoRouteValues is null)
            {
                return Task.CompletedTask;
            }

            BindModel(bindingContext, umbracoRouteValues.PublishedRequest.PublishedContent, bindingContext.ModelType);
            return Task.CompletedTask;
        }

        // source is the model that we have
        // modelType is the type of the model that we need to bind to
        //
        // create a model object of the modelType by mapping:
        // { ContentModel, ContentModel<TContent>, IPublishedContent }
        // to
        // { ContentModel, ContentModel<TContent>, IPublishedContent }

        /// <summary>
        /// Attempts to bind the model
        /// </summary>
        public void BindModel(ModelBindingContext bindingContext, object source, Type modelType)
        {
            // Null model, return
            if (source == null)
            {
                return;
            }

            // If types already match, return
            Type sourceType = source.GetType();
            if (sourceType.Inherits(modelType))
            {
                bindingContext.Result = ModelBindingResult.Success(source);
                return;
            }

            // Try to grab the content
            var sourceContent = source as IPublishedContent; // check if what we have is an IPublishedContent
            if (sourceContent == null && sourceType.Implements<IContentModel>())
            {
                // else check if it's an IContentModel, and get the content
                sourceContent = ((IContentModel)source).Content;
            }

            if (sourceContent == null)
            {
                // else check if we can convert it to a content
                Attempt<IPublishedContent> attempt1 = source.TryConvertTo<IPublishedContent>();
                if (attempt1.Success)
                {
                    sourceContent = attempt1.Result;
                }
            }

            // If we have a content
            if (sourceContent != null)
            {
                // If model is IPublishedContent, check content type and return
                if (modelType.Implements<IPublishedContent>())
                {
                    if (sourceContent.GetType().Inherits(modelType) == false)
                    {
                        ThrowModelBindingException(true, false, sourceContent.GetType(), modelType);
                    }

                    bindingContext.Result = ModelBindingResult.Success(sourceContent);
                    return;
                }

                // If model is ContentModel, create and return
                if (modelType == typeof(ContentModel))
                {
                    bindingContext.Result = ModelBindingResult.Success(new ContentModel(sourceContent));
                    return;
                }

                // If model is ContentModel<TContent>, check content type, then create and return
                if (modelType.IsGenericType && modelType.GetGenericTypeDefinition() == typeof(ContentModel<>))
                {
                    Type targetContentType = modelType.GetGenericArguments()[0];
                    if (sourceContent.GetType().Inherits(targetContentType) == false)
                    {
                        ThrowModelBindingException(true, true, sourceContent.GetType(), targetContentType);
                    }

                    bindingContext.Result = ModelBindingResult.Success(Activator.CreateInstance(modelType, sourceContent));
                    return;
                }
            }

            // Last chance : try to convert
            Attempt<object> attempt2 = source.TryConvertTo(modelType);
            if (attempt2.Success)
            {
                bindingContext.Result = ModelBindingResult.Success(attempt2.Result);
                return;
            }

            // Fail
            ThrowModelBindingException(false, false, sourceType, modelType);
            return;
        }

        private void ThrowModelBindingException(bool sourceContent, bool modelContent, Type sourceType, Type modelType)
        {
            var msg = new StringBuilder();

            // prepare message
            msg.Append("Cannot bind source");
            if (sourceContent)
            {
                msg.Append(" content");
            }

            msg.Append(" type ");
            msg.Append(sourceType.FullName);
            msg.Append(" to model");
            if (modelContent)
            {
                msg.Append(" content");
            }

            msg.Append(" type ");
            msg.Append(modelType.FullName);
            msg.Append(".");

            // raise event, to give model factories a chance at reporting
            // the error with more details, and optionally request that
            // the application restarts.
            var args = new ModelBindingError(sourceType, modelType, msg);
            _eventAggregator.Publish(args);

            throw new ModelBindingException(msg.ToString());
        }
    }
}