DefaultViewComponentHelper.cs

// 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;
using System.Collections.Generic;
using System.Reflection;
using System.Text.Encodings.Web;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Html;
using Microsoft.AspNetCore.Mvc.Rendering;
using Microsoft.AspNetCore.Mvc.ViewFeatures;
using Microsoft.AspNetCore.Mvc.ViewFeatures.Internal;
using Microsoft.Extensions.Internal;

namespace Microsoft.AspNetCore.Mvc.ViewComponents
{
    /// <summary>
    /// Default implementation for <see cref="IViewComponentHelper"/>.
    /// </summary>
    public class DefaultViewComponentHelper : IViewComponentHelper, IViewContextAware
    {
        private readonly IViewComponentDescriptorCollectionProvider _descriptorProvider;
        private readonly HtmlEncoder _htmlEncoder;
        private readonly IViewComponentInvokerFactory _invokerFactory;
        private readonly IViewComponentSelector _selector;
        private readonly IViewBufferScope _viewBufferScope;
        private ViewContext _viewContext;

        /// <summary>
        /// Initializes a new instance of <see cref="DefaultViewComponentHelper"/>.
        /// </summary>
        /// <param name="descriptorProvider">The <see cref="IViewComponentDescriptorCollectionProvider"/>
        /// used to locate view components.</param>
        /// <param name="htmlEncoder">The <see cref="HtmlEncoder"/>.</param>
        /// <param name="selector">The <see cref="IViewComponentSelector"/>.</param>
        /// <param name="invokerFactory">The <see cref="IViewComponentInvokerFactory"/>.</param>
        /// <param name="viewBufferScope">The <see cref="IViewBufferScope"/> that manages the lifetime of
        /// <see cref="ViewBuffer"/> instances.</param>
        public DefaultViewComponentHelper(
            IViewComponentDescriptorCollectionProvider descriptorProvider,
            HtmlEncoder htmlEncoder,
            IViewComponentSelector selector,
            IViewComponentInvokerFactory invokerFactory,
#pragma warning disable PUB0001 // Pubternal type in public API
            IViewBufferScope viewBufferScope
#pragma warning restore PUB0001
            )
        {
            if (descriptorProvider == null)
            {
                throw new ArgumentNullException(nameof(descriptorProvider));
            }

            if (htmlEncoder == null)
            {
                throw new ArgumentNullException(nameof(htmlEncoder));
            }

            if (selector == null)
            {
                throw new ArgumentNullException(nameof(selector));
            }

            if (invokerFactory == null)
            {
                throw new ArgumentNullException(nameof(invokerFactory));
            }

            if (viewBufferScope == null)
            {
                throw new ArgumentNullException(nameof(viewBufferScope));
            }

            _descriptorProvider = descriptorProvider;
            _htmlEncoder = htmlEncoder;
            _selector = selector;
            _invokerFactory = invokerFactory;
            _viewBufferScope = viewBufferScope;
        }

        /// <inheritdoc />
        public void Contextualize(ViewContext viewContext)
        {
            if (viewContext == null)
            {
                throw new ArgumentNullException(nameof(viewContext));
            }

            _viewContext = viewContext;
        }

        /// <inheritdoc />
        public Task<IHtmlContent> InvokeAsync(string name, object arguments)
        {
            if (name == null)
            {
                throw new ArgumentNullException(nameof(name));
            }

            var descriptor = _selector.SelectComponent(name);
            if (descriptor == null)
            {
                throw new InvalidOperationException(Resources.FormatViewComponent_CannotFindComponent(
                    name,
                    nameof(ViewComponentAttribute),
                    ViewComponentConventions.ViewComponentSuffix,
                    nameof(NonViewComponentAttribute)));
            }

            return InvokeCoreAsync(descriptor, arguments);
        }

        /// <inheritdoc />
        public Task<IHtmlContent> InvokeAsync(Type componentType, object arguments)
        {
            if (componentType == null)
            {
                throw new ArgumentNullException(nameof(componentType));
            }

            var descriptor = SelectComponent(componentType);
            return InvokeCoreAsync(descriptor, arguments);
        }

        private ViewComponentDescriptor SelectComponent(Type componentType)
        {
            var descriptors = _descriptorProvider.ViewComponents;
            for (var i = 0; i < descriptors.Items.Count; i++)
            {
                var descriptor = descriptors.Items[i];
                if (descriptor.TypeInfo == componentType?.GetTypeInfo())
                {
                    return descriptor;
                }
            }

            throw new InvalidOperationException(Resources.FormatViewComponent_CannotFindComponent(
                componentType.FullName,
                nameof(ViewComponentAttribute),
                ViewComponentConventions.ViewComponentSuffix,
                nameof(NonViewComponentAttribute)));
        }

        // Internal for testing
        internal IDictionary<string, object> GetArgumentDictionary(ViewComponentDescriptor descriptor, object arguments)
        {
            if (arguments != null)
            {
                if (descriptor.Parameters.Count == 1 && descriptor.Parameters[0].ParameterType.IsAssignableFrom(arguments.GetType()))
                {
                    return new Dictionary<string, object>(capacity: 1, comparer: StringComparer.OrdinalIgnoreCase)
                    {
                        { descriptor.Parameters[0].Name, arguments }
                    };
                }
            }

            return PropertyHelper.ObjectToDictionary(arguments);
        }

        private async Task<IHtmlContent> InvokeCoreAsync(ViewComponentDescriptor descriptor, object arguments)
        {
            var argumentDictionary = GetArgumentDictionary(descriptor, arguments);

            var viewBuffer = new ViewBuffer(_viewBufferScope, descriptor.FullName, ViewBuffer.ViewComponentPageSize);
            using (var writer = new ViewBufferTextWriter(viewBuffer, _viewContext.Writer.Encoding))
            {
                var context = new ViewComponentContext(descriptor, argumentDictionary, _htmlEncoder, _viewContext, writer);

                var invoker = _invokerFactory.CreateInstance(context);
                if (invoker == null)
                {
                    throw new InvalidOperationException(
                        Resources.FormatViewComponent_IViewComponentFactory_ReturnedNull(descriptor.FullName));
                }

                await invoker.InvokeAsync(context);
                return viewBuffer;
            }
        }
    }
}