// 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.Diagnostics;
using System.Globalization;
using System.Threading.Tasks;
using Microsoft.AspNet.Mvc.Diagnostics;
using Microsoft.AspNet.Mvc.Rendering;
using Microsoft.AspNet.Mvc.ViewEngines;
using Microsoft.AspNet.Mvc.ViewFeatures;
using Microsoft.Extensions.DependencyInjection;

namespace Microsoft.AspNet.Mvc.ViewComponents
{
    /// <summary>
    /// A <see cref="IViewComponentResult"/> that renders a partial view when executed.
    /// </summary>
    public class ViewViewComponentResult : IViewComponentResult
    {
        // {0} is the component name, {1} is the view name.
        private const string ViewPathFormat = "Components/{0}/{1}";
        private const string DefaultViewName = "Default";

        private DiagnosticSource _diagnosticSource;

        /// <summary>
        /// Gets or sets the view name.
        /// </summary>
        public string ViewName { get; set; }

        /// <summary>
        /// Gets or sets the <see cref="ViewDataDictionary"/>.
        /// </summary>
        public ViewDataDictionary ViewData { get; set; }

        /// <summary>
        /// Gets or sets the <see cref="ITempDataDictionary"/> instance.
        /// </summary>
        public ITempDataDictionary TempData { get; set; }

        /// <summary>
        /// Gets or sets the <see cref="ViewEngine"/>.
        /// </summary>
        public IViewEngine ViewEngine { get; set; }

        /// <summary>
        /// Locates and renders a view specified by <see cref="ViewName"/>. If <see cref="ViewName"/> is <c>null</c>,
        /// then the view name searched for is<c>&quot;Default&quot;</c>.
        /// </summary>
        /// <param name="context">The <see cref="ViewComponentContext"/> for the current component execution.</param>
        /// <remarks>
        /// This method synchronously calls and blocks on <see cref="ExecuteAsync(ViewComponentContext)"/>.
        /// </remarks>
        public void Execute(ViewComponentContext context)
        {
            if (context == null)
            {
                throw new ArgumentNullException(nameof(context));
            }

            var task = ExecuteAsync(context);
            task.GetAwaiter().GetResult();
        }

        /// <summary>
        /// Locates and renders a view specified by <see cref="ViewName"/>. If <see cref="ViewName"/> is <c>null</c>,
        /// then the view name searched for is<c>&quot;Default&quot;</c>.
        /// </summary>
        /// <param name="context">The <see cref="ViewComponentContext"/> for the current component execution.</param>
        /// <returns>A <see cref="Task"/> which will complete when view rendering is completed.</returns>
        public async Task ExecuteAsync(ViewComponentContext context)
        {
            if (context == null)
            {
                throw new ArgumentNullException(nameof(context));
            }

            var viewContext = context.ViewContext;
            var viewData = ViewData ?? context.ViewData;
            var viewEngine = ViewEngine ?? ResolveViewEngine(context);
            var isNullOrEmptyViewName = string.IsNullOrEmpty(ViewName);

            ViewEngineResult result = null;
            IEnumerable<string> originalLocations = null;
            if (!isNullOrEmptyViewName)
            {
                // If view name was passed in is already a path, the view engine will handle this.
                result = viewEngine.GetView(viewContext.ExecutingFilePath, ViewName, isPartial: true);
                originalLocations = result.SearchedLocations;
            }

            if (result == null || !result.Success)
            {
                // This will produce a string like:
                //
                //  Components/Cart/Default
                //
                // The view engine will combine this with other path info to search paths like:
                //
                //  Views/Shared/Components/Cart/Default.cshtml
                //  Views/Home/Components/Cart/Default.cshtml
                //  Areas/Blog/Views/Shared/Components/Cart/Default.cshtml
                //
                // This supports a controller or area providing an override for component views.
                var viewName = isNullOrEmptyViewName ? DefaultViewName : ViewName;
                var qualifiedViewName = string.Format(
                    CultureInfo.InvariantCulture,
                    ViewPathFormat,
                    context.ViewComponentDescriptor.ShortName,
                    viewName);

                result = viewEngine.FindView(viewContext, qualifiedViewName, isPartial: true);
            }

            var view = result.EnsureSuccessful(originalLocations).View;
            using (view as IDisposable)
            {
                if (_diagnosticSource == null)
                {
                    _diagnosticSource = viewContext.HttpContext.RequestServices.GetRequiredService<DiagnosticSource>();
                }

                _diagnosticSource.ViewComponentBeforeViewExecute(context, view);

                var childViewContext = new ViewContext(
                    viewContext,
                    view,
                    ViewData ?? context.ViewData,
                    context.Writer);
                await view.RenderAsync(childViewContext);

                _diagnosticSource.ViewComponentAfterViewExecute(context, view);
            }
        }

        private static IViewEngine ResolveViewEngine(ViewComponentContext context)
        {
            return context.ViewContext.HttpContext.RequestServices.GetRequiredService<ICompositeViewEngine>();
        }
    }
}