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

#nullable enable

using System;
using System.Security.Claims;
using System.Security.Principal;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc.ModelBinding;
using Microsoft.AspNetCore.Mvc.Rendering;
using Microsoft.AspNetCore.Mvc.Routing;
using Microsoft.AspNetCore.Mvc.ViewComponents;
using Microsoft.AspNetCore.Mvc.ViewEngines;
using Microsoft.AspNetCore.Mvc.ViewFeatures;
using Microsoft.AspNetCore.Routing;
using Microsoft.Extensions.DependencyInjection;

namespace Microsoft.AspNetCore.Mvc
{
    /// <summary>
    /// A base class for view components.
    /// </summary>
    [ViewComponent]
    public abstract class ViewComponent
    {
        private IUrlHelper? _url;
        private dynamic? _viewBag;
        private ViewComponentContext? _viewComponentContext;
        private ICompositeViewEngine? _viewEngine;

        /// <summary>
        /// Gets the <see cref="Http.HttpContext"/>.
        /// </summary>
        public HttpContext HttpContext => ViewContext?.HttpContext!;

        /// <summary>
        /// Gets the <see cref="HttpRequest"/>.
        /// </summary>
        public HttpRequest Request => ViewContext?.HttpContext?.Request!;

        /// <summary>
        /// Gets the <see cref="IPrincipal"/> for the current user.
        /// </summary>
        public IPrincipal User => ViewContext?.HttpContext?.User!;

        /// <summary>
        /// Gets the <see cref="ClaimsPrincipal"/> for the current user.
        /// </summary>
        public ClaimsPrincipal UserClaimsPrincipal => ViewContext?.HttpContext?.User!;

        /// <summary>
        /// Gets the <see cref="RouteData"/> for the current request.
        /// </summary>
        public RouteData RouteData => ViewContext?.RouteData!;

        /// <summary>
        /// Gets the view bag.
        /// </summary>
        public dynamic ViewBag
        {
            get
            {
                if (_viewBag == null)
                {
                    _viewBag = new DynamicViewData(() => ViewData);
                }

                return _viewBag;
            }
        }

        /// <summary>
        /// Gets the <see cref="ModelStateDictionary"/>.
        /// </summary>
        public ModelStateDictionary ModelState => ViewData?.ModelState!;

        /// <summary>
        /// Gets or sets the <see cref="IUrlHelper"/>.
        /// </summary>
        public IUrlHelper Url
        {
            get
            {
                if (_url == null)
                {
                    // May be null in unit-testing scenarios.
                    var services = ViewComponentContext.ViewContext?.HttpContext?.RequestServices;
                    var factory = services?.GetRequiredService<IUrlHelperFactory>();
                    _url = factory?.GetUrlHelper(ViewComponentContext.ViewContext!);
                }

                return _url!;
            }
            set
            {
                if (value == null)
                {
                    throw new ArgumentNullException(nameof(value));
                }

                _url = value;
            }
        }

        /// <summary>
        /// Gets or sets the <see cref="ViewComponentContext"/>.
        /// </summary>
        [ViewComponentContext]
        public ViewComponentContext ViewComponentContext
        {
            get
            {
                // This should run only for the ViewComponent unit test scenarios.
                if (_viewComponentContext == null)
                {
                    _viewComponentContext = new ViewComponentContext();
                }

                return _viewComponentContext;
            }
            set
            {
                if (value == null)
                {
                    throw new ArgumentNullException(nameof(value));
                }

                _viewComponentContext = value;
            }
        }

        /// <summary>
        /// Gets the <see cref="ViewContext"/>.
        /// </summary>
        public ViewContext ViewContext => ViewComponentContext.ViewContext;

        /// <summary>
        /// Gets the <see cref="ViewDataDictionary"/>.
        /// </summary>
        public ViewDataDictionary ViewData => ViewComponentContext.ViewData;

        /// <summary>
        /// Gets the <see cref="ITempDataDictionary"/>.
        /// </summary>
        public ITempDataDictionary TempData => ViewComponentContext.TempData;

        /// <summary>
        /// Gets or sets the <see cref="ICompositeViewEngine"/>.
        /// </summary>
        public ICompositeViewEngine ViewEngine
        {
            get
            {
                if (_viewEngine == null)
                {
                    // May be null in unit-testing scenarios.
                    var services = ViewComponentContext.ViewContext?.HttpContext?.RequestServices;
                    _viewEngine = services?.GetRequiredService<ICompositeViewEngine>();
                }

                return _viewEngine!;
            }
            set
            {
                if (value == null)
                {
                    throw new ArgumentNullException(nameof(value));
                }

                _viewEngine = value;
            }
        }

        /// <summary>
        /// Returns a result which will render HTML encoded text.
        /// </summary>
        /// <param name="content">The content, will be HTML encoded before output.</param>
        /// <returns>A <see cref="ContentViewComponentResult"/>.</returns>
        public ContentViewComponentResult Content(string content)
        {
            if (content == null)
            {
                throw new ArgumentNullException(nameof(content));
            }

            return new ContentViewComponentResult(content);
        }

        /// <summary>
        /// Returns a result which will render the partial view with name <c>&quot;Default&quot;</c>.
        /// </summary>
        /// <returns>A <see cref="ViewViewComponentResult"/>.</returns>
        public ViewViewComponentResult View()
        {
            return View(viewName: null);
        }

        /// <summary>
        /// Returns a result which will render the partial view with name <paramref name="viewName"/>.
        /// </summary>
        /// <param name="viewName">The name of the partial view to render.</param>
        /// <returns>A <see cref="ViewViewComponentResult"/>.</returns>
        public ViewViewComponentResult View(string? viewName)
        {
            return View(viewName, ViewData.Model);
        }

        /// <summary>
        /// Returns a result which will render the partial view with name <c>&quot;Default&quot;</c>.
        /// </summary>
        /// <param name="model">The model object for the view.</param>
        /// <returns>A <see cref="ViewViewComponentResult"/>.</returns>
        public ViewViewComponentResult View<TModel>(TModel? model)
        {
            return View(viewName: null, model: model);
        }

        /// <summary>
        /// Returns a result which will render the partial view with name <paramref name="viewName"/>.
        /// </summary>
        /// <param name="viewName">The name of the partial view to render.</param>
        /// <param name="model">The model object for the view.</param>
        /// <returns>A <see cref="ViewViewComponentResult"/>.</returns>
        public ViewViewComponentResult View<TModel>(string? viewName, TModel? model)
        {
            var viewData = new ViewDataDictionary<TModel?>(ViewData, model);
            return new ViewViewComponentResult
            {
                ViewEngine = ViewEngine,
                ViewName = viewName,
                ViewData = viewData
            };
        }
    }
}
