using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Web.Mvc;
using Umbraco.Core.IO;
using Umbraco.Web.Models;

namespace Umbraco.Web.Mvc
{
    /// <summary>
    /// A view engine to look into the template location specified in the config for the front-end/Rendering part of the cms,
    /// this includes paths to render partial macros and media item templates.
    /// </summary>
    public class RenderViewEngine : RazorViewEngine
    {
        private readonly IEnumerable<string> _supplementedViewLocations = new[] { "/{0}.cshtml" };
        //NOTE: we will make the main view location the last to be searched since if it is the first to be searched and there is both a view and a partial
        // view in both locations and the main view is rendering a partial view with the same name, we will get a stack overflow exception.
        // http://issues.umbraco.org/issue/U4-1287, http://issues.umbraco.org/issue/U4-1215
        private readonly IEnumerable<string> _supplementedPartialViewLocations = new[] { "/Partials/{0}.cshtml", "/MacroPartials/{0}.cshtml", "/{0}.cshtml" };

        /// <summary>
        /// Constructor
        /// </summary>
        public RenderViewEngine()
        {
            const string templateFolder = Constants.ViewLocation;

            // the Render view engine doesn't support Area's so make those blank
            ViewLocationFormats = _supplementedViewLocations.Select(x => templateFolder + x).ToArray();
            PartialViewLocationFormats = _supplementedPartialViewLocations.Select(x => templateFolder + x).ToArray();

            AreaPartialViewLocationFormats = Array.Empty<string>();
            AreaViewLocationFormats = Array.Empty<string>();

            EnsureFoldersAndFiles();
        }

        /// <summary>
        /// Ensures that the correct web.config for razor exists in the /Views folder, the partials folder exist and the ViewStartPage exists.
        /// </summary>
        private static void EnsureFoldersAndFiles()
        {
            var viewFolder = IOHelper.MapPath(Constants.ViewLocation);

            // ensure the web.config file is in the ~/Views folder
            Directory.CreateDirectory(viewFolder);
            var webConfigPath = Path.Combine(viewFolder, "web.config");
            if (File.Exists(webConfigPath) == false)
            {
                using (var writer = File.CreateText(webConfigPath))
                {
                    writer.Write(Strings.WebConfigTemplate);
                }
            }

            //auto create the partials folder
            var partialsFolder = Path.Combine(viewFolder, "Partials");
            Directory.CreateDirectory(partialsFolder);

            // We could create a _ViewStart page if it isn't there as well, but we may not allow editing of this page in the back office.
        }

        public override ViewEngineResult FindView(ControllerContext controllerContext, string viewName, string masterName, bool useCache)
        {
            return ShouldFindView(controllerContext, false)
                ? base.FindView(controllerContext, viewName, masterName, useCache)
                : new ViewEngineResult(new string[] { });
        }

        public override ViewEngineResult FindPartialView(ControllerContext controllerContext, string partialViewName, bool useCache)
        {
            return ShouldFindView(controllerContext, true)
                ? base.FindPartialView(controllerContext, partialViewName, useCache)
                : new ViewEngineResult(new string[] { });
        }

        /// <summary>
        /// Determines if the view should be found, this is used for view lookup performance and also to ensure
        /// less overlap with other user's view engines. This will return true if the Umbraco back office is rendering
        /// and its a partial view or if the umbraco front-end is rendering but nothing else.
        /// </summary>
        /// <param name="controllerContext"></param>
        /// <param name="isPartial"></param>
        /// <returns></returns>
        private static bool ShouldFindView(ControllerContext controllerContext, bool isPartial)
        {
            var umbracoToken = controllerContext.GetDataTokenInViewContextHierarchy(Core.Constants.Web.UmbracoDataToken);

            // first check if we're rendering a partial view for the back office, or surface controller, etc...
            // anything that is not IUmbracoRenderModel as this should only pertain to Umbraco views.
            if (isPartial && !(umbracoToken is ContentModel))
                return true;

            // only find views if we're rendering the umbraco front end
            return umbracoToken is ContentModel;
        }
    }
}