// Copyright (c) Microsoft Corporation. All rights reserved. See License.txt in the project root for license information.

using System.Collections.Generic;
using System.Linq;

namespace System.Web.WebPages
{
    public sealed class DisplayModeProvider
    {
        public static readonly string MobileDisplayModeId = "Mobile";
        public static readonly string DefaultDisplayModeId = String.Empty;
        private static readonly object _displayModeKey = new object();
        private static readonly DisplayModeProvider _instance = new DisplayModeProvider();

        private readonly List<IDisplayMode> _displayModes = new List<IDisplayMode>
        {
            new DefaultDisplayMode(MobileDisplayModeId)
            {
                ContextCondition = context => context.GetOverriddenBrowser().IsMobileDevice
            },
            new DefaultDisplayMode()
        };

        internal DisplayModeProvider()
        {
            // The type is a psuedo-singleton. A user would gain nothing from constructing it since we won't use anything but DisplayModeProvider.Instance internally.
        }

        /// <summary>
        /// Restricts the search for Display Info to Display Modes either equal to or following the current
        /// Display Mode in Modes. For example, a page being rendered in the Default Display Mode will not
        /// display Mobile partial views in order to achieve a consistent look and feel.
        /// </summary>
        public bool RequireConsistentDisplayMode { get; set; }

        public static DisplayModeProvider Instance
        {
            get { return _instance; }
        }

        /// <summary>
        /// All Display Modes that are available to handle a request.
        /// </summary>
        public IList<IDisplayMode> Modes
        {
            get { return _displayModes; }
        }

        /// <summary>
        /// Returns any IDisplayMode that can handle the given request.
        /// </summary>
        public IEnumerable<IDisplayMode> GetAvailableDisplayModesForContext(HttpContextBase httpContext, IDisplayMode currentDisplayMode)
        {
            return GetAvailableDisplayModesForContext(httpContext, currentDisplayMode, RequireConsistentDisplayMode).ToList();
        }

        internal IEnumerable<IDisplayMode> GetAvailableDisplayModesForContext(HttpContextBase httpContext, IDisplayMode currentDisplayMode, bool requireConsistentDisplayMode)
        {
            IEnumerable<IDisplayMode> possibleDisplayModes = (requireConsistentDisplayMode && currentDisplayMode != null) ? Modes.SkipWhile(mode => mode != currentDisplayMode) : Modes;
            return possibleDisplayModes.Where(mode => mode.CanHandleContext(httpContext));
        }

        /// <summary>
        /// Returns DisplayInfo from the first IDisplayMode in Modes that can handle the given request and locate the virtual path.
        /// If currentDisplayMode is not null and RequireConsistentDisplayMode is set to true the search for DisplayInfo will only
        /// start with the currentDisplayMode.
        /// </summary>
        public DisplayInfo GetDisplayInfoForVirtualPath(string virtualPath, HttpContextBase httpContext, Func<string, bool> virtualPathExists, IDisplayMode currentDisplayMode)
        {
            return GetDisplayInfoForVirtualPath(virtualPath, httpContext, virtualPathExists, currentDisplayMode, RequireConsistentDisplayMode);
        }

        internal DisplayInfo GetDisplayInfoForVirtualPath(string virtualPath, HttpContextBase httpContext, Func<string, bool> virtualPathExists, IDisplayMode currentDisplayMode,
                                                          bool requireConsistentDisplayMode)
        {
            IEnumerable<IDisplayMode> possibleDisplayModes = GetAvailableDisplayModesForContext(httpContext, currentDisplayMode, requireConsistentDisplayMode);
            return possibleDisplayModes.Select(mode => mode.GetDisplayInfo(httpContext, virtualPath, virtualPathExists))
                .FirstOrDefault(info => info != null);
        }

        internal static IDisplayMode GetDisplayMode(HttpContextBase context)
        {
            return context != null ? context.Items[_displayModeKey] as IDisplayMode : null;
        }

        internal static void SetDisplayMode(HttpContextBase context, IDisplayMode displayMode)
        {
            if (context != null)
            {
                context.Items[_displayModeKey] = displayMode;
            }
        }
    }
}