using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Web;
using System.Web.Mvc;

namespace arkAS.Common.Helpers
{
    public static class HtmlRenderExtensions
    {

        /// <summary>
        /// Delegate script/resource/etc injection until the end of the page
        /// <para>@via https://stackoverflow.com/a/14127332/1037948 and http://jadnb.wordpress.com/2011/02/16/rendering-scripts-from-partial-views-at-the-end-in-mvc/ </para>
        /// </summary>
        private class DelayedInjectionBlock : IDisposable
        {
            /// <summary>
            /// Unique internal storage key
            /// </summary>
            private const string CACHE_KEY = "DCCF8C78-2E36-4567-B0CF-FE052ACCE309"; // "DelayedInjectionBlocks";

            /// <summary>
            /// Internal storage identifier for remembering unique/isOnlyOne items
            /// </summary>
            private const string UNIQUE_IDENTIFIER_KEY = CACHE_KEY;

            /// <summary>
            /// What to use as internal storage identifier if no identifier provided (since we can't use null as key)
            /// </summary>
            private const string EMPTY_IDENTIFIER = "";

            /// <summary>
            /// Retrieve a context-aware list of cached output delegates from the given helper; uses the helper's context rather than singleton HttpContext.Current.Items
            /// </summary>
            /// <param name="helper">the helper from which we use the context</param>
            /// <param name="identifier">optional unique sub-identifier for a given injection block</param>
            /// <returns>list of delayed-execution callbacks to render internal content</returns>
            public static Queue<string> GetQueue(HtmlHelper helper, string identifier = null)
            {
                return _GetOrSet(helper, new Queue<string>(), identifier ?? EMPTY_IDENTIFIER);
            }

            /// <summary>
            /// Retrieve a context-aware list of cached output delegates from the given helper; uses the helper's context rather than singleton HttpContext.Current.Items
            /// </summary>
            /// <param name="helper">the helper from which we use the context</param>
            /// <param name="defaultValue">the default value to return if the cached item isn't found or isn't the expected type; can also be used to set with an arbitrary value</param>
            /// <param name="identifier">optional unique sub-identifier for a given injection block</param>
            /// <returns>list of delayed-execution callbacks to render internal content</returns>
            private static T _GetOrSet<T>(HtmlHelper helper, T defaultValue, string identifier = EMPTY_IDENTIFIER) where T : class
            {
                var storage = GetStorage(helper);

                // return the stored item, or set it if it does not exist
                return (T)(storage.ContainsKey(identifier) ? storage[identifier] : (storage[identifier] = defaultValue));
            }

            /// <summary>
            /// Get the storage, but if it doesn't exist or isn't the expected type, then create a new "bucket"
            /// </summary>
            /// <param name="helper"></param>
            /// <returns></returns>
            public static Dictionary<string, object> GetStorage(HtmlHelper helper)
            {
                var storage = helper.ViewContext.HttpContext.Items[CACHE_KEY] as Dictionary<string, object>;
                if (storage == null) helper.ViewContext.HttpContext.Items[CACHE_KEY] = (storage = new Dictionary<string, object>());
                return storage;
            }


            private readonly HtmlHelper helper;
            private readonly string identifier;
            private readonly string isOnlyOne;

            /// <summary>
            /// Create a new using block from the given helper (used for trapping appropriate context)
            /// </summary>
            /// <param name="helper">the helper from which we use the context</param>
            /// <param name="identifier">optional unique identifier to specify one or many injection blocks</param>
            /// <param name="isOnlyOne">extra identifier used to ensure that this item is only added once; if provided, content should only appear once in the page (i.e. only the first block called for this identifier is used)</param>
            public DelayedInjectionBlock(HtmlHelper helper, string identifier = null, string isOnlyOne = null)
            {
                this.helper = helper;

                // start a new writing context
                ((WebViewPage)this.helper.ViewDataContainer).OutputStack.Push(new StringWriter());

                this.identifier = identifier ?? EMPTY_IDENTIFIER;
                this.isOnlyOne = isOnlyOne;
            }

            /// <summary>
            /// Append the internal content to the context's cached list of output delegates
            /// </summary>
            public void Dispose()
            {
                // render the internal content of the injection block helper
                // make sure to pop from the stack rather than just render from the Writer
                // so it will remove it from regular rendering
                var content = ((WebViewPage)this.helper.ViewDataContainer).OutputStack;
                var renderedContent = content.Count == 0 ? string.Empty : content.Pop().ToString();
                // if we only want one, remove the existing
                var queue = GetQueue(this.helper, this.identifier);

                // get the index of the existing item from the alternate storage
                var existingIdentifiers = _GetOrSet(this.helper, new Dictionary<string, int>(), UNIQUE_IDENTIFIER_KEY);

                // only save the result if this isn't meant to be unique, or
                // if it's supposed to be unique and we haven't encountered this identifier before
                if (null == this.isOnlyOne || !existingIdentifiers.ContainsKey(this.isOnlyOne))
                {
                    // remove the new writing context we created for this block
                    // and save the output to the queue for later
                    queue.Enqueue(renderedContent);

                    // only remember this if supposed to
                    if (null != this.isOnlyOne) existingIdentifiers[this.isOnlyOne] = queue.Count; // save the index, so we could remove it directly (if we want to use the last instance of the block rather than the first)
                }
            }
        }


        /// <summary>
        /// <para>Start a delayed-execution block of output -- this will be rendered/printed on the next call to <see cref="RenderDelayed"/>.</para>
        /// <para>
        /// <example>
        /// Print once in "default block" (usually rendered at end via <code>@Html.RenderDelayed()</code>).  Code:
        /// <code>
        /// @using (Html.Delayed()) {
        ///     <b>show at later</b>
        ///     <span>@Model.Name</span>
        ///     etc
        /// }
        /// </code>
        /// </example>
        /// </para>
        /// <para>
        /// <example>
        /// Print once (i.e. if within a looped partial), using identified block via <code>@Html.RenderDelayed("one-time")</code>.  Code:
        /// <code>
        /// @using (Html.Delayed("one-time", isOnlyOne: "one-time")) {
        ///     <b>show me once</b>
        ///     <span>@Model.First().Value</span>
        /// }
        /// </code>
        /// </example>
        /// </para>
        /// </summary>
        /// <param name="helper">the helper from which we use the context</param>
        /// <param name="injectionBlockId">optional unique identifier to specify one or many injection blocks</param>
        /// <param name="isOnlyOne">extra identifier used to ensure that this item is only added once; if provided, content should only appear once in the page (i.e. only the first block called for this identifier is used)</param>
        /// <returns>using block to wrap delayed output</returns>
        public static IDisposable Delayed(this HtmlHelper helper, string injectionBlockId = null, string isOnlyOne = null)
        {
            return new DelayedInjectionBlock(helper, injectionBlockId, isOnlyOne);
        }

        /// <summary>
        /// Render all queued output blocks injected via <see cref="Delayed"/>.
        /// <para>
        /// <example>
        /// Print all delayed blocks using default identifier (i.e. not provided)
        /// <code>
        /// @using (Html.Delayed()) {
        ///     <b>show me later</b>
        ///     <span>@Model.Name</span>
        ///     etc
        /// }
        /// </code>
        /// -- then later --
        /// <code>
        /// @using (Html.Delayed()) {
        ///     <b>more for later</b>
        ///     etc
        /// }
        /// </code>
        /// -- then later --
        /// <code>
        /// @Html.RenderDelayed() // will print both delayed blocks
        /// </code>
        /// </example>
        /// </para>
        /// <para>
        /// <example>
        /// Allow multiple repetitions of rendered blocks, using same <code>@Html.Delayed()...</code> as before.  Code:
        /// <code>
        /// @Html.RenderDelayed(removeAfterRendering: false); /* will print */
        /// @Html.RenderDelayed() /* will print again because not removed before */
        /// </code>
        /// </example>
        /// </para>

        /// </summary>
        /// <param name="helper">the helper from which we use the context</param>
        /// <param name="injectionBlockId">optional unique identifier to specify one or many injection blocks</param>
        /// <param name="removeAfterRendering">only render this once</param>
        /// <returns>rendered output content</returns>
        public static MvcHtmlString RenderDelayed(this HtmlHelper helper, string injectionBlockId = null, bool removeAfterRendering = true)
        {
            var stack = DelayedInjectionBlock.GetQueue(helper, injectionBlockId);

            if (removeAfterRendering)
            {
                var sb = new StringBuilder(
#if DEBUG
                string.Format("<!-- delayed-block: {0} -->", injectionBlockId)
#endif
                );
                // .count faster than .any
                while (stack.Count > 0)
                {
                    sb.AppendLine(stack.Dequeue());
                }
                return MvcHtmlString.Create(sb.ToString());
            }

            return MvcHtmlString.Create(
#if DEBUG
                string.Format("<!-- delayed-block: {0} -->", injectionBlockId) +
#endif
            string.Join(Environment.NewLine, stack));
        }


    }
}