using System.IO;
using Markdig.Syntax.Inlines;

namespace MfGames.Markdown.Gemtext.Renderers.Gemtext.Inlines
{
    /// <summary>
    /// A Gemtext renderer for a <see cref="LinkInline" />.
    /// </summary>
    /// <seealso cref="GemtextObjectRenderer{LinkInline}" />
    public class LinkInlineRenderer : GemtextObjectRenderer<LinkInline>
    {
        /// <summary>
        /// Writes out any gathered links in a block.
        /// </summary>
        /// <param name="renderer">The renderer being used.</param>
        public static void WriteGatheredLinks(GemtextRenderer renderer)
        {
            // If we have no gathered links, then there is nothing to do.
            if (renderer.GatheredLinks.Count <= 0)
            {
                return;
            }

            // Put some space between the previous object and this one, then
            // write out each link which is already formatted.
            renderer.WriteLine();

            foreach (var link in renderer.GatheredLinks)
            {
                renderer.WriteLine();
                renderer.Write(link);
            }

            // Clear out the list of links.
            renderer.GatheredLinks.Clear();
        }

        protected override void Write(GemtextRenderer renderer, LinkInline link)
        {
            // Figure out the various states we have.
            bool outside = !renderer.LinkInsideBlock;
            bool insert = !outside
                && renderer.BlockLinkHandling == BlockLinkHandling.InsertLine;
            bool gather = !outside
                && renderer.BlockLinkHandling switch
                {
                    BlockLinkHandling.DocumentEnd => true,
                    BlockLinkHandling.ParagraphEnd => true,
                    _ => false,
                };
            bool hasText = link.FirstChild != null;
            bool footnotes = renderer.EndLinkInlineFormatting
                == EndLinkInlineFormatting.Footnote;

            // Bare links and ones where we insert into the paragraph have
            // their own line.
            string? url = link.GetDynamicUrl != null
                ? link.GetDynamicUrl() ?? link.Url
                : link.Url;

            if (outside || insert)
            {
                // Make sure we are at the beginning of the line before
                // rendering the link.
                renderer.EnsureLine();
                renderer.Write("=> ");
                renderer.Write(url);

                // If we have text, we need a space after the URL and before
                // the text.
                if (hasText)
                {
                    renderer.Write(" ");
                }
            }

            // Render the text for the link if we have it.
            if (hasText)
            {
                renderer.WriteChildren(link);
            }

            // If we are gathering, then write out a footnote.
            if (gather)
            {
                int footnoteNumber = renderer.NextFootnoteNumber++;
                string linkText = footnotes
                    ? footnoteNumber + ": " + url
                    : GetLinkText(link);

                if (footnotes)
                {
                    renderer.Write($"[{footnoteNumber}]");
                }

                renderer.GatheredLinks.Add("=> " + url + " " + linkText);
            }

            // If we are inserting a line in the paragraph, we need a final
            // newline so the text of the paragraph continues on the next
            // line.
            if (insert)
            {
                renderer.WriteLine();
            }
        }

        private static string GetLinkText(LinkInline link)
        {
            // This little bit of nasty code basically spins up a new renderer
            // to get the text of the link by itself. Then we return that
            // directly so it can be rendered as a link.
            StringWriter writer = new();
            GemtextRenderer renderer = new(writer);

            renderer.WriteChildren(link);
            writer.Close();

            string text = writer.ToString();

            return text;
        }
    }
}