using System;
using System.IO;

using Markdig;
using Markdig.Parsers;
using Markdig.Syntax;

using MfGames.Markdown.Gemtext.Renderers;

namespace MfGames.Markdown.Gemtext
{
    /// <summary>
    /// The static class that corresponds to Markdig.Markdown. This is written
    /// with the same pattern, but since `Markdown` is a static, we can't tack
    /// onto that.
    /// </summary>
    public static class MarkdownGemtext
    {
        private static readonly MarkdownPipeline DefaultPipeline;

        static MarkdownGemtext()
        {
            DefaultPipeline = new MarkdownPipelineBuilder()
                .Build();
        }

        /// <summary>
        /// Converts the given Markdown
        /// </summary>
        /// <param name="markdown">A Markdown text.</param>
        /// <param name="pipeline">The pipeline used for the conversion.</param>
        /// <param name="context">A parser context used for the parsing.</param>
        /// <returns>The result of the conversion</returns>
        public static string ToGemtext(
            string markdown,
            MarkdownPipeline? pipeline = null,
            MarkdownParserContext? context = null)
        {
            if (markdown == null)
            {
                throw new ArgumentNullException(nameof(markdown));
            }

            pipeline ??= DefaultPipeline;

            MarkdownDocument document = MarkdownParser
                .Parse(markdown, pipeline, context);

            return ToGemtext(document, pipeline);
        }

        /// <summary>
        /// Converts a Markdown document to HTML.
        /// </summary>
        /// <param name="document">A Markdown document.</param>
        /// <param name="pipeline">The pipeline used for the conversion.</param>
        /// <returns>The result of the conversion</returns>
        /// <exception cref="ArgumentNullException">if markdown document variable is null</exception>
        public static string ToGemtext(
            this MarkdownDocument document,
            MarkdownPipeline? pipeline = null)
        {
            // Make sure we have sane parameters.
            if (document == null)
            {
                throw new ArgumentNullException(nameof(document));
            }

            pipeline ??= DefaultPipeline;

            // Set up the writer to contain the markdown and the Gemtext
            // renderer.
            var writer = new StringWriter();
            GemtextRenderer renderer = new(writer);

            pipeline.Setup(renderer);

            // Render the Markdown into Gemtext and re turn the results.
            renderer.Render(document);
            renderer.Writer.Flush();

            return renderer.Writer.ToString() ?? string.Empty;
        }
    }
}