/// <summary>
///     Parses a Markdown file into a <see cref = "MarkdownParseResult"/> containing
///     front matter, rendered HTML, plain text, and a table of contents.
/// </summary>
public sealed class MarkdownParser
{
    private readonly FrontMatterExtractor _frontMatterExtractor;
    private readonly MarkdownPipeline _pipeline;
    private readonly TocGenerator _tocGenerator;
    /// <summary>
    ///     Creates a new Markdown parser with all MokaDocs extensions configured.
    /// </summary>
    /// <param name = "options">Optional parser configuration.</param>
    public MarkdownParser(MarkdownParserOptions? options = null)
    {
        options ??= new MarkdownParserOptions();
        _frontMatterExtractor = new FrontMatterExtractor();
        _tocGenerator = new TocGenerator();
        _pipeline = BuildPipeline(options);
    }

    /// <summary>
    ///     Parses a Markdown string into structured content.
    /// </summary>
    /// <param name = "markdown">The raw Markdown content (may include YAML front matter).</param>
    /// <returns>The fully parsed result.</returns>
    public MarkdownParseResult Parse(string markdown)
    {
        // Step 1: Extract front matter
        FrontMatterResult fmResult = _frontMatterExtractor.Extract(markdown);
        // Step 2: Parse Markdown body
        MarkdownDocument document = Markdig.Markdown.Parse(fmResult.Body, _pipeline);
        // Step 3: Generate ToC
        TableOfContents toc = _tocGenerator.Generate(document);
        // Step 4: Render HTML
        using var writer = new StringWriter();
        var renderer = new HtmlRenderer(writer);
        _pipeline.Setup(renderer);
        renderer.Render(document);
        writer.Flush();
        string html = writer.ToString();
        // Step 5: Extract plain text (for search indexing)
        string plainText = ExtractPlainText(document);
        return new MarkdownParseResult
        {
            FrontMatter = fmResult.FrontMatter,
            Html = html,
            PlainText = plainText,
            TableOfContents = toc
        };
    }

#region Private Helpers
    private static MarkdownPipeline BuildPipeline(MarkdownParserOptions options)
    {
        MarkdownPipelineBuilder builder = new MarkdownPipelineBuilder().UseAdvancedExtensions() // Tables, footnotes, task lists, auto-links, etc.
        .UseYamlFrontMatter().UseEmojiAndSmiley();
        // Admonitions use Markdig's built-in CustomContainers extension
        // (included via UseAdvancedExtensions) which renders ::: note → <div class="note">
        // Our CSS styles .note, .tip, .warning, .danger, .info, .caution, .important
        // UI Components (card, steps, link-cards, code-group)
        builder.Extensions.Add(new ComponentExtension());
        // Auto-generate IDs on headings
        builder.UseAutoIdentifiers(AutoIdentifierOptions.GitHub);
        // Mermaid diagram support — renders ```mermaid blocks as <pre class="mermaid">
        builder.Extensions.AddIfNotAlready<MermaidExtension>();
        // Blazor preview support — renders ```blazor-preview blocks as preview containers
        builder.Extensions.AddIfNotAlready<BlazorPreviewExtension>();
        // REPL support — renders ```csharp-repl blocks as interactive containers
        builder.Extensions.AddIfNotAlready<ReplExtension>();
        // Changelog support — renders :::changelog blocks as rich timeline UI
        builder.Extensions.Add(new ChangelogExtension());
        return builder.Build();
    }

    private static string ExtractPlainText(MarkdownDocument document)
    {
        var sb = new StringBuilder();
        foreach (Block block in document.AllDescendants())
        {
            if (block is ParagraphBlock paragraph && paragraph.Inline is not null)
            {
                foreach (Inline inline in paragraph.Inline)
                {
                    AppendInlineText(sb, inline);
                }

                sb.AppendLine();
            }
            else if (block is HeadingBlock heading && heading.Inline is not null)
            {
                foreach (Inline inline in heading.Inline)
                {
                    AppendInlineText(sb, inline);
                }

                sb.AppendLine();
            }
        }

        return sb.ToString().Trim();
    }

    private static void AppendInlineText(StringBuilder sb, Inline inline)
    {
        switch (inline)
        {
            case LiteralInline literal:
                sb.Append(literal.Content);
                break;
            case CodeInline code:
                sb.Append(code.Content);
                break;
            case ContainerInline container:
                foreach (Inline child in container)
                {
                    AppendInlineText(sb, child);
                }

                break;
            case LineBreakInline:
                sb.Append(' ');
                break;
        }
    }
#endregion
}