/// <summary>
///     Markdig extension that renders fenced code blocks with the "csharp-repl" (or "csharp repl")
///     language as interactive REPL containers with a <c>data-repl="true"</c> attribute.
///     The REPL plugin later enhances these with Run buttons and output panels.
/// </summary>
/// <remarks>
///     This extension is designed to coexist with <see cref = "MermaidExtension"/> by wrapping
///     whatever CodeBlock renderer is currently in the pipeline (including MermaidCodeBlockRenderer).
///     Registration order: Mermaid first, then REPL.
/// </remarks>
public sealed class ReplExtension : IMarkdownExtension
{
    /// <inheritdoc/>
    public void Setup(MarkdownPipelineBuilder pipeline)
    {
    // No block parser changes needed — we reuse the built-in FencedCodeBlock parser.
    }

    /// <inheritdoc/>
    public void Setup(MarkdownPipeline pipeline, IMarkdownRenderer renderer)
    {
        if (renderer is HtmlRenderer htmlRenderer)
        {
            // Find whatever renderer currently handles CodeBlock (could be default
            // CodeBlockRenderer or MermaidCodeBlockRenderer). We wrap it so both
            // Mermaid and REPL code blocks are handled correctly.
            IMarkdownObjectRenderer? existingRenderer = null;
            foreach (IMarkdownObjectRenderer r in htmlRenderer.ObjectRenderers)
            {
                if (r is HtmlObjectRenderer<CodeBlock> codeBlockHandler)
                {
                    existingRenderer = codeBlockHandler;
                    break;
                }
            }

            if (existingRenderer != null)
            {
                htmlRenderer.ObjectRenderers.Remove(existingRenderer);
            }

            htmlRenderer.ObjectRenderers.AddIfNotAlready(new ReplCodeBlockRenderer(existingRenderer as HtmlObjectRenderer<CodeBlock>));
        }
    }
}