From 8eba71c643b573bf3892c9255b46cf934943e6c6 Mon Sep 17 00:00:00 2001
From: Anirudh Oppiliappan <x@icyphox.sh>
Date: Thu, 01 May 2025 16:48:23 +0000
Subject: [PATCH] appview: pages/markup: render markdown with transformations

---
 appview/pages/markup/format.go | 26 ++++++++++++++++++++++++++
 appview/pages/markup/markdown.go | 75 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 appview/pages/markup/readme.go | 26 --------------------------
 3 file(s) changed, 100 insertion(s)(+), 27 deletion(s)(-)

diff --git a/appview/pages/markup/format.go b/appview/pages/markup/format.go
new file mode 100644
--- /dev/null
+++ b/appview/pages/markup/format.go
@@ -0,0 +1,26 @@
+package markup
+
+import "strings"
+
+type Format string
+
+const (
+	FormatMarkdown Format = "markdown"
+	FormatText     Format = "text"
+)
+
+var FileTypes map[Format][]string = map[Format][]string{
+	FormatMarkdown: []string{".md", ".markdown", ".mdown", ".mkdn", ".mkd"},
+}
+
+func GetFormat(filename string) Format {
+	for format, extensions := range FileTypes {
+		for _, extension := range extensions {
+			if strings.HasSuffix(filename, extension) {
+				return format
+			}
+		}
+	}
+	// default format
+	return FormatText
+}
diff --git a/appview/pages/markup/markdown.go b/appview/pages/markup/markdown.go
--- a/appview/pages/markup/markdown.go
+++ b/appview/pages/markup/markdown.go
@@ -3,22 +3,95 @@
 
 import (
 	"bytes"
+	"path"
 
 	"github.com/yuin/goldmark"
+	"github.com/yuin/goldmark/ast"
 	"github.com/yuin/goldmark/extension"
 	"github.com/yuin/goldmark/parser"
+	"github.com/yuin/goldmark/text"
+	"github.com/yuin/goldmark/util"
 )
 
-func RenderMarkdown(source string) string {
+// RendererType defines the type of renderer to use based on context
+type RendererType int
+
+const (
+	// RendererTypeRepoMarkdown is for repository documentation markdown files
+	RendererTypeRepoMarkdown RendererType = iota
+	// RendererTypeIssueComment is for issue comments
+	RendererTypeIssueComment
+	// RendererTypePullComment is for pull request comments
+	RendererTypePullComment
+	// RendererTypeDefault is the default renderer with minimal transformations
+	RendererTypeDefault
+)
+
+// RenderContext holds the contextual data for rendering markdown.
+// It can be initialized empty, and that'll skip any transformations
+// and use the default renderer (RendererTypeDefault).
+type RenderContext struct {
+	Ref          string
+	FullRepoName string
+	RendererType RendererType
+}
+
+func (rctx *RenderContext) RenderMarkdown(source string) string {
 	md := goldmark.New(
 		goldmark.WithExtensions(extension.GFM),
 		goldmark.WithParserOptions(
 			parser.WithAutoHeadingID(),
 		),
 	)
+
+	if rctx != nil {
+		var transformers []util.PrioritizedValue
+
+		transformers = append(transformers, util.Prioritized(&MarkdownTransformer{rctx: rctx}, 10000))
+
+		md.Parser().AddOptions(
+			parser.WithASTTransformers(transformers...),
+		)
+	}
+
 	var buf bytes.Buffer
 	if err := md.Convert([]byte(source), &buf); err != nil {
 		return source
 	}
 	return buf.String()
+}
+
+type MarkdownTransformer struct {
+	rctx *RenderContext
+}
+
+func (a *MarkdownTransformer) Transform(node *ast.Document, reader text.Reader, pc parser.Context) {
+	_ = ast.Walk(node, func(n ast.Node, entering bool) (ast.WalkStatus, error) {
+		if !entering {
+			return ast.WalkContinue, nil
+		}
+
+		switch a.rctx.RendererType {
+		case RendererTypeRepoMarkdown:
+			a.rctx.relativeLinkTransformer(n.(*ast.Link))
+		case RendererTypeDefault:
+			a.rctx.relativeLinkTransformer(n.(*ast.Link))
+			// more types here like RendererTypeIssue/Pull etc.
+		}
+
+		return ast.WalkContinue, nil
+	})
+}
+
+func (rctx *RenderContext) relativeLinkTransformer(link *ast.Link) {
+	dst := string(link.Destination)
+
+	if len(dst) == 0 || dst[0] == '#' ||
+		bytes.Contains(link.Destination, []byte("://")) ||
+		bytes.HasPrefix(link.Destination, []byte("mailto:")) {
+		return
+	}
+
+	newPath := path.Join("/", rctx.FullRepoName, "tree", rctx.Ref, dst)
+	link.Destination = []byte(newPath)
 }
diff --git a/appview/pages/markup/readme.go b/appview/pages/markup/readme.go
deleted file mode 100644
--- a/appview/pages/markup/readme.go
+++ /dev/null
@@ -1,26 +0,0 @@
-package markup
-
-import "strings"
-
-type Format string
-
-const (
-	FormatMarkdown Format = "markdown"
-	FormatText     Format = "text"
-)
-
-var FileTypes map[Format][]string = map[Format][]string{
-	FormatMarkdown: []string{".md", ".markdown", ".mdown", ".mkdn", ".mkd"},
-}
-
-func GetFormat(filename string) Format {
-	for format, extensions := range FileTypes {
-		for _, extension := range extensions {
-			if strings.HasSuffix(filename, extension) {
-				return format
-			}
-		}
-	}
-	// default format
-	return FormatText
-}

--
tangled.sh