Optimize walkdir for pages

moves.go

@@ -1,8 +1,8 @@
 package main
 
 import (
+	"bytes"
 	"fmt"
-	"io/fs"
 	"log"
 	"net/http"
 	"os"
@@ -44,20 +44,21 @@ func (h *handler) handleMove(w http.ResponseWriter, r *http.Request, srcURL, src
 		return
 	}
 
-	// Phase 1: walk the tree and rewrite every index.md whose content changes.
-	// Keep the pre-rewrite bytes in memory so we can revert on failure.
+	// Phase 1: walk the tree and rewrite every index.md that references the
+	// moved path. Keep the pre-rewrite bytes in memory so we can revert on
+	// failure. The walker only reads directory listings and files literally
+	// named index.md; hidden directories are pruned. A cheap substring check
+	// skips parsing files that cannot contain a relevant link.
 	rewritten := map[string][]byte{}
-	walkErr := filepath.WalkDir(h.root, func(fsPath string, d fs.DirEntry, err error) error {
-		if err != nil {
-			return err
-		}
-		if d.IsDir() || d.Name() != "index.md" {
-			return nil
-		}
+	needle := []byte("[[" + oldPath)
+	walkErr := walkIndexFiles(h.root, func(fsPath string) error {
 		orig, err := os.ReadFile(fsPath)
 		if err != nil {
 			return err
 		}
+		if !bytes.Contains(orig, needle) {
+			return nil
+		}
 		updated, changed := rewriteWikiLinks(orig, oldPath, newPath)
 		if !changed {
 			return nil
@@ -186,6 +187,36 @@ func rollbackRewrites(rewritten map[string][]byte) {
 	}
 }
 
+// walkIndexFiles visits every `index.md` under root, skipping hidden
+// directories (names beginning with `.`). Unlike filepath.WalkDir this does
+// not stat each regular file — on spinning disks that saves the bulk of the
+// traversal cost when folders contain many non-page files (photos, archives).
+func walkIndexFiles(root string, visit func(fsPath string) error) error {
+	entries, err := os.ReadDir(root)
+	if err != nil {
+		return err
+	}
+	for _, e := range entries {
+		name := e.Name()
+		if strings.HasPrefix(name, ".") {
+			continue
+		}
+		full := filepath.Join(root, name)
+		if e.IsDir() {
+			if err := walkIndexFiles(full, visit); err != nil {
+				return err
+			}
+			continue
+		}
+		if name == "index.md" {
+			if err := visit(full); err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}
+
 // writeFileAtomic writes data to a temp file in the same directory as path
 // and renames it into place so readers never observe a partial file.
 func writeFileAtomic(path string, data []byte, perm os.FileMode) error {