feat: sort markdown files by directory depth

The TUI file list sorted purely by note path, so markdown files in child directories could appear before files in the directory where Glow was launched.

Rank discovered files by path depth first, then preserve the existing path sort within each depth so root-level documents are listed before nested documents.

Fixes #272

ui/sort.go

@@ -2,11 +2,24 @@ package ui
 
 import (
 	"cmp"
+	"path/filepath"
 	"slices"
+	"strings"
 )
 
 func sortMarkdowns(mds []*markdown) {
 	slices.SortStableFunc(mds, func(a, b *markdown) int {
+		if n := cmp.Compare(markdownPathDepth(a.Note), markdownPathDepth(b.Note)); n != 0 {
+			return n
+		}
 		return cmp.Compare(a.Note, b.Note)
 	})
 }
+
+func markdownPathDepth(path string) int {
+	path = filepath.ToSlash(filepath.Clean(path))
+	if path == "." {
+		return 0
+	}
+	return strings.Count(path, "/")
+}

ui/sort_test.go

@@ -0,0 +1,33 @@
+package ui
+
+import "testing"
+
+func TestSortMarkdownsOrdersByDirectoryDepth(t *testing.T) {
+	mds := []*markdown{
+		{Note: "docs/reference/api.md"},
+		{Note: "docs/guide.md"},
+		{Note: "README.md"},
+		{Note: "CONTRIBUTING.md"},
+		{Note: "docs/reference/cli.md"},
+	}
+
+	sortMarkdowns(mds)
+
+	got := make([]string, 0, len(mds))
+	for _, md := range mds {
+		got = append(got, md.Note)
+	}
+
+	want := []string{
+		"CONTRIBUTING.md",
+		"README.md",
+		"docs/guide.md",
+		"docs/reference/api.md",
+		"docs/reference/cli.md",
+	}
+	for i := range want {
+		if got[i] != want[i] {
+			t.Fatalf("expected %v, got %v", want, got)
+		}
+	}
+}