Add -default-view to choose timeline or grid as the site root

The view named by -default-view (timeline, the default, or grid) is published
at the site root; the other is served under /timeline/ or /grid/. viewBase and
pageURL derive every page path, pager link and the Timeline<->Grid cross-link
from the single setting, and Build removes both timeline/ and grid/ on each run
so flipping the default never leaves a stale root behind.

Reimplemented on trunk (which has albums and the /manage feature) rather than
cherry-picked, since the original was written against an earlier base. Credit
for the edit/delete and default-view ideas goes to Santhosh Raju, now noted in
a README Contributors section.

- main.go: -default-view flag, validated (fatal on anything but timeline/grid)
- module.nix: services.photogallery.defaultView enum option
- templates: timeline/grid/day/album/albums cross-links use TimelineURL/GridURL
- tests: timeline-root, grid-root, and switch-cleanup

generator.go

@@ -27,6 +27,11 @@ const (
 	mediumMaxSize   = 1600
 	defaultPageSize = 60
 
+	// The two paginated views. The one chosen as -default-view is published at
+	// the site root, the other under /<name>/.
+	viewTimeline = "timeline"
+	viewGrid     = "grid"
+
 	// Open Graph preview image, shared to WhatsApp/Telegram/etc. Kept to a
 	// 1200px longest side and squeezed under ogTargetBytes: WhatsApp is widely
 	// reported to drop the preview entirely once the image passes ~300 KB, so
@@ -80,15 +85,19 @@ type Generator struct {
 	serifFamily string
 	mlFamily    string
 	pageSize    int
+	defaultView string
 	mu          sync.Mutex
 	tmpl        *template.Template
 }
 
-func NewGenerator(contentDir, outputDir, baseURL, author, handle, bio, bioAlt, fontsURL, serifFamily, mlFamily string, pageSize int) *Generator {
+func NewGenerator(contentDir, outputDir, baseURL, author, handle, bio, bioAlt, fontsURL, serifFamily, mlFamily string, pageSize int, defaultView string) *Generator {
 	tmpl := template.Must(template.ParseFS(assets, "templates/*.html"))
 	if pageSize < 1 {
 		pageSize = defaultPageSize
 	}
+	if defaultView != viewGrid {
+		defaultView = viewTimeline
+	}
 	return &Generator{
 		contentDir:  contentDir,
 		outputDir:   outputDir,
@@ -101,10 +110,33 @@ func NewGenerator(contentDir, outputDir, baseURL, author, handle, bio, bioAlt, f
 		serifFamily: serifFamily,
 		mlFamily:    mlFamily,
 		pageSize:    pageSize,
+		defaultView: defaultView,
 		tmpl:        tmpl,
 	}
 }
 
+// viewBase returns the URL prefix a view is published under: "" for the default
+// view, which owns the site root, and "/<view>" for the other one.
+func (g *Generator) viewBase(view string) string {
+	if view == g.defaultView {
+		return ""
+	}
+	return "/" + view
+}
+
+// pageURL returns the URL of the 1-based page n of a view rooted at base.
+func pageURL(base string, n int) string {
+	if n == 1 {
+		return base + "/"
+	}
+	return base + "/page/" + strconv.Itoa(n) + "/"
+}
+
+// timelineURL and gridURL are the roots of each view, for cross-links in the
+// page headers.
+func (g *Generator) timelineURL() string { return pageURL(g.viewBase(viewTimeline), 1) }
+func (g *Generator) gridURL() string     { return pageURL(g.viewBase(viewGrid), 1) }
+
 func (g *Generator) initial() string {
 	for _, r := range g.author {
 		return strings.ToUpper(string(r))
@@ -124,19 +156,19 @@ func (g *Generator) Build() error {
 	}
 
 	// Drop fully-derived HTML trees before regenerating them, so a deleted
-	// post, a retag or a changed date leaves no orphaned page behind. These are
-	// cheap to rewrite (no up-to-date skipping applies to HTML), unlike the
-	// image renditions, which are pruned by slug just below.
-	for _, d := range []string{"photo", "day", "album", "page"} {
+	// post, a retag, a changed date or a flipped -default-view leaves no
+	// orphaned page behind. These are cheap to rewrite (no up-to-date skipping
+	// applies to HTML), unlike the image renditions, which are pruned by slug
+	// just below. Both "timeline" and "grid" are removed: whichever is the
+	// default owns the site root and has no dir of its own, so a dir by that
+	// name can only be a leftover from the opposite -default-view.
+	for _, d := range []string{"photo", "day", "album", "page", "timeline", "grid"} {
 		if err := os.RemoveAll(filepath.Join(g.outputDir, d)); err != nil {
 			return err
 		}
 	}
-	if err := os.RemoveAll(filepath.Join(g.outputDir, "grid", "page")); err != nil {
-		return err
-	}
 
-	for _, d := range []string{"images", "thumbs", "medium", "og", "photo", "grid", "day", "album", "albums", "static"} {
+	for _, d := range []string{"images", "thumbs", "medium", "og", "photo", "day", "album", "albums", "static"} {
 		if err := os.MkdirAll(filepath.Join(g.outputDir, d), 0755); err != nil {
 			return err
 		}
@@ -467,17 +499,17 @@ func generateOG(src, dst string, maxDim int) error {
 	return os.WriteFile(dst, buf.Bytes(), 0644)
 }
 
-// renderGridPages writes the paginated square-grid view under public/grid/:
-// grid/index.html and grid/page/N/index.html, chunking photos into pageSize
-// slices for progressive pagination. The grid is the secondary view; the
-// timeline is the site root.
+// renderGridPages writes the paginated square-grid view. When grid is the
+// -default-view it is the site root (index.html + page/N/); otherwise it lives
+// under /grid/. Photos are chunked into pageSize slices for progressive
+// pagination.
 func (g *Generator) renderGridPages(photos []Photo) error {
 	total := len(photos)
 	totalPages := (total + g.pageSize - 1) / g.pageSize
 	if totalPages == 0 {
 		totalPages = 1
 	}
-	gridDir := filepath.Join(g.outputDir, "grid")
+	base := g.viewBase(viewGrid)
 
 	for i := 0; i < totalPages; i++ {
 		start := i * g.pageSize
@@ -487,27 +519,19 @@ func (g *Generator) renderGridPages(photos []Photo) error {
 		}
 		slice := photos[start:end]
 
-		dst := filepath.Join(gridDir, "index.html")
-		if i > 0 {
-			dir := filepath.Join(gridDir, "page", strconv.Itoa(i+1))
-			if err := os.MkdirAll(dir, 0755); err != nil {
-				return err
-			}
-			dst = filepath.Join(dir, "index.html")
+		dir := filepath.Join(g.outputDir, filepath.FromSlash(pageURL(base, i+1)))
+		if err := os.MkdirAll(dir, 0755); err != nil {
+			return err
 		}
+		dst := filepath.Join(dir, "index.html")
 
 		prev := ""
 		next := ""
-		switch i {
-		case 0:
-			// no prev
-		case 1:
-			prev = "/grid/"
-		default:
-			prev = "/grid/page/" + strconv.Itoa(i) + "/"
+		if i > 0 {
+			prev = pageURL(base, i)
 		}
 		if i+1 < totalPages {
-			next = "/grid/page/" + strconv.Itoa(i+2) + "/"
+			next = pageURL(base, i+2)
 		}
 
 		data := map[string]any{
@@ -517,6 +541,8 @@ func (g *Generator) renderGridPages(photos []Photo) error {
 			"TotalPages":  totalPages,
 			"PrevURL":     prev,
 			"NextURL":     next,
+			"TimelineURL": g.timelineURL(),
+			"GridURL":     g.gridURL(),
 			"BaseURL":     g.baseURL,
 			"Year":        time.Now().Year(),
 			"Author":      g.author,
@@ -604,35 +630,29 @@ func chunkDayGroups(groups []DayGroup, target int) [][]DayGroup {
 	return pages
 }
 
-// renderTimelinePages writes the day-grouped timeline as the site root:
-// index.html and page/N/index.html. Photos are grouped by day, then packed
+// renderTimelinePages writes the day-grouped timeline. When timeline is the
+// -default-view (the default) it is the site root (index.html + page/N/);
+// otherwise it lives under /timeline/. Photos are grouped by day, then packed
 // into pages of roughly pageSize without splitting a day across pages.
 func (g *Generator) renderTimelinePages(photos []Photo) error {
 	pages := chunkDayGroups(groupByDay(photos), g.pageSize)
 	totalPages := len(pages)
+	base := g.viewBase(viewTimeline)
 
 	for i, groups := range pages {
-		dst := filepath.Join(g.outputDir, "index.html")
-		if i > 0 {
-			dir := filepath.Join(g.outputDir, "page", strconv.Itoa(i+1))
-			if err := os.MkdirAll(dir, 0755); err != nil {
-				return err
-			}
-			dst = filepath.Join(dir, "index.html")
+		dir := filepath.Join(g.outputDir, filepath.FromSlash(pageURL(base, i+1)))
+		if err := os.MkdirAll(dir, 0755); err != nil {
+			return err
 		}
+		dst := filepath.Join(dir, "index.html")
 
 		prev := ""
 		next := ""
-		switch i {
-		case 0:
-			// no prev
-		case 1:
-			prev = "/"
-		default:
-			prev = "/page/" + strconv.Itoa(i) + "/"
+		if i > 0 {
+			prev = pageURL(base, i)
 		}
 		if i+1 < totalPages {
-			next = "/page/" + strconv.Itoa(i+2) + "/"
+			next = pageURL(base, i+2)
 		}
 
 		data := map[string]any{
@@ -642,6 +662,8 @@ func (g *Generator) renderTimelinePages(photos []Photo) error {
 			"TotalPages":  totalPages,
 			"PrevURL":     prev,
 			"NextURL":     next,
+			"TimelineURL": g.timelineURL(),
+			"GridURL":     g.gridURL(),
 			"BaseURL":     g.baseURL,
 			"Year":        time.Now().Year(),
 			"Author":      g.author,
@@ -673,6 +695,8 @@ func (g *Generator) renderDayPages(photos []Photo) error {
 			"Count":       grp.Count,
 			"Photos":      grp.Photos,
 			"Total":       len(photos),
+			"TimelineURL": g.timelineURL(),
+			"GridURL":     g.gridURL(),
 			"BaseURL":     g.baseURL,
 			"Year":        time.Now().Year(),
 			"Author":      g.author,