cmd/foodster/handlers.go

@@ -215,6 +215,50 @@ func fragment(w http.ResponseWriter, r *http.Request, c templ.Component) {
 	}
 }
 
+// isDatastar reports whether the request came from the client library, which
+// tags its own. Everything below keeps working without JavaScript: the same
+// handlers redirect instead of patching when the header is absent.
+func isDatastar(r *http.Request) bool {
+	return r.Header.Get("Datastar-Request") != ""
+}
+
+// patchElements sends one Datastar event carrying several elements, each
+// matched to the page by its id. A text/html response can only replace one
+// element, and the catalog has to move its list and its forms together —
+// opening an edit form also has to un-highlight whatever was open before.
+//
+// ponytail: about twenty lines instead of the SDK, which brought four modules
+// for an SSE generator we would otherwise never call.
+func patchElements(w http.ResponseWriter, r *http.Request, components ...templ.Component) {
+	w.Header().Set("Content-Type", "text/event-stream")
+	w.Header().Set("Cache-Control", "no-cache")
+
+	var out strings.Builder
+	out.WriteString("event: datastar-patch-elements\n")
+	for _, c := range components {
+		var html strings.Builder
+		if err := c.Render(r.Context(), &html); err != nil {
+			log.Printf("patch %s: %v", r.URL.Path, err)
+			return
+		}
+		// One `data: elements` line per line of HTML, as the protocol wants.
+		for _, line := range strings.Split(html.String(), "\n") {
+			if strings.TrimSpace(line) == "" {
+				continue
+			}
+			out.WriteString("data: elements ")
+			out.WriteString(line)
+			out.WriteString("\n")
+		}
+	}
+	out.WriteString("\n")
+
+	io.WriteString(w, out.String())
+	if f, ok := w.(http.Flusher); ok {
+		f.Flush()
+	}
+}
+
 // searchBoard re-renders the dish board as the search box is typed into.
 func (a *app) searchBoard(w http.ResponseWriter, r *http.Request) {
 	var signals searchSignals
@@ -410,7 +454,20 @@ type catalogView struct {
 	DeleteKind string
 }
 
+// catalog renders the whole page. show patches the same state in place, so
+// nothing navigates: both build the view the same way.
 func (a *app) catalog(w http.ResponseWriter, r *http.Request) {
+	a.renderCatalog(w, r, a.catalogState(r))
+}
+
+// show is what every catalog link actually calls. It patches the list and both
+// forms rather than loading a page, so opening an edit form or asking to
+// delete a row leaves the scroll position exactly where it was.
+func (a *app) show(w http.ResponseWriter, r *http.Request) {
+	a.patchCatalog(w, r, a.catalogState(r))
+}
+
+func (a *app) catalogState(r *http.Request) catalogView {
 	v := catalogView{
 		Main:   mainForm{Categories: map[string]bool{}, HasSides: true},
 		Search: strings.TrimSpace(r.URL.Query().Get("haku")),
@@ -446,10 +503,11 @@ func (a *app) catalog(w http.ResponseWriter, r *http.Request) {
 		}
 	}
 
-	a.renderCatalog(w, r, v)
+	return v
 }
 
-func (a *app) renderCatalog(w http.ResponseWriter, r *http.Request, v catalogView) {
+// fillCatalog loads the lists into a view built from the request.
+func (a *app) fillCatalog(v *catalogView) {
 	if v.Main.Categories == nil {
 		v.Main.Categories = map[string]bool{}
 	}
@@ -465,9 +523,20 @@ func (a *app) renderCatalog(w http.ResponseWriter, r *http.Request, v catalogVie
 	if v.Sides, err = listSides(a.db, v.Search); err != nil {
 		log.Printf("list sides: %v", err)
 	}
+}
+
+func (a *app) renderCatalog(w http.ResponseWriter, r *http.Request, v catalogView) {
+	a.fillCatalog(&v)
 	render(w, r, catalogPage(v))
 }
 
+// patchCatalog swaps the list and both forms in one event. They move together:
+// opening an edit form also has to clear whatever delete was being confirmed.
+func (a *app) patchCatalog(w http.ResponseWriter, r *http.Request, v catalogView) {
+	a.fillCatalog(&v)
+	patchElements(w, r, catalogList(v), mainForm_(v.Main), sideForm_(v.Side))
+}
+
 // saveMain adds or updates a main dish. A rejected form is re-rendered with
 // the values still in it; a good one redirects, so refresh cannot re-submit.
 func (a *app) saveMain(w http.ResponseWriter, r *http.Request) {
@@ -508,11 +577,28 @@ func (a *app) saveMain(w http.ResponseWriter, r *http.Request) {
 			log.Printf("save main: %v", err)
 			form.Err = "Tallennus epäonnistui."
 		default:
-			http.Redirect(w, r, "/ruuat", http.StatusSeeOther)
+			// Saved: hand back a blank form so it collapses, and a list with
+			// the dish in it.
+			a.finishCatalog(w, r, catalogView{})
 			return
 		}
 	}
-	a.renderCatalog(w, r, catalogView{Main: form})
+	a.finishCatalog(w, r, catalogView{Main: form})
+}
+
+// finishCatalog answers a catalog write: a patch for Datastar, a redirect for
+// a plain form post. Without the redirect, submitting with JavaScript off
+// would leave the browser sitting on a POST it could not reload.
+func (a *app) finishCatalog(w http.ResponseWriter, r *http.Request, v catalogView) {
+	if isDatastar(r) {
+		a.patchCatalog(w, r, v)
+		return
+	}
+	if v.Main.Err != "" || v.Side.Err != "" {
+		a.renderCatalog(w, r, v)
+		return
+	}
+	http.Redirect(w, r, "/ruuat", http.StatusSeeOther)
 }
 
 func (a *app) saveSide(w http.ResponseWriter, r *http.Request) {
@@ -537,11 +623,11 @@ func (a *app) saveSide(w http.ResponseWriter, r *http.Request) {
 			log.Printf("save side: %v", err)
 			form.Err = "Tallennus epäonnistui."
 		default:
-			http.Redirect(w, r, "/ruuat", http.StatusSeeOther)
+			a.finishCatalog(w, r, catalogView{})
 			return
 		}
 	}
-	a.renderCatalog(w, r, catalogView{Side: form})
+	a.finishCatalog(w, r, catalogView{Side: form})
 }
 
 // deleteDish soft-deletes, so log entries keep resolving the name (PRD §6).
@@ -565,7 +651,7 @@ func (a *app) deleteDish(w http.ResponseWriter, r *http.Request) {
 		http.Error(w, "poisto epäonnistui", http.StatusInternalServerError)
 		return
 	}
-	http.Redirect(w, r, "/ruuat", http.StatusSeeOther)
+	a.finishCatalog(w, r, catalogView{})
 }
 
 // importDishes takes a bundle either pasted into the textarea or uploaded as a

cmd/foodster/main.go

@@ -162,6 +162,7 @@ func routes(db *sql.DB, loc *time.Location, password string) http.Handler {
 	mux.HandleFunc("POST /poista", a.delete)
 	mux.HandleFunc("GET /ruuat", a.catalog)
 	mux.HandleFunc("GET /ruuat/etsi", a.searchCatalog)
+	mux.HandleFunc("GET /ruuat/nayta", a.show)
 	mux.HandleFunc("POST /ruuat/paaruoka", a.saveMain)
 	mux.HandleFunc("POST /ruuat/lisuke", a.saveSide)
 	mux.HandleFunc("POST /ruuat/poista", a.deleteDish)

cmd/foodster/views.templ

@@ -43,6 +43,12 @@ func dayURL(base string, d, now time.Time) string {
 	return base + "?pvm=" + isoDate(d)
 }
 
+// showURL turns a catalog page link into the patch endpoint behind it, so the
+// href and the Datastar call never drift apart.
+func showURL(pageURL string) string {
+	return strings.Replace(pageURL, "/ruuat?", "/ruuat/nayta?", 1)
+}
+
 // dayAnchor names the element a day expands into.
 func dayAnchor(d time.Time) string {
 	return "paiva-" + isoDate(d)
@@ -689,25 +695,39 @@ templ emptyNote(search string) {
 // rowActions is a pencil and a bin, until the bin is tapped: then the row
 // asks. An icon is a smaller target to hit by accident than a word, and the
 // dish disappears from every picker the moment it goes.
+// Every control here is a real link or form, so the page still works without
+// JavaScript. Datastar intercepts them and patches the list in place instead,
+// which is the whole point: a delete confirmation halfway down a long list
+// must not send the browser back to the top.
 templ rowActions(v catalogView, editURL string, id int64, kind string) {
 	if v.DeleteID == id && v.DeleteKind == kind {
 		<div class="rowactions confirming">
 			<span>Poista?</span>
-			<form method="post" action="/ruuat/poista">
+			<form
+				method="post"
+				action="/ruuat/poista"
+				data-on:submit__prevent="@post('/ruuat/poista', {contentType: 'form'})"
+			>
 				<input type="hidden" name="id" value={ strconv.FormatInt(id, 10) }/>
 				<input type="hidden" name="tyyppi" value={ kind }/>
 				<button type="submit" class="del">Kyllä</button>
 			</form>
-			<a href="/ruuat">Peruuta</a>
+			<a href="/ruuat" data-on:click__prevent="@get('/ruuat/nayta')">Peruuta</a>
 		</div>
 	} else {
 		<div class="rowactions">
-			<a href={ templ.SafeURL(editURL) } aria-label="Muokkaa" title="Muokkaa">
+			<a
+				href={ templ.SafeURL(editURL) }
+				data-on:click__prevent={ "@get('" + showURL(editURL) + "')" }
+				aria-label="Muokkaa"
+				title="Muokkaa"
+			>
 				@iconPencil()
 			</a>
 			<a
 				class="del"
 				href={ templ.SafeURL("/ruuat?poista=" + strconv.FormatInt(id, 10) + "&tyyppi=" + kind) }
+				data-on:click__prevent={ "@get('/ruuat/nayta?poista=" + strconv.FormatInt(id, 10) + "&tyyppi=" + kind + "')" }
 				aria-label="Poista"
 				title="Poista"
 			>
@@ -746,7 +766,11 @@ templ mainForm_(f mainForm) {
 		if f.Err != "" {
 			<p class="formerr">{ f.Err }</p>
 		}
-		<form method="post" action="/ruuat/paaruoka">
+		<form
+			method="post"
+			action="/ruuat/paaruoka"
+			data-on:submit__prevent="@post('/ruuat/paaruoka', {contentType: 'form'})"
+		>
 			if f.ID != 0 {
 				<input type="hidden" name="id" value={ strconv.FormatInt(f.ID, 10) }/>
 			}
@@ -774,7 +798,7 @@ templ mainForm_(f mainForm) {
 			<button class="primary" type="submit">Tallenna</button>
 		</form>
 		if f.ID != 0 {
-			<a class="ghost" href="/ruuat">Peruuta</a>
+			<a class="ghost" href="/ruuat" data-on:click__prevent="@get('/ruuat/nayta')">Peruuta</a>
 		}
 	</details>
 }
@@ -803,7 +827,11 @@ templ sideForm_(f sideForm) {
 		if f.Err != "" {
 			<p class="formerr">{ f.Err }</p>
 		}
-		<form method="post" action="/ruuat/lisuke">
+		<form
+			method="post"
+			action="/ruuat/lisuke"
+			data-on:submit__prevent="@post('/ruuat/lisuke', {contentType: 'form'})"
+		>
 			if f.ID != 0 {
 				<input type="hidden" name="id" value={ strconv.FormatInt(f.ID, 10) }/>
 			}
@@ -814,7 +842,7 @@ templ sideForm_(f sideForm) {
 			<button class="primary" type="submit">Tallenna</button>
 		</form>
 		if f.ID != 0 {
-			<a class="ghost" href="/ruuat">Peruuta</a>
+			<a class="ghost" href="/ruuat" data-on:click__prevent="@get('/ruuat/nayta')">Peruuta</a>
 		}
 	</details>
 }

scripts/smoke.sh

@@ -268,9 +268,34 @@ check "the bin asks before deleting" \
 check "the dish is still there while it asks" \
 	"$(curl -s -u ":$pass" "http://$addr/ruuat?poista=$uusi&tyyppi=paa")" "Uunikala"
 
-check "confirming the delete redirects back to the catalog" \
-	"$(curl -s -o /dev/null -w '%{redirect_url}' -u ":$pass" \
+# ---- the catalog patches in place instead of navigating -----------------
+
+# A delete confirmation halfway down a long list must not send the browser
+# back to the top, so these answer with a Datastar patch rather than a page.
+patch=$(curl -s -u ":$pass" -H 'Datastar-Request: true' \
+	"http://$addr/ruuat/nayta?poista=$uusi&tyyppi=paa")
+check "asking to delete patches rather than navigates" "$patch" "event: datastar-patch-elements"
+check "the patch carries the list" "$patch" 'id="ruokalista"'
+check "and both forms, so an open one closes" "$patch" 'id="paaruoka"'
+check "the row it patches in is asking" "$patch" "Poista?"
+
+check "patches are served as an event stream" \
+	"$(curl -s -o /dev/null -w '%{content_type}' -u ":$pass" -H 'Datastar-Request: true' \
+		"http://$addr/ruuat/nayta")" "text/event-stream"
+
+check "deleting from Datastar patches too" \
+	"$(curl -s -u ":$pass" -H 'Datastar-Request: true' \
 		-d "id=$uusi&tyyppi=paa" "http://$addr/ruuat/poista")" \
+	"event: datastar-patch-elements"
+
+refute "and the dish is gone from the patched list" \
+	"$(curl -s -u ":$pass" -H 'Datastar-Request: true' "http://$addr/ruuat/nayta")" \
+	"Uunikala"
+
+# Without the header it must still be an ordinary redirect, for no JavaScript.
+check "a plain form post still redirects" \
+	"$(curl -s -o /dev/null -w '%{redirect_url}' -u ":$pass" \
+		-d 'nimi=Testiruoka&kategoria=fish' "http://$addr/ruuat/paaruoka")" \
 	"/ruuat"
 
 refute "the dish is gone once confirmed" \