CUB-135: Subscribe to SSE in React and update UI

Reviewed-on: #41

backend/cmd/server/main.go

@@ -12,6 +12,7 @@ import (
 	"github.com/CubeCraft-Creations/Extrudex/backend/internal/config"
 	"github.com/CubeCraft-Creations/Extrudex/backend/internal/db"
 	"github.com/CubeCraft-Creations/Extrudex/backend/internal/router"
+	"github.com/CubeCraft-Creations/Extrudex/backend/internal/sse"
 )
 
 func main() {
@@ -39,15 +40,24 @@ func main() {
 
 	slog.Info("database connected")
 
+	// Create SSE broadcaster and start it
+	sseBC := sse.NewBroadcaster(128)
+	sseBC.Start()
+	defer sseBC.Stop()
+
+	slog.Info("sse broadcaster started")
+
 	// Create router
-	r := router.New(cfg, dbPool)
+	r := router.New(cfg, dbPool, sseBC)
 
 	// Create HTTP server
+	// WriteTimeout is 0 for SSE support — the Chi middleware.Timeout(60s)
+	// handles request-level timeouts on non-SSE routes.
 	server := &http.Server{
 		Addr:         ":" + cfg.Port,
 		Handler:      r,
 		ReadTimeout:  15 * time.Second,
-		WriteTimeout: 15 * time.Second,
+		WriteTimeout: 0, // disabled for SSE long-lived connections
 		IdleTimeout:  60 * time.Second,
 	}
 

backend/internal/router/router.go

@@ -8,13 +8,14 @@ import (
 	"github.com/CubeCraft-Creations/Extrudex/backend/internal/handlers"
 	"github.com/CubeCraft-Creations/Extrudex/backend/internal/repositories"
 	"github.com/CubeCraft-Creations/Extrudex/backend/internal/services"
+	"github.com/CubeCraft-Creations/Extrudex/backend/internal/sse"
 	"github.com/go-chi/chi/v5"
 	"github.com/go-chi/chi/v5/middleware"
 	"github.com/jackc/pgx/v5/pgxpool"
 )
 
 // New creates and configures a Chi router with all middleware and handlers mounted.
-func New(cfg *config.Config, dbPool *pgxpool.Pool) chi.Router {
+func New(cfg *config.Config, dbPool *pgxpool.Pool, sseBC *sse.Broadcaster) chi.Router {
 	r := chi.NewRouter()
 
 	// Middleware
@@ -22,7 +23,7 @@ func New(cfg *config.Config, dbPool *pgxpool.Pool) chi.Router {
 	r.Use(middleware.RealIP)
 	r.Use(middleware.Logger)
 	r.Use(middleware.Recoverer)
-	r.Use(middleware.Timeout(60 * time.Second))
+	// Timeout middleware is applied per-route below to exclude SSE
 
 	// CORS
 	r.Use(func(next http.Handler) http.Handler {
@@ -38,9 +39,9 @@ func New(cfg *config.Config, dbPool *pgxpool.Pool) chi.Router {
 		})
 	})
 
-	// Health check
+	// Health check (with timeout)
 	healthHandler := handlers.NewHealthHandler(dbPool)
-	r.Get("/health", healthHandler.ServeHTTP)
+	r.With(middleware.Timeout(30 * time.Second)).Get("/health", healthHandler.ServeHTTP)
 
 	// ── Repositories ──────────────────────────────────────────────────────
 	materialRepo := repositories.NewMaterialRepository(dbPool)
@@ -61,8 +62,9 @@ func New(cfg *config.Config, dbPool *pgxpool.Pool) chi.Router {
 	printJobHandler := handlers.NewPrintJobHandler(printJobService)
 	usageLogHandler := handlers.NewUsageLogHandler(usageLogRepo)
 
-	// ── API Routes ────────────────────────────────────────────────────────
+	// ── API Routes (with timeout) ─────────────────────────────────────────
 	r.Route("/api", func(r chi.Router) {
+		r.Use(middleware.Timeout(60 * time.Second))
 		r.Get("/materials", materialHandler.List)
 
 		r.Route("/filaments", func(r chi.Router) {
@@ -78,6 +80,10 @@ func New(cfg *config.Config, dbPool *pgxpool.Pool) chi.Router {
 		r.Get("/printers", printerHandler.List)
 		r.Get("/print-jobs", printJobHandler.List)
 		r.Get("/usage-logs", usageLogHandler.List)
+
+		// SSE Events stream
+		sseHandler := sse.NewHandler(sseBC)
+		r.Get("/events", sseHandler.ServeHTTP)
 	})
 
 	return r

backend/internal/sse/broadcaster.go

@@ -0,0 +1,133 @@
+package sse
+
+import (
+	"log/slog"
+	"sync"
+)
+
+// client represents a single SSE subscriber — identified by its send channel.
+type client struct {
+	ch chan string
+}
+
+// Broadcaster receives Events on its input channel and fans them out to every
+// connected client. Subscribe adds a new client; Unsubscribe removes one.
+// Start must be called before the broadcaster accepts events.
+type Broadcaster struct {
+	input       chan Event
+	subscribe   chan client
+	unsubscribe chan client
+	clients     map[chan string]struct{}
+	done        chan struct{}
+	once        sync.Once
+}
+
+// NewBroadcaster creates a Broadcaster. bufSize controls the buffer depth for
+// the input channel as well as for each per-client outbound channel.
+func NewBroadcaster(bufSize int) *Broadcaster {
+	if bufSize <= 0 {
+		bufSize = 64
+	}
+	return &Broadcaster{
+		input:       make(chan Event, bufSize),
+		subscribe:   make(chan client),
+		unsubscribe: make(chan client),
+		clients:     make(map[chan string]struct{}),
+		done:        make(chan struct{}),
+	}
+}
+
+// Publish pushes an event into the broadcaster. Safe for concurrent use.
+func (b *Broadcaster) Publish(ev Event) {
+	select {
+	case b.input <- ev:
+	case <-b.done:
+		// Silently drop during shutdown.
+	}
+}
+
+// Start launches the broadcaster's fan-out loop in a goroutine.
+// It must be called before Publish is used.
+func (b *Broadcaster) Start() {
+	go b.loop()
+}
+
+// Stop terminates the fan-out loop and closes all client channels.
+// It is safe to call multiple times.
+func (b *Broadcaster) Stop() {
+	b.once.Do(func() {
+		close(b.done)
+	})
+}
+
+// Subscribe returns a new client channel that receives SSE-formatted strings.
+func (b *Broadcaster) Subscribe() chan string {
+	c := client{ch: make(chan string, 64)}
+	select {
+	case b.subscribe <- c:
+	case <-b.done:
+		// Broadcaster already stopped — return a closed chan so the handler
+		// can bail out quickly.
+		ch := make(chan string)
+		close(ch)
+		return ch
+	}
+	return c.ch
+}
+
+// Unsubscribe removes a client channel and closes it.
+func (b *Broadcaster) Unsubscribe(ch chan string) {
+	c := client{ch: ch}
+	select {
+	case b.unsubscribe <- c:
+	case <-b.done:
+		// Already shutting down — channels will be cleaned up by Stop.
+	}
+}
+
+// loop is the core fan-out goroutine.
+func (b *Broadcaster) loop() {
+	for {
+		select {
+		case ev := <-b.input:
+			sse := ev.toSSE()
+			for ch := range b.clients {
+				// Non-blocking send — slow clients are dropped.
+				select {
+				case ch <- sse:
+				default:
+					slog.Warn("sse broadcaster: dropping event for slow client", "type", ev.Type)
+				}
+			}
+
+		case c := <-b.subscribe:
+			b.clients[c.ch] = struct{}{}
+			slog.Debug("sse broadcaster: client connected", "total_clients", len(b.clients))
+
+		case c := <-b.unsubscribe:
+			if _, ok := b.clients[c.ch]; ok {
+				delete(b.clients, c.ch)
+				close(c.ch)
+				slog.Debug("sse broadcaster: client disconnected", "total_clients", len(b.clients))
+			}
+
+		case <-b.done:
+			// Drain remaining events in input before shutting down.
+			for ev := range b.input {
+				sse := ev.toSSE()
+				for ch := range b.clients {
+					select {
+					case ch <- sse:
+					default:
+					}
+				}
+			}
+			// Close all remaining client channels.
+			for ch := range b.clients {
+				close(ch)
+			}
+			b.clients = nil
+			return
+		}
+	}
+}

backend/internal/sse/events.go

@@ -0,0 +1,92 @@
+// Package sse provides Server-Sent Events infrastructure for real-time updates.
+// Includes event types, a central broadcaster, and an HTTP handler.
+package sse
+
+import (
+	"encoding/json"
+	"time"
+)
+
+// EventType identifies the category of an SSE event.
+type EventType string
+
+const (
+	EventPrinterStatus  EventType = "printer.status"
+	EventJobStarted     EventType = "job.started"
+	EventJobCompleted   EventType = "job.completed"
+	EventFilamentLow    EventType = "filament.low"
+)
+
+// Event is a JSON-serializable SSE event pushed through the broadcaster.
+type Event struct {
+	Type      EventType       `json:"type"`
+	Payload   json.RawMessage `json:"payload"`
+	Timestamp time.Time       `json:"timestamp"`
+}
+
+// PrinterStatusPayload carries printer online/offline/printing state.
+type PrinterStatusPayload struct {
+	PrinterID   int    `json:"printer_id"`
+	PrinterName string `json:"printer_name"`
+	Status      string `json:"status"` // "online", "offline", "printing"
+}
+
+// JobStartedPayload carries initial print job info.
+type JobStartedPayload struct {
+	JobID      int    `json:"job_id"`
+	JobName    string `json:"job_name"`
+	PrinterID  int    `json:"printer_id"`
+	SpoolID    *int   `json:"spool_id,omitempty"`
+}
+
+// JobCompletedPayload carries final print job data including usage.
+type JobCompletedPayload struct {
+	JobID           int     `json:"job_id"`
+	JobName         string  `json:"job_name"`
+	PrinterID       int     `json:"printer_id"`
+	DurationSeconds *int    `json:"duration_seconds,omitempty"`
+	TotalGramsUsed  *float64 `json:"total_grams_used,omitempty"`
+	TotalCostUSD    *float64 `json:"total_cost_usd,omitempty"`
+}
+
+// FilamentLowPayload alerts that a spool is below its threshold.
+type FilamentLowPayload struct {
+	SpoolID       int    `json:"spool_id"`
+	SpoolName     string `json:"spool_name"`
+	RemainingGrams int   `json:"remaining_grams"`
+	ThresholdGrams int   `json:"threshold_grams"`
+}
+
+// NewEvent creates an Event with the current timestamp from a typed payload.
+func NewEvent(eventType EventType, payload any) (Event, error) {
+	raw, err := json.Marshal(payload)
+	if err != nil {
+		return Event{}, err
+	}
+	return Event{
+		Type:      eventType,
+		Payload:   raw,
+		Timestamp: time.Now().UTC(),
+	}, nil
+}
+
+// MustEvent creates an Event and panics on marshal failure (for use with
+// known-good payloads in tests and internal wiring).
+func MustEvent(eventType EventType, payload any) Event {
+	ev, err := NewEvent(eventType, payload)
+	if err != nil {
+		panic("sse.MustEvent: failed to marshal payload: " + err.Error())
+	}
+	return ev
+}
+
+// toSSE formats this Event as a standard SSE message string ready to be
+// written to a response writer. The format is:
+//
+//	event: <type>
+//	data: <json>
+//
+func (e Event) toSSE() string {
+	data, _ := json.Marshal(e)
+	return "event: " + string(e.Type) + "\n" + "data: " + string(data) + "\n\n"
+}

backend/internal/sse/handler.go

@@ -0,0 +1,59 @@
+package sse
+
+import (
+	"net/http"
+)
+
+// Handler is the HTTP handler for the GET /api/events SSE stream.
+// It registers a client with the broadcaster, streams events as they arrive,
+// and unregisters on disconnect.
+type Handler struct {
+	bc *Broadcaster
+}
+
+// NewHandler creates a Handler backed by the given Broadcaster.
+func NewHandler(bc *Broadcaster) *Handler {
+	return &Handler{bc: bc}
+}
+
+// ServeHTTP implements the SSE streaming endpoint.
+// Flusher is required; clients that do not support flushing receive a 501.
+func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	flusher, ok := w.(http.Flusher)
+	if !ok {
+		http.Error(w, "streaming not supported", http.StatusNotImplemented)
+		return
+	}
+
+	// SSE-specific headers
+	w.Header().Set("Content-Type", "text/event-stream")
+	w.Header().Set("Cache-Control", "no-cache")
+	w.Header().Set("Connection", "keep-alive")
+	w.Header().Set("X-Accel-Buffering", "no") // Disable nginx buffering
+
+	// Write headers immediately
+	flusher.Flush()
+
+	// Subscribe to the broadcaster
+	ch := h.bc.Subscribe()
+	defer h.bc.Unsubscribe(ch)
+
+	// Use request context for cancellation when the client disconnects.
+	ctx := r.Context()
+
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case msg, ok := <-ch:
+			if !ok {
+				return
+			}
+			_, err := w.Write([]byte(msg))
+			if err != nil {
+				return
+			}
+			flusher.Flush()
+		}
+	}
+}

frontend/src/App.tsx

@@ -1,28 +1,35 @@
-import { useState, useEffect } from 'react'
+import { QueryClient, QueryClientProvider } from '@tanstack/react-query'
+import { BrowserRouter, Routes, Route } from 'react-router-dom'
+import InventoryPage from './pages/InventoryPage'
+import ToastContainer from './components/ToastContainer'
+import { useSSE } from './hooks/useSSE'
 
-function App() {
-  const [health, setHealth] = useState<any>(null)
+const queryClient = new QueryClient()
 
-  useEffect(() => {
-    fetch('/api/health')
-      .then(r => r.json())
-      .then(setHealth)
-      .catch(console.error)
-  }, [])
-
-  return (
-    <div className="min-h-screen flex items-center justify-center">
-      <div className="p-6 rounded-lg bg-slate-800 shadow-xl max-w-md w-full">
-        <h1 className="text-2xl font-bold mb-4 text-emerald-400">Extrudex</h1>
-        <p className="text-slate-300 mb-4">React frontend scaffold</p>
-        {health && (
-          <pre className="text-xs bg-slate-900 p-3 rounded overflow-auto">
-            {JSON.stringify(health, null, 2)}
-          </pre>
-        )}
-      </div>
-    </div>
-  )
+function SSEProvider({ children }: { children: React.ReactNode }) {
+  useSSE()
+  return <>{children}</>
 }
 
-export default App
+export default function App() {
+  return (
+    <QueryClientProvider client={queryClient}>
+      <BrowserRouter>
+        <SSEProvider>
+          <div className="min-h-screen bg-slate-900 text-slate-50">
+            <header className="bg-slate-800 border-b border-slate-700 px-4 py-3 flex items-center gap-3 sticky top-0 z-20">
+              <div className="w-8 h-8 rounded bg-emerald-500 flex items-center justify-center text-slate-900 font-bold text-lg">E</div>
+              <h1 className="text-lg font-semibold">Extrudex</h1>
+            </header>
+            <main className="p-4">
+              <Routes>
+                <Route path="/" element={<InventoryPage />} />
+              </Routes>
+            </main>
+          </div>
+          <ToastContainer />
+        </SSEProvider>
+      </BrowserRouter>
+    </QueryClientProvider>
+  )
+}

frontend/src/components/ColorSwatch.tsx

@@ -0,0 +1,18 @@
+interface ColorSwatchProps {
+  colorHex: string
+  size?: number
+}
+
+export default function ColorSwatch({ colorHex, size = 24 }: ColorSwatchProps) {
+  return (
+    <div
+      className="rounded-full border border-slate-600 shadow-sm inline-block"
+      style={{
+        backgroundColor: colorHex.startsWith('#') ? colorHex : `#${colorHex}`,
+        width: size,
+        height: size,
+      }}
+      title={colorHex}
+    />
+  )
+}

frontend/src/components/PrinterStatusBadge.tsx

@@ -0,0 +1,17 @@
+import { Printer } from 'lucide-react'
+
+const STYLES = {
+  online: 'bg-emerald-600 text-white',
+  offline: 'bg-slate-600 text-slate-200',
+  printing: 'bg-blue-600 text-white animate-pulse',
+}
+
+export default function PrinterStatusBadge({ status, name }: { status: string; name?: string }) {
+  const style = STYLES[status as keyof typeof STYLES] ?? STYLES.offline
+  return (
+    <span className={`inline-flex items-center gap-1.5 rounded-full px-2.5 py-1 text-xs font-medium ${style}`}>
+      <Printer size={12} />
+      {name ? `${name} · ${status}` : status}
+    </span>
+  )
+}

frontend/src/components/ToastContainer.tsx

@@ -0,0 +1,70 @@
+import { useEffect, useState, useCallback } from 'react'
+import { X, CheckCircle, AlertTriangle, Info } from 'lucide-react'
+import { addToastListener, type ToastMessage } from '../hooks/useSSE'
+
+const ICONS = {
+  info: Info,
+  success: CheckCircle,
+  warning: AlertTriangle,
+}
+
+const STYLES = {
+  info: 'border-blue-600 bg-blue-900/40 text-blue-100',
+  success: 'border-emerald-600 bg-emerald-900/40 text-emerald-100',
+  warning: 'border-amber-600 bg-amber-900/40 text-amber-100',
+}
+
+export default function ToastContainer() {
+  const [toasts, setToasts] = useState<ToastMessage[]>([])
+
+  const remove = useCallback((id: string) => {
+    setToasts(prev => prev.filter(t => t.id !== id))
+  }, [])
+
+  useEffect(() => {
+    return addToastListener((toast) => {
+      setToasts(prev => {
+        // Prevent duplicate identical toasts within 3 seconds
+        const now = Date.now()
+        const recent = prev.filter(
+          t => t.title === toast.title && now - parseInt(t.id.split('-').pop() || '0', 10) < 3000
+        )
+        if (recent.length > 0) return prev
+        return [...prev.slice(-4), toast]
+      })
+      // Auto-dismiss after 5 seconds
+      setTimeout(() => remove(toast.id), 5000)
+    })
+  }, [remove])
+
+  return (
+    <div className="fixed bottom-4 right-4 z-50 flex flex-col gap-2 max-w-sm w-full pointer-events-none">
+      {toasts.map((toast) => {
+        const Icon = ICONS[toast.type]
+        return (
+          <div
+            key={toast.id}
+            className={`pointer-events-auto rounded-lg border px-4 py-3 shadow-lg backdrop-blur-sm transition-all ${STYLES[toast.type]}`}
+          >
+            <div className="flex items-start gap-3">
+              <Icon size={18} className="mt-0.5 shrink-0" />
+              <div className="flex-1 min-w-0">
+                <p className="text-sm font-semibold leading-snug">{toast.title}</p>
+                {toast.body && (
+                  <p className="text-xs opacity-80 mt-0.5">{toast.body}</p>
+                )}
+              </div>
+              <button
+                onClick={() => remove(toast.id)}
+                className="shrink-0 -mr-1 -mt-1 p-1 rounded hover:bg-white/10 text-current opacity-70 hover:opacity-100 transition-opacity"
+                aria-label="Dismiss"
+              >
+                <X size={14} />
+              </button>
+            </div>
+          </div>
+        )
+      })}
+    </div>
+  )
+}

frontend/src/hooks/useSSE.ts

@@ -0,0 +1,193 @@
+import { useEffect, useRef, useCallback } from 'react'
+import { useQueryClient } from '@tanstack/react-query'
+
+export type SSEEventType =
+  | 'printer.status'
+  | 'job.started'
+  | 'job.completed'
+  | 'filament.low'
+
+export interface SSEEvent {
+  type: SSEEventType
+  payload: unknown
+  timestamp: string
+}
+
+export interface ToastMessage {
+  id: string
+  type: 'info' | 'success' | 'warning'
+  title: string
+  body?: string
+}
+
+let toastListeners: Array<(toast: ToastMessage) => void> = []
+
+export function addToastListener(cb: (toast: ToastMessage) => void) {
+  toastListeners.push(cb)
+  return () => {
+    toastListeners = toastListeners.filter(l => l !== cb)
+  }
+}
+
+function emitToast(toast: ToastMessage) {
+  toastListeners.forEach(cb => cb(toast))
+}
+
+const RECONNECT_BASE_MS = 1000
+const RECONNECT_MAX_MS = 30000
+
+export function useSSE(enabled = true) {
+  const queryClient = useQueryClient()
+  const esRef = useRef<EventSource | null>(null)
+  const reconnectTimerRef = useRef<ReturnType<typeof setTimeout> | null>(null)
+  const attemptRef = useRef(0)
+
+  const connect = useCallback(() => {
+    if (!enabled) return
+    if (esRef.current) {
+      esRef.current.close()
+    }
+
+    const es = new EventSource('/api/events')
+    esRef.current = es
+
+    es.onopen = () => {
+      attemptRef.current = 0
+    }
+
+    es.addEventListener('printer.status', (e) => {
+      try {
+        const data = JSON.parse(e.data) as SSEEvent
+        const payload = data.payload as {
+          printer_id: number
+          printer_name: string
+          status: string
+        }
+        // Update printer list cache if it exists
+        queryClient.setQueryData(['printers'], (old: unknown) => {
+          if (!Array.isArray(old)) return old
+          return old.map((p: any) =>
+            p.id === payload.printer_id
+              ? { ...p, status: payload.status, name: payload.printer_name }
+              : p
+          )
+        })
+      } catch {
+        // ignore malformed event
+      }
+    })
+
+    es.addEventListener('job.started', (e) => {
+      try {
+        const data = JSON.parse(e.data) as SSEEvent
+        const payload = data.payload as {
+          job_id: number
+          job_name: string
+          printer_id: number
+          spool_id?: number
+        }
+        emitToast({
+          id: `job-started-${payload.job_id}-${Date.now()}`,
+          type: 'info',
+          title: `Job started: ${payload.job_name}`,
+          body: `Printer #${payload.printer_id}`,
+        })
+        // Invalidate print jobs list
+        queryClient.invalidateQueries({ queryKey: ['print-jobs'] })
+      } catch {
+        // ignore malformed event
+      }
+    })
+
+    es.addEventListener('job.completed', (e) => {
+      try {
+        const data = JSON.parse(e.data) as SSEEvent
+        const payload = data.payload as {
+          job_id: number
+          job_name: string
+          printer_id: number
+          duration_seconds?: number
+          total_grams_used?: number
+          total_cost_usd?: number
+        }
+        const parts: string[] = []
+        if (payload.duration_seconds != null) {
+          const mins = Math.round(payload.duration_seconds / 60)
+          parts.push(`${mins} min`)
+        }
+        if (payload.total_grams_used != null) {
+          parts.push(`${payload.total_grams_used.toFixed(1)} g used`)
+        }
+        emitToast({
+          id: `job-completed-${payload.job_id}-${Date.now()}`,
+          type: 'success',
+          title: `Job completed: ${payload.job_name}`,
+          body: parts.join(' · ') || `Printer #${payload.printer_id}`,
+        })
+        queryClient.invalidateQueries({ queryKey: ['print-jobs'] })
+        queryClient.invalidateQueries({ queryKey: ['filaments'] })
+      } catch {
+        // ignore malformed event
+      }
+    })
+
+    es.addEventListener('filament.low', (e) => {
+      try {
+        const data = JSON.parse(e.data) as SSEEvent
+        const payload = data.payload as {
+          spool_id: number
+          spool_name: string
+          remaining_grams: number
+          threshold_grams: number
+        }
+        emitToast({
+          id: `filament-low-${payload.spool_id}-${Date.now()}`,
+          type: 'warning',
+          title: `Low filament: ${payload.spool_name}`,
+          body: `${payload.remaining_grams} g remaining (threshold ${payload.threshold_grams} g)`,
+        })
+        // Update filament inventory cache in place for instant UI feedback
+        queryClient.setQueryData(['filaments'], (old: unknown) => {
+          if (!old || typeof old !== 'object') return old
+          const o = old as { data?: Array<Record<string, unknown>>; total?: number }
+          if (!Array.isArray(o.data)) return old
+          return {
+            ...o,
+            data: o.data.map((f) =>
+              (f.id as number) === payload.spool_id
+                ? { ...f, remaining_grams: payload.remaining_grams }
+                : f
+            ),
+          }
+        })
+      } catch {
+        // ignore malformed event
+      }
+    })
+
+    es.onerror = () => {
+      es.close()
+      // Exponential backoff with jitter
+      const base = Math.min(RECONNECT_MAX_MS, RECONNECT_BASE_MS * 2 ** attemptRef.current)
+      const jitter = Math.random() * 1000
+      const delay = base + jitter
+      attemptRef.current += 1
+      reconnectTimerRef.current = setTimeout(() => {
+        connect()
+      }, delay)
+    }
+  }, [enabled, queryClient])
+
+  useEffect(() => {
+    connect()
+    return () => {
+      if (reconnectTimerRef.current) {
+        clearTimeout(reconnectTimerRef.current)
+      }
+      if (esRef.current) {
+        esRef.current.close()
+        esRef.current = null
+      }
+    }
+  }, [connect])
+}

frontend/src/pages/InventoryPage.tsx

@@ -0,0 +1,339 @@
+import { useState, useMemo } from 'react'
+import { useQuery } from '@tanstack/react-query'
+import { Search, Filter, ChevronLeft, ChevronRight, Trash2, Pencil, Plus, AlertTriangle } from 'lucide-react'
+import ColorSwatch from '../components/ColorSwatch'
+import { fetchFilaments, deleteFilament } from '../services/filamentService'
+import type { FilamentSpool, FilamentFilter } from '../types/filament'
+
+const PAGE_SIZE = 20
+
+type SortField = 'name' | 'remaining_grams' | 'cost_usd'
+type SortDir = 'asc' | 'desc'
+
+export default function InventoryPage() {
+  const [search, setSearch] = useState('')
+  const [material, setMaterial] = useState('')
+  const [finish, setFinish] = useState('')
+  const [lowStockOnly, setLowStockOnly] = useState(false)
+  const [sortBy, setSortBy] = useState<SortField>('name')
+  const [sortDir, setSortDir] = useState<SortDir>('asc')
+  const [page, setPage] = useState(0)
+  const [deleteId, setDeleteId] = useState<number | null>(null)
+
+  const filter: FilamentFilter = useMemo(() => ({
+    material: material || undefined,
+    finish: finish || undefined,
+    low_stock: lowStockOnly,
+    sort_by: sortBy,
+    sort_dir: sortDir,
+    limit: PAGE_SIZE,
+    offset: page * PAGE_SIZE,
+  }), [material, finish, lowStockOnly, sortBy, sortDir, page])
+
+  const { data, isLoading, error, refetch } = useQuery({
+    queryKey: ['filaments', filter],
+    queryFn: () => fetchFilaments(filter),
+  })
+
+  const filaments = data?.data ?? []
+  const total = data?.total ?? 0
+  const totalPages = Math.max(1, Math.ceil(total / PAGE_SIZE))
+
+  // Client-side search filter (name/barcode) since backend may not support it yet.
+  const filtered = useMemo(() => {
+    if (!search.trim()) return filaments
+    const q = search.toLowerCase()
+    return filaments.filter(
+      (f: FilamentSpool) =>
+        f.name.toLowerCase().includes(q) ||
+        (f.barcode && f.barcode.toLowerCase().includes(q))
+    )
+  }, [filaments, search])
+
+  const handleSort = (field: SortField) => {
+    if (sortBy === field) {
+      setSortDir(prev => (prev === 'asc' ? 'desc' : 'asc'))
+    } else {
+      setSortBy(field)
+      setSortDir('asc')
+    }
+    setPage(0)
+  }
+
+  const handleDelete = async (id: number) => {
+    await deleteFilament(id)
+    setDeleteId(null)
+    refetch()
+  }
+
+  const SortIndicator = ({ field }: { field: SortField }) => {
+    if (sortBy !== field) return <span className="text-slate-600 ml-1">↕</span>
+    return <span className="text-emerald-400 ml-1">{sortDir === 'asc' ? '↑' : '↓'}</span>
+  }
+
+  return (
+    <div className="space-y-4">
+      {/* Header */}
+      <div className="flex flex-col sm:flex-row sm:items-center sm:justify-between gap-3">
+        <div>
+          <h2 className="text-xl font-bold text-slate-100">Filament Inventory</h2>
+          <p className="text-sm text-slate-400">{total} spool(s) total</p>
+        </div>
+        <button className="inline-flex items-center gap-2 rounded-lg bg-emerald-600 px-4 py-2 text-sm font-semibold text-white hover:bg-emerald-500 active:bg-emerald-700 transition-colors">
+          <Plus size={16} /> Add Spool
+        </button>
+      </div>
+
+      {/* Filters */}
+      <div className="flex flex-col lg:flex-row gap-3">
+        {/* Search */}
+        <div className="relative flex-1">
+          <Search size={16} className="absolute left-3 top-1/2 -translate-y-1/2 text-slate-400" />
+          <input
+            type="text"
+            placeholder="Search by name or barcode…"
+            value={search}
+            onChange={e => { setSearch(e.target.value); setPage(0) }}
+            className="w-full rounded-lg bg-slate-800 border border-slate-700 pl-9 pr-3 py-2 text-sm text-slate-100 placeholder-slate-500 focus:outline-none focus:ring-2 focus:ring-emerald-500 focus:border-emerald-500"
+          />
+        </div>
+
+        {/* Material filter */}
+        <select
+          value={material}
+          onChange={e => { setMaterial(e.target.value); setPage(0) }}
+          className="rounded-lg bg-slate-800 border border-slate-700 px-3 py-2 text-sm text-slate-100 focus:outline-none focus:ring-2 focus:ring-emerald-500"
+        >
+          <option value="">All Materials</option>
+          <option value="PLA">PLA</option>
+          <option value="PETG">PETG</option>
+          <option value="ABS">ABS</option>
+          <option value="TPU">TPU</option>
+          <option value="ASA">ASA</option>
+          <option value="Nylon">Nylon</option>
+          <option value="PC">PC</option>
+        </select>
+
+        {/* Finish filter */}
+        <select
+          value={finish}
+          onChange={e => { setFinish(e.target.value); setPage(0) }}
+          className="rounded-lg bg-slate-800 border border-slate-700 px-3 py-2 text-sm text-slate-100 focus:outline-none focus:ring-2 focus:ring-emerald-500"
+        >
+          <option value="">All Finishes</option>
+          <option value="Basic">Basic</option>
+          <option value="Silk">Silk</option>
+          <option value="Matte">Matte</option>
+          <option value="Glossy">Glossy</option>
+          <option value="Wood">Wood</option>
+          <option value="Marble">Marble</option>
+        </select>
+
+        {/* Low stock toggle */}
+        <label className="inline-flex items-center gap-2 rounded-lg bg-slate-800 border border-slate-700 px-3 py-2 text-sm text-slate-100 cursor-pointer select-none hover:bg-slate-750">
+          <Filter size={14} className="text-amber-400" />
+          <input
+            type="checkbox"
+            checked={lowStockOnly}
+            onChange={e => { setLowStockOnly(e.target.checked); setPage(0) }}
+            className="accent-amber-500"
+          />
+          Low Stock Only
+        </label>
+      </div>
+
+      {/* Loading / Error */}
+      {isLoading && (
+        <div className="text-center py-12 text-slate-400">Loading spools…</div>
+      )}
+      {error && (
+        <div className="text-center py-12 text-red-400">
+          Failed to load inventory.
+          <button onClick={() => refetch()} className="ml-2 underline hover:text-red-300">Retry</button>
+        </div>
+      )}
+
+      {/* Desktop Table */}
+      {!isLoading && !error && (
+        <>
+          <div className="hidden md:block overflow-x-auto rounded-lg border border-slate-700">
+            <table className="w-full text-sm">
+              <thead className="bg-slate-800 text-slate-300">
+                <tr>
+                  <th className="px-4 py-3 text-left font-semibold cursor-pointer select-none hover:text-slate-100" onClick={() => handleSort('name')}>
+                    Name <SortIndicator field="name" />
+                  </th>
+                  <th className="px-4 py-3 text-left font-semibold">Material</th>
+                  <th className="px-4 py-3 text-left font-semibold">Finish</th>
+                  <th className="px-4 py-3 text-left font-semibold">Color</th>
+                  <th className="px-4 py-3 text-right font-semibold cursor-pointer select-none hover:text-slate-100" onClick={() => handleSort('remaining_grams')}>
+                    Remaining <SortIndicator field="remaining_grams" />
+                  </th>
+                  <th className="px-4 py-3 text-right font-semibold cursor-pointer select-none hover:text-slate-100" onClick={() => handleSort('cost_usd')}>
+                    Cost <SortIndicator field="cost_usd" />
+                  </th>
+                  <th className="px-4 py-3 text-center font-semibold">Status</th>
+                  <th className="px-4 py-3 text-right font-semibold">Actions</th>
+                </tr>
+              </thead>
+              <tbody className="divide-y divide-slate-700">
+                {filtered.length === 0 && (
+                  <tr>
+                    <td colSpan={8} className="px-4 py-8 text-center text-slate-500">No spools found.</td>
+                  </tr>
+                )}
+                {filtered.map((spool: FilamentSpool) => {
+                  const isLow = spool.remaining_grams <= spool.low_stock_threshold_grams
+                  return (
+                    <tr key={spool.id} className={`${isLow ? 'bg-red-900/20' : 'bg-slate-800/50'} hover:bg-slate-700/50 transition-colors`}>
+                      <td className="px-4 py-3 font-medium text-slate-100">{spool.name}</td>
+                      <td className="px-4 py-3 text-slate-300">{spool.material_base?.name ?? '—'}</td>
+                      <td className="px-4 py-3 text-slate-300">{spool.material_finish?.name ?? '—'}</td>
+                      <td className="px-4 py-3">
+                        <div className="flex items-center gap-2">
+                          <ColorSwatch colorHex={spool.color_hex} size={20} />
+                          <span className="text-xs text-slate-400 uppercase">{spool.color_hex}</span>
+                        </div>
+                      </td>
+                      <td className="px-4 py-3 text-right tabular-nums text-slate-200">{spool.remaining_grams.toLocaleString()} g</td>
+                      <td className="px-4 py-3 text-right tabular-nums text-slate-300">{spool.cost_usd != null ? `$${spool.cost_usd.toFixed(2)}` : '—'}</td>
+                      <td className="px-4 py-3 text-center">
+                        {isLow ? (
+                          <span className="inline-flex items-center gap-1 rounded-full bg-red-900/50 border border-red-700 px-2 py-0.5 text-xs font-medium text-red-300">
+                            <AlertTriangle size={12} /> Low
+                          </span>
+                        ) : (
+                          <span className="inline-flex items-center rounded-full bg-emerald-900/30 border border-emerald-700 px-2 py-0.5 text-xs font-medium text-emerald-300">OK</span>
+                        )}
+                      </td>
+                      <td className="px-4 py-3 text-right">
+                        <div className="flex items-center justify-end gap-2">
+                          <button className="p-1.5 rounded hover:bg-slate-600 text-slate-400 hover:text-blue-400 transition-colors" title="Edit">
+                            <Pencil size={14} />
+                          </button>
+                          <button
+                            onClick={() => setDeleteId(spool.id)}
+                            className="p-1.5 rounded hover:bg-slate-600 text-slate-400 hover:text-red-400 transition-colors"
+                            title="Delete"
+                          >
+                            <Trash2 size={14} />
+                          </button>
+                        </div>
+                      </td>
+                    </tr>
+                  )
+                })}
+              </tbody>
+            </table>
+          </div>
+
+          {/* Mobile Cards */}
+          <div className="md:hidden space-y-3">
+            {filtered.length === 0 && (
+              <div className="text-center py-12 text-slate-500">No spools found.</div>
+            )}
+            {filtered.map((spool: FilamentSpool) => {
+              const isLow = spool.remaining_grams <= spool.low_stock_threshold_grams
+              return (
+                <div key={spool.id} className={`rounded-lg border ${isLow ? 'border-red-700 bg-red-900/10' : 'border-slate-700 bg-slate-800'} p-4 space-y-2`}>
+                  <div className="flex items-start justify-between">
+                    <div>
+                      <div className="font-semibold text-slate-100">{spool.name}</div>
+                      <div className="text-xs text-slate-400 mt-0.5">{spool.material_base?.name ?? '—'} · {spool.material_finish?.name ?? '—'}</div>
+                    </div>
+                    {isLow ? (
+                      <span className="inline-flex items-center gap-1 rounded-full bg-red-900/50 border border-red-700 px-2 py-0.5 text-xs font-medium text-red-300">
+                        <AlertTriangle size={12} /> Low
+                      </span>
+                    ) : (
+                      <span className="inline-flex items-center rounded-full bg-emerald-900/30 border border-emerald-700 px-2 py-0.5 text-xs font-medium text-emerald-300">OK</span>
+                    )}
+                  </div>
+
+                  <div className="flex items-center gap-3 text-sm">
+                    <div className="flex items-center gap-2">
+                      <ColorSwatch colorHex={spool.color_hex} size={20} />
+                      <span className="text-slate-400 uppercase text-xs">{spool.color_hex}</span>
+                    </div>
+                  </div>
+
+                  <div className="flex items-center justify-between text-sm">
+                    <span className="text-slate-400">Remaining: <span className="text-slate-200 font-medium tabular-nums">{spool.remaining_grams.toLocaleString()} g</span></span>
+                    <span className="text-slate-400">{spool.cost_usd != null ? `$${spool.cost_usd.toFixed(2)}` : '—'}</span>
+                  </div>
+
+                  <div className="flex items-center justify-end gap-2 pt-1">
+                    <button className="flex items-center gap-1 rounded-md bg-slate-700 px-3 py-1.5 text-xs font-medium text-slate-200 hover:bg-slate-600">
+                      <Pencil size={12} /> Edit
+                    </button>
+                    <button
+                      onClick={() => setDeleteId(spool.id)}
+                      className="flex items-center gap-1 rounded-md bg-red-900/30 border border-red-700 px-3 py-1.5 text-xs font-medium text-red-300 hover:bg-red-900/50"
+                    >
+                      <Trash2 size={12} /> Delete
+                    </button>
+                  </div>
+                </div>
+              )
+            })}
+          </div>
+
+          {/* Pagination */}
+          <div className="flex items-center justify-between pt-2">
+            <span className="text-sm text-slate-400">
+              Showing {page * PAGE_SIZE + 1}–{Math.min((page + 1) * PAGE_SIZE, total)} of {total}
+            </span>
+            <div className="flex items-center gap-2">
+              <button
+                onClick={() => setPage(p => Math.max(0, p - 1))}
+                disabled={page === 0}
+                className="p-2 rounded-lg bg-slate-800 border border-slate-700 text-slate-300 hover:bg-slate-700 disabled:opacity-40 disabled:cursor-not-allowed transition-colors"
+              >
+                <ChevronLeft size={16} />
+              </button>
+              <span className="text-sm text-slate-300 tabular-nums">{page + 1} / {totalPages}</span>
+              <button
+                onClick={() => setPage(p => Math.min(totalPages - 1, p + 1))}
+                disabled={page >= totalPages - 1}
+                className="p-2 rounded-lg bg-slate-800 border border-slate-700 text-slate-300 hover:bg-slate-700 disabled:opacity-40 disabled:cursor-not-allowed transition-colors"
+              >
+                <ChevronRight size={16} />
+              </button>
+            </div>
+          </div>
+        </>
+      )}
+
+      {/* Delete confirmation modal */}
+      {deleteId !== null && (
+        <div className="fixed inset-0 z-50 flex items-center justify-center bg-black/60 backdrop-blur-sm p-4">
+          <div className="w-full max-w-sm rounded-xl bg-slate-800 border border-slate-700 p-6 shadow-2xl space-y-4">
+            <div className="flex items-center gap-3">
+              <div className="flex h-10 w-10 items-center justify-center rounded-full bg-red-900/30">
+                <AlertTriangle size={20} className="text-red-400" />
+              </div>
+              <div>
+                <h3 className="text-lg font-semibold text-slate-100">Delete Spool?</h3>
+                <p className="text-sm text-slate-400">This action cannot be undone.</p>
+              </div>
+            </div>
+            <div className="flex justify-end gap-3">
+              <button
+                onClick={() => setDeleteId(null)}
+                className="rounded-lg bg-slate-700 px-4 py-2 text-sm font-medium text-slate-200 hover:bg-slate-600 transition-colors"
+              >
+                Cancel
+              </button>
+              <button
+                onClick={() => handleDelete(deleteId)}
+                className="rounded-lg bg-red-600 px-4 py-2 text-sm font-medium text-white hover:bg-red-500 transition-colors"
+              >
+                Delete
+              </button>
+            </div>
+          </div>
+        </div>
+      )}
+    </div>
+  )
+}

frontend/src/services/filamentService.ts

@@ -0,0 +1,24 @@
+import axios from 'axios'
+import type { FilamentSpool, ListResponse, FilamentFilter } from '../types/filament'
+
+const API_BASE = '/api'
+
+export async function fetchFilaments(filter: FilamentFilter): Promise<ListResponse<FilamentSpool>> {
+  const params = new URLSearchParams()
+  if (filter.material) params.set('material', filter.material)
+  if (filter.finish) params.set('finish', filter.finish)
+  if (filter.color) params.set('color', filter.color)
+  if (filter.low_stock) params.set('low_stock', 'true')
+  if (filter.search) params.set('search', filter.search)
+  if (filter.sort_by) params.set('sort_by', filter.sort_by)
+  if (filter.sort_dir) params.set('sort_dir', filter.sort_dir)
+  if (filter.limit !== undefined) params.set('limit', String(filter.limit))
+  if (filter.offset !== undefined) params.set('offset', String(filter.offset))
+
+  const res = await axios.get<ListResponse<FilamentSpool>>(`${API_BASE}/filaments?${params.toString()}`)
+  return res.data
+}
+
+export async function deleteFilament(id: number): Promise<void> {
+  await axios.delete(`${API_BASE}/filaments/${id}`)
+}

frontend/src/types/filament.ts

@@ -0,0 +1,72 @@
+// Extrudex domain types
+
+export interface MaterialBase {
+  id: number
+  name: string
+  density_g_cm3: number
+  extrusion_temp_min?: number
+  extrusion_temp_max?: number
+  bed_temp_min?: number
+  bed_temp_max?: number
+  created_at: string
+  updated_at: string
+}
+
+export interface MaterialFinish {
+  id: number
+  name: string
+  description?: string
+  created_at: string
+  updated_at: string
+}
+
+export interface MaterialModifier {
+  id: number
+  name: string
+  description?: string
+  created_at: string
+  updated_at: string
+}
+
+export interface FilamentSpool {
+  id: number
+  name: string
+  material_base_id: number
+  material_base?: MaterialBase
+  material_finish_id: number
+  material_finish?: MaterialFinish
+  material_modifier_id?: number
+  material_modifier?: MaterialModifier
+  color_hex: string
+  brand?: string
+  diameter_mm: number
+  initial_grams: number
+  remaining_grams: number
+  spool_weight_grams?: number
+  cost_usd?: number
+  low_stock_threshold_grams: number
+  notes?: string
+  barcode?: string
+  deleted_at?: string
+  created_at: string
+  updated_at: string
+}
+
+export interface ListResponse<T> {
+  data: T[]
+  total: number
+  limit: number
+  offset: number
+}
+
+export interface FilamentFilter {
+  material?: string
+  finish?: string
+  color?: string
+  low_stock?: boolean
+  search?: string
+  sort_by?: string
+  sort_dir?: 'asc' | 'desc'
+  limit?: number
+  offset?: number
+}