CUB-117: Port Moonraker + MQTT printer integrations to Go

- Moonraker REST client with GetPrinterInfo, GetPrintStats, GetPrintHistory
- Moonraker WebSocket client with auto-reconnect + telemetry parsing
- MQTT client via paho.mqtt.golang with TLS support for Bambu Lab
- Moonraker poller worker: background polling, dedup, usage logging to PostgreSQL
- MQTT subscriber worker: Bambu telemetry parsing, print job tracking
- Config: 7 new env vars (MOONRAKER_URL, MQTT_BROKER, etc.)
- main.go: per-printer worker discovery, graceful shutdown

backend/internal/workers/mqtt_subscriber.go

@@ -0,0 +1,170 @@
+package workers
+
+import (
+	"context"
+	"fmt"
+	"log/slog"
+	"sync"
+	"time"
+
+	"github.com/CubeCraft-Creations/Extrudex/backend/internal/clients"
+	"github.com/jackc/pgx/v5/pgxpool"
+)
+
+// bambuJobState tracks the active print job detected via MQTT.
+type bambuJobState struct {
+	gcodeFile  string
+	gcodeState string
+	percent    int
+}
+
+// MQTTSubscriber listens to Bambu Lab MQTT telemetry topics and logs
+// filament usage events to PostgreSQL.
+type MQTTSubscriber struct {
+	Client *clients.MQTTClient
+	pool   *pgxpool.Pool
+
+	printerID   int
+	printerName string
+
+	mu    sync.Mutex
+	state bambuJobState
+}
+
+// MQTTSubscriberConfig holds configuration for the MQTT subscriber worker.
+type MQTTSubscriberConfig struct {
+	Pool        *pgxpool.Pool
+	PrinterID   int
+	PrinterName string
+}
+
+// NewMQTTSubscriber creates a new MQTTSubscriber worker. Set Client after
+// construction to wire the handler.
+func NewMQTTSubscriber(cfg MQTTSubscriberConfig) *MQTTSubscriber {
+	return &MQTTSubscriber{
+		pool:        cfg.Pool,
+		printerID:   cfg.PrinterID,
+		printerName: cfg.PrinterName,
+	}
+}
+
+// Run connects to MQTT and blocks until ctx is cancelled.
+func (w *MQTTSubscriber) Run(ctx context.Context) error {
+	slog.Info("mqtt subscriber: starting",
+		"printer_id", w.printerID,
+		"printer_name", w.printerName,
+	)
+
+	if w.Client == nil {
+		return fmt.Errorf("mqtt subscriber: Client is nil")
+	}
+
+	if err := w.Client.Connect(); err != nil {
+		return fmt.Errorf("mqtt subscriber: connect failed: %w", err)
+	}
+	defer w.Client.Disconnect()
+
+	slog.Info("mqtt subscriber: connected", "printer_id", w.printerID)
+
+	<-ctx.Done()
+	slog.Info("mqtt subscriber: shutting down", "printer_id", w.printerID)
+	return nil
+}
+
+// HandleBambuReport is the MQTT callback for Bambu telemetry messages.
+func (w *MQTTSubscriber) HandleBambuReport(report clients.BambuPrintReport) error {
+	w.mu.Lock()
+	prev := w.state
+	current := bambuJobState{
+		gcodeFile:  report.Print.GcodeFile,
+		gcodeState: report.Print.GcodeState,
+		percent:    report.Print.McPercent,
+	}
+	w.state = current
+	w.mu.Unlock()
+
+	if prev.gcodeState == current.gcodeState && prev.gcodeFile == current.gcodeFile {
+		return nil
+	}
+
+	slog.Info("mqtt subscriber: state change",
+		"printer_id", w.printerID,
+		"file", current.gcodeFile,
+		"state", current.gcodeState,
+		"percent", current.percent,
+	)
+
+	ctx, cancel := context.WithTimeout(context.Background(), 15*time.Second)
+	defer cancel()
+
+	switch current.gcodeState {
+	case "RUNNING":
+		return w.handleState(ctx, current, "printing")
+	case "FINISH":
+		return w.handleState(ctx, current, "completed")
+	case "FAILED":
+		return w.handleState(ctx, current, "failed")
+	}
+	return nil
+}
+
+func (w *MQTTSubscriber) handleState(ctx context.Context, s bambuJobState, status string) error {
+	jobID, err := w.ensurePrintJob(ctx, s.gcodeFile, status)
+	if err != nil {
+		return err
+	}
+
+	if status == "completed" || status == "failed" {
+		_, _ = w.pool.Exec(ctx, `
+			UPDATE print_jobs SET
+				job_status_id = (SELECT id FROM job_statuses WHERE name = $2),
+				completed_at = CASE WHEN $2 = 'completed' THEN NOW() ELSE completed_at END,
+				updated_at = NOW()
+			WHERE id = $1
+		`, jobID, status)
+	} else {
+		_, _ = w.pool.Exec(ctx, `
+			UPDATE print_jobs SET
+				job_status_id = (SELECT id FROM job_statuses WHERE name = $2),
+				started_at = COALESCE(started_at, NOW()),
+				updated_at = NOW()
+			WHERE id = $1
+		`, jobID, status)
+	}
+
+	slog.Info("mqtt subscriber: job updated",
+		"printer_id", w.printerID, "job_id", jobID, "status", status)
+	return nil
+}
+
+func (w *MQTTSubscriber) ensurePrintJob(ctx context.Context, filename, status string) (int, error) {
+	var jobID int
+	err := w.pool.QueryRow(ctx, `
+		SELECT id FROM print_jobs
+		WHERE printer_id = $1 AND file_name = $2 AND deleted_at IS NULL
+		ORDER BY created_at DESC LIMIT 1
+	`, w.printerID, filename).Scan(&jobID)
+
+	if err == nil {
+		return jobID, nil
+	}
+
+	var statusID int
+	err = w.pool.QueryRow(ctx, `SELECT id FROM job_statuses WHERE name = $1`, status).Scan(&statusID)
+	if err != nil {
+		return 0, fmt.Errorf("mqtt subscriber: unknown status '%s': %w", status, err)
+	}
+
+	err = w.pool.QueryRow(ctx, `
+		INSERT INTO print_jobs (printer_id, job_name, file_name, job_status_id, started_at)
+		VALUES ($1, $2, $2, $3, NOW())
+		RETURNING id
+	`, w.printerID, filename, statusID).Scan(&jobID)
+	if err != nil {
+		return 0, fmt.Errorf("mqtt subscriber: create print_job failed: %w", err)
+	}
+
+	slog.Info("mqtt subscriber: created print job",
+		"job_id", jobID, "file", filename, "status", status)
+	return jobID, nil
+}