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/clients/moonraker.go

@@ -0,0 +1,171 @@
+// Package clients provides client implementations for printer integrations:
+// Moonraker REST + WebSocket (Klipper-based printers) and MQTT (Bambu Lab).
+package clients
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"strings"
+	"time"
+)
+
+// ── Moonraker response types ────────────────────────────────────────────────
+
+// moonrakerRPC is the generic JSON-RPC wrapper Moonraker uses for responses.
+type moonrakerRPC struct {
+	Result json.RawMessage `json:"result"`
+	Error  *moonrakerError `json:"error"`
+}
+
+type moonrakerError struct {
+	Code    int    `json:"code"`
+	Message string `json:"message"`
+}
+
+// ── Public DTOs ─────────────────────────────────────────────────────────────
+
+// MoonrakerPrinterInfo represents the /printer/info response.
+type MoonrakerPrinterInfo struct {
+	State        string `json:"state"`
+	StateMessage string `json:"state_message"`
+	KlippyReady  bool   `json:"klippy_ready"`
+}
+
+// MoonrakerPrintStats represents the print_stats object from
+// /printer/objects/query?print_stats.
+type MoonrakerPrintStats struct {
+	State          string  `json:"state"`
+	Filename       *string `json:"filename"`
+	FilamentUsedMm float64 `json:"filament_used"`
+	PrintDuration  float64 `json:"print_duration"`
+	Message        *string `json:"message"`
+}
+
+// MoonrakerPrintJob represents a single entry in /server/history/items.
+type MoonrakerPrintJob struct {
+	JobID              string                 `json:"job_id"`
+	Filename           string                 `json:"filename"`
+	Status             string                 `json:"status"`
+	FilamentUsedMm     float64                `json:"filament_used"`
+	PrintDuration      float64                `json:"print_duration"`
+	TotalDuration      float64                `json:"total_duration"`
+	StartTime          *float64               `json:"start_time"`
+	EndTime            *float64               `json:"end_time"`
+	Metadata           map[string]interface{} `json:"metadata"`
+}
+
+// MoonrakerHistoryResponse wraps the /server/history/items response.
+type MoonrakerHistoryResponse struct {
+	Items      []MoonrakerPrintJob `json:"items"`
+	TotalCount int                 `json:"count"`
+}
+
+// ── Client ──────────────────────────────────────────────────────────────────
+
+// MoonrakerClient is an HTTP client for the Moonraker REST API on
+// Klipper-based printers (e.g., Elegoo Centauri Carbon).
+type MoonrakerClient struct {
+	baseURL    string
+	httpClient *http.Client
+}
+
+// NewMoonrakerClient creates a MoonrakerClient that targets the given
+// base URL (e.g., "http://192.168.1.50:7125"). The internal HTTP client
+// uses a 15-second timeout.
+func NewMoonrakerClient(baseURL string) *MoonrakerClient {
+	baseURL = strings.TrimRight(baseURL, "/")
+	return &MoonrakerClient{
+		baseURL: baseURL,
+		httpClient: &http.Client{
+			Timeout: 15 * time.Second,
+		},
+	}
+}
+
+// GetPrinterInfo calls GET /printer/info and returns the Klipper state.
+// Returns nil when the printer is unreachable or the response cannot be parsed.
+func (c *MoonrakerClient) GetPrinterInfo(ctx context.Context) (*MoonrakerPrinterInfo, error) {
+	var info MoonrakerPrinterInfo
+	if err := c.getJSON(ctx, "/printer/info", &info); err != nil {
+		return nil, err
+	}
+	return &info, nil
+}
+
+// GetPrintStats calls GET /printer/objects/query?print_stats and returns
+// real-time print statistics including filament consumption.
+// Returns nil when no print is active or the printer is unreachable.
+func (c *MoonrakerClient) GetPrintStats(ctx context.Context) (*MoonrakerPrintStats, error) {
+	var stats MoonrakerPrintStats
+	// Moonraker wraps the object in status.print_stats
+	var wrapper struct {
+		Status struct {
+			PrintStats MoonrakerPrintStats `json:"print_stats"`
+		} `json:"status"`
+	}
+	if err := c.getJSON(ctx, "/printer/objects/query?print_stats", &wrapper); err != nil {
+		return nil, err
+	}
+	stats = wrapper.Status.PrintStats
+	return &stats, nil
+}
+
+// GetPrintHistory calls GET /server/history/items and returns recent print
+// jobs. limit controls the maximum number of items (clamped 1-100).
+func (c *MoonrakerClient) GetPrintHistory(ctx context.Context, limit int) (*MoonrakerHistoryResponse, error) {
+	if limit < 1 {
+		limit = 1
+	}
+	if limit > 100 {
+		limit = 100
+	}
+	var history MoonrakerHistoryResponse
+	if err := c.getJSON(ctx, fmt.Sprintf("/server/history/items?limit=%d", limit), &history); err != nil {
+		return nil, err
+	}
+	return &history, nil
+}
+
+// ── Internal helpers ────────────────────────────────────────────────────────
+
+func (c *MoonrakerClient) getJSON(ctx context.Context, path string, target interface{}) error {
+	url := c.baseURL + path
+
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
+	if err != nil {
+		return fmt.Errorf("moonraker: failed to build request: %w", err)
+	}
+	req.Header.Set("Accept", "application/json")
+
+	resp, err := c.httpClient.Do(req)
+	if err != nil {
+		return fmt.Errorf("moonraker: request failed (%s): %w", url, err)
+	}
+	defer resp.Body.Close()
+
+	body, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return fmt.Errorf("moonraker: failed to read body: %w", err)
+	}
+
+	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
+		return fmt.Errorf("moonraker: %s returned HTTP %d: %s", url, resp.StatusCode, string(body))
+	}
+
+	// Moonraker wraps responses in {"result": ...}
+	var rpc moonrakerRPC
+	if err := json.Unmarshal(body, &rpc); err != nil {
+		return fmt.Errorf("moonraker: failed to parse response: %w", err)
+	}
+	if rpc.Error != nil && rpc.Error.Message != "" {
+		return fmt.Errorf("moonraker: api error: %s", rpc.Error.Message)
+	}
+
+	if err := json.Unmarshal(rpc.Result, target); err != nil {
+		return fmt.Errorf("moonraker: failed to unmarshal result: %w (raw: %s)", err, string(rpc.Result))
+	}
+	return nil
+}