Update worker to get differents printer types

print_queue

configuration/config.toml

@@ -5,8 +5,6 @@ signature = "Anonymous"
 
 # Printer settings
 [printer]
-vendor_id = 0x04b8
-device_id = 0x0e28
 upload_folder = "src/static/uploads"
 
 # Raspberry Pi Configuration

src/main.py

@@ -36,7 +36,6 @@ import werkzeug.exceptions
 from flask_socketio import SocketIO
 from flask_limiter import Limiter
 from flask_limiter.util import get_remote_address
-from printer import Printer  # The wrapper for the printer class
 from raspberry import Raspberry  # The Raspberry pi control Class
 from web import Web  # Wrapper for the web routes and API
 from print_queue import PrintQueue
@@ -73,11 +72,7 @@ except OSError as e:
 
 app.logger.debug("Config file loaded !")
 
-# Define the USB connections here.
-vendor_id = configuration_file["printer"]["vendor_id"]
-device_id = configuration_file["printer"]["device_id"]
 UPLOAD_FOLDER = str(configuration_file["printer"]["upload_folder"])
-
 try:
     os.mkdir(UPLOAD_FOLDER)
     app.logger.debug("Directory %s created successfully.", UPLOAD_FOLDER)
@@ -98,14 +93,12 @@ app.config["ALLOWED_EXTENSIONS"] = ALLOWED_EXTENSIONS
 app.config["MAX_CONTENT_LENGTH"] = 10 * 1000 * 1000  # Maximum 3Mb for a file upload
 app.config["TEMPLATES_AUTO_RELOAD"] = True
 
-# Printer connection
-# Uses the class defined in the printer.py file
-printer = Printer(app, 0x04B8, 0x0E28)
-printer.init_printer()
+# Queue creation
+print_queue = PrintQueue(app)
 
 # Find out if we are running on a Raspberry Pi
 rpi = Raspberry(
-    printer,
+    print_queue,
     app,
     socketio,
     configuration_file["rpi"]["button_gpio_port_number"],
@@ -113,18 +106,20 @@ rpi = Raspberry(
     configuration_file["rpi"]["flash_gpio_port_number"],
     configuration_file["rpi"]["flash"],
 )
-
 RASPBERRY_PI_CONNECTED = rpi.is_raspberry_pi()
 
-# Queue creation
-print_queue = PrintQueue(app)
 
 #  Web & API management
 web = Web(app, print_queue)
 
 # Start worker thread
-worker = PrintWorker(app, print_queue, printer, socketio)
+# When created, the worker will try to find printers connected to the system
+try:
+    worker = PrintWorker(app, print_queue, socketio)
     worker.start()
+except Exception as e:
+    app.logger.error("Could not start the worker because %s ", str(e))
+    sys.exit(-1)
 
 # The rate limit
 limiter = Limiter(
@@ -304,6 +299,7 @@ def api_print_image():
     return "OK", 200
 
 
+# TODO: This might not depend on the Raspberry Pi
 @app.route("/api/camera/picture", methods=["GET"])
 def camera_picture():
     """Returns a picture taken by the camera on a raspberry pi"""
@@ -321,6 +317,10 @@ def api_queue_status():
     """API endpoint for entire queue"""
     return jsonify(web.get_queue_state())
 
+@app.route("/api/queue/completed", methods=["GET"])
+def api_queue_completed():
+    """API endpoint that returns the finished tasks"""
+    return jsonify(web.get_queue_completed())
 
 @app.route("/api/worker", methods=["GET"])
 def api_worker_state():

src/print_queue.py

@@ -76,7 +76,13 @@ class PrintQueue:
         """Return current queue state"""
         with self._lock:
             self.app.logger.debug("Return current queue state")
-            return [{"task_id": t.task_id, "status": t.status} for t in self._queue]
+            return [{"task_id": t.task_id, "status": t.status, "type": str(t.task_type) } for t in self._queue]
+
+    def get_queue_completed(self):
+        """Return completed queue elements"""
+        with self._lock:
+            self.app.logger.debug("Return completed queue elements")
+            return self._completed_tasks
 
     def get_status(self, task_id):
         """Get full status info for a task"""

src/printer.py

@@ -1,115 +1,126 @@
 """
 This class manages connexion to a Printer
 """
-# import brother_ql
 from time import sleep
 import os.path
+from abc import ABC, abstractmethod
+from dataclasses import dataclass
+
+from enum import Enum
+import uuid
+import usb.core
+import threading
 
 from PIL import Image, ImageEnhance
 import numpy as np
 
-# Importing the module to manage the connection to the printer.
+
+# Importing the modules needed for each supported printer Type
 import escpos.printer
+from brother_ql.models import ModelsManager
+from brother_ql.backends import backend_factory
+from brother_ql import labels
+from brother_ql.raster import BrotherQLRaster
+from brother_ql.conversion import convert
+from brother_ql.backends.helpers import send
 
-
-class Printer():
+class PrinterType(Enum):
      """
-    # The connection is based on the ESC/POS library
+     What are the capacities of a Printer ?
+     """
+     EPSON = "epson"
+     BROTHER = "brother"
 
-    ## Connection to the USB printer
+# For Brother-QL Printers
+@dataclass
+class PrinterInfo:
+    identifier: str
+    backend: str
+    protocol: str
+    vendor_id: str
+    product_id: str
+    serial_number: str
+    name: str = "Brother QL Printer"
+    model: str = "QL-570"
+    status: str = "unknown"
+    label_type: str = "unknown"
+    label_size : str = "unknown"
+    label_width: int = 0
+    label_height: int = 0
 
-    ## Making sure the printer is alive
+    def __getitem__(self, item):
+        return getattr(self, item)
 
-    ## Making sure it has paper
+    def __setitem__(self, key, value):
+        setattr(self, key, value)
 
-    ## Define default print settings
-
-    ## Print starting message, log time of first print, cut.
-
-    ## Annonce readyness : return a positive pong message.
+class Printer(ABC):
+    """
+    If it outputs printed paper and speaks like a printer, then it must be a printer.
     """
 
-    # Is the printer ready to accept a new print ?
-    ready = False
-
-    def __init__(self, app, device_id, vendor_id):
-        super().__init__()
+    def __init__(self, app, vendor_id, device_id, printer_type: PrinterType):
+        """
+        We initialize a Printer via it's USB connexion, and generate a unique ID
+        """
+        self.id = uuid.uuid4()
         self.app = app
-        self.ready = False
-        self.printer = None
-        self.device_id = device_id
         self.vendor_id = vendor_id
+        self.device_id = device_id
+        self.ready = False
+        self.printer_type = printer_type
+        self._lock = threading.Lock()
+
+    @abstractmethod
+    def _has_paper(self) -> bool:
+        """Check if the printer has papier"""
+
+    @abstractmethod
+    def _state(self) -> bool:
+        """Reports the state of the Printer"""
+
+    @abstractmethod
+    def print_task(self, task_type, data)-> None:
+        """Takes a PrintTask and executes it"""
+
+
+class EscPosPrinter(Printer):
+    """
+    Create a new ESC/POS based printer.
+    """
+
+    def __init__(self, app, vendor_id, device_id):
+        """
+        Create a connexion to a ESC/POS Printer via USB,
+        Making sure the printer is alive,
+        Making sure it has paper,
+        Define default print settings
+        """
+        super().__init__(app,vendor_id,device_id, printer_type=PrinterType.EPSON)
+        self.printer = None
         self.usb_args = {}
-        self.usb_args["idVendor"] = self.device_id
-        self.usb_args["idProduct"] = self.vendor_id
+        self.usb_args["idVendor"] = self.vendor_id
+        self.usb_args["idProduct"] = self.device_id
 
-    def check_paper(self) -> bool:
-        """
-        On printers that support it, we check that the printer has paper
-        """
-        self.app.logger.debug("Checking paper status...")
-        self.printer.open(self.usb_args)
-        status = self.printer.paper_status()
-        match status:
-            case 0:
-                self.app.logger.error("Printer has no more paper, aborting...")
-                self.printer.close()
-                raise RuntimeError("No more paper in the printer")
-            case 1:
-                self.app.logger.warning(
-                    "Printer needs paper to be changed very soon ! "
-                )
-                self.printer.close()
-            case 2:
-                self.app.logger.debug("Printer has paper, good to go")
-                self.printer.close()
-
-    def init_printer(self):
-        """
-        Check if the printer online ? Is the communication with the printer successfull ?
-        """
-
-        # TODO: This could happen directly when creating a new Printer class
-        if os.getenv("FLASK_DEBUG"):
-            waiting_elapsed = 3
-        else:
-            waiting_elapsed = 10
-
-        self.app.logger.debug("Waiting for printer to get online...")
-
-        while not self.ready:
         try:
             # This also calls open(), which we need to close()
             # or else the device will appear as busy.
             p = escpos.printer.Usb(
-                    self.device_id, self.vendor_id, 0, profile="TM-P80"
+                self.vendor_id, self.device_id, 0, profile="TM-P80"
             )
-            except RuntimeError as e:
+        except escpos.exceptions.DeviceNotFoundError as e:
             self.app.logger.error(
-                    "The USB device is not plugged in, trying again %s : %s",
-                    waiting_elapsed,
+                "The USB device is not plugged in : %s",
                 str(e),
             )
+        except Exception as e:
+            self.app.logger.error("Printer could not be connected : %s ", str(e))
 
         try:
             if p.is_online():
-                    self.ready = True
                 self.app.logger.debug("Printer online !")
-            except RuntimeError as e:
-                self.app.logger.error(
-                    "Error while getting the printer online %s : %s",
-                    waiting_elapsed,
-                    str(e),
-                )
-
-            sleep(1)
-            waiting_elapsed -= 1
-            if waiting_elapsed < 1:
-                self.app.logger.error(
-                    "Printer took more than 30 seconds to get online, aborting..."
-                )
-                waiting_elapsed = 1  # Reset the waiting time for the next print.
-                return False
+        except Exception as e:
+            raise e
 
         # Setting up the printing options.
         p.set(
@@ -130,14 +141,37 @@ class Printer():
         # Beware : if we print every time the printer becomes ready, it means
         # we are printing before and after every print !
         self.printer = p
+        self.printer.close() # We close the connexion to the Printer
+
+        try:
+            self._has_paper()
+        except Exception as e:
+            raise e
+
         self.ready = True
+
+    def _has_paper(self):
+        """Check if the printer has paper left"""
+        self.app.logger.debug("Checking paper status...")
+        self.printer.open(self.usb_args)
+        status = self.printer.paper_status()
+        match status:
+            case 0:
+                self.app.logger.error("Printer has no more paper, aborting...")
+                self.printer.close()
+                raise RuntimeError("No more paper in the printer")
+            case 1:
+                self.app.logger.warning(
+                    "Printer needs paper to be changed very soon ! "
+                )
+                self.printer.close()
+                return True
+            case 2:
+                self.app.logger.debug("Printer has paper, good to go")
                 self.printer.close()
-
-        self.check_paper()
-
                 return True
 
-    def _print_sms(self, msg, signature="", bold=False):
+    def _print_txt(self, msg, signature="", bold=False):
 
         if not isinstance(msg, str):
             self.app.logger.error(
@@ -255,14 +289,14 @@ class Printer():
         try:
             self.printer.open(self.usb_args)
             self.printer.qr(content, center=True)
+            self.printer.textln(content)
             self.printer.close()
         except RuntimeError as e:
             self.printer.close()
             self.app.logger.error(str(e))
-            return False
+            raise e
 
         self.app.logger.info("Printed a QR")
-        return True
 
     def _cut(self):
         try:
@@ -277,20 +311,190 @@ class Printer():
         self.app.logger.info("Did a cut")
         return True
 
+    def _state(self):
+        return self.printer.is_online() and self.ready and self._has_paper()
+
     def print_task(self, task_type, data):
         """Execute actual print based on task type"""
+        with self._lock:
+            if self._state:
+                self._state = False
                 match (task_type.value):
                     case "text":
-                self._print_sms(data["txt"], signature=data["sign"])
+                        self._print_txt(data["txt"], signature=data["sign"])
+                        self._state = True
                     case "image":
                         self._print_img(
                             data["img"], signature=data["sign"], process=data["process"]
                         )
+                        self._state = True
                     case "cut":
                         self._cut()
+                        self._state = True
+                    case "qr":
+                        self._qr(data["txt"])
+                        self._state = True
                     case _:
                         raise RuntimeError("This task type is not supported")
+            else:
+                raise RuntimeError("The printer is not ready to print yet !")
 
+class BrotherPrinter(Printer):
+    """
+    Manages connexion and capabilities of a BrotherQL Printer
+    """
+
+    def __init__(self, app, vendor_id, device_id):
+        super().__init__(app, vendor_id="",device_id="", printer_type=PrinterType.BROTHER)
+        self.printer = None
+        self.usb_args = {}
+        self.usb_args["idVendor"] = self.device_id
+        self.usb_args["idProduct"] = self.vendor_id
+        self.model_manager = ModelsManager()
+
+        # Code taken from https://github.com/5shekel/printit/blob/master/printer_utils.py
+
+        backend = backend_factory("pyusb")
+        available_devices = backend["list_available_devices"]()
+
+        for printer in available_devices:
+            self.app.logger.debug(f"Found device: {printer}")
+            identifier = printer["identifier"]
+            parts = identifier.split("/")
+
+            if len(parts) < 4:
+                self.app.logger.warning(f"Skipping device with invalid identifier format: {identifier}")
+                continue
+
+            protocol = parts[0]
+            device_info = parts[2]
+            serial_number = parts[3]
+
+        try:
+            product_id_int = int(self.device_id, 16)
+            for m in self.model_manager.iter_elements():
+                if m.product_id == product_id_int:
+                    model = m.identifier
+                    break
+            self.app.logger.debug(f"Matched printer model: {model}")
+        except ValueError:
+            self.app.logger.warning(f"Invalid product ID format: {product_id}")
+
+        self.printer_info = PrinterInfo(
+            identifier=identifier,
+            backend="pyusb",
+            model=model,
+            protocol=protocol,
+            vendor_id=vendor_id,
+            product_id=self.device_id,
+            serial_number=serial_number,
+        )
+
+        self.ready = True
+
+
+    def _has_paper(self):
+        raise NotImplementedError("This printer model does not support this.")
+
+    def _state(self):
+        return self.ready
+
+    def _print_img(self,data):
+        """
+        Print a raster image via a Brother QL printer
+        """
+        self.ready = False
+        label_type = "102"
+        rotate = 0
+        dither = False
+        try:
+            # Prepare the image for printing
+            qlr = BrotherQLRaster(self.printer_info["model"])
+
+            instructions = convert(
+                qlr=qlr,
+                images=[data["img"]],
+                label=label_type,
+                rotate=rotate,
+                threshold=70,
+                dither=dither,
+                compress=True,
+                red=False,
+                dpi_600=False,
+                hq=False,
+                cut=True,
+            )
+
+            # Debug logging
+            if FLASK_DEBUG:
+                self.app.logger.debug(f"""
+                Print parameters:
+                - Label type: {label_type}
+                - Rotate: {rotate}
+                - Dither: {dither}
+                - Model: {self.printer_info['model']}
+                - Backend: {self.printer_info['backend']}
+                - Identifier: {self.printer_info['identifier']}
+                """)
+
+            # Try to print using Python API
+            # send() =  status = {
+            #     'instructions_sent': True, # The instructions were sent to the printer.
+            #     'outcome': 'unknown', # String description of the outcome of the sending operation like: 'unknown', 'sent', 'printed', 'error'
+            #     'printer_state': None, # If the selected backend supports reading back the printer state, this key will contain it.
+            #     'did_print': False, # If True, a print was produced. It defaults to False if the outcome is uncertain (due to a backend without read-back capability).
+            #     'ready_for_next_job': False, # If True, the printer is ready to receive the next instructions. It defaults to False if the state is unknown.
+            # }
+            status = send(
+                instructions=instructions,
+                printer_identifier= self.printer_info["identifier"],
+                backend_identifier="pyusb"
+            )
+
+            if not status["did_print"] or status["outcome"] == "error" or status["outcome"] == "unknown":
+                raise RuntimeError("Failed to print using Python API")
+
+            if status["printer_state"]:
+                self.ready = bool(status["printer_state"])
+            else:
+                self.ready = True
+
+        except usb.core.USBError as e:
+            # Treat timeout errors as successful since they often occur after print completion
+            if e.errno == 110:  # Operation timed out
+                self.app.logger.debug("USB timeout occurred - this is normal and the print likely completed")
+                self.app.logger.debug("Print completed (timeout is normal)")
+                self.ready = True
+
+            error_msg = f"USBError encountered: {e}"
+            self.app.logger.debug(error_msg)
+            raise RuntimeError from e
+
+        except Exception as e:
+            error_msg = f"Unexpected error during printing: {str(e)}"
+            self.app.logger.debug(error_msg)
+            raise RuntimeError from e
+
+    def print_task(self, task_type, data):
+        """Execute actual print based on task type"""
+        with self._lock:
+            if self._state:
+                self._state = False
+                match (task_type.value):
+                    case "image":
+                        self._print_img(data["img"])
+                        self._state = True
+                    case "cut":
+                        # The cut happens by default on Brother QL printers.
+                        self._state = True
+                    case _:
+                        raise RuntimeError("This task type is not supported")
+            else:
+                raise RuntimeError("The printer is not ready to print yet !")
+
+        # These values are by default for now
+
+        # raise NotImplementedError("This printer type is not implemented yet")
 
 def _process_image(self, path):
     brightness_factor = 1.5  # Used only if image is too dark

src/printers.py

@@ -0,0 +1,131 @@
+"""
+A collection of Printers.
+
+It has methods to discover printers, and provides an interface for the methods expected from printers.
+"""
+from collections.abc import Mapping, Set
+import usb.core
+import usb.util
+from printer import Printer, EscPosPrinter, BrotherPrinter, PrinterType
+
+class Printers():
+    """
+    Finds and creates a set of Printer that can be used by the Workers to print.
+    """
+    def __init__(self, app):
+        """
+        Discover printers connected to the computer and return a Collection of Printer()
+        """
+        self.app = app
+        self.printers = self._discover_printers()
+
+    def _discover_printers(self) -> Set[Printer]:
+        """
+        Gets connected USB printer devices using the pyusb library.
+
+        We analyse the USB devices, get the ones that match
+        the printer class ( 7 ) and for Brother and EPSON printers,
+        try to create a Printer object that can be used by the Worker class
+        to execute prints.
+
+        Returns a set of Printer
+        """
+
+        self.app.logger.debug("Discovering USB Devices connected to this system")
+
+        printers = set()
+
+        # Find all connected USB devices
+        devices = usb.core.find(find_all=True,custom_match=_FindClass(7))
+        if not devices:
+            self.app.logger.warning("No USB devices of class 7 ( printers ) found or pyusb could not access the bus.")
+            raise RuntimeError("No USB devices of class 7 ( printers ) found or pyusb could not access the bus.")
+
+        for dev in devices:
+            # Attempt to get the manufacturer and product strings
+            try:
+                manufacturer = usb.util.get_string(dev, dev.iManufacturer)
+            except Exception:
+                manufacturer = "Unknown"
+
+            try:
+                product = usb.util.get_string(dev, dev.iProduct)
+            except Exception:
+                product = "Unknown"
+            self.app.logger.debug("Looking at %s %s (%s:%s)", manufacturer, product, hex(dev.idVendor), hex(dev.idProduct))
+
+            if manufacturer == "EPSON":
+                try:
+                    # We create a new EscPosPrinter()
+                    self.app.logger.debug("Trying to creat a new EPSON printer")
+                    prid = dev.idProduct
+                    vendir = dev.idVendor
+                    escpos_printer = EscPosPrinter(self.app, vendor_id=vendir, device_id=prid)
+                except Exception as e:
+                    raise e
+
+                # If the object creation is successfull, we add it to the list of Printers
+                printers.add(escpos_printer)
+                self.app.logger.debug("Found a %s printer" % manufacturer )
+
+                # We already found the type of printer,
+                # we don't need an extra comparaison.
+                continue
+
+            # or a Brother Printer
+            if manufacturer == "Brother":
+                try:
+                    # We create a new BrotherPrinter()
+                    self.app.logger.debug("Trying to creat a new BROTHER printer")
+                    prid = dev.idProduct
+                    vendir = dev.idVendor
+                    brother_printer = BrotherPrinter(self.app, vendor_id=vendir,device_id=prid)
+                except Exception as e:
+                    self.app.logger.error("Could not create a %s printer class with %s:%s" % product, dev.idVendor, dev.idProduct)
+                    raise e
+
+                # If the object creation is successfull, we add it to the list of Printers
+                printers.add(brother_printer)
+                self.app.logger.debug("Found a %s printer" % manufacturer )
+
+        self.app.logger.debug("Found %s printers" % len(printers))
+        return printers
+
+    def any(self) -> Printer:
+        """
+        Return a dict key: UUID, value: Printer, with any connected printer.
+        """
+        if len(self.printers) > 0:
+            for i in self.printers:
+                return i
+        else:
+            raise RuntimeError("No printers available")
+
+    def get_printer(self, printer_type):
+        """
+        Return a specific printer
+
+        printer_type -- a printer type
+        """
+        return NotImplementedError()
+
+
+class _FindClass():
+    def __init__(self, class_):
+        self._class = class_
+    def __call__(self, device):
+        # first, let's check the device
+        if device.bDeviceClass == self._class:
+            return True
+        # ok, transverse all devices to find an
+        # interface that matches our class
+        for cfg in device:
+            # find_descriptor: what's it?
+            intf = usb.util.find_descriptor(
+                                        cfg,
+                                        bInterfaceClass=self._class
+                                )
+            if intf is not None:
+                return True
+
+        return False

src/task.py

@@ -30,6 +30,7 @@ class TaskType(Enum):
     TEXT = "text"
     IMAGE = "image"
     CUT = "cut"
+    QR = "qr"
 
 
 class PrintTask(ABC):
@@ -37,13 +38,11 @@ class PrintTask(ABC):
     A print task holds information about what we are looking to print.
     """
 
-    def __init__(self, task_type):
+    def __init__(self, task_type: TaskType):
         self.task_id = self._generate_id()
         self.task_type = task_type
         self.status = "pending"  # pending, processing, completed, failed
 
-        print("Created a new " + str(self.task_type) + " with ID " + self.task_id)
-
     @abstractmethod
     def get_print_data(self):
         """Return data formatted for printer"""
@@ -67,6 +66,15 @@ class TextTask(PrintTask):
     def get_print_data(self):
         return {"txt": self.content, "sign": self.signature}
 
+class QRTask(TextTask):
+    """This task prints a QR-Code, the signature is ignore and is always the content itself"""
+    def __init__(self, content):
+        super().__init__(content, signature="")
+        self.content = content
+        self.signature = content
+
+    def get_print_data(self):
+        return {"txt": self.content, "sign": self.signature}
 
 class ImageTask(PrintTask):
     """

src/web.py

@@ -1,7 +1,6 @@
+import os
 from flask import flash
 from werkzeug.utils import secure_filename
-import time
-import os
 from task import TextTask, ImageTask, CutTask
 
 
@@ -99,11 +98,12 @@ class Web(object):
                     + str(os.path.join(self.app.config["UPLOAD_FOLDER"], filename))
                 )
                 return True
-            else:
+
             self.app.logger.error(
                 "Could not save file because the filename is forbidden"
             )
             return False
+
         else:
             self.app.logger.error(
                 "Could not save file, it seems to be null ? : " + str(filename)
@@ -113,3 +113,7 @@ class Web(object):
     def get_queue_state(self):
         """Return current queue state"""
         return self.print_queue.get_queue_state()
+
+    def get_queue_completed(self):
+        """Return completed queue elements"""
+        return self.print_queue.get_queue_completed()

src/worker.py

@@ -4,32 +4,68 @@
 
 import threading
 import time
+from printers import Printers
 
 
 class PrintWorker(threading.Thread):
-    def __init__(self, app, print_queue, printer, socketio=None):
+    def __init__(self, app, print_queue, socketio=None):
         super().__init__(daemon=True)
         self.app = app
         self.print_queue = print_queue
-        self.printer = printer
+        self.printer = None
+        self._lock = threading.Lock()
         self.socketio = socketio  # Optional
         self.running = True
         self.state = "idle"  # idle, printing, dead, drinking-a-beer
-
         self.app.logger.debug("Ho great, I'm alive... I'm ready to work another day...")
 
+        try:
+            self.printers = Printers(self.app)
+            self.printers_obj = self.printers.printers
+            self.printers = iter(self.printers.printers)
+        except RuntimeError as e:
+            self.app.logger.warning("Could not get any Printers")
+            raise e
+
     def run(self):
         """Background thread that processes queue items"""
-        self.app.logger.info("Worker started working.")
+        self.app.logger.debug("Worker %s started working.", threading.get_ident())
+        self.app.logger.debug("Current threads : %s" % threading.active_count())
+        self.app.logger.debug("Threads actives : %s " %  threading.enumerate())
+
         while True:
-            if not self.running or not self.printer.ready:
+
+            # If the printer is dead or asleep, it can't work.
+            if not self.running:
                 time.sleep(0.2)
                 continue
 
+            # If we have no available printer, we look at the list printers we know about, and try to find one that is available.
+            # When we find a printer, we acquire it
+            # When we are finished with a printer, we release it to the world.
+            while not self.printer or not self.printer.ready:
+                time.sleep(1)
+                try:
+                    self.app.logger.debug("Changing printers")
+                    self.printer = next(self.printers)
+                    self.app.logger.debug("The worker got a %s printer and it's %s", self.printer.printer_type, "Ready" if self.printer.ready else "Not ready")
+                except Exception as e:
+                    self.app.logger.error(str(e))
+                    self.printer = None
+
+            if self.state != "idle":
+                self.app.logger("We are not idle, waiting...")
+                time.sleep(1)
+                continue
+
+            self.state = "printing"
+
+            with self._lock:
                 try:
                     task = self.print_queue.dequeue()
                 except Exception as e:
                     self.app.logger.error("Could not get a new task ! %s ", str(e))
+                    self.state = "idle"
                     raise RuntimeError(
                         "We could not get a new task because " + str(e)
                     ) from e
@@ -38,26 +74,31 @@ class PrintWorker(threading.Thread):
                     try:
                         self.app.logger.info("Got a new task")
                         self.app.logger.debug("Got task %s", task.task_id)
-                    self.state = "printing"
                         task.status = "processing"
                         self._emit_status(task.task_id, "processing")
 
                         print_data = task.get_print_data()
+
                         try:
                             self.printer.print_task(task.task_type, print_data)
                         except RuntimeError as e:
+                            self.state = "idle"
                             self.app.logger.error("Could not print : %s", str(e))
                             raise e
 
                         task.status = "completed"
                         self.print_queue.mark_completed(task.task_id, "completed")
                         self._emit_status(task.task_id, "completed")
+                        self.app.logger.debug("Finished printing task %s " % task.task_id)
+                        self.state = "idle"
 
                     except RuntimeError as e:
                         task.status = "failed"
+                        self.state = "idle"
                         self.print_queue.mark_completed(task.task_id, "failed")
                         self._emit_status(task.task_id, "failed", error=str(e))
-                    print(f"Print task {task.task_id} failed: {e}")
+                        self.app.logger.error("Could not print task %s because %s " % task.task_id, str(e))
+
                 else:
                     # When they are no new tasks to handle, we put the thread to sleep.
                     self.state = "idle"
@@ -104,4 +145,5 @@ class PrintWorker(threading.Thread):
             "is_running": self.running,
             "queue_size": len(self.print_queue),
             "state": self.state,
+            "printers": len(self.printers_obj),
         }