split off dependencies for optional installation (#546)

* add inheritance diagrams to all printers and exceptions
* split off printer implementations into separate files
* add wrapper that thros RuntimeError if not importable
* add dependency check for lp
* add dependency check for pyserial
* added check for usability
* import Win32Raw
* include WIn32Raw in documentation
* enable all extras on tox
* update github workflow

src/escpos/printer/cups.py

@@ -0,0 +1,180 @@
+#!/usr/bin/python
+#  -*- coding: utf-8 -*-
+"""This module contains the implementation of the CupsPrinter printer driver.
+
+:author: python-escpos developers
+:organization: `python-escpos <https://github.com/python-escpos>`_
+:copyright: Copyright (c) 2012-2023 Bashlinux and python-escpos
+:license: MIT
+"""
+
+import functools
+import tempfile
+
+from ..escpos import Escpos
+
+#: keeps track if the pycups dependency could be loaded (:py:class:`escpos.printer.CupsPrinter`)
+_DEP_PYCUPS = False
+
+try:
+    import cups
+
+    _DEP_PYCUPS = True
+except ImportError:
+    pass
+
+
+# TODO: dev build mode that let's the wrapper bypass?
+
+
+def is_usable() -> bool:
+    """Indicate whether this component can be used due to dependencies."""
+    usable = False
+    if _DEP_PYCUPS:
+        usable = True
+    return usable
+
+
+def dependency_pycups(func):
+    """Indicate dependency on pycups."""
+
+    @functools.wraps(func)
+    def wrapper(*args, **kwargs):
+        """Throw a RuntimeError if pycups is not imported."""
+        if not is_usable():
+            raise RuntimeError(
+                "Printing with PyCups requires the pycups library to"
+                "be installed. Please refer to the documentation on"
+                "what to install and install the dependencies for pycups."
+            )
+        return func(*args, **kwargs)
+
+    return wrapper
+
+
+class CupsPrinter(Escpos):
+    """Simple CUPS printer connector.
+
+    .. note::
+
+        Requires ``pycups`` which in turn needs the cups development library package:
+            - Ubuntu/Debian: ``libcups2-dev``
+            - OpenSuse/Fedora: ``cups-devel``
+
+    inheritance:
+
+    .. inheritance-diagram:: escpos.printer.CupsPrinter
+        :parts: 1
+
+    """
+
+    @staticmethod
+    def is_usable() -> bool:
+        """Indicate whether this printer class is usable.
+
+        Will return True if dependencies are available.
+        Will return False if not.
+        """
+        return is_usable()
+
+    @dependency_pycups
+    def __init__(self, printer_name=None, *args, **kwargs):
+        """Class constructor for CupsPrinter.
+
+        :param printer_name: CUPS printer name (Optional)
+        :type printer_name: str
+        :param host: CUPS server host/ip (Optional)
+        :type host: str
+        :param port: CUPS server port (Optional)
+        :type port: int
+        """
+        Escpos.__init__(self, *args, **kwargs)
+        host, port = args or (
+            kwargs.get("host", cups.getServer()),
+            kwargs.get("port", cups.getPort()),
+        )
+        cups.setServer(host)
+        cups.setPort(port)
+        self.conn = cups.Connection()
+        self.tmpfile = None
+        self.printer_name = printer_name
+        self.job_name = ""
+        self.pending_job = False
+        self.open()
+
+    @property
+    def printers(self):
+        """Available CUPS printers."""
+        return self.conn.getPrinters()
+
+    def open(self, job_name="python-escpos"):
+        """Set up a new print job and target the printer.
+
+        A call to this method is required to send new jobs to
+        the same CUPS connection.
+
+        Defaults to default CUPS printer.
+        Creates a new temporary file buffer.
+        """
+        self.job_name = job_name
+        if self.printer_name not in self.printers:
+            self.printer_name = self.conn.getDefault()
+        self.tmpfile = tempfile.NamedTemporaryFile(delete=True)
+
+    def _raw(self, msg):
+        """Append any command sent in raw format to temporary file.
+
+        :param msg: arbitrary code to be printed
+        :type msg: bytes
+        """
+        self.pending_job = True
+        try:
+            self.tmpfile.write(msg)
+        except ValueError:
+            self.pending_job = False
+            raise ValueError("Printer job not opened")
+
+    @dependency_pycups
+    def send(self):
+        """Send the print job to the printer."""
+        if self.pending_job:
+            # Rewind tempfile
+            self.tmpfile.seek(0)
+            # Print temporary file via CUPS printer.
+            self.conn.printFile(
+                self.printer_name,
+                self.tmpfile.name,
+                self.job_name,
+                {"document-format": cups.CUPS_FORMAT_RAW},
+            )
+        self._clear()
+
+    def _clear(self):
+        """Finish the print job.
+
+        Remove temporary file.
+        """
+        self.tmpfile.close()
+        self.pending_job = False
+
+    def _read(self):
+        """Return a single-item array with the accepting state of the print queue.
+
+        states: idle = [3], printing a job = [4], stopped = [5]
+        """
+        printer = self.printers.get(self.printer_name, {})
+        state = printer.get("printer-state")
+        if not state:
+            return []
+        return [state]
+
+    def close(self):
+        """Close CUPS connection.
+
+        Send pending job to the printer if needed.
+        """
+        if self.pending_job:
+            self.send()
+        if self.conn:
+            print("Closing CUPS connection to printer {}".format(self.printer_name))
+            self.conn = None