#!/usr/bin/python
# -*- coding: utf-8 -*-
"""Magic Encode.
This module tries to convert an UTF-8 string to an encoded string for the printer.
It uses trial and error in order to guess the right codepage.
The code is based on the encoding-code in py-xml-escpos by @fvdsn.
:author: `Patrick Kanzler <dev@pkanzler.de>`_
:organization: `python-escpos <https://github.com/python-escpos>`_
:copyright: Copyright (c) 2016 Patrick Kanzler and Frédéric van der Essen
:license: MIT
"""
import re
from builtins import bytes
import six
from .codepages import CodePages
from .constants import CODEPAGE_CHANGE
from .exceptions import Error
[docs]
class Encoder:
"""Take available code spaces and pick the right one for a given character.
Note: To determine the code page, it needs to do the conversion, and
thus already knows what the final byte in the target encoding would
be. Nevertheless, the API of this class does not return the byte.
The caller use to do the character conversion itself.
"""
def __init__(self, codepage_map):
"""Initialize encoder."""
self.codepages = codepage_map
self.available_encodings = set(codepage_map.keys())
self.available_characters = {}
self.used_encodings = set()
[docs]
def get_sequence(self, encoding):
"""Get a sequence."""
return int(self.codepages[encoding])
[docs]
def get_encoding_name(self, encoding):
"""Return a canonical encoding name.
Given an encoding provided by the user, will return a
canonical encoding name; and also validate that the encoding
is supported.
.. todo:: Support encoding aliases: pc437 instead of cp437.
"""
encoding = CodePages.get_encoding_name(encoding)
if encoding not in self.codepages:
raise ValueError(
(
f'Encoding "{encoding}" cannot be used for the current profile. '
f'Valid encodings are: {",".join(self.codepages.keys())}'
)
)
return encoding
@staticmethod
def _get_codepage_char_list(encoding):
"""Get codepage character list.
Gets characters 128-255 for a given code page, as an array.
:param encoding: The name of the encoding. This must appear in the CodePage list
"""
codepage = CodePages.get_encoding(encoding)
if "data" in codepage:
encodable_chars = list("".join(codepage["data"]))
assert len(encodable_chars) == 128
return encodable_chars
elif "python_encode" in codepage:
encodable_chars = [" "] * 128
for i in range(0, 128):
codepoint = i + 128
try:
encodable_chars[i] = bytes([codepoint]).decode(
codepage["python_encode"]
)
except UnicodeDecodeError:
# Non-encodable character, just skip it
pass
return encodable_chars
raise LookupError(f"Can't find a known encoding for {encoding}")
def _get_codepage_char_map(self, encoding):
"""Get codepage character map.
Process an encoding and return a map of UTF-characters to code points
in this encoding.
This is generated once only, and returned from a cache.
:param encoding: The name of the encoding.
"""
# Skip things that were loaded previously
if encoding in self.available_characters:
return self.available_characters[encoding]
codepage_char_list = self._get_codepage_char_list(encoding)
codepage_char_map = dict(
(utf8, i + 128) for (i, utf8) in enumerate(codepage_char_list)
)
self.available_characters[encoding] = codepage_char_map
return codepage_char_map
[docs]
def can_encode(self, encoding, char):
"""Determine if a character is encodable in the given code page.
:param encoding: The name of the encoding.
:param char: The character to attempt to encode.
"""
available_map = {}
try:
available_map = self._get_codepage_char_map(encoding)
except LookupError:
return False
# Decide whether this character is encodeable in this code page
is_ascii = ord(char) < 128
is_encodable = char in available_map
return is_ascii or is_encodable
@staticmethod
def _encode_char(char, charmap, defaultchar):
"""Encode a single character with the given encoding map.
:param char: char to encode
:param charmap: dictionary for mapping characters in this code page
"""
if ord(char) < 128:
return ord(char)
if char in charmap:
return charmap[char]
return ord(defaultchar)
[docs]
def encode(self, text, encoding, defaultchar="?"):
"""Encode text under the given encoding.
:param text: Text to encode
:param encoding: Encoding name to use (must be defined in capabilities)
:param defaultchar: Fallback for non-encodable characters
"""
codepage_char_map = self._get_codepage_char_map(encoding)
output_bytes = bytes(
[self._encode_char(char, codepage_char_map, defaultchar) for char in text]
)
return output_bytes
def __encoding_sort_func(self, item):
key, index = item
used = key in self.used_encodings
return (not used, index)
[docs]
def find_suitable_encoding(self, char):
"""Search in a specific order for a suitable encoding.
It is the following order:
1. code pages that we already tried before; there is a good
chance they might work again, reducing the search space,
and by re-using already used encodings we might also
reduce the number of codepage change instruction we have
to send. Still, any performance gains will presumably be
fairly minor.
2. code pages in lower ESCPOS slots first. Presumably, they
are more likely to be supported, so if a printer profile
is missing or incomplete, we might increase our change
that the code page we pick for this character is actually
supported.
"""
sorted_encodings = sorted(self.codepages.items(), key=self.__encoding_sort_func)
for encoding, _ in sorted_encodings:
if self.can_encode(encoding, char):
# This encoding worked; at it to the set of used ones.
self.used_encodings.add(encoding)
return encoding
[docs]
def split_writable_text(encoder, text, encoding):
"""Split up the writable text.
Splits off as many characters from the beginning of text as
are writable with "encoding". Returns a 2-tuple (writable, rest).
"""
if not encoding:
return None, text
for idx, char in enumerate(text):
if encoder.can_encode(encoding, char):
continue
return text[:idx], text[idx:]
return text, None
[docs]
class MagicEncode:
"""Help switching to the right code page.
A helper that helps us to automatically switch to the right
code page to encode any given Unicode character.
This will consider the printers supported codepages, according
to the printer profile, and if a character cannot be encoded
with the current profile, it will attempt to find a suitable one.
If the printer does not support a suitable code page, it can
insert an error character.
"""
def __init__(
self, driver, encoding=None, disabled=False, defaultsymbol="?", encoder=None
):
"""Initialize magic encode.
:param driver:
:param encoding: If you know the current encoding of the printer
when initializing this class, set it here. If the current
encoding is unknown, the first character emitted will be a
codepage switch.
:param disabled:
:param defaultsymbol:
:param encoder:
"""
if disabled and not encoding:
raise Error("If you disable magic encode, you need to define an encoding!")
self.driver = driver
self.encoder = encoder or Encoder(driver.profile.get_code_pages())
self.encoding = self.encoder.get_encoding_name(encoding) if encoding else None
self.defaultsymbol = defaultsymbol
self.disabled = disabled
[docs]
def force_encoding(self, encoding):
"""Set a fixed encoding. The change is emitted right away.
From now one, this buffer will switch the code page anymore.
However, it will still keep track of the current code page.
"""
if not encoding:
self.disabled = False
else:
self.write_with_encoding(encoding, None)
self.disabled = True
[docs]
def write(self, text):
"""Write the text, automatically switching encodings."""
if self.disabled:
self.write_with_encoding(self.encoding, text)
return
if re.findall(r"[\u4e00-\u9fa5]", text):
self.driver._raw(text.encode("GB18030"))
return
# See how far we can go into the text with the current encoding
to_write, text = split_writable_text(self.encoder, text, self.encoding)
if to_write:
self.write_with_encoding(self.encoding, to_write)
while text:
# See if any of the code pages that the printer profile
# supports can encode this character.
encoding = self.encoder.find_suitable_encoding(text[0])
if not encoding:
self._handle_character_failed(text[0])
text = text[1:]
continue
# Write as much text as possible with the encoding found.
to_write, text = split_writable_text(self.encoder, text, encoding)
if to_write:
self.write_with_encoding(encoding, to_write)
def _handle_character_failed(self, char):
"""Write a default symbol.
Called when no codepage was found to render a character.
"""
# Writing the default symbol via write() allows us to avoid
# unnecesary codepage switches.
self.write(self.defaultsymbol)
[docs]
def write_with_encoding(self, encoding, text):
"""Write the text and inject necessary codepage switches."""
if text is not None and type(text) is not str:
raise Error(
f"The supplied text has to be unicode, but is of type {type(text)}."
)
# We always know the current code page; if the new codepage
# is different, emit a change command.
if encoding != self.encoding:
self.encoding = encoding
self.driver._raw(
CODEPAGE_CHANGE + six.int2byte(self.encoder.get_sequence(encoding))
)
if text:
self.driver._raw(self.encoder.encode(text, encoding))