Source code for pystrich.ean13

"""EAN-13 barcode encoder

All needed by the user is done via the EAN13Encoder class:

>>> encoder = EAN13Encoder("012345678901")
>>> encoder.save("test.png")

Implemented by Helen Taylor for HUDORA GmbH.
Updated and ported to Python 3 by Michael Mulqueen for Method B Ltd.

Detailed documentation on the format here:
http://www.barcodeisland.com/ean13.phtml

You may use this under a BSD License.
"""

from __future__ import annotations

from functools import reduce

from pystrich.bar_encoder import Bar1DEncoder
from pystrich.exceptions import PyStrichInvalidInput

from . import encoding
from .renderer import EAN13Renderer, EAN13RenderOptions

GUARDS = ("101", "01010", "101")




class EAN13Encoder(Bar1DEncoder):
    """Encode a 12- or 13-digit code as an EAN-13 1D barcode.

    The check digit is computed for you. If a 13-digit code is supplied, its
    final digit is discarded and recomputed.

    Typical use::

        encoder = EAN13Encoder("012345678901")
        encoder.save("ean13.png")

    :ivar code: The 12-digit input (number system + manufacturer + product).
    :ivar check_digit: The computed mod-10 check digit.
    :ivar full_code: The 13-digit code including check digit.
    :ivar left_bars: Bar pattern for the left half of the symbol.
    :ivar right_bars: Bar pattern for the right half.
    :ivar options: Render-time options dict (empty if none were supplied).
    :ivar width: Pixel width of the most recently rendered image.
    :ivar height: Pixel height of the most recently rendered image.
    """

    options: EAN13RenderOptions
    code: str
    check_digit: int
    full_code: str
    left_bars: str
    right_bars: str

    def __init__(
        self,
        code: str,
        options: EAN13RenderOptions | None = None,
    ) -> None:
        """Validate ``code`` and compute its check digit.

        :param code: A string of 12 digits in the form ``nnmmmmmppppp``,
            where ``n`` is the number system, ``m`` is the manufacturer code
            and ``p`` is the product code. A 13-digit code is also accepted;
            its final digit is treated as a check digit and recomputed.
        :param options: Optional dict tweaking the rendered output. See
            :class:`pystrich.ean13.EAN13RenderOptions` for accepted keys.
        :raises pystrich.exceptions.PyStrichInvalidInput: if ``code`` is not
            exactly 12 (or 13) digits.
        """
        super().__init__(options)

        # Normalise to 12 digits: a 13-digit input has its trailing check
        # digit dropped (we recompute it below).
        if len(code) == 13:
            code = code[:-1]
        if not (code.isdigit() and len(code) == 12):
            raise PyStrichInvalidInput("code must be 12 or 13 digits long")
        self.code = code
        self.check_digit = self.calculate_check_digit()
        self.full_code = self.code + str(self.check_digit)
        self.left_bars = ""
        self.right_bars = ""
        self.encode()



    def encode(self) -> tuple[str, str]:
        """Encode the barcode number and return the left and right
        data strings"""

        parity_values = self.get_parity()

        self.left_bars = ""
        self.right_bars = ""

        # Exclude the first number system digit, this was
        # for determining the left parity
        for parity, digit in zip(parity_values, self.full_code[1:7], strict=False):
            self.left_bars += encoding.get_left_encoded(int(digit), parity)
        for digit in self.full_code[7:]:
            self.right_bars += encoding.get_right_encoded(int(digit))

        return self.left_bars, self.right_bars




    def get_parity(self) -> tuple[int, int, int, int, int, int]:
        """Return the parity mappings applicable to this code"""
        return encoding.parity_table[int(self.code[0])]




    def calculate_check_digit(self) -> int:
        """Compute the EAN-13 mod-10 check digit for :attr:`code`.

        Working right-to-left across the 12-digit input, odd-positioned
        digits are weighted by 3 and even-positioned digits by 1; the check
        digit is the value that brings the weighted sum to a multiple of 10.
        """

        def sum_str(total, digit):
            """add a stringified digit to the total sum"""
            return total + int(digit)

        # sum the "odd" digits (1,3,5,7,9,11) and multiply by 3
        oddsum = reduce(sum_str, self.code[1::2], 0)

        # sum the "even" digits (0,2,4,6,8,10)
        evensum = reduce(sum_str, self.code[:12:2], 0)

        # add them up
        total = oddsum * 3 + evensum

        # check digit is the number that can be added to the total
        # to get to a multiple of 10
        return (10 - (total % 10)) % 10




    def init_renderer(self) -> EAN13Renderer:
        """Construct an :class:`EAN13Renderer` for the encoded code.

        :rtype: :class:`EAN13Renderer`
        """
        return EAN13Renderer(
            self.full_code,
            self.left_bars,
            self.right_bars,
            GUARDS,
            self.options,
        )