2 files changed, 196 insertions, 0 deletions
diff --git a/stdnum/sg/__init__.py b/stdnum/sg/__init__.py
new file mode 100644
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+++ b/stdnum/sg/__init__.py
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+# __init__.py - collection of Singapore numbers
+# coding: utf-8
+#
+# Copyright (C) 2020 Leandro Regueiro
+#
+# This library is free software; you can redistribute it and/or
+# modify it under the terms of the GNU Lesser General Public
+# License as published by the Free Software Foundation; either
+# version 2.1 of the License, or (at your option) any later version.
+#
+# This library is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+# Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public
+# License along with this library; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+# 02110-1301 USA
+
+"""Collection of Singapore numbers."""
+
+# provide aliases
+from stdnum.sg import uen as vat  # noqa: F401
diff --git a/stdnum/sg/uen.py b/stdnum/sg/uen.py
new file mode 100644
index 0000000..2b49be1
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+++ b/stdnum/sg/uen.py
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+# uen.py - functions for handling Singapore UEN numbers
+# coding: utf-8
+#
+# Copyright (C) 2020 Leandro Regueiro
+# Copyright (C) 2020 Arthur de Jong
+#
+# This library is free software; you can redistribute it and/or
+# modify it under the terms of the GNU Lesser General Public
+# License as published by the Free Software Foundation; either
+# version 2.1 of the License, or (at your option) any later version.
+#
+# This library is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+# Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public
+# License along with this library; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+# 02110-1301 USA
+
+"""UEN (Singapore's Unique Entity Number).
+
+The Unique Entity Number (UEN) is a 9 or 10 digit identification issued by
+the government of Singapore to businesses that operate with within Singapore.
+
+
+Accounting and Corporate Regulatory Authority (ACRA)
+
+There are three different formats:
+
+* Business (ROB): It consists of 8 digits followed by a check letter.
+* Local Company (ROC): It consists of 9 digits (the 4 leftmost digits
+  represent the year of issuance) followed by a check letter.
+* Others: Consists of 10 characters, begins with either the R letter, or the
+  S letter or the T letter followed by 2 digits representing the last two
+  digits of the issuance year, followed by two letters representing the
+  entity type, 4 digits and finally a check letter.
+
+More information:
+
+* https://www.oecd.org/tax/automatic-exchange/crs-implementation-and-assistance/tax-identification-numbers/Singapore-TIN.pdf
+* https://www.uen.gov.sg/ueninternet/faces/pages/admin/aboutUEN.jspx
+
+>>> validate('00192200M')
+'00192200M'
+>>> validate('197401143C')
+'197401143C'
+>>> validate('S16FC0121D')
+'S16FC0121D'
+>>> validate('T01FC6132D')
+'T01FC6132D'
+>>> validate('123456')
+Traceback (most recent call last):
+    ...
+InvalidLength: ...
+"""
+
+# There are some references to special 10-digit (or 7-digit) numbers that
+# start with an F for foreign companies but it is unclear whether this is
+# still current and not even examples of these numbers could be found.
+
+from datetime import datetime
+
+from stdnum.exceptions import *
+from stdnum.util import clean, isdigits
+
+
+OTHER_UEN_ENTITY_TYPES = (
+    'CC', 'CD', 'CH', 'CL', 'CM', 'CP', 'CS', 'CX', 'DP', 'FB', 'FC', 'FM',
+    'FN', 'GA', 'GB', 'GS', 'HS', 'LL', 'LP', 'MB', 'MC', 'MD', 'MH', 'MM',
+    'MQ', 'NB', 'NR', 'PA', 'PB', 'PF', 'RF', 'RP', 'SM', 'SS', 'TC', 'TU',
+    'VH', 'XL',
+)
+
+
+def compact(number):
+    """Convert the number to the minimal representation.
+
+    This converts to uppercase and removes surrounding whitespace. It
+    also replaces the whitespace in UEN for foreign companies with
+    zeroes.
+    """
+    return clean(number).upper().strip()
+
+
+def calc_business_check_digit(number):
+    """Calculate the check digit for the Business (ROB) number."""
+    number = compact(number)
+    weights = (10, 4, 9, 3, 8, 2, 7, 1)
+    return 'XMKECAWLJDB'[sum(int(n) * w for n, w in zip(number, weights)) % 11]
+
+
+def _validate_business(number):
+    """Perform validation on UEN - Business (ROB) numbers."""
+    if not isdigits(number[:-1]):
+        raise InvalidFormat()
+    if not number[-1].isalpha():
+        raise InvalidFormat()
+    if number[-1] != calc_business_check_digit(number):
+        raise InvalidChecksum()
+    return number
+
+
+def calc_local_company_check_digit(number):
+    """Calculate the check digit for the Local Company (ROC) number."""
+    number = compact(number)
+    weights = (10, 8, 6, 4, 9, 7, 5, 3, 1)
+    return 'ZKCMDNERGWH'[sum(int(n) * w for n, w in zip(number, weights)) % 11]
+
+
+def _validate_local_company(number):
+    """Perform validation on UEN - Local Company (ROC) numbers."""
+    if not isdigits(number[:-1]):
+        raise InvalidFormat()
+    current_year = str(datetime.now().year)
+    if number[:4] > current_year:
+        raise InvalidComponent()
+    if number[-1] != calc_local_company_check_digit(number):
+        raise InvalidChecksum()
+    return number
+
+
+def calc_other_check_digit(number):
+    """Calculate the check digit for the other entities number."""
+    number = compact(number)
+    alphabet = 'ABCDEFGHJKLMNPQRSTUVWX0123456789'
+    weights = (4, 3, 5, 3, 10, 2, 2, 5, 7)
+    return alphabet[(sum(alphabet.index(n) * w for n, w in zip(number, weights)) - 5) % 11]
+
+
+def _validate_other(number):
+    """Perform validation on other UEN numbers."""
+    if number[0] not in ('R', 'S', 'T'):
+        raise InvalidComponent()
+    if not isdigits(number[1:3]):
+        raise InvalidFormat()
+    current_year = str(datetime.now().year)
+    if number[0] == 'T' and number[1:3] > current_year[2:]:
+        raise InvalidComponent()
+    if number[3:5] not in OTHER_UEN_ENTITY_TYPES:
+        raise InvalidComponent()
+    if not isdigits(number[5:-1]):
+        raise InvalidFormat()
+    if number[-1] != calc_other_check_digit(number):
+        raise InvalidChecksum()
+    return number
+
+
+def validate(number):
+    """Check if the number is a valid Singapore UEN number."""
+    number = compact(number)
+    if len(number) not in (9, 10):
+        raise InvalidLength()
+    if len(number) == 9:
+        return _validate_business(number)
+    if isdigits(number[0]):
+        return _validate_local_company(number)
+    return _validate_other(number)
+
+
+def is_valid(number):
+    """Check if the number is a valid Singapore UEN number."""
+    try:
+        return bool(validate(number))
+    except ValidationError:
+        return False
+
+
+def format(number):
+    """Reformat the number to the standard presentation format."""
+    return compact(number)