Truncate product titles used when creating PayPal payments

PayPal requires that item names be at most 127 characters long. XCOM-564.

ecommerce/extensions/payment/processors/paypal.py

@@ -12,6 +12,8 @@ import paypalrestsdk
 from ecommerce.extensions.order.constants import PaymentEventTypeName
 from ecommerce.extensions.payment.processors import BasePaymentProcessor
 from ecommerce.extensions.payment.models import PaypalWebProfile
+from ecommerce.extensions.payment.utils import middle_truncate
+
 
 logger = logging.getLogger(__name__)
 
@@ -84,7 +86,8 @@ class Paypal(BasePaymentProcessor):
                     'items': [
                         {
                             'quantity': line.quantity,
-                            'name': line.product.title,
+                            # PayPal requires that item names be at most 127 characters long.
+                            'name': middle_truncate(line.product.title, 127),
                             'price': unicode(line.price_incl_tax),
                             'currency': line.stockrecord.price_currency,
                         }

ecommerce/extensions/payment/tests/test_utils.py

+from django.test import TestCase
+
+from ecommerce.extensions.payment.utils import middle_truncate
+
+
+class UtilsTests(TestCase):
+    def test_truncation(self):
+        """Verify that the truncation utility behaves as expected."""
+        length = 10
+        string = 'x' * length
+
+        # Verify that the original string is returned when no truncation is necessary.
+        self.assertEqual(string, middle_truncate(string, length))
+        self.assertEqual(string, middle_truncate(string, length + 1))
+
+        # Verify that truncation occurs when expected.
+        self.assertEqual('xxx...xxx', middle_truncate(string, length - 1))
+        self.assertEqual('xx...xx', middle_truncate(string, length - 2))
+
+        self.assertRaises(ValueError, middle_truncate, string, 0)

ecommerce/extensions/payment/utils.py

+from django.utils.translation import ugettext_lazy as _
+
+
+def middle_truncate(string, chars):
+    """Truncate the provided string, if necessary.
+
+    Cuts excess characters from the middle of the string and replaces
+    them with a string indicating that truncation has occurred.
+
+    Arguments:
+        string (unicode or str): The string to be truncated.
+        chars (int): The character limit for the truncated string.
+
+    Returns:
+        Unicode: The truncated string, of length less than or equal to `chars`.
+            If no truncation was required, the original string is returned.
+
+    Raises:
+        ValueError: If the provided character limit is less than the length of
+            the truncation indicator.
+    """
+    if len(string) <= chars:
+        return string
+
+    # Translators: This is a string placed in the middle of a truncated string
+    # to indicate that truncation has occurred. For example, if a title may only
+    # be at most 11 characters long, "A Very Long Title" (17 characters) would be
+    # truncated to "A Ve...itle".
+    indicator = _('...')
+
+    indicator_length = len(indicator)
+    if chars < indicator_length:
+        raise ValueError
+
+    slice_size = (chars - indicator_length) / 2
+    start, end = string[:slice_size], string[-slice_size:]
+    truncated = u'{start}{indicator}{end}'.format(start=start, indicator=indicator, end=end)
+
+    return truncated