client: iter_transactions() supports date ranges longer than a month.

This works by extracting the date-crawling code from get_transaction() to a
separate method. Now iter_transactions() will similarly make API requests
with different month-long date ranges until covers the entire date range the
user requested.

paypal_rest/client.py

@@ -19,6 +19,7 @@ import datetime
 import enum
 import logging
 import math
+import operator
 import urllib.parse as urlparse
 
 import requests
@@ -285,6 +286,47 @@ class PayPalAPIClient:
         ]
         self.logger.error(" — ".join(parts))
 
+    def _iter_date_params(
+            self,
+            start_date: datetime.datetime,
+            end_date: datetime.datetime,
+            params: Optional[Params]=None,
+    ) -> Iterator[Params]:
+        """Generate parameters with date windows to cover a wider span
+
+        The PayPal transaction search API only allows the ``start_date`` and
+        ``end_date`` to be a month apart. Given a user's desired date range and
+        other API parameters, this method generates parameters with different
+        date pairs to cover the entire date range.
+
+        Normally the method keeps incrementing ``start_date`` until the user's
+        desired ``end_date`` is reached. If the ``start_date`` if later than the
+        ``end_date``, instead it works backwards: it uses the ``start_date``
+        argument as the first ``end_date`` parameter, and keeps decrementing it
+        until the ``start_date`` parameter reaches the other end of the range.
+        """
+        if start_date > end_date:
+            key1 = 'end_date'
+            key2 = 'start_date'
+            days_sign = operator.neg
+            pred = operator.gt
+            limit_func = max
+        else:
+            key1 = 'start_date'
+            key2 = 'end_date'
+            days_sign = operator.pos
+            pred = operator.lt
+            limit_func = min
+        retval = collections.ChainMap(params or {}).new_child()
+        retval[key1] = start_date.isoformat(timespec='seconds')
+        next_date = start_date
+        date_diff = datetime.timedelta(days=days_sign(30))
+        while pred(next_date, end_date):
+            next_date = limit_func(next_date + date_diff, end_date)
+            retval[key2] = next_date.isoformat(timespec='seconds')
+            yield retval
+            retval[key1] = retval[key2]
+
     def get_subscription(
             self,
             subscription_id: str,
@@ -323,20 +365,14 @@ class PayPalAPIClient:
         if start_date is None:
             # The API only goes back three years
             start_date = now - datetime.timedelta(days=365 * 3)
-        date_diff = datetime.timedelta(days=30)
         response: APIResponse = {'transaction_details': None}
-        while end_date > start_date and not response['transaction_details']:
+        for params in self._iter_date_params(end_date, start_date, {
-            search_start = max(end_date - date_diff, start_date)
-            response = self._get_json('/v1/reporting/transactions', {
                 'transaction_id': transaction_id,
                 'fields': fields.param_value(),
-                'start_date': search_start.isoformat(timespec='seconds'),
+        }):
-                'end_date': end_date.isoformat(timespec='seconds'),
+            response = self._get_json('/v1/reporting/transactions', params)
-            })
-            end_date = search_start
             if response['transaction_details']:
                 return Transaction(response['transaction_details'][0])
-        else:
         raise ValueError(f"transaction {transaction_id!r} not found")
 
     def iter_transactions(
@@ -351,10 +387,9 @@ class PayPalAPIClient:
         ``fields`` is a TransactionsFields object that flags the information to
         include in returned Transactions.
         """
-        for page in self._iter_pages('/v1/reporting/transactions', {
+        for params in self._iter_date_params(start_date, end_date, {
                 'fields': fields.param_value(),
-                'start_date': start_date.isoformat(timespec='seconds'),
-                'end_date': end_date.isoformat(timespec='seconds'),
         }):
+            for page in self._iter_pages('/v1/reporting/transactions', params):
                 for txn_source in page['transaction_details']:
                     yield Transaction(txn_source)

setup.py

@@ -25,7 +25,7 @@ with README_PATH.open() as readme_file:
 
 setup(
     name='paypal_rest',
-    version='1.0.0',
+    version='1.0.1',
     author='Software Freedom Conservancy',
     author_email='info@sfconservancy.org',
     license='GNU AGPLv3+',

tests/test_client.py

@@ -26,7 +26,7 @@ from paypal_rest import client as client_mod
 from paypal_rest import transaction as txn_mod
 
 START_DATE = datetime.datetime(2020, 10, 1, 12, tzinfo=datetime.timezone.utc)
-END_DATE = START_DATE.replace(month=START_DATE.month + 1)
+END_DATE = START_DATE.replace(day=25)
 
 def test_transaction_type():
     txn_id = 'TYPETEST123456789'
@@ -87,6 +87,53 @@ def test_transaction_fields_formatting(fields):
         for name in session._requests[0].params.get('fields', '').split(',')
     }
 
+@pytest.mark.parametrize('days_diff', [10, 45, 89])
+def test_iter_transactions_date_window(days_diff):
+    start_date = START_DATE
+    end_date = start_date + datetime.timedelta(days=days_diff)
+    session = MockSession(
+        MockResponse({'page': 1, 'total_pages': 1, 'transaction_details': []}),
+        infinite=True,
+    )
+    paypal = client_mod.PayPalAPIClient(session)
+    assert not any(paypal.iter_transactions(start_date, end_date))
+    req_count = len(session._requests)
+    assert req_count == ((days_diff // 30) + 1)
+    start_str = start_date.isoformat(timespec='seconds')
+    end_str = end_date.isoformat(timespec='seconds')
+    prev_end = start_str
+    for number, request in enumerate(session._requests, 1):
+        assert request.params['start_date'] == prev_end
+        if number == req_count:
+            assert request.params['end_date'] == end_str
+        else:
+            assert prev_end < request.params['end_date'] < end_str
+            prev_end = request.params['end_date']
+
+@pytest.mark.parametrize('days_diff', [10, 45, 89])
+def test_get_transactions_date_window(days_diff):
+    end_date = END_DATE
+    start_date = end_date - datetime.timedelta(days=days_diff)
+    session = MockSession(
+        MockResponse({'page': 1, 'total_pages': 1, 'transaction_details': []}),
+        infinite=True,
+    )
+    paypal = client_mod.PayPalAPIClient(session)
+    with pytest.raises(ValueError):
+        paypal.get_transaction('DATEWINDOW1234567', end_date, start_date)
+    req_count = len(session._requests)
+    assert req_count == ((days_diff // 30) + 1)
+    start_str = start_date.isoformat(timespec='seconds')
+    end_str = end_date.isoformat(timespec='seconds')
+    prev_start = end_str
+    for number, request in enumerate(session._requests, 1):
+        assert request.params['end_date'] == prev_start
+        if number == req_count:
+            assert request.params['start_date'] == start_str
+        else:
+            assert prev_start > request.params['start_date'] > start_str
+            prev_start = request.params['start_date']
+
 @pytest.mark.parametrize('name', [
     'BAD_REQUEST',
     'UNAUTHORIZED',