data: Add is_credit() and is_debit() methods to Posting.

The main motivation for this change is to make sure that higher-level
code deals with the fact that self.units.number can be None, and has
an easy way to do so.

I'm not sure all our code is *currently* doing the right thing for this
case, because I'm not sure it will ever actually come up. It's possible
that earlier Beancount plugins fill in decimal amounts for postings
that are originally loaded with self.units.number=None. I'll have to see
later whether this case comes up in reality, and then deal with it if so.
For now the safest strategy seems to be that most code should operate
when self.units.number is None.

conservancy_beancount/data.py

@@ -21,11 +21,13 @@ throughout Conservancy tools.
 
 import collections
 import decimal
+import operator
 
 from beancount.core import account as bc_account
 
 from typing import (
     cast,
+    Callable,
     Iterable,
     Iterator,
     MutableMapping,
@@ -215,13 +217,33 @@ class Posting(BasePosting):
     # If it did, this declaration would pass without issue.
     meta: Metadata  # type:ignore[assignment]
 
-    def is_payment(self, threshold: DecimalCompat=0) -> bool:
-        threshold = cast(decimal.Decimal, threshold)
-        return (
-            self.account.is_real_asset()
-            and self.units.number is not None
-            and self.units.number < -abs(threshold)
-        )
+    def _compare_amount(self,
+                        op: Callable[[decimal.Decimal], decimal.Decimal],
+                        threshold: DecimalCompat,
+                        default: Optional[bool],
+    ) -> Optional[bool]:
+        if self.units.number is None:
+            return default
+        else:
+            return op(self.units.number) > threshold
+
+    def is_credit(self,
+                  threshold: DecimalCompat=0,
+                  default: Optional[bool]=None,
+    ) -> Optional[bool]:
+        return self._compare_amount(operator.pos, threshold, default)
+
+    def is_debit(self,
+                  threshold: DecimalCompat=0,
+                  default: Optional[bool]=None,
+    ) -> Optional[bool]:
+        return self._compare_amount(operator.neg, threshold, default)
+
+    def is_payment(self,
+                  threshold: DecimalCompat=0,
+                  default: Optional[bool]=None,
+    ) -> Optional[bool]:
+        return self.account.is_real_asset() and self.is_debit(threshold, default)
 
 
 def iter_postings(txn: Transaction) -> Iterator[Posting]:

conservancy_beancount/plugin/meta_approval.py

@@ -29,7 +29,7 @@ class MetaApproval(core._RequireLinksPostingMetadataHook):
     CREDIT_CARD_ACCT = 'Liabilities:CreditCard'
 
     def __init__(self, config: configmod.Config) -> None:
-        self.payment_threshold = -abs(config.payment_threshold())
+        self.payment_threshold = config.payment_threshold()
 
     def _run_on_txn(self, txn: Transaction) -> bool:
         if not super()._run_on_txn(txn):
@@ -37,11 +37,11 @@ class MetaApproval(core._RequireLinksPostingMetadataHook):
         assets_sum = decimal.Decimal(0)
         creditcard_sum = decimal.Decimal(0)
         for post in data.iter_postings(txn):
-            if post.is_payment(self.payment_threshold):
-                assets_sum += post.units.number or 0
+            if post.is_payment():
+                assets_sum -= post.units.number or 0
             elif post.account.is_under(self.CREDIT_CARD_ACCT):
                 creditcard_sum += post.units.number or 0
-        return (assets_sum + creditcard_sum) < 0
+        return (assets_sum - creditcard_sum) > self.payment_threshold
 
     def _run_on_post(self, txn: Transaction, post: data.Posting) -> bool:
-        return post.is_payment()
+        return post.is_payment(0) is not False

conservancy_beancount/plugin/meta_tax_implication.py

@@ -48,4 +48,4 @@ class MetaTaxImplication(core._NormalizePostingMetadataHook):
         self.payment_threshold = config.payment_threshold()
 
     def _run_on_post(self, txn: Transaction, post: data.Posting) -> bool:
-        return post.is_payment(self.payment_threshold)
+        return post.is_payment(self.payment_threshold) is not False

tests/test_data_posting.py

@@ -39,25 +39,64 @@ NON_PAYMENT_ACCOUNTS = {
     'UnearnedIncome:MatchPledges',
 }
 
+AMOUNTS = [
+    None,
+    '-25.50',
+    0,
+    '25.75',
+]
+
 def Posting(account, number,
             currency='USD', cost=None, price=None, flag=None,
             **meta):
     if not meta:
         meta = None
+    if number is not None:
+        number = Decimal(number)
     return data.Posting(
         data.Account(account),
-        bc_amount.Amount(Decimal(number), currency),
+        bc_amount.Amount(number, currency),
         cost,
         price,
         flag,
         meta,
     )
 
-def check_all_thresholds(post, threshold, expected):
-    assert post.is_payment(threshold) is expected
-    assert post.is_payment(-threshold) is expected
-    assert post.is_payment(Decimal(threshold)) is expected
-    assert post.is_payment(Decimal(-threshold)) is expected
+def check_all_thresholds(expected, method, threshold, *args):
+    assert method(threshold, *args) is expected
+    assert method(Decimal(threshold), *args) is expected
+
+@pytest.mark.parametrize('amount', AMOUNTS)
+def test_is_credit(amount):
+    expected = None if amount is None else float(amount) > 0
+    assert Posting('Assets:Cash', amount).is_credit() is expected
+
+def test_is_credit_threshold():
+    post = Posting('Assets:Cash', 25)
+    check_all_thresholds(True, post.is_credit, 0)
+    check_all_thresholds(True, post.is_credit, 20)
+    check_all_thresholds(False, post.is_credit, 40)
+
+def test_is_credit_default():
+    post = Posting('Assets:Cash', None)
+    assert post.is_credit(default=True) is True
+    assert post.is_credit(default=False) is False
+
+@pytest.mark.parametrize('amount', AMOUNTS)
+def test_is_debit(amount):
+    expected = None if amount is None else float(amount) < 0
+    assert Posting('Assets:Cash', amount).is_debit() is expected
+
+def test_is_debit_threshold():
+    post = Posting('Assets:Cash', -25)
+    check_all_thresholds(True, post.is_debit, 0)
+    check_all_thresholds(True, post.is_debit, 20)
+    check_all_thresholds(False, post.is_debit, 40)
+
+def test_is_debit_default():
+    post = Posting('Assets:Cash', None)
+    assert post.is_debit(default=True) is True
+    assert post.is_debit(default=False) is False
 
 @pytest.mark.parametrize('acct', PAYMENT_ACCOUNTS)
 def test_is_payment(acct):
@@ -71,24 +110,24 @@ def test_is_payment(acct):
 def test_is_not_payment_account(acct, amount, threshold):
     post = Posting(acct, -amount)
     assert not post.is_payment()
-    check_all_thresholds(post, threshold, False)
+    check_all_thresholds(False, post.is_payment, threshold)
 
 @pytest.mark.parametrize('acct', PAYMENT_ACCOUNTS)
 def test_is_payment_with_threshold(acct):
     threshold = len(acct) * 10
     post = Posting(acct, -500)
-    check_all_thresholds(post, threshold, True)
+    check_all_thresholds(True, post.is_payment, threshold)
 
 @pytest.mark.parametrize('acct', PAYMENT_ACCOUNTS)
 def test_is_not_payment_by_threshold(acct):
     threshold = len(acct) * 10
     post = Posting(acct, -9)
-    check_all_thresholds(post, threshold, False)
+    check_all_thresholds(False, post.is_payment, threshold)
 
 @pytest.mark.parametrize('acct', PAYMENT_ACCOUNTS)
 def test_is_not_payment_but_credit(acct):
     post = Posting(acct, 9)
     assert not post.is_payment()
-    check_all_thresholds(post, 0, False)
-    check_all_thresholds(post, 5, False)
-    check_all_thresholds(post, 10, False)
+    check_all_thresholds(False, post.is_payment, 0)
+    check_all_thresholds(False, post.is_payment, 5)
+    check_all_thresholds(False, post.is_payment, 10)