feat: configure member number allocation strategy

tests/test_repository.py

@@ -1,4 +1,5 @@
 import json
+from concurrent.futures import ThreadPoolExecutor
 from decimal import Decimal
 
 import pytest
@@ -184,6 +185,43 @@ def test_custom_pattern_and_manual_mode(tmp_path) -> None:
         repository.create_member(first_name="Duplicate", last_name="Member", member_number="special-7")
 
 
+def test_member_number_strategy_fills_gaps_or_uses_max_plus_one(tmp_path) -> None:
+    repository = MemberRepository(tmp_path)
+    repository.initialize()
+    repository.create_member(first_name="One", last_name="Member", member_number="MA-001")
+    repository.create_member(first_name="Three", last_name="Member", member_number="MA-003")
+
+    repository.save_member_number_policy(
+        mode="automatic",
+        pattern="MA-{number:03d}",
+        allocation_strategy="next_free",
+    )
+    assert repository.preview_member_number() == "MA-002"
+    assert repository.get_member_number_policy()["allocation_strategy"] == "next_free"
+
+    repository.save_member_number_policy(
+        mode="automatic",
+        pattern="MA-{number:03d}",
+        allocation_strategy="max_plus_one",
+    )
+    assert repository.preview_member_number() == "MA-004"
+    created = repository.create_member(first_name="Four", last_name="Member")
+    assert created.member_number == "MA-004"
+
+
+def test_concurrent_automatic_member_numbers_are_unique(tmp_path) -> None:
+    MemberRepository(tmp_path).initialize()
+
+    def create(index: int) -> str:
+        repository = MemberRepository(tmp_path)
+        return repository.create_member(first_name=f"Member {index}", last_name="Concurrent").member_number
+
+    with ThreadPoolExecutor(max_workers=8) as executor:
+        numbers = list(executor.map(create, range(16)))
+
+    assert len(numbers) == len(set(numbers)) == 16
+
+
 @pytest.mark.parametrize("pattern", ["", "CCMA-{year}", "{unknown}-{number}", "{number!r}"])
 def test_invalid_member_number_patterns_are_rejected(pattern) -> None:
     with pytest.raises(RepositoryError):