feat(fusion_accounting_followup): level_resolver service

Made-with: Cursor

fusion_accounting_followup/services/level_resolver.py

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+"""Level resolver: which follow-up level should fire for this partner?
+
+Pure-Python: caller passes the aging report + the configured levels list,
+and we pick the highest-numbered level whose threshold is met."""
+
+from dataclasses import dataclass
+
+
+@dataclass
+class FollowupLevelSpec:
+    sequence: int
+    name: str
+    delay_days: int
+    tone: str
+
+    def __post_init__(self):
+        if self.tone not in ('gentle', 'firm', 'legal'):
+            raise ValueError(f"Invalid tone: {self.tone}")
+
+
+def resolve_level(*, aging_report, levels: list[FollowupLevelSpec]) -> FollowupLevelSpec | None:
+    """Pick the highest-sequence level whose delay_days has been crossed by
+    the most-overdue line in the aging report. Returns None if no overdue
+    lines or no levels configured."""
+    if not levels or not aging_report:
+        return None
+    max_days_overdue = _max_days_overdue(aging_report)
+    if max_days_overdue <= 0:
+        return None
+    levels_sorted = sorted(levels, key=lambda l: l.sequence, reverse=True)
+    for level in levels_sorted:
+        if level.delay_days <= max_days_overdue:
+            return level
+    return None
+
+
+def _max_days_overdue(aging_report) -> int:
+    """Return the actual max days-overdue tracked on the report, falling
+    back to the highest populated bucket's lower bound when an older
+    aging report (without `max_days_overdue`) is passed in."""
+    tracked = getattr(aging_report, 'max_days_overdue', 0) or 0
+    if tracked:
+        return tracked
+    max_days = 0
+    for b in aging_report.buckets:
+        if b.name == 'current' or b.amount <= 0:
+            continue
+        if b.days_max is None:
+            max_days = max(max_days, b.days_min)
+        else:
+            max_days = max(max_days, b.days_min)
+    return max_days