"""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