"""Budget and runway alert evaluation."""

from __future__ import annotations

from dataclasses import dataclass

from fin_hub.services.runway import RunwayResult


@dataclass(frozen=True)
class BudgetAlert:
    code: str
    severity: str
    summary: str
    detail: dict

    def as_dict(self) -> dict:
        return {
            "code": self.code,
            "severity": self.severity,
            "summary": self.summary,
            "detail": self.detail,
        }


def evaluate_budget_alerts(
    *,
    runway: RunwayResult,
    allocated: float | None = None,
    spent: float | None = None,
) -> list[BudgetAlert]:
    alerts: list[BudgetAlert] = []
    if runway.below_threshold and runway.monthly_burn > 0:
        alerts.append(
            BudgetAlert(
                code="runway_below_threshold",
                severity="high",
                summary=(
                    f"Projected runway {runway.months_remaining:.1f} months "
                    f"is below threshold {runway.alert_threshold_months:.1f}"
                ),
                detail=runway.as_dict(),
            )
        )
    if allocated is not None and spent is not None and allocated > 0:
        utilisation = spent / allocated
        if utilisation >= 0.8:
            alerts.append(
                BudgetAlert(
                    code="budget_pressure",
                    severity="medium" if utilisation < 1.0 else "high",
                    summary=f"Budget utilisation at {utilisation * 100:.0f}%",
                    detail={
                        "allocated": allocated,
                        "spent": spent,
                        "utilisation": utilisation,
                    },
                )
            )
    return alerts