from __future__ import annotations

from dataclasses import dataclass
from typing import Any


@dataclass(frozen=True)
class GateDecision:
    passed: bool
    error_code: str | None = None
    error_message: str | None = None


def evaluate_step_gate(step_key: str, payload: dict[str, Any]) -> GateDecision:
    if payload.get("success") is False:
        return GateDecision(
            passed=False,
            error_code=str(payload.get("error_code") or "step_reported_failure"),
            error_message=str(payload.get("error") or "Step returned success=false"),
        )

    if step_key == "demand_classify" and payload.get("failed_batches"):
        return GateDecision(False, "classification_failed_batches", "Classification has failed batches")

    if step_key in {"demand_grade", "demand_expand", "video_discovery"}:
        failed = int(payload.get("failed", payload.get("failed_count", 0)) or 0)
        if failed > 0:
            return GateDecision(
                False,
                "business_failures",
                f"{step_key} reported {failed} failed item(s)",
            )

    return GateDecision(True)