"""Metrics — quality signals without golden dataset.

Checks that work immediately:
- Arithmetic: sum == price * qty (free signal of LLM/data errors)
- JSON fix rate: how often _safe_json_parse has to repair LLM output
"""
from decimal import Decimal, InvalidOperation


def check_arithmetic(ops: list) -> list[dict]:
    """Check sum == price * qty for ADD/UPDATE operations.
    Returns list of mismatches: [{action, name, price, qty, expected_sum, actual_sum, diff}]
    """
    mismatches = []
    for op in ops:
        action = op.get("action", "")
        if action not in ("ADD", "UPDATE"):
            continue

        row = op.get("new_row") or op.get("new_values") or {}
        price = _to_decimal(row.get("price"))
        qty = _to_decimal(row.get("qty"))
        actual_sum = _to_decimal(row.get("sum"))

        if price is None or qty is None or actual_sum is None:
            continue  # can't check without all three

        expected = price * qty
        if expected != actual_sum:
            mismatches.append({
                "action": action,
                "name": row.get("name", "")[:100],
                "price": float(price),
                "qty": float(qty),
                "expected_sum": float(expected),
                "actual_sum": float(actual_sum),
                "diff": float(actual_sum - expected),
            })
    return mismatches


class ClassifyMetrics:
    """Track _safe_json_parse fix rate per batch."""
    def __init__(self):
        self.total = 0
        self.fixes = 0  # how many times JSON needed repair

    def record(self, needed_fix: bool):
        self.total += 1
        if needed_fix:
            self.fixes += 1

    @property
    def fix_rate(self) -> float:
        return self.fixes / self.total if self.total else 0.0

    def summary(self) -> dict:
        return {
            "total_classifications": self.total,
            "json_fixes": self.fixes,
            "json_fix_rate": round(self.fix_rate, 3),
        }


def _to_decimal(val) -> Decimal | None:
    """Safe conversion to Decimal."""
    if val is None or val == "":
        return None
    try:
        return Decimal(str(val))
    except (InvalidOperation, ValueError):
        return None