from dataclasses import dataclass
from decimal import Decimal, InvalidOperation


@dataclass
class RoundingResult:
    mode: str = "EXACT"
    confidence: float = 1.0
    suggestion: str = ""


def detect_rounding(cobol_value: str, java_value: str) -> RoundingResult:
    c = _to_decimal(cobol_value)
    j = _to_decimal(java_value)

    if c is None or j is None:
        return RoundingResult(mode="UNKNOWN", confidence=0.0, suggestion="cannot parse values")

    if c == j:
        return RoundingResult(mode="EXACT", confidence=1.0, suggestion="values are identical")

    diff = abs(float(c - j))
    magnitude = max(abs(float(c)), abs(float(j)), 1.0)
    relative_diff = diff / magnitude

    if diff < 2.0:
        mode = "TRUNCATE"
        confidence = 0.6
        suggestion = f"Likely TRUNCATE rounding: COBOL truncates, Java rounds or retains precision. Diff: {diff}"
    elif diff < 100.0:
        mode = "ROUNDING"
        confidence = 0.4
        suggestion = f"Possible rounding difference. Diff: {diff}"
    else:
        mode = "SIGNIFICANT"
        confidence = 0.9
        suggestion = f"Values differ significantly (diff={diff}) — not a rounding issue"

    return RoundingResult(mode=mode, confidence=confidence, suggestion=suggestion)


def _to_decimal(val: str):
    try:
        return Decimal(str(val).strip())
    except (InvalidOperation, ValueError):
        return None