import re
from dataclasses import dataclass, field
from datetime import date
from decimal import Decimal


class ParserError(Exception):
    pass


@dataclass(frozen=True)
class ParsedTransaction:
    booking_date: date
    value_date: date | None
    amount: Decimal
    purpose: str
    counterparty: str


@dataclass
class ParsedStatement:
    bank: str
    iban: str | None
    period_start: date | None
    period_end: date | None
    opening_balance: Decimal | None
    closing_balance: Decimal | None
    transactions: list[ParsedTransaction] = field(default_factory=list)


def parse_german_amount(s: str) -> Decimal:
    s = s.strip().replace(" ", "").replace("\xa0", "")
    neg = s.endswith("-") or s.startswith("-") or s.endswith("S")
    s = s.strip("+-SH")
    value = Decimal(s.replace(".", "").replace(",", "."))
    return -value if neg else value


def parse_german_date(s: str, default_year: int | None = None) -> date:
    m = re.fullmatch(r"(\d{2})\.(\d{2})\.(\d{4})?", s.strip())
    if not m:
        raise ParserError(f"Kein Datum: {s!r}")
    year = int(m.group(3)) if m.group(3) else default_year
    if year is None:
        raise ParserError(f"Jahr fehlt: {s!r}")
    try:
        return date(year, int(m.group(2)), int(m.group(1)))
    except ValueError:
        raise ParserError(f"Ungültiges Datum: {s!r}")