"""DATEV CSV format helper (Buchungsstapel).

Generates CSV in DATEV-compatible format with headers:
Datum, Konto, Gegenkonto, Betrag, Belegfeld, Buchungstext
"""

import csv
import io
from datetime import date
from decimal import Decimal
from typing import Any


# DATEV Buchungsstapel CSV headers
DATEV_HEADERS = [
    "Datum",
    "Konto",
    "Gegenkonto",
    "Betrag",
    "Belegfeld",
    "Buchungstext",
]


def generate_datev_csv(sales: list[Any]) -> str:
    """Generate DATEV CSV content from a list of sale objects.

    Each sale produces one booking row:
    - Datum: sale_date in DD.MM.YYYY format
    - Konto: buyer account (1200 = Forderungen aus Lieferungen/Leistungen)
    - Gegenkonto: revenue account (8400 = Erlöse aus Warenverkäufen)
    - Betrag: sale_price as decimal with comma separator
    - Belegfeld: sale ID (short form)
    - Buchungstext: vehicle make + model + FIN

    Args:
        sales: List of Sale model instances with nested vehicle and buyer.

    Returns:
        CSV string with DATEV headers and one row per sale.
    """
    output = io.StringIO()
    writer = csv.writer(output, delimiter=";", quoting=csv.QUOTE_MINIMAL)

    # Write header row
    writer.writerow(DATEV_HEADERS)

    for sale in sales:
        # Format date as DD.MM.YYYY (DATEV convention)
        datum = sale.sale_date.strftime("%d.%m.%Y") if sale.sale_date else ""

        # Account numbers (standard DATEV SKR03)
        konto = "1200"  # Forderungen aus LuL
        gegenkonto = "8400"  # Erlöse aus Warenverkäufen

        # Amount with comma as decimal separator (DATEV convention)
        betrag = _format_amount(sale.sale_price)

        # Belegfeld: short sale ID (first 8 chars)
        belegfeld = str(sale.id)[:8].upper()

        # Buchungstext: vehicle description
        vehicle = getattr(sale, "vehicle", None)
        if vehicle:
            buchungstext = f"{vehicle.make} {vehicle.model} {vehicle.fin}"
        else:
            buchungstext = f"Verkauf {str(sale.id)[:8]}"

        writer.writerow([datum, konto, gegenkonto, betrag, belegfeld, buchungstext])

    return output.getvalue()


def _format_amount(amount: Decimal) -> str:
    """Format a Decimal amount for DATEV CSV (comma as decimal separator)."""
    if amount is None:
        return "0,00"
    # Convert to string with 2 decimal places, replace dot with comma
    formatted = f"{amount:.2f}"
    return formatted.replace(".", ",")


def validate_datev_csv(csv_content: str) -> bool:
    """Validate that CSV content has correct DATEV headers and structure.

    Args:
        csv_content: CSV string to validate.

    Returns:
        True if valid, False otherwise.
    """
    if not csv_content or not csv_content.strip():
        return False

    reader = csv.reader(io.StringIO(csv_content), delimiter=";")
    try:
        header = next(reader)
    except StopIteration:
        return False

    if header != DATEV_HEADERS:
        return False

    # Check at least that rows have 6 columns each
    for row in reader:
        if len(row) != 6:
            return False

    return True