"""Keep ALSO's approved period amount authoritative on order lines."""
from decimal import Decimal, InvalidOperation, ROUND_HALF_UP
from datetime import datetime, timedelta
import calendar
import re

from fastapi import HTTPException


def _number(value):
    try:
        result = Decimal(str(value))
        if not result.is_finite():
            raise InvalidOperation
        return result
    except (InvalidOperation, TypeError, ValueError):
        raise HTTPException(409, 'ALSO-linjen mangler et gyldigt godkendt periodebeløb')


def period_amount_line(line):
    """Return a copy; never rewrite saved history or normalize other sources."""
    if line.get('source_type') != 'also_cloud':
        return dict(line)
    amount = _number(line.get('amount'))
    if amount < 0 or amount != amount.quantize(Decimal('.01'), rounding=ROUND_HALF_UP):
        raise HTTPException(409, 'ALSO-periodebeløbet kræver afklaring før eksport')
    if _number(line.get('discount_percentage', 0)) != 0:
        raise HTTPException(409, 'ALSO-periodebeløbet må ikke kombineres med linjerabat')
    result = dict(line)
    meta = dict(line.get('meta') or {})
    if meta.get('also_period_amount_version') != 1:
        quantity = _number(line.get('quantity'))
        monthly_price = _number(line.get('unit_price'))
        if quantity <= 0 or monthly_price < 0:
            raise HTTPException(409, 'ALSO-linjen mangler gyldigt licensantal eller månedspris')
        meta.update(also_license_quantity=str(quantity), also_monthly_unit_price=str(monthly_price),
                    also_period_amount_version=1)
        quantity_text = format(quantity, 'f').rstrip('0').rstrip('.') if '.' in str(quantity) else str(quantity)
        price_text = f'{monthly_price:.2f}'.replace('.', ',')
        license_text = 'licens' if quantity == 1 else 'licenser'
        description = result.get('description') or 'Cloud abonnement'
        title, separator, rest = description.partition('\n')
        currency_text = 'kr.' if result.get('currency', 'DKK') == 'DKK' else result['currency']
        explanation = f'{quantity_text} {license_text} á {price_text} {currency_text}/måned.'
        interval = meta.get('billing_period')
        period_text = _period_text(interval)
        result['description'] = title + '\n' + explanation + (
            ' ' + period_text if period_text else ('\n' + rest if separator else ''))
    result['description'] = re.sub(r'\s*Reference:\s*[^\n]*', '', result.get('description', ''), flags=re.IGNORECASE).strip()
    result.update(quantity=1.0, unit_price=float(amount), amount=float(amount),
                  discount_percentage=0.0, meta=meta)
    return result


def _period_text(interval):
    """ALSO Marketplace intervals have an exclusive end date."""
    match = re.fullmatch(r'\s*(\d{2})[./-](\d{2})[./-](\d{4})\s*-\s*(\d{2})[./-](\d{2})[./-](\d{4})\s*', str(interval or ''))
    if not match:
        return None
    try:
        day, month, year, end_day, end_month, end_year = map(int, match.groups())
        start = datetime(year, month, day).date()
        end = datetime(end_year, end_month, end_day).date()
    except ValueError:
        raise HTTPException(409, 'ALSO-linjen har en ugyldig periode')
    if end <= start:
        raise HTTPException(409, 'ALSO-periodens slutdato skal være efter startdatoen')
    last = end - timedelta(days=1)
    start_text = start.strftime('%d.%m.') if start.year == last.year else start.strftime('%d.%m.%Y')
    text = f'Periode: {start_text}–{last:%d.%m.%Y}, {(end-start).days}'
    if (start.year, start.month) == (last.year, last.month):
        text += f' af {calendar.monthrange(start.year, start.month)[1]}'
    return text + ' dage.'


def check_period_amounts(lines, saved_lines):
    """Reject stale browsers and altered amounts before either export backend runs."""
    saved = {str(line.get('line_key')): line for line in saved_lines}
    seen = set()
    for line in lines:
        old = saved.get(str(line.get('line_key')))
        if line.get('source_type') != 'also_cloud' and (not old or old.get('source_type') != 'also_cloud'):
            continue
        if not old or old.get('source_type') != 'also_cloud' or line.get('source_type') != 'also_cloud':
            raise HTTPException(409, 'ALSO-eksport kræver den gemte godkendte ordrekladde')
        key = str(line.get('line_key'))
        if key in seen or line.get('source_id') != old.get('source_id'):
            raise HTTPException(409, 'ALSO-kildelinjen mangler entydig identitet eller er valgt flere gange')
        seen.add(key)
        expected = period_amount_line(old)
        if (line.get('product_id') != old.get('product_id')
                or line.get('description') != expected.get('description')
                or line.get('currency', 'DKK') != old.get('currency', 'DKK')
                or any(_number(line.get(key, 0)) != _number(expected[key])
                       for key in ('quantity', 'unit_price', 'discount_percentage'))):
            raise HTTPException(409, 'ALSO-linjen matcher ikke det godkendte periodebeløb. Genindlæs kladden og kontrollér linjerne før eksport.')