"""Offline example: reconcile payments and shipments without losing exceptions.

CSV columns: order_id, counterparty_id, amount, plus payment_id / shipment_id.
Repeated event IDs are quarantined for review, not silently counted twice.
Run: python3 reconcile_registers.py payments.csv shipments.csv result.csv
"""
import csv
import sys
from collections import Counter, defaultdict
from decimal import Decimal

KEYS = ("order_id", "counterparty_id")


def read_register(filename):
    with open(filename, encoding="utf-8-sig", newline="") as source:
        return list(csv.DictReader(source))


def _totals(rows, event_id, keys):
    counts = Counter(row[event_id] for row in rows)
    amounts = defaultdict(Decimal)
    present, duplicates = set(), set()
    for row in rows:
        key = tuple(row[field].strip() for field in keys)
        if not all(key) or not row[event_id].strip():
            raise ValueError("Missing reconciliation key or event ID")
        amount = Decimal(row["amount"])
        if not amount.is_finite():
            raise ValueError("Non-finite amount")
        present.add(key)
        if counts[row[event_id]] > 1:
            duplicates.add(key)
        else:
            amounts[key] += amount
    return amounts, present, duplicates


def reconcile(payments, shipments, keys=KEYS,
              ids=("payment_id", "shipment_id")):
    paid, pkeys, pdups = _totals(payments, ids[0], keys)
    shipped, skeys, sdups = _totals(shipments, ids[1], keys)
    rows = []
    for key in sorted(pkeys | skeys):
        duplicate = key in pdups or key in sdups
        delta = None
        if duplicate:
            status = "Проверить дубли"
        elif key not in pkeys:
            status = "Нет оплаты"
        elif key not in skeys:
            status = "Нет отгрузки"
        else:
            delta = paid[key] - shipped[key]
            status = ("Частичная оплата" if delta < 0 else
                      "Оплата больше отгрузки" if delta > 0 else "Совпало")
        rows.append({
            **dict(zip(keys, key)),
            "paid": "" if key not in pkeys or key in pdups else str(paid[key]),
            "shipped": "" if key not in skeys or key in sdups else str(shipped[key]),
            "delta": "" if delta is None else str(delta),
            "status": status,
        })
    return rows


def write_csv(filename, rows):
    with open(filename, "w", encoding="utf-8-sig", newline="") as target:
        writer = csv.DictWriter(target, fieldnames=[*KEYS, "paid", "shipped", "delta", "status"])
        writer.writeheader()
        writer.writerows(rows)


if __name__ == "__main__":
    if len(sys.argv) != 4:
        raise SystemExit("Usage: reconcile_registers.py payments.csv shipments.csv result.csv")
    write_csv(sys.argv[3], reconcile(read_register(sys.argv[1]), read_register(sys.argv[2])))