import statistics
from collections import Counter, defaultdict
from decimal import Decimal

from sqlalchemy import select
from sqlalchemy.orm import Session

from app.models.tables import RecurringItem, Transaction


def _max_consecutive_months(months: list[tuple[int, int]]) -> int:
    if not months:
        return 0
    best = current = 1
    for prev, cur in zip(months, months[1:]):
        prev_idx = prev[0] * 12 + prev[1]
        cur_idx = cur[0] * 12 + cur[1]
        current = current + 1 if cur_idx == prev_idx + 1 else 1
        best = max(best, current)
    return best


def suggest_recurring(session: Session) -> list[dict]:
    txs = session.execute(
        select(Transaction).where(Transaction.status == "confirmed")
    ).scalars().all()
    groups: dict[tuple, list[Transaction]] = defaultdict(list)
    for t in txs:
        groups[(t.account_id, t.counterparty, t.amount)].append(t)

    existing = {(r.name, Decimal(r.amount))
               for r in session.execute(select(RecurringItem)).scalars()}

    suggestions: list[dict] = []
    for (_account_id, counterparty, amount), items in groups.items():
        months = sorted({(t.booking_date.year, t.booking_date.month) for t in items})
        if _max_consecutive_months(months) < 3:
            continue
        name = counterparty
        if (name, Decimal(amount)) in existing:
            continue
        due_day = int(statistics.median(sorted(t.booking_date.day for t in items)))
        cat_counts = Counter(t.category_id for t in items if t.category_id is not None)
        category_id = cat_counts.most_common(1)[0][0] if cat_counts else None
        suggestions.append({
            "name": name,
            "amount": Decimal(amount),
            "rhythm": "monthly",
            "due_day": due_day,
            "category_id": category_id,
        })
    return suggestions