"""Transit (self-transfer) detection rules.

Identifies transactions that are internal transfers between the victim's
own accounts (e.g. bank -> Alipay -> WeChat) and should NOT be counted
as fraud loss.
"""
from datetime import datetime

from app.models.transaction import TransactionRecord

SELF_KEYWORDS = ["本人", "自己", "余额", "充值", "提现", "银行卡转入", "银行卡充值"]
FEE_TRANSIT_WINDOW_SECONDS = 120
FEE_TOLERANCE_RATIO = 0.02


def is_self_transfer(tx: TransactionRecord, known_self_accounts: list[str]) -> bool:
    """Check if a transaction is an inter-account transfer by the victim."""
    counterparty = (tx.counterparty_name or "").lower()
    remark = (tx.remark or "").lower()

    # Rule 1: counterparty matches known self accounts
    for acct in known_self_accounts:
        if acct and acct.lower() in counterparty:
            return True

    # Rule 2: counterparty contains self-transfer keywords
    for kw in SELF_KEYWORDS:
        if kw in counterparty or kw in remark:
            return True

    # Rule 3: counterparty references another payment app owned by victim
    app_keywords = ["支付宝", "微信", "银行卡", "数字钱包"]
    victim_patterns = [f"{app}-" for app in app_keywords] + app_keywords
    for pat in victim_patterns:
        if pat in counterparty:
            if tx.direction.value == "out":
                return True

    return False


def is_fee_tolerant_transit_pair(tx_a: TransactionRecord, tx_b: TransactionRecord) -> bool:
    """Two-way transfer pattern: opposite direction, close time, similar amount."""
    if tx_a.direction.value == tx_b.direction.value:
        return False

    amount_a = float(tx_a.amount or 0)
    amount_b = float(tx_b.amount or 0)
    if amount_a <= 0 or amount_b <= 0:
        return False

    time_a = tx_a.trade_time
    time_b = tx_b.trade_time
    if not isinstance(time_a, datetime) or not isinstance(time_b, datetime):
        return False
    if abs((time_a - time_b).total_seconds()) > FEE_TRANSIT_WINDOW_SECONDS:
        return False

    amount_base = max(amount_a, amount_b)
    if amount_base <= 0:
        return False
    diff_ratio = abs(amount_a - amount_b) / amount_base
    return diff_ratio <= FEE_TOLERANCE_RATIO