from datetime import UTC, datetime
from decimal import Decimal
from enum import StrEnum
from typing import Annotated, Literal, Self

from pydantic import BaseModel, Field, model_validator
from pydantic_extra_types.country import CountryAlpha2
from pydantic_extra_types.currency_code import Currency
from ulid import ULID

from .ref import ChannelRef, TransactionRef


class TransactionStatus(StrEnum):
    """交易状态"""

    PENDING = "PENDING"
    COMPLETED = "COMPLETED"
    FAILED = "FAILED"
    REFUNDED = "REFUNDED"


class DcFlag(StrEnum):
    """借贷方向"""

    DEBIT = "DEBIT"
    CREDIT = "CREDIT"


class FxRate(BaseModel):
    """汇率快照"""

    from_ccy: Annotated[Currency, "源币种"]
    to_ccy: Annotated[Currency, "目标币种"]
    rate: Annotated[Decimal, "汇率"]


class BaseTransaction(BaseModel):
    """基础交易模型"""

    id: ULID = Field(default_factory=ULID)
    version: Annotated[int, "乐观锁版本号", Field(default=0)]
    ref_transactions: Annotated[
        list[TransactionRef], "关联的交易引用列表", Field(default_factory=list)
    ]
    txn_date: Annotated[datetime, "交易日期"]
    clearing_date: Annotated[datetime | None, "清算日期", Field(default=None)]
    posting_date: Annotated[datetime | None, "入账日期", Field(default=None)]
    created_at: Annotated[datetime, "创建时间", Field(default_factory=lambda: datetime.now(UTC))]
    updated_at: Annotated[datetime, "更新时间", Field(default_factory=lambda: datetime.now(UTC))]
    deleted_at: Annotated[datetime | None, "软删除时间（None=未删除）", Field(default=None)]
    txn_amt: Annotated[Decimal, "交易金额"]
    txn_ccy: Annotated[Currency, "交易币种"]
    posting_amt: Annotated[Decimal | None, "入账金额", Field(default=None)]
    posting_ccy: Annotated[Currency | None, "入账币种", Field(default=None)]
    comm_amt: Annotated[Decimal | None, "手续费金额", Field(default=None)]
    comm_ccy: Annotated[Currency | None, "手续费币种", Field(default=None)]
    surcharge_amt: Annotated[Decimal | None, "服务费金额", Field(default=None)]
    surcharge_ccy: Annotated[Currency | None, "服务费币种", Field(default=None)]
    disc_amt: Annotated[Decimal | None, "折扣金额", Field(default=None)]
    disc_ccy: Annotated[Currency | None, "折扣币种", Field(default=None)]
    fx_rates: Annotated[list[FxRate] | None, "汇率快照列表", Field(default=None)]
    dc_flag: Annotated[DcFlag, "借贷方向"]
    ref_channel: Annotated[ChannelRef, "关联的渠道引用列表"]
    cp: Annotated[str | ChannelRef, "对手方（字符串描述或渠道引用）"]
    acq_inst: Annotated[str | None, "收单机构", Field(default=None)]
    clearing_network: Annotated[str | None, "清算网络", Field(default=None)]
    txn_sts: Annotated[TransactionStatus, "交易状态", Field(default=TransactionStatus.COMPLETED)]
    description: Annotated[str | None, "交易描述", Field(default=None)]
    memo: Annotated[str | None, "备注", Field(default=None)]
    raw_description: Annotated[str | None, "原始交易描述", Field(default=None)]
    raw_data: Annotated[dict | None, "原始数据", Field(default=None)]

    txn_scene: Annotated[str | None, "交易场景", Field(default=None)]

    @model_validator(mode="after")
    def _validate_amt_ccy_pairs(self) -> Self:
        pairs = [
            ("posting_amt", "posting_ccy"),
            ("comm_amt", "comm_ccy"),
            ("surcharge_amt", "surcharge_ccy"),
            ("disc_amt", "disc_ccy"),
        ]
        for amt_field, ccy_field in pairs:
            amt = getattr(self, amt_field)
            ccy = getattr(self, ccy_field)
            if (amt is None) != (ccy is None):
                msg = f"{amt_field} and {ccy_field} must both be None or both have values"
                raise ValueError(msg)
        return self

    @model_validator(mode="after")
    def _validate_accounting_equation(self) -> Self:
        """
        会计恒等式校验（同币种）

        - CREDIT: posting_amt = txn_amt + surcharge_amt - comm_amt - disc_amt
        - DEBIT: posting_amt = txn_amt + surcharge_amt + comm_amt - disc_amt
        """
        if self.posting_amt is None or self.posting_ccy != self.txn_ccy:
            return self

        expected = self.txn_amt
        if self.surcharge_amt is not None and self.surcharge_ccy == self.txn_ccy:
            expected += self.surcharge_amt
        if self.disc_amt is not None and self.disc_ccy == self.txn_ccy:
            expected -= self.disc_amt

        if self.dc_flag == DcFlag.CREDIT:
            if self.comm_amt is not None and self.comm_ccy == self.txn_ccy:
                expected -= self.comm_amt
        elif self.dc_flag == DcFlag.DEBIT:
            if self.comm_amt is not None and self.comm_ccy == self.txn_ccy:
                expected += self.comm_amt

        if self.posting_amt != expected:
            msg = (
                f"Accounting equation mismatch ({self.dc_flag.value}): "
                f"posting_amt({self.posting_amt}) != "
                f"txn_amt({self.txn_amt}) + surcharge_amt({self.surcharge_amt})"
                f" {'+' if self.dc_flag == DcFlag.DEBIT else '-'} comm_amt({self.comm_amt})"
                f" - disc_amt({self.disc_amt})"
            )
            raise ValueError(msg)
        return self


class MiscInTransaction(BaseTransaction):
    """其他收入交易"""

    txn_scene: Annotated[Literal["MISC_IN"], "交易场景"] = "MISC_IN"
    dc_flag: Annotated[DcFlag, "借贷方向"] = DcFlag.CREDIT


class MiscOutTransaction(BaseTransaction):
    """其他支出交易"""

    txn_scene: Annotated[Literal["MISC_OUT"], "交易场景"] = "MISC_OUT"
    dc_flag: Annotated[DcFlag, "借贷方向"] = DcFlag.DEBIT


class PaymentTransaction(MiscOutTransaction):
    """支付交易"""

    txn_scene: Annotated[Literal["PAYMENT"], "交易场景"] = "PAYMENT"
    merchant_name: Annotated[str | None, "商户名称", Field(default=None)]


class EcomPaymentTransaction(PaymentTransaction):
    """电子商务支付交易"""

    txn_scene: Annotated[Literal["ECOM_PAYMENT"], "交易场景"] = "ECOM_PAYMENT"
    order_id: Annotated[str | None, "订单ID", Field(default=None)]


class PosPaymentTransaction(PaymentTransaction):
    """POS支付交易"""

    txn_scene: Annotated[Literal["POS_PAYMENT"], "交易场景"] = "POS_PAYMENT"
    geo: Annotated[
        tuple[CountryAlpha2] | tuple[CountryAlpha2, str] | None, "地理信息", Field(default=None)
    ]


class ATMTransaction(BaseTransaction):
    """ATM交易"""

    txn_scene: Annotated[Literal["ATM"], "交易场景"] = "ATM"
    geo: Annotated[
        tuple[CountryAlpha2] | tuple[CountryAlpha2, str] | None, "地理信息", Field(default=None)
    ]


class TransferTransaction(BaseTransaction):
    """转账交易"""

    txn_scene: Annotated[Literal["TRANSFER"], "交易场景"] = "TRANSFER"


type Transaction = Annotated[
    MiscInTransaction
    | MiscOutTransaction
    | TransferTransaction
    | PaymentTransaction
    | EcomPaymentTransaction
    | PosPaymentTransaction
    | ATMTransaction,
    Field(discriminator="txn_scene"),
]