"""Read models and shared calculations for reconciliation checkpoints."""

from dataclasses import dataclass
from datetime import date, datetime
from decimal import Decimal
from uuid import UUID

from django.db.models import DecimalField, F, Sum, Value, Window
from django.db.models.functions import Coalesce, RowNumber

from finance.models import ReconciliationCheckpoint, Transaction


_MONEY_FIELD = DecimalField(max_digits=24, decimal_places=2)
_ZERO = Decimal("0.00")


@dataclass(frozen=True)
class CheckpointStatus:
    checkpoint_id: UUID
    account_id: UUID
    account_name: str
    currency: str
    as_of_date: date
    created_at: datetime
    institution_balance: Decimal
    snapshot_ledger_balance: Decimal
    snapshot_difference: Decimal
    live_ledger_balance: Decimal
    live_difference: Decimal
    state: str


def ledger_balance_through(account_id: UUID, as_of_date: date) -> Decimal:
    from finance.services.base import money

    total = Transaction.objects.filter(
        account_id=account_id,
        posting_date__lte=as_of_date,
    ).aggregate(
        total=Coalesce(
            Sum("amount"),
            Value(_ZERO),
            output_field=_MONEY_FIELD,
        )
    )["total"]
    return money(total, allow_zero=True)


def checkpoint_status(checkpoint: ReconciliationCheckpoint) -> CheckpointStatus:
    account = checkpoint.account
    live_ledger_balance = ledger_balance_through(checkpoint.account_id, checkpoint.as_of_date)
    live_difference = checkpoint.institution_balance - live_ledger_balance
    if live_difference == _ZERO:
        state = "reconciled"
    elif checkpoint.difference_at_creation == _ZERO:
        state = "changed_since_reconciliation"
    else:
        state = "difference"
    return CheckpointStatus(
        checkpoint_id=checkpoint.pk,
        account_id=account.pk,
        account_name=account.name,
        currency=account.currency,
        as_of_date=checkpoint.as_of_date,
        created_at=checkpoint.created_at,
        institution_balance=checkpoint.institution_balance,
        snapshot_ledger_balance=checkpoint.ledger_balance_at_creation,
        snapshot_difference=checkpoint.difference_at_creation,
        live_ledger_balance=live_ledger_balance,
        live_difference=live_difference,
        state=state,
    )


def checkpoint_history(account_id: UUID) -> list[CheckpointStatus]:
    checkpoints = ReconciliationCheckpoint.objects.filter(
        account_id=account_id,
    ).select_related("account").order_by("-as_of_date", "-created_at", "-id")
    return [checkpoint_status(checkpoint) for checkpoint in checkpoints]


def latest_checkpoint_statuses(currency: str) -> list[CheckpointStatus]:
    checkpoints = ReconciliationCheckpoint.objects.filter(
        account__archived=False,
        account__currency=currency,
    ).annotate(
        account_rank=Window(
            expression=RowNumber(),
            partition_by=[F("account_id")],
            order_by=["-as_of_date", "-created_at", "-id"],
        )
    ).filter(account_rank=1).select_related("account").order_by(
        "-as_of_date", "-created_at", "-id"
    )
    return [checkpoint_status(checkpoint) for checkpoint in checkpoints]