"""Payroll balances reconstructed from configured source input lines."""

from __future__ import annotations

from collections.abc import Iterable
from decimal import Decimal

from finance.enums import ApprovalStatus, InputSource
from finance.models import PayrollBalanceAdjustment, PayrollInputLine, PayrollPeriod
from finance.payroll.components import get_payroll_components
from payroll_core.balances import carryover_contribution


def opening_balances(
    period: PayrollPeriod,
    employee_ids: Iterable[int],
) -> dict[int, Decimal]:
    """Return the cumulative balance from approved configured earlier lines."""

    requested_ids = set(employee_ids)
    if not requested_ids:
        return {}
    lines = list(
        PayrollInputLine.objects.filter(
            employee_id__in=requested_ids,
            period__currency=period.currency,
            period__date_to__lt=period.date_from,
            status=ApprovalStatus.APPROVED,
            include_in_carryover=True,
        )
        .exclude(
            source=InputSource.API,
            source_ref__startswith="payroll-carryover:",
        )
        .values("period_id", "employee_id", "component_code", "amount")
    )
    source_periods = {
        source.pk: source
        for source in PayrollPeriod.objects.filter(
            pk__in={line["period_id"] for line in lines}
        )
    }
    components_by_period = {
        period_id: {
            component.code: component
            for component in get_payroll_components(source_period)
            if component.include_in_carryover
        }
        for period_id, source_period in source_periods.items()
    }
    balances = {}
    for line in lines:
        component = components_by_period.get(line["period_id"], {}).get(
            line["component_code"]
        )
        if component is None:
            continue
        balances[line["employee_id"]] = balances.get(
            line["employee_id"], Decimal("0.00")
        ) + carryover_contribution(
            component.kind,
            line["amount"],
            version=source_periods[line["period_id"]].balance_rules_version,
        )
    # Effective-period corrections enter the opening balance exactly once per
    # cumulative reconstruction. They never become payroll input lines.
    for adjustment in PayrollBalanceAdjustment.objects.filter(
        employee_id__in=requested_ids,
        effective_period__currency=period.currency,
        effective_period__date_from__lte=period.date_from,
        voided_at__isnull=True,
    ):
        balances[adjustment.employee_id] = (
            balances.get(adjustment.employee_id, Decimal("0.00"))
            + adjustment.contribution
        )
    return balances