F-r-ldraledigplannerare/backend/app/services/leave_snapshot.py

"""Shared derivation for a `ParentalLeaveFetch` snapshot.

Both the FK scraper (`app.scrapers.fk_scraper`) and manual entry
(`app.services.fetch_data_service.ManualFetchService`) hand a parent's raw
"days left" numbers to `build_snapshot`, which is the ONE place that derives
everything else (tier totals, days used, reserved/transferable split) and
validates the result. Neither caller is allowed to re-derive any of this
itself — see PLANNING_ENGINE_SPEC.md and the "Bug A" note in
`app.utils.tip_predicates.default_tier_pool_share` for what happens when two
call sites disagree.

Domain: a child has `rules.total_days_per_child` days total (390
sjukpenningnivå + 90 lägstanivå). Split across two parents each gets half
(195 + 45 = 240); `rules.reserved_days_per_parent` (90) of each parent's
share is reserved (non-transferable). A sole parent gets the full 480
(390 + 90). `total_days` here is always the ONE PARENT's total (240 or 480),
never the per-child combined figure.
"""

from __future__ import annotations

from datetime import datetime
from uuid import UUID, uuid4

from app.config import settings
from app.entities.parental_leave import ParentalLeaveFetch, TierData
from app.utils.errors import ValidationError

_VALID_SOURCES = ("scraped", "manual", "deduced")


def build_snapshot(
    *,
    personal_data_uuid: UUID,
    workspace_id: UUID,
    child_id: UUID,
    source: str,
    total_days: int,
    sjukpenning_left: int,
    lagsta_niva_left: int,
    dubbeldagar_left: int,
    reserved_days_left: int | None = None,
    fetched_at: datetime | None = None,
) -> ParentalLeaveFetch:
    """Derive and validate a full `ParentalLeaveFetch` snapshot.

    `reserved_days_left`, when omitted, is derived assuming transferable
    (non-reserved) days are always consumed before reserved ones — the same
    assumption the FK scraper's page reading has always made, since FK's UI
    doesn't expose the reserved/transferable split directly. When the caller
    already knows the reserved split (e.g. a future, more detailed manual
    form), passing it directly skips that assumption.
    """
    if source not in _VALID_SOURCES:
        raise ValidationError(
            f"source must be one of {_VALID_SOURCES}, got {source!r}",
            message_key="parentalLeave.invalidSource",
            data={"source": source},
        )

    rules = settings.rules

    # -- Tier totals (standard FK allocation for this parent) --
    # `total_days` is this ONE parent's total (240 with a partner, 480 solo);
    # split it into tiers using the same 390:90 ratio as the whole-child pool
    # so 240 -> (195, 45) and 480 -> (390, 90) without hardcoding either.
    lagsta_niva_total = (
        rules.lagsta_niva_days * total_days // (rules.sjukpenning_days + rules.lagsta_niva_days)
    )
    sjukpenning_total = total_days - lagsta_niva_total

    days_left = sjukpenning_left + lagsta_niva_left
    days_used = total_days - days_left
    sjukpenning_used = sjukpenning_total - sjukpenning_left
    lagsta_niva_used = lagsta_niva_total - lagsta_niva_left

    # -- Reserved / transferable split --
    # Reserved days cannot be transferred to the other parent; the
    # long-standing assumption (matches FK's own "spend transferable first")
    # is that transferable days are used up before any reserved day is.
    reserved_days_total = rules.reserved_days_per_parent
    if reserved_days_left is None:
        transferable_total = total_days - reserved_days_total
        transferable_used = min(days_used, transferable_total)
        reserved_used = days_used - transferable_used
        reserved_days_left = reserved_days_total - reserved_used
        transferable_days_left = transferable_total - transferable_used
    else:
        transferable_days_left = days_left - reserved_days_left

    # -- Validate before returning --
    if days_left < 0:
        raise ValidationError(
            f"days_left is negative ({days_left}) — FK data inconsistency",
            message_key="parentalLeave.negativeDaysLeft",
            data={"days_left": days_left},
        )
    if sjukpenning_left < 0:
        raise ValidationError(
            f"sjukpenning_left is negative ({sjukpenning_left})",
            message_key="parentalLeave.negativeSjukpenningLeft",
            data={"sjukpenning_left": sjukpenning_left},
        )
    if sjukpenning_left > sjukpenning_total:
        raise ValidationError(
            f"sjukpenning_left ({sjukpenning_left}) exceeds sjukpenning_total "
            f"({sjukpenning_total})",
            message_key="parentalLeave.sjukpenningExceedsTotal",
            data={"sjukpenning_left": sjukpenning_left, "sjukpenning_total": sjukpenning_total},
        )
    if lagsta_niva_left < 0:
        raise ValidationError(
            f"lagsta_niva_left is negative ({lagsta_niva_left})",
            message_key="parentalLeave.negativeLagstaNivaLeft",
            data={"lagsta_niva_left": lagsta_niva_left},
        )
    if lagsta_niva_left > lagsta_niva_total:
        raise ValidationError(
            f"lagsta_niva_left ({lagsta_niva_left}) exceeds lagsta_niva_total "
            f"({lagsta_niva_total})",
            message_key="parentalLeave.lagstaNivaExceedsTotal",
            data={"lagsta_niva_left": lagsta_niva_left, "lagsta_niva_total": lagsta_niva_total},
        )
    if reserved_days_left < 0:
        raise ValidationError(
            f"reserved_days_left is negative ({reserved_days_left})",
            message_key="parentalLeave.negativeReservedDaysLeft",
            data={"reserved_days_left": reserved_days_left},
        )
    if reserved_days_left > reserved_days_total:
        raise ValidationError(
            f"reserved_days_left ({reserved_days_left}) > reserved_days_total "
            f"({reserved_days_total})",
            message_key="parentalLeave.reservedExceedsTotal",
            data={
                "reserved_days_left": reserved_days_left,
                "reserved_days_total": reserved_days_total,
            },
        )
    if transferable_days_left < 0:
        raise ValidationError(
            f"transferable_days_left is negative ({transferable_days_left})",
            message_key="parentalLeave.negativeTransferableDaysLeft",
            data={"transferable_days_left": transferable_days_left},
        )
    if dubbeldagar_left < 0:
        raise ValidationError(
            f"dubbeldagar_left is negative ({dubbeldagar_left})",
            message_key="parentalLeave.negativeDubbeldagarLeft",
            data={"dubbeldagar_left": dubbeldagar_left},
        )
    if dubbeldagar_left > rules.max_dubbeldagar:
        raise ValidationError(
            f"dubbeldagar_left ({dubbeldagar_left}) exceeds rules.max_dubbeldagar "
            f"({rules.max_dubbeldagar})",
            message_key="parentalLeave.dubbeldagarExceedsMax",
            data={"dubbeldagar_left": dubbeldagar_left, "max_dubbeldagar": rules.max_dubbeldagar},
        )

    now = fetched_at or datetime.now()
    tier_data = TierData(
        sjukpenning_total=sjukpenning_total,
        sjukpenning_used=sjukpenning_used,
        sjukpenning_left=sjukpenning_left,
        lagsta_niva_total=lagsta_niva_total,
        lagsta_niva_used=lagsta_niva_used,
        lagsta_niva_left=lagsta_niva_left,
    )

    return ParentalLeaveFetch(
        id=uuid4(),
        personal_data_uuid=personal_data_uuid,
        workspace_id=workspace_id,
        child_id=child_id,
        source=source,
        fetched_at=now,
        total_days=total_days,
        days_used=days_used,
        days_left=days_left,
        reserved_days_total=reserved_days_total,
        reserved_days_left=reserved_days_left,
        transferable_days_left=transferable_days_left,
        dubbeldagar_left=dubbeldagar_left,
        tier_data=tier_data,
        created_at=now,
        updated_at=now,
    )