"""Add preschool_planning_days: per-year record of "studiedagar" taken.

`Child.preschool_planning_days_per_year` (see `app/entities/child.py`) is a
single default count of annual preschool closure/planning days used by
`app/services/allocation_service.py::_preschool_reserve_days`, which
multiplies it by the number of years in the planning horizon and subtracts
the lump sum from both parents' parental-leave pools. There was never a
per-year record of the true count, nor of how many were actually taken.

This table adds that per-year record: `planned_days` (may differ from the
child's default for a specific year) and `taken_days` (nullable — `NULL`
means "not recorded yet", distinct from "recorded as zero", which is the
whole point of the feature). A missing row for a (child, year) still falls
back to `child.preschool_planning_days_per_year` at the service layer (see
`app/services/preschool_planning_days_service.py`); wiring the allocation
engine to consume these rows is a follow-up, not part of this migration.

A plain `CREATE TABLE` suffices — nothing existing changes, and there is
nothing to backfill: before this migration no per-year figure could be
recorded, so the correct history is "none".

Must stay byte-for-byte equivalent to the `preschool_planning_days` table in
`app/db/connection.py`'s `_FULL_SCHEMA` —
`tests/integration/test_schema_parity.py` asserts exactly that.

Revision ID: 007
Revises: 006
Create Date: 2026-09-20
"""

from __future__ import annotations

from alembic import op

revision: str = "007"
down_revision: str | None = "006"
branch_labels: str | None = None
depends_on: str | None = None


def upgrade() -> None:
    op.execute(
        """
        CREATE TABLE IF NOT EXISTS preschool_planning_days (
            id TEXT PRIMARY KEY,
            child_id TEXT NOT NULL,
            year INTEGER NOT NULL,
            planned_days INTEGER NOT NULL,
            taken_days INTEGER,
            created_at TIMESTAMP NOT NULL,
            updated_at TIMESTAMP NOT NULL,
            UNIQUE(child_id, year),
            FOREIGN KEY (child_id) REFERENCES child(id) ON DELETE CASCADE
        )
        """
    )
    op.execute(
        """
        CREATE INDEX IF NOT EXISTS idx_preschool_planning_days_child
            ON preschool_planning_days (child_id)
        """
    )


def downgrade() -> None:
    op.execute("DROP INDEX IF EXISTS idx_preschool_planning_days_child")
    op.execute("DROP TABLE IF EXISTS preschool_planning_days")