alembic/versions/d9c6533f8a1b_add_category_validity.py

@@ -0,0 +1,102 @@
+"""add temporal validity to categories
+
+Revision ID: d9c6533f8a1b
+Revises: 78ec55b9e1d1
+Create Date: 2026-10-25 00:00:00.000000
+
+"""
+
+from collections.abc import Sequence
+
+import sqlalchemy as sa
+
+from alembic import op
+
+# revision identifiers, used by Alembic.
+revision: str = "d9c6533f8a1b"
+down_revision: str | Sequence[str] | None = "78ec55b9e1d1"
+branch_labels: str | Sequence[str] | None = None
+depends_on: str | Sequence[str] | None = None
+
+
+def upgrade() -> None:
+    with op.batch_alter_table("category") as batch_op:
+        batch_op.drop_constraint("uq_category_name_parent", type_="unique")
+        batch_op.add_column(
+            sa.Column(
+                "valid_from",
+                sa.DateTime(timezone=True),
+                nullable=True,
+                info={
+                    "description": "UTC start of validity; NULL means valid since the indefinite past."
+                },
+            )
+        )
+        batch_op.add_column(
+            sa.Column(
+                "valid_to",
+                sa.DateTime(timezone=True),
+                nullable=True,
+                info={
+                    "description": "UTC end of validity; NULL means the version is currently valid."
+                },
+            )
+        )
+        batch_op.add_column(
+            sa.Column(
+                "last_action",
+                sa.String(),
+                nullable=False,
+                server_default="created",
+                info={
+                    "description": "Most recent lifecycle action recorded for this category version."
+                },
+            )
+        )
+
+    # Existing rows predate temporal tracking, so their start is unbounded.
+    op.execute("UPDATE category SET last_action = 'migrated'")
+
+    # Separate root and non-root indexes so NULL parent IDs are unique too.
+    op.create_index(
+        "uq_category_active_name_parent",
+        "category",
+        ["name", "parent_id"],
+        unique=True,
+        sqlite_where=sa.text("valid_to IS NULL AND parent_id IS NOT NULL"),
+        postgresql_where=sa.text("valid_to IS NULL AND parent_id IS NOT NULL"),
+    )
+    op.create_index(
+        "uq_category_active_root_name",
+        "category",
+        ["name"],
+        unique=True,
+        sqlite_where=sa.text("valid_to IS NULL AND parent_id IS NULL"),
+        postgresql_where=sa.text("valid_to IS NULL AND parent_id IS NULL"),
+    )
+
+
+def downgrade() -> None:
+    bind = op.get_bind()
+    has_temporal_history = bind.execute(
+        sa.text(
+            "SELECT 1 FROM category "
+            "WHERE valid_from IS NOT NULL OR valid_to IS NOT NULL LIMIT 1"
+        )
+    ).first()
+    if has_temporal_history:
+        raise RuntimeError(
+            "Cannot downgrade category validity while temporal history exists; "
+            "the downgrade would discard it."
+        )
+
+    op.drop_index("uq_category_active_root_name", table_name="category")
+    op.drop_index("uq_category_active_name_parent", table_name="category")
+
+    with op.batch_alter_table("category") as batch_op:
+        batch_op.drop_column("last_action")
+        batch_op.drop_column("valid_to")
+        batch_op.drop_column("valid_from")
+        batch_op.create_unique_constraint(
+            "uq_category_name_parent", ["name", "parent_id"]
+        )

src/ingest/b4w.py

@@ -1,4 +1,6 @@
+from datetime import UTC, datetime
 from pathlib import Path
+from typing import Any
 
 from sqlalchemy.orm import Session
 
@@ -17,20 +19,125 @@ def upsert_category(
 ) -> CategoryDb | None:
     if category is None:
         return None
-    parameters = {
-        "name": category.name,
-        "parent": upsert_category(session, category.parent),
+    parent = upsert_category(session, category.parent, do_commit=do_commit)
+    parent_id = parent.id if parent else None
+    matching_rows = session.query(CategoryDb).filter_by(
+        name=category.name, parent_id=parent_id
+    )
+    active = matching_rows.filter(CategoryDb.valid_to.is_(None)).one_or_none()
+    if active is not None:
+        return active
+
+    parameters = {"name": category.name, "parent": parent}
+    parameters_existing = {**parameters, "valid_to": None}
+    parameters_new: dict[str, Any] = {
+        **parameters,
+        "valid_from": None,
+        "valid_to": None,
+        "last_action": "created",
     }
+    historical = matching_rows.filter(CategoryDb.valid_to.is_not(None)).first()
+    if historical is not None:
+        parameters_new["valid_from"] = _utc_datetime(None)
+        parameters_new["last_action"] = "changed"
+
     return _upsert(
         session,
         CategoryDb,
-        parameters,
-        parameters,
+        parameters_existing,
+        parameters_new,
         do_update=False,
         do_commit=do_commit,
     )
 
 
+def _utc_datetime(value: datetime | None) -> datetime:
+    if value is None:
+        return datetime.now(UTC)
+    if value.tzinfo is None or value.utcoffset() is None:
+        return value.replace(tzinfo=UTC)
+    return value.astimezone(UTC)
+
+
+def _ensure_after_valid_from(category: CategoryDb, effective_at: datetime) -> None:
+    if category.valid_from is None:
+        return
+    valid_from = _utc_datetime(category.valid_from)
+    if effective_at <= valid_from:
+        raise ValueError("The action time must be later than valid_from")
+
+
+def change_category(
+    session: Session,
+    category_id: int,
+    replacement: Category,
+    effective_at: datetime | None = None,
+    do_commit: bool = True,
+) -> CategoryDb:
+    """Close an active category version and start its replacement version."""
+    current = (
+        session.query(CategoryDb).filter_by(id=category_id, valid_to=None).one_or_none()
+    )
+    if current is None:
+        raise ValueError(f"No active category found with id {category_id}")
+
+    action_time = _utc_datetime(effective_at)
+    _ensure_after_valid_from(current, action_time)
+    parent = upsert_category(session, replacement.parent, do_commit=False)
+    parent_id = parent.id if parent else None
+
+    if current.name == replacement.name and current.parent_id == parent_id:
+        return current
+
+    replacement_active = (
+        session.query(CategoryDb)
+        .filter_by(name=replacement.name, parent_id=parent_id, valid_to=None)
+        .one_or_none()
+    )
+
+    current.valid_to = action_time
+    current.last_action = "changed"
+    session.flush()
+
+    if replacement_active is None:
+        replacement_active = CategoryDb(
+            name=replacement.name,
+            parent=parent,
+            valid_from=action_time,
+            valid_to=None,
+            last_action="changed",
+        )
+        session.add(replacement_active)
+        session.flush()
+
+    if do_commit:
+        session.commit()
+    return replacement_active
+
+
+def retire_category(
+    session: Session,
+    category_id: int,
+    effective_at: datetime | None = None,
+    do_commit: bool = True,
+) -> CategoryDb:
+    """Close an active category version without creating a replacement."""
+    category = (
+        session.query(CategoryDb).filter_by(id=category_id, valid_to=None).one_or_none()
+    )
+    if category is None:
+        raise ValueError(f"No active category found with id {category_id}")
+
+    action_time = _utc_datetime(effective_at)
+    _ensure_after_valid_from(category, action_time)
+    category.valid_to = action_time
+    category.last_action = "retired"
+    session.flush()
+    if do_commit:
+        session.commit()
+    return category
+
+
 def upsert_b4w(
     session: Session, data: B4wExport, do_update=False, do_commit=True
 ) -> B4wDb | None:

src/models/b4w.py

@@ -1,8 +1,17 @@
-from datetime import date
+from datetime import UTC, date, datetime
 from decimal import Decimal
 
 from pydantic import Field, computed_field, field_validator
-from sqlalchemy import Date, ForeignKey, Integer, String, UniqueConstraint
+from sqlalchemy import (
+    Date,
+    DateTime,
+    ForeignKey,
+    Index,
+    Integer,
+    String,
+    TypeDecorator,
+    text,
+)
 from sqlalchemy.orm import Mapped, mapped_column, relationship
 
 from src.constants import IBAN_PATTERN, Currency
@@ -118,10 +127,48 @@ class Category(ExportBaseModel):
         return f'Category.from_str("{self.__str__()}")'
 
 
+class UTCDateTime(TypeDecorator[datetime]):
+    """Store UTC timestamps and return timezone-aware UTC values on every dialect."""
+
+    impl = DateTime
+    cache_ok = True
+
+    def load_dialect_impl(self, dialect):
+        return dialect.type_descriptor(DateTime(timezone=True))
+
+    def process_bind_param(self, value: datetime | None, dialect):
+        if value is None:
+            return None
+        if value.tzinfo is None or value.utcoffset() is None:
+            return value.replace(tzinfo=UTC)
+        return value.astimezone(UTC)
+
+    def process_result_value(self, value: datetime | None, dialect):
+        if value is None:
+            return None
+        if value.tzinfo is None or value.utcoffset() is None:
+            return value.replace(tzinfo=UTC)
+        return value.astimezone(UTC)
+
+
 class CategoryDb(BaseModelDb):
     __tablename__ = "category"
     __table_args__ = (
-        UniqueConstraint("name", "parent_id", name="uq_category_name_parent"),
+        Index(
+            "uq_category_active_name_parent",
+            "name",
+            "parent_id",
+            unique=True,
+            sqlite_where=text("valid_to IS NULL AND parent_id IS NOT NULL"),
+            postgresql_where=text("valid_to IS NULL AND parent_id IS NOT NULL"),
+        ),
+        Index(
+            "uq_category_active_root_name",
+            "name",
+            unique=True,
+            sqlite_where=text("valid_to IS NULL AND parent_id IS NULL"),
+            postgresql_where=text("valid_to IS NULL AND parent_id IS NULL"),
+        ),
     )
 
     id: Mapped[int] = mapped_column(primary_key=True, autoincrement=True)
@@ -129,6 +176,29 @@ class CategoryDb(BaseModelDb):
     parent_id: Mapped[int | None] = mapped_column(
         ForeignKey("category.id"), nullable=True
     )
+    valid_from: Mapped[datetime | None] = mapped_column(
+        UTCDateTime(),
+        nullable=True,
+        info={
+            "description": "UTC start of validity; NULL means valid since the indefinite past."
+        },
+    )
+    valid_to: Mapped[datetime | None] = mapped_column(
+        UTCDateTime(),
+        nullable=True,
+        info={
+            "description": "UTC end of validity; NULL means the version is currently valid."
+        },
+    )
+    last_action: Mapped[str] = mapped_column(
+        String,
+        nullable=False,
+        default="created",
+        server_default="created",
+        info={
+            "description": "Most recent lifecycle action recorded for this category version."
+        },
+    )
 
     # Relationships
     parent = relationship(

tests/test_helper_db.py

@@ -1,7 +1,11 @@
+from datetime import UTC, datetime
+
+import pytest
 from sqlalchemy import select
+from sqlalchemy.exc import IntegrityError
 from sqlalchemy.orm import Session
 
-from src.ingest.b4w import upsert_category
+from src.ingest.b4w import change_category, retire_category, upsert_category
 from src.models import Category
 from src.models.b4w import CategoryDb
 
@@ -17,6 +21,13 @@ def test_upsert_category_returns_orm_object(db_session: Session):
     assert str(result.name) == "dummy"
     assert str(result.parent.name) == "dummy_parent_2"
     assert str(result.parent.parent.name) == "dummy_parent_1"
+    assert result.valid_from is None
+    assert result.valid_to is None
+    assert result.last_action == "created"
+    assert all(
+        CategoryDb.__table__.c[name].info.get("description")
+        for name in ("valid_from", "valid_to", "last_action")
+    )
 
 
 def test_upsert_category_writes_new_to_db(db_session: Session):
@@ -45,3 +56,77 @@ def test_upsert_category_skips_existing(db_session: Session):
         select(CategoryDb).filter_by(name="try_again_and_again")
     ).all()
     assert len(result) == 1
+
+
+def test_change_category_closes_old_version_and_starts_new_one(
+    db_session: Session,
+):
+    original = upsert_category(
+        db_session, Category.from_str("old_category"), do_commit=False
+    )
+    assert original is not None
+    effective_at = datetime(2026, 10, 16, 12, tzinfo=UTC)
+
+    replacement = change_category(
+        db_session,
+        original.id,
+        Category.from_str("new_category"),
+        effective_at=effective_at,
+        do_commit=False,
+    )
+
+    assert original.valid_from is None
+    assert original.valid_to == effective_at
+    assert original.last_action == "changed"
+    assert replacement.name == "new_category"
+    assert replacement.valid_from == effective_at
+    assert replacement.valid_to is None
+    assert replacement.last_action == "changed"
+
+    db_session.expire(original)
+    db_session.expire(replacement)
+    assert original.valid_to == effective_at
+    assert replacement.valid_from == effective_at
+
+    # A historical name can be introduced again as a new active version.
+    reintroduced = upsert_category(
+        db_session, Category.from_str("old_category"), do_commit=False
+    )
+    assert reintroduced is not None
+    assert reintroduced.id != original.id
+    assert reintroduced.valid_from is not None
+    assert reintroduced.valid_from > original.valid_to
+    assert reintroduced.last_action == "changed"
+
+
+def test_retire_category_closes_active_version(db_session: Session):
+    category = upsert_category(
+        db_session, Category.from_str("category_to_retire"), do_commit=False
+    )
+    assert category is not None
+    effective_at = datetime(2026, 10, 16, 12, tzinfo=UTC)
+
+    retired = retire_category(
+        db_session, category.id, effective_at=effective_at, do_commit=False
+    )
+
+    assert retired.valid_to == effective_at
+    assert retired.last_action == "retired"
+    assert (
+        db_session.query(CategoryDb)
+        .filter_by(name="category_to_retire", valid_to=None)
+        .one_or_none()
+        is None
+    )
+
+
+def test_active_root_categories_are_unique(db_session: Session):
+    db_session.add_all(
+        [
+            CategoryDb(name="duplicate_root"),
+            CategoryDb(name="duplicate_root"),
+        ]
+    )
+
+    with pytest.raises(IntegrityError):
+        db_session.flush()