feat: add iCal calendar subscriptions

migrations/versions/0020_calendar_subscriptions.py

@@ -1,15 +1,15 @@
-"""tombstone for reverted calendar subscriptions
+"""restore calendar subscriptions after the reverted release
 
 Revision ID: 0020_calendar_subscriptions
 Revises: 0019_backup_imports
 
-The calendar subscription feature (backend/calendar.py, backend/calendar_router.py)
-was reverted from main, but this revision id was already applied to the production
-database. Keeping an empty migration under the same revision id lets
-`alembic upgrade head` succeed on databases stamped at this revision.
+The original revision reached production before the feature was reverted. Existing
+databases may therefore already contain the table while fresh databases do not.
+Keep the revision id and make the schema operation idempotent for both cases.
 """
 
-from alembic import op  # noqa: F401
+import sqlalchemy as sa
+from alembic import op
 
 revision = "0020_calendar_subscriptions"
 down_revision = "0019_backup_imports"
@@ -18,11 +18,35 @@ depends_on = None
 
 
 def upgrade() -> None:
-    # Intentionally empty: the feature was reverted. The leftover
-    # calendar_subscriptions table on already-migrated databases is harmless
-    # and intentionally left in place.
-    pass
+    bind = op.get_bind()
+    if "calendar_subscriptions" in sa.inspect(bind).get_table_names():
+        return
+    op.create_table(
+        "calendar_subscriptions",
+        sa.Column("id", sa.Uuid(), nullable=False),
+        sa.Column("user_id", sa.Uuid(), nullable=False),
+        sa.Column("name", sa.String(length=120), nullable=False),
+        sa.Column("url", sa.Text(), nullable=False),
+        sa.Column("color", sa.String(length=32), nullable=False),
+        sa.Column("enabled", sa.Boolean(), nullable=False),
+        sa.Column("ics_cache", sa.Text(), nullable=True),
+        sa.Column("etag", sa.String(length=512), nullable=True),
+        sa.Column("last_modified", sa.String(length=512), nullable=True),
+        sa.Column("refreshed_at", sa.DateTime(timezone=True), nullable=True),
+        sa.Column("last_error", sa.Text(), nullable=True),
+        sa.Column("created_at", sa.DateTime(timezone=True), nullable=False),
+        sa.Column("updated_at", sa.DateTime(timezone=True), nullable=False),
+        sa.ForeignKeyConstraint(["user_id"], ["users.id"], ondelete="CASCADE"),
+        sa.PrimaryKeyConstraint("id"),
+    )
+    op.create_index(
+        "ix_calendar_subscriptions_user_id", "calendar_subscriptions", ["user_id"]
+    )
 
 
 def downgrade() -> None:
-    pass
+    bind = op.get_bind()
+    if "calendar_subscriptions" not in sa.inspect(bind).get_table_names():
+        return
+    op.drop_index("ix_calendar_subscriptions_user_id", table_name="calendar_subscriptions")
+    op.drop_table("calendar_subscriptions")