Jul 16 - Fill the gaps between Single-tenant mode and Multi-tenant mode - MT3

migrations/versions/phase42_area_qr_token.py

@@ -0,0 +1,67 @@
+"""phase42 — areas.qr_token for per-area public QR landing pages
+
+Adds a unique, unguessable token per area. Each area's QR encodes
+/f/area/<qr_token>, a login-free summary scoped to that area plus a
+"report a problem" form.
+
+Ported from the single-tenant chain (phase39_area_public_token) and adapted:
+the MT column is named `qr_token` (matching `facilities.qr_token` from
+phase38_facility_qr), not `public_token`, and is VARCHAR(64) to match the
+facility column and MT's `secrets.token_urlsafe(32)` generator.
+
+Unlike the ST original, existing areas are NOT backfilled: MT mints tokens
+lazily via `Area.ensure_qr_token()` on first use, exactly as
+`Facility.ensure_qr_token()` already does. A backfill would mint tokens for
+areas nobody ever prints a code for.
+
+Uses INFORMATION_SCHEMA checks — safe to re-run on every tenant DB.
+"""
+
+revision      = 'phase42_area_qr_token'
+down_revision = 'phase41_auditor_role'
+branch_labels = None
+depends_on    = None
+
+from alembic import op
+import sqlalchemy as sa
+
+
+def _column_exists(conn, table, column):
+    return conn.execute(sa.text(
+        "SELECT COUNT(*) FROM INFORMATION_SCHEMA.COLUMNS "
+        "WHERE TABLE_SCHEMA = DATABASE() "
+        "AND TABLE_NAME = :t AND COLUMN_NAME = :c"
+    ), {"t": table, "c": column}).scalar() > 0
+
+
+def _index_exists(conn, table, index):
+    return conn.execute(sa.text(
+        "SELECT COUNT(*) FROM INFORMATION_SCHEMA.STATISTICS "
+        "WHERE TABLE_SCHEMA = DATABASE() "
+        "AND TABLE_NAME = :t AND INDEX_NAME = :i"
+    ), {"t": table, "i": index}).scalar() > 0
+
+
+def upgrade():
+    bind = op.get_bind()
+
+    if not _column_exists(bind, 'areas', 'qr_token'):
+        op.execute(sa.text(
+            "ALTER TABLE areas ADD COLUMN qr_token VARCHAR(64) NULL"
+        ))
+
+    # Unique index tolerates multiple NULLs in MySQL, so it can be created
+    # immediately — no backfill needed before enforcing uniqueness.
+    if not _index_exists(bind, 'areas', 'uq_area_qr_token'):
+        op.execute(sa.text(
+            "CREATE UNIQUE INDEX uq_area_qr_token ON areas (qr_token)"
+        ))
+
+
+def downgrade():
+    bind = op.get_bind()
+
+    if _index_exists(bind, 'areas', 'uq_area_qr_token'):
+        op.execute(sa.text("DROP INDEX uq_area_qr_token ON areas"))
+    if _column_exists(bind, 'areas', 'qr_token'):
+        op.execute(sa.text("ALTER TABLE areas DROP COLUMN qr_token"))