Add allow_zero_price_sales toggle: config UI, POS enforcement and backend validation

pos/blueprints/service_order_bp.py

@@ -38,6 +38,29 @@ from blueprints.config_bp import _get_workshop_permissions, _DEFAULT_WORKSHOP_PE
 service_order_bp = Blueprint('service_orders', __name__, url_prefix='/pos/api/service-orders')
 
 
+def _tenant_allows_zero_price(conn):
+    """Return True if the tenant allows selling items at $0. Defaults to True."""
+    cur = conn.cursor()
+    cur.execute("SELECT value FROM tenant_config WHERE key = 'allow_zero_price_sales'")
+    row = cur.fetchone()
+    cur.close()
+    return str(row[0]).lower() in ('true', '1', 'yes') if row else True
+
+
+def _validate_zero_price(conn, items):
+    """Raise ValueError if any item line would be <= $0 and the tenant forbids it."""
+    if _tenant_allows_zero_price(conn):
+        return
+    for item in items:
+        unit_price = float(item.get('unit_price', 0) or 0)
+        quantity = float(item.get('quantity', 1) or 1)
+        discount_pct = float(item.get('discount_pct', 0) or 0)
+        line_total = unit_price * quantity * (1 - discount_pct / 100)
+        if line_total <= 0:
+            name = item.get('name') or item.get('part_number') or item.get('inventory_id')
+            raise ValueError(f"No está permitido vender artículos en $0 ({name})")
+
+
 # Roles allowed to access the workshop module at all.
 _WORKSHOP_VIEW_ROLES = {'owner', 'admin', 'counter', 'cashier', 'workshop', 'mechanic'}
 
@@ -174,6 +197,7 @@ def create_order_from_pos():
     )
     conn = get_tenant_conn(g.tenant_id)
     try:
+        _validate_zero_price(conn, items)
         result = create_service_order(conn, {
             'tenant_id': g.tenant_id,
             'branch_id': data.get('branch_id', g.branch_id),