implemented latch method

inventory_provider/routes/jobs.py

 from flask import Blueprint, current_app, jsonify
 from inventory_provider.tasks import worker
+from inventory_provider.tasks import common as worker_common
 from inventory_provider.routes import common
 
 routes = Blueprint("inventory-data-job-routes", __name__)
@@ -36,3 +37,27 @@ def reload_router_config(equipment_name):
 @common.require_accepts_json
 def check_task_status(task_id):
     return jsonify(worker.check_task_status(task_id))
+
+@routes.route("latchdb", methods=['GET', 'POST'])
+def latch_db():
+
+    config = current_app.config["INVENTORY_PROVIDER_CONFIG"]
+    db_ids = config['redis-databases']
+    db_ids = sorted(set(db_ids))
+
+    r = worker_common.get_next_redis(config)
+    latch = worker_common.get_latch(r)
+    if not latch:
+        latch = {
+            'current': db_ids[0],
+            'next': db_ids[0]
+        }
+
+    next_idx = db_ids.index(latch['next'])
+    next_idx = (next_idx + 1) % len(db_ids)
+
+    worker_common.set_latch(
+        config, new_current=latch['next'], new_next=db_ids[next_idx])
+
+    r = worker_common.get_current_redis(config)
+    return jsonify(worker_common.get_latch(r))

inventory_provider/tasks/common.py

@@ -35,13 +35,28 @@ def get_latch(r):
     return latch
 
 
+def set_latch(config, new_current, new_next):
+
+    for db in config['redis-databases']:
+        latch = {
+            'current': new_current,
+            'next': new_next,
+            'this': db
+        }
+
+        r = _get_redis(config, dbid=db)
+        r.set('db:latch', json.dumps(latch))
+
+
 def _get_redis(config, dbid=None):
 
     if dbid is None:
         logger.debug('no db specified, using minimum as first guess')
         dbid = min(config['redis-databases'])
 
-    assert dbid in config['redis-databases']
+    if dbid not in config['redis-databases']:
+        logger.error('tried to connect to unknown db id: {}'.format(dbid))
+        dbid = min(config['redis-databases'])
 
     kwargs = {
         'db': dbid,
@@ -81,7 +96,7 @@ def get_next_redis(config):
     if latch and latch['this'] == latch['next']:
         return r
 
-    if latch:
+    if latch and latch['next'] in config['redis-databases']:
         next_id = latch['next']
     else:
         logger.warning("next db not configured, deriving default value")