control: Parse optional "manager.json"

Parse the optional "manager.json" configuration file which currently
provides a single optional attribute "power_on_delay". When the
"power_on_delay" attribute is not present, it is defaulted to 0.

An example "manager.json" file:
```
{
    "power_on_delay": 20
}
```

Tested:
    Power on delay of 0 when no "manager.json" file present
    Power on delay of 0 when no "power_on_delay" JSON attribute present
    Power on delay set to value given in "power_on_delay"

Change-Id: I5506ad4e853bdea249b9a794ce335261fdfcaa9f
Signed-off-by: Matthew Barth <msbarth@us.ibm.com>
diff --git a/control/json/manager.cpp b/control/json/manager.cpp
new file mode 100644
index 0000000..0ec0d0d
--- /dev/null
+++ b/control/json/manager.cpp
@@ -0,0 +1,52 @@
+/**
+ * Copyright © 2020 IBM Corporation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+#include "manager.hpp"
+
+#include "json_config.hpp"
+#include "json_parser.hpp"
+
+#include <sdbusplus/bus.hpp>
+
+#include <filesystem>
+
+namespace phosphor::fan::control::json
+{
+
+Manager::Manager(sdbusplus::bus::bus& bus)
+{
+    // Manager JSON config file is optional
+    auto confFile =
+        fan::JsonConfig::getConfFile(bus, confAppName, confFileName, true);
+    if (!confFile.empty())
+    {
+        _jsonObj = fan::JsonConfig::load(confFile);
+    }
+}
+
+unsigned int Manager::getPowerOnDelay()
+{
+    auto powerOnDelay = 0;
+
+    // Parse optional "power_on_delay" from JSON object
+    if (!_jsonObj.empty() && _jsonObj.contains("power_on_delay"))
+    {
+        powerOnDelay = _jsonObj["power_on_delay"].get<unsigned int>();
+    }
+
+    return powerOnDelay;
+}
+
+} // namespace phosphor::fan::control::json