regulators: Complete PresenceDetection class

Complete implementation of the PresenceDetection class.  Implement the
execute() method that executes one or more actions to determine if a
device is present.

Cache the results so that subsequent calls to execute() will return the
cached value.  Executing the actions may be expensive, requiring one or
more D-Bus calls.

Provide a clearCache() method to be called on each boot to clear the
cached value.

Signed-off-by: Bob King <Bob_King@wistron.com>
Change-Id: Ie0e3dfde10f2df8ca8b56ec14ce723f356e97dfc
diff --git a/phosphor-regulators/src/presence_detection.cpp b/phosphor-regulators/src/presence_detection.cpp
new file mode 100644
index 0000000..3ed5350
--- /dev/null
+++ b/phosphor-regulators/src/presence_detection.cpp
@@ -0,0 +1,64 @@
+/**
+ * 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 "presence_detection.hpp"
+
+#include "action_environment.hpp"
+#include "action_utils.hpp"
+#include "chassis.hpp"
+#include "device.hpp"
+#include "exception_utils.hpp"
+#include "system.hpp"
+
+#include <exception>
+
+namespace phosphor::power::regulators
+{
+
+bool PresenceDetection::execute(Services& services, System& system,
+                                Chassis& /*chassis*/, Device& device)
+{
+    // If no presence value is cached
+    if (!isPresent.has_value())
+    {
+        // Initially assume device is present
+        isPresent = true;
+
+        // Execute actions to find device presence
+        try
+        {
+            // Create ActionEnvironment
+            ActionEnvironment environment{system.getIDMap(), device.getID(),
+                                          services};
+
+            // Execute the actions and cache resulting value
+            isPresent = action_utils::execute(actions, environment);
+        }
+        catch (const std::exception& e)
+        {
+            // Log error messages in journal
+            services.getJournal().logError(exception_utils::getMessages(e));
+            services.getJournal().logError("Unable to determine presence of " +
+                                           device.getID());
+
+            // TODO: Create error log entry
+        }
+    }
+
+    return isPresent.value();
+}
+
+} // namespace phosphor::power::regulators