presence: Add fallback redundancy policy

Add a fallback redundancy implementation of the RedundancyPolicy
interface.

The fallback policy associates multiple PresenceSensor instances
to a single fan, and "falls-back" on secondary sensor implementations
when the primary sensor cannot see the fan.

Change-Id: I6468d77d97b8916b3ff33bcd0cd28a102d1aaba1
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>

1 files changed, 79 insertions, 0 deletions

diff --git a/presence/fallback.hpp b/presence/fallback.hpp
new file mode 100644
index 0000000..a1a5b29
--- /dev/null
+++ b/presence/fallback.hpp
@@ -0,0 +1,79 @@
+#pragma once
+
+#include <functional>
+#include <vector>
+#include "fan.hpp"
+#include "rpolicy.hpp"
+
+namespace phosphor
+{
+namespace fan
+{
+namespace presence
+{
+
+class PresenceSensor;
+
+/**
+ * @class Fallback
+ * @brief Fallback redundancy policy.
+ *
+ * The fallback redundancy policy falls back to
+ * subsequent presence sensors when the active
+ * sensor indicates not present and a fallback
+ * sensor indicates the fan is present.
+ */
+class Fallback : public RedundancyPolicy
+{
+    public:
+        Fallback() = delete;
+        Fallback(const Fallback&) = default;
+        Fallback& operator=(const Fallback&) = default;
+        Fallback(Fallback&&) = default;
+        Fallback& operator=(Fallback&&) = default;
+        ~Fallback() = default;
+
+        /**
+         * @brief Construct a fallback policy.
+         *
+         * @param[in] fan - The fan associated with the policy.
+         * @param[in] s - The set of sensors associated with the policy.
+         */
+        Fallback(
+                const Fan& fan,
+                const std::vector<std::reference_wrapper<PresenceSensor>>& s) :
+            RedundancyPolicy(fan), sensors(s)
+        {
+            activeSensor = sensors.begin();
+        }
+
+        /**
+         * @brief stateChanged
+         *
+         * Update the inventory and execute the fallback
+         * policy.
+         *
+         * @param[in] present - The new presence state according
+         *             to the active sensor.
+         */
+        void stateChanged(bool present) override;
+
+        /**
+         * @brief monitor
+         *
+         * Start monitoring the fan.
+         */
+        void monitor() override;
+
+    private:
+
+        /** @brief All presence sensors in the redundancy set. */
+        std::vector<std::reference_wrapper<PresenceSensor>> sensors;
+
+        /** @brief The active presence sensor. */
+        decltype(sensors)::iterator activeSensor;
+};
+
+} // namespace presence
+} // namespace fan
+} // namespace phosphor