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>

3 files changed, 181 insertions, 0 deletions

diff --git a/presence/Makefile.am b/presence/Makefile.am
index 2a5976c..33f13a3 100644
--- a/presence/Makefile.am
+++ b/presence/Makefile.am
@@ -5,6 +5,7 @@ sbin_PROGRAMS = \
 	phosphor-fan-presence-tach
 
 phosphor_fan_presence_tach_SOURCES = \
+	fallback.cpp \
 	fan.cpp \
 	gpio.cpp \
 	tach.cpp \
diff --git a/presence/fallback.cpp b/presence/fallback.cpp
new file mode 100644
index 0000000..625d74a
--- /dev/null
+++ b/presence/fallback.cpp
@@ -0,0 +1,101 @@
+/**
+ * Copyright © 2017 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 <algorithm>
+#include <phosphor-logging/log.hpp>
+#include "fan.hpp"
+#include "fallback.hpp"
+#include "psensor.hpp"
+
+namespace phosphor
+{
+namespace fan
+{
+namespace presence
+{
+
+void Fallback::stateChanged(bool present)
+{
+    if (!present)
+    {
+        // Starting with the first backup, find the first
+        // sensor that reports the fan as present, if any.
+        auto it = std::find_if(
+                std::next(activeSensor),
+                sensors.end(),
+                [](auto& s){return s.get().present();});
+
+        if (it != sensors.end())
+        {
+            // A backup sensor disagrees with the active sensor.
+            // Switch to the backup.
+            activeSensor->get().stop();
+            present = it->get().start();
+
+            while (activeSensor != it)
+            {
+                // Callout the broken sensors.
+                activeSensor->get().fail();
+                ++activeSensor;
+            }
+            phosphor::logging::log<phosphor::logging::level::INFO>(
+                    "Using backup presence sensor.",
+                    phosphor::logging::entry(
+                        "FAN=%s", std::get<1>(fan)));
+            activeSensor = it;
+        }
+    }
+
+    setPresence(fan, present);
+}
+
+void Fallback::monitor()
+{
+    // Find the first sensor that says the fan is present
+    // and set it as the active sensor.
+    activeSensor = std::find_if(
+            sensors.begin(),
+            sensors.end(),
+            [](auto& s){return s.get().present();});
+    if (activeSensor == sensors.end())
+    {
+        // The first sensor is working or all sensors
+        // agree the fan isn't present.  Use the first sensor.
+        activeSensor = sensors.begin();
+    }
+
+    if (activeSensor != sensors.begin())
+    {
+        phosphor::logging::log<phosphor::logging::level::INFO>(
+                "Using backup presence sensor.",
+                phosphor::logging::entry(
+                    "FAN=%s", std::get<1>(fan)));
+    }
+
+    // Callout the broken sensors.
+    auto it = sensors.begin();
+    while (it != activeSensor)
+    {
+        it->get().fail();
+        ++it;
+    }
+
+    // Start the active sensor and set the initial state.
+    setPresence(fan, activeSensor->get().start());
+}
+
+} // namespace presence
+} // namespace fan
+} // namespace phosphor
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