Implemented sensor class

Sensor class was introduced, it monitors
xyz.openbmc_project.Sensor.Value, for change and notifies all
listeners.

Tested:
  - Unit tested with service stub that provides dbus interface
    xyz.openbmc_project.Sensor.Value
  - All changes are delivered to listeners
  - All other unit tests are passing

Change-Id: I8c9d58cc986c1fe2a4d2386815d559814016efa6
Signed-off-by: Krzysztof Grobelny <krzysztof.grobelny@intel.com>
diff --git a/src/interfaces/sensor.hpp b/src/interfaces/sensor.hpp
index dbeb158..07c7897 100644
--- a/src/interfaces/sensor.hpp
+++ b/src/interfaces/sensor.hpp
@@ -1,5 +1,7 @@
 #pragma once
 
+#include <chrono>
+#include <memory>
 #include <ostream>
 #include <string>
 #include <string_view>
@@ -8,6 +10,8 @@
 namespace interfaces
 {
 
+class SensorListener;
+
 class Sensor
 {
   public:
@@ -28,11 +32,17 @@
             return std::tie(type, service, path) <
                    std::tie(other.type, other.service, other.path);
         }
+
+        inline std::string str() const
+        {
+            return type + ":" + service + ":" + path;
+        }
     };
 
     virtual ~Sensor() = default;
 
     virtual Id id() const = 0;
+    virtual void registerForUpdates(const std::weak_ptr<SensorListener>&) = 0;
 };
 
 } // namespace interfaces
diff --git a/src/interfaces/sensor_listener.hpp b/src/interfaces/sensor_listener.hpp
new file mode 100644
index 0000000..9a2f0a2
--- /dev/null
+++ b/src/interfaces/sensor_listener.hpp
@@ -0,0 +1,19 @@
+#pragma once
+
+#include <optional>
+
+namespace interfaces
+{
+
+class Sensor;
+
+class SensorListener
+{
+  public:
+    virtual ~SensorListener() = default;
+
+    virtual void sensorUpdated(interfaces::Sensor&, uint64_t) = 0;
+    virtual void sensorUpdated(interfaces::Sensor&, uint64_t, double) = 0;
+};
+
+} // namespace interfaces
diff --git a/src/sensor.cpp b/src/sensor.cpp
new file mode 100644
index 0000000..d38fbd9
--- /dev/null
+++ b/src/sensor.cpp
@@ -0,0 +1,168 @@
+#include "sensor.hpp"
+
+#include "utils/detached_timer.hpp"
+
+#include <boost/container/flat_map.hpp>
+#include <phosphor-logging/log.hpp>
+#include <sdbusplus/asio/property.hpp>
+#include <sdbusplus/bus/match.hpp>
+
+#include <functional>
+#include <iostream>
+
+Sensor::Sensor(interfaces::Sensor::Id sensorId, boost::asio::io_context& ioc,
+               const std::shared_ptr<sdbusplus::asio::connection>& bus) :
+    sensorId(std::move(sensorId)),
+    ioc(ioc), bus(bus)
+{}
+
+Sensor::Id Sensor::makeId(std::string_view service, std::string_view path)
+{
+    return Id("Sensor", service, path);
+}
+
+Sensor::Id Sensor::id() const
+{
+    return sensorId;
+}
+
+void Sensor::async_read()
+{
+    uniqueCall([this](auto lock) { async_read(std::move(lock)); });
+}
+
+void Sensor::async_read(std::shared_ptr<utils::UniqueCall::Lock> lock)
+{
+    makeSignalMonitor();
+
+    sdbusplus::asio::getProperty<double>(
+        *bus, sensorId.service, sensorId.path,
+        "xyz.openbmc_project.Sensor.Value", "Value",
+        [lock, id = sensorId,
+         weakSelf = weak_from_this()](boost::system::error_code ec) {
+            phosphor::logging::log<phosphor::logging::level::ERR>(
+                "DBus 'GetProperty' call failed on Sensor Value",
+                phosphor::logging::entry("sensor=%s, ec=%lu", id.str().c_str(),
+                                         ec.value()));
+
+            if (auto self = weakSelf.lock())
+            {
+
+                constexpr auto retryIntervalAfterFailedRead =
+                    std::chrono::seconds(30);
+                utils::makeDetachedTimer(
+                    self->ioc, retryIntervalAfterFailedRead, [weakSelf] {
+                        if (auto self = weakSelf.lock())
+                        {
+                            self->async_read();
+                        }
+                    });
+            }
+        },
+        [lock, weakSelf = weak_from_this()](double newValue) {
+            if (auto self = weakSelf.lock())
+            {
+                self->updateValue(newValue);
+            }
+        });
+}
+
+void Sensor::registerForUpdates(
+    const std::weak_ptr<interfaces::SensorListener>& weakListener)
+{
+    if (auto listener = weakListener.lock())
+    {
+        listeners.emplace_back(weakListener);
+
+        if (value)
+        {
+            listener->sensorUpdated(*this, timestamp, *value);
+        }
+        else
+        {
+            async_read();
+        }
+    }
+}
+
+void Sensor::updateValue(double newValue)
+{
+    timestamp = std::time(0);
+
+    if (value == newValue)
+    {
+        for (const auto& weakListener : listeners)
+        {
+            if (auto listener = weakListener.lock())
+            {
+                listener->sensorUpdated(*this, timestamp);
+            }
+        }
+    }
+    else
+    {
+        value = newValue;
+
+        for (const auto& weakListener : listeners)
+        {
+            if (auto listener = weakListener.lock())
+            {
+                listener->sensorUpdated(*this, timestamp, *value);
+            }
+        }
+    }
+}
+
+void Sensor::makeSignalMonitor()
+{
+    if (signalMonitor)
+    {
+        return;
+    }
+
+    using namespace std::string_literals;
+
+    const auto param = "type='signal',member='PropertiesChanged',path='"s +
+                       sensorId.path +
+                       "',arg0='xyz.openbmc_project.Sensor.Value'"s;
+
+    signalMonitor = std::make_unique<sdbusplus::bus::match::match>(
+        *bus, param,
+        [weakSelf = weak_from_this()](sdbusplus::message::message& message) {
+            signalProc(weakSelf, message);
+        });
+}
+
+void Sensor::signalProc(const std::weak_ptr<Sensor>& weakSelf,
+                        sdbusplus::message::message& message)
+{
+    if (auto self = weakSelf.lock())
+    {
+        std::string iface;
+        boost::container::flat_map<std::string, ValueVariant>
+            changed_properties;
+        std::vector<std::string> invalidated_properties;
+
+        message.read(iface, changed_properties, invalidated_properties);
+
+        if (iface == "xyz.openbmc_project.Sensor.Value")
+        {
+            const auto it = changed_properties.find("Value");
+            if (it != changed_properties.end())
+            {
+                if (auto val = std::get_if<double>(&it->second))
+                {
+                    self->updateValue(*val);
+                }
+                else
+                {
+                    phosphor::logging::log<phosphor::logging::level::ERR>(
+                        "Failed to receive Value from Sensor "
+                        "PropertiesChanged signal",
+                        phosphor::logging::entry("sensor=%s",
+                                                 self->sensorId.path.c_str()));
+                }
+            }
+        }
+    }
+}
diff --git a/src/sensor.hpp b/src/sensor.hpp
new file mode 100644
index 0000000..1374c54
--- /dev/null
+++ b/src/sensor.hpp
@@ -0,0 +1,52 @@
+#pragma once
+
+#include "interfaces/sensor.hpp"
+#include "interfaces/sensor_listener.hpp"
+#include "utils/unique_call.hpp"
+
+#include <boost/asio/high_resolution_timer.hpp>
+#include <sdbusplus/asio/connection.hpp>
+
+#include <memory>
+
+class Sensor final :
+    public interfaces::Sensor,
+    public std::enable_shared_from_this<Sensor>
+{
+    using ValueVariant = std::variant<std::monostate, double>;
+
+  public:
+    Sensor(interfaces::Sensor::Id sensorId, boost::asio::io_context& ioc,
+           const std::shared_ptr<sdbusplus::asio::connection>& bus);
+
+    Sensor(const Sensor&) = delete;
+    Sensor& operator=(const Sensor&) = delete;
+
+    static Id makeId(std::string_view service, std::string_view path);
+
+    Id id() const override;
+    void registerForUpdates(
+        const std::weak_ptr<interfaces::SensorListener>& weakListener) override;
+
+  private:
+    static std::optional<double> readValue(const ValueVariant& v);
+    static void signalProc(const std::weak_ptr<Sensor>& weakSelf,
+                           sdbusplus::message::message&);
+
+    void async_read();
+    void async_read(std::shared_ptr<utils::UniqueCall::Lock>);
+    void makeSignalMonitor();
+    void updateValue(double);
+
+    interfaces::Sensor::Id sensorId;
+    boost::asio::io_context& ioc;
+    std::shared_ptr<sdbusplus::asio::connection> bus;
+    std::chrono::milliseconds timerInterval = std::chrono::milliseconds(0);
+    std::optional<boost::asio::high_resolution_timer> timer;
+
+    utils::UniqueCall uniqueCall;
+    std::vector<std::weak_ptr<interfaces::SensorListener>> listeners;
+    uint64_t timestamp = 0;
+    std::optional<double> value;
+    std::unique_ptr<sdbusplus::bus::match::match> signalMonitor;
+};
diff --git a/src/utils/detached_timer.hpp b/src/utils/detached_timer.hpp
new file mode 100644
index 0000000..21343f9
--- /dev/null
+++ b/src/utils/detached_timer.hpp
@@ -0,0 +1,28 @@
+#pragma once
+
+#include <boost/asio/io_context.hpp>
+#include <boost/asio/spawn.hpp>
+#include <boost/asio/steady_timer.hpp>
+
+#include <chrono>
+
+namespace utils
+{
+
+template <class F>
+void makeDetachedTimer(boost::asio::io_context& ioc,
+                       std::chrono::milliseconds delay, F&& fun)
+{
+    auto timer = std::make_unique<boost::asio::steady_timer>(ioc);
+    timer->expires_after(delay);
+    timer->async_wait([timer = std::move(timer),
+                       fun = std::move(fun)](boost::system::error_code ec) {
+        if (ec)
+        {
+            return;
+        }
+        fun();
+    });
+}
+
+} // namespace utils
diff --git a/src/utils/unique_call.hpp b/src/utils/unique_call.hpp
new file mode 100644
index 0000000..db10786
--- /dev/null
+++ b/src/utils/unique_call.hpp
@@ -0,0 +1,30 @@
+#pragma once
+
+#include <memory>
+#include <utility>
+
+namespace utils
+{
+
+class UniqueCall
+{
+  public:
+    struct Lock
+    {};
+
+    template <class Functor, class... Args>
+    void operator()(Functor&& functor, Args&&... args)
+    {
+        if (lock.expired())
+        {
+            auto l = std::make_shared<Lock>();
+            lock = l;
+            functor(std::move(l), std::forward<Args>(args)...);
+        }
+    }
+
+  private:
+    std::weak_ptr<Lock> lock;
+};
+
+} // namespace utils