Add Timer class

The class provides for a timer, callback invocation on timer expiry, and
timer control/cleanup. This will be used in subsequent commits.

Change-Id: Ic8f43264a47903732b590a360ef0d8af765d5a20
Signed-off-by: Nagaraju Goruganti <ngorugan@in.ibm.com>
diff --git a/timer.cpp b/timer.cpp
new file mode 100644
index 0000000..ceb4c29
--- /dev/null
+++ b/timer.cpp
@@ -0,0 +1,89 @@
+#include <chrono>
+#include <system_error>
+#include <string.h>
+#include "timer.hpp"
+
+namespace phosphor
+{
+namespace state
+{
+namespace manager
+{
+static std::chrono::microseconds getTime()
+{
+    using namespace std::chrono;
+    auto usec = steady_clock::now().time_since_epoch();
+    return duration_cast<microseconds>(usec);
+}
+
+int Timer::state(timer::Action value)
+{
+    action_ = value;
+    return sd_event_source_set_enabled(eventSource_.get(), action_);
+}
+
+timer::Action Timer::getAction() const
+{
+    return action_;
+}
+
+std::chrono::microseconds Timer::getDuration() const
+{
+    return duration_;
+}
+
+Timer::Timer(EventPtr& event, std::function<void()> callback,
+             std::chrono::microseconds usec, timer::Action action) :
+    event_(event),
+    callback_(callback), duration_(usec), action_(action)
+{
+    // Add infinite expiration time
+    sd_event_source* sourcePtr = nullptr;
+
+    auto r = sd_event_add_time(event_.get(), &sourcePtr,
+                               CLOCK_MONOTONIC,            // Time base
+                               (getTime() + usec).count(), // When to fire
+                               0,              // Use default event accuracy
+                               timeoutHandler, // Callback handler on timeout
+                               this);          // User data
+
+    if (r < 0)
+    {
+        throw std::system_error(r, std::generic_category(), strerror(-r));
+    }
+
+    eventSource_.reset(sourcePtr);
+}
+
+int Timer::timeoutHandler(sd_event_source* eventSrc, uint64_t usec,
+                          void* userData)
+{
+    auto timer = static_cast<Timer*>(userData);
+
+    if (timer->getAction() == timer::ON)
+    {
+        auto r = sd_event_source_set_time(
+            eventSrc, (getTime() + timer->getDuration()).count());
+        if (r < 0)
+        {
+            throw std::system_error(r, std::generic_category(), strerror(-r));
+        }
+
+        r = sd_event_source_set_enabled(eventSrc, timer::ON);
+        if (r < 0)
+        {
+            throw std::system_error(r, std::generic_category(), strerror(-r));
+        }
+    }
+
+    if (timer->callback_)
+    {
+        timer->callback_();
+    }
+
+    return 0;
+}
+
+} // namespace manager
+} // namespace state
+} // namespace phosphor