AWS Level 2 Provider FindKey

wxdata/include/scwx/provider/aws_level2_data_provider.hpp

@@ -30,7 +30,8 @@ public:
 
    size_t cache_size() const;
 
-   size_t ListObjects(std::chrono::system_clock::time_point date);
+   std::string FindKey(std::chrono::system_clock::time_point time);
+   size_t      ListObjects(std::chrono::system_clock::time_point date);
    std::shared_ptr<wsr88d::Ar2vFile> LoadObjectByKey(const std::string& key);
    void                              Refresh();
 

wxdata/include/scwx/util/map.hpp

@@ -0,0 +1,41 @@
+#pragma once
+
+#include <map>
+#include <optional>
+
+namespace scwx
+{
+namespace util
+{
+
+template<class Key, class T>
+std::optional<T> GetBoundedElement(std::map<Key, T>& map, Key key)
+{
+   std::optional<T> element = std::nullopt;
+
+   // Find the first element greater than the key requested
+   auto it = map.upper_bound(key);
+
+   // An element with a key greater was found
+   if (it != map.cend())
+   {
+      // Are there elements prior to this element?
+      if (it != map.cbegin())
+      {
+         // Get the element immediately preceding, this the element we are
+         // looking for
+         element = (--it)->second;
+      }
+   }
+   else if (map.size() > 0)
+   {
+      // An element with a key greater was not found. If it exists, it must be
+      // the last element.
+      element = map.rbegin()->second;
+   }
+
+   return element;
+}
+
+} // namespace util
+} // namespace scwx