Resolve "Migrate code to OTB 8.x"

Closes #5 (closed)

include/otbStringHelpers.h

 /*
- * Copyright(C) 2005-2021 Centre National d'Etudes Spatiales(CNES)
+ * Copyright(C) 2005-2023 Centre National d'Etudes Spatiales(CNES)
  *
  * This file is part of Orfeo Toolbox
  *
@@ -20,7 +20,7 @@
 #ifndef otbStringHelpers_h
 #define otbStringHelpers_h
 
-#if defined(DRAFT_OTB8) || OTB_VERSION_MAJOR >= 8
+#if OTB_VERSION_MAJOR >= 8
 #include "otbImageMetadata.h"
 #else
 #include "otbImageKeywordlist.h"
@@ -69,7 +69,7 @@ inline std::string sto<std::string>(std::string const& s)
  * \return the metadata found associated to the `key` decoded as a `T` type.
  * \todo move this function to `StringUtilities.h`
  */
-#if defined(DRAFT_OTB8) || OTB_VERSION_MAJOR >= 8
+#if OTB_VERSION_MAJOR >= 8
 template <typename T>
 inline
 T value_or_unless(
@@ -109,7 +109,60 @@ T value_or_unless(
 }
 #endif
 
+#if OTB_VERSION_MAJOR >= 8
+/**
+ * Helper function to fetch data from keyword lists.
+ * \tparam T  Type of the element to find
+ * \param[in] kwl            Keyword list where to search for
+ * \param[in] key            Name of the element to search and decode
+ * \param[in] context        Context to help build error message
+ *
+ * \throw itk::ExceptionObject with the `context` as message if there is no
+ * metadata associated to the `key`
+ * \throw itk::ExceptionObject with the `context` as message if the metadata
+ * found at the `key` cannot be converted to a `T`
+ * \return the metadata found associated to the `key` decoded as a `T` type.
+ * \todo move this function to `StringUtilities.h`
+ */
+template <typename T>
+inline
+T value_or_throw(
+    otb::ImageMetadata const& kwl,
+    std::string const& key,
+    otb::string_view context)
+{
+  if (kwl.Has(key))
+  {
+    auto const& value = kwl[key];
+    return to<T>(value, "converting metadata '"+key+"' "+context);
+  }
+  else
+  {
+    throw std::runtime_error("Cannot fetch metadata '"+key+"' " +context);
+  }
 }
+#else
+template <typename T>
+inline
+T value_or_throw(
+    otb::ImageKeywordlist const& kwl,
+    std::string const& key,
+    otb::string_view context)
+{
+  if (kwl.HasKey(key))
+  {
+    auto const& value = kwl.GetMetadataByKey(key);
+    return to<T>(value, context);
+  }
+  else
+  {
+    throw std::runtime_error("Cannot fetch metadata '"+ key + "' while " + context);
+  }
+}
+#endif
+
+}
+
 // otb namespace