From a06585835ee109524c555316269f22ed6f8b7407 Mon Sep 17 00:00:00 2001
From: odlomax <oliver.lomax@metoffice.gov.uk>
Date: Mon, 14 Oct 2024 11:00:58 +0100
Subject: [PATCH] Refactored spherical vector interpolation method.

---
 .../method/sphericalvector/SphericalVector.cc | 84 ++++++++-----------
 1 file changed, 34 insertions(+), 50 deletions(-)

diff --git a/src/atlas/interpolation/method/sphericalvector/SphericalVector.cc b/src/atlas/interpolation/method/sphericalvector/SphericalVector.cc
index 65e4e41d0..20416b2dd 100644
--- a/src/atlas/interpolation/method/sphericalvector/SphericalVector.cc
+++ b/src/atlas/interpolation/method/sphericalvector/SphericalVector.cc
@@ -7,6 +7,9 @@
 
 #include "atlas/interpolation/method/sphericalvector/SphericalVector.h"
 
+#include <cmath>
+#include <variant>
+
 #include "atlas/array/ArrayView.h"
 #include "atlas/field/Field.h"
 #include "atlas/field/FieldSet.h"
@@ -203,59 +206,40 @@ template <typename MatMul>
 void SphericalVector::interpolate_vector_field(const Field& sourceField,
                                                Field& targetField,
                                                const MatMul& matMul) {
-  ATLAS_ASSERT_MSG(sourceField.variables() == 2 || sourceField.variables() == 3,
-                   "Vector field can only have 2 or 3 components.");
-
-  if (sourceField.datatype().kind() == array::DataType::KIND_REAL64) {
-    interpolate_vector_field<double>(sourceField, targetField, matMul);
-    return;
-  }
-
-  if (sourceField.datatype().kind() == array::DataType::KIND_REAL32) {
-    interpolate_vector_field<float>(sourceField, targetField, matMul);
-    return;
-  }
+  const auto sourceViewVariant = array::make_view_variant(sourceField);
+
+  const auto sourceViewVisitor = [&](auto sourceView) {
+    if constexpr (array::is_rank<2, 3>(sourceView) &&
+                  array::is_non_const_value_type<float, double>(sourceView)) {
+      using SourceView = std::decay_t<decltype(sourceView)>;
+      using Value = typename SourceView::non_const_value_type;
+      constexpr auto Rank = SourceView::rank();
+      auto targetView = array::make_view<Value, Rank>(targetField);
+
+      switch (sourceField.variables()) {
+        case 2:
+          return matMul.apply(sourceView, targetView, twoVector);
+        case 3:
+          return matMul.apply(sourceView, targetView, threeVector);
+        default:
+          ATLAS_THROW_EXCEPTION("Error: no support for " +
+                              std::to_string(sourceField.variables()) +
+                              " variable vector fields.\n" +
+                                " Number of variables must be 2 or 3.");
+      }
+
+    } else {
+      ATLAS_THROW_EXCEPTION(
+          "Error: no support for rank = " + std::to_string(sourceField.rank()) +
+              " and value type = " + sourceField.datatype().str() + ".\n" +
+              "Vector field must have rank 2 or 3 with value type "
+              "float or double");
+    }
+  };
 
-  ATLAS_NOTIMPLEMENTED;
+  std::visit(sourceViewVisitor, sourceViewVariant);
 };
 
-template <typename Value, typename MatMul>
-void SphericalVector::interpolate_vector_field(const Field& sourceField,
-                                               Field& targetField,
-                                               const MatMul& matMul) {
-  if (sourceField.rank() == 2) {
-    interpolate_vector_field<Value, 2>(sourceField, targetField, matMul);
-    return;
-  }
-
-  if (sourceField.rank() == 3) {
-    interpolate_vector_field<Value, 3>(sourceField, targetField, matMul);
-    return;
-  }
-
-  ATLAS_NOTIMPLEMENTED;
-}
-
-template <typename Value, int Rank, typename MatMul>
-void SphericalVector::interpolate_vector_field(const Field& sourceField,
-                                               Field& targetField,
-                                               const MatMul& matMul) {
-  const auto sourceView = array::make_view<Value, Rank>(sourceField);
-  auto targetView = array::make_view<Value, Rank>(targetField);
-
-  if (sourceField.variables() == 2) {
-    matMul.apply(sourceView, targetView, twoVector);
-    return;
-  }
-
-  if (sourceField.variables() == 3) {
-    matMul.apply(sourceView, targetView, threeVector);
-    return;
-  }
-
-  ATLAS_NOTIMPLEMENTED;
-}
-
 }  // namespace method
 }  // namespace interpolation
 }  // namespace atlas