Utils: Break out expression parsing and evaluation

Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Change-Id: I16101a37220be56722cedd273d5788393aa860fa
diff --git a/include/Expression.hpp b/include/Expression.hpp
new file mode 100644
index 0000000..b832e72
--- /dev/null
+++ b/include/Expression.hpp
@@ -0,0 +1,36 @@
+/*
+// Copyright (c) 2017 Intel Corporation
+// Copyright (c) 2022 IBM Corp.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+*/
+
+#pragma once
+
+#include <optional>
+#include <string>
+
+namespace expression
+{
+enum class Operation
+{
+    addition,
+    division,
+    multiplication,
+    subtraction,
+    modulo,
+};
+
+std::optional<Operation> parseOperation(std::string& op);
+int evaluate(int a, Operation op, int b);
+} // namespace expression
diff --git a/include/Utils.hpp b/include/Utils.hpp
index 13c199c..c54559a 100644
--- a/include/Utils.hpp
+++ b/include/Utils.hpp
@@ -40,15 +40,6 @@
 using MapperGetSubTreeResponse =
     boost::container::flat_map<std::string, DBusObject>;
 
-enum class TemplateOperation
-{
-    addition,
-    division,
-    multiplication,
-    subtraction,
-    modulo,
-};
-
 namespace properties
 {
 constexpr const char* interface = "org.freedesktop.DBus.Properties";
diff --git a/meson.build b/meson.build
index 80893ab..5f733af 100644
--- a/meson.build
+++ b/meson.build
@@ -210,6 +210,7 @@
         executable(
             'test_entity_manager',
             'test/test_entity-manager.cpp',
+            'src/Expression.cpp',
             'src/Utils.cpp',
             cpp_args: test_boost_args,
             dependencies: [
diff --git a/src/Expression.cpp b/src/Expression.cpp
new file mode 100644
index 0000000..43fcaf7
--- /dev/null
+++ b/src/Expression.cpp
@@ -0,0 +1,79 @@
+/*
+// Copyright (c) 2017 Intel Corporation
+// Copyright (c) 2022 IBM Corp.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+*/
+
+#include "Expression.hpp"
+
+#include <stdexcept>
+
+namespace expression
+{
+std::optional<Operation> parseOperation(std::string& op)
+{
+    if (op == "+")
+    {
+        return Operation::addition;
+    }
+    if (op == "-")
+    {
+        return Operation::subtraction;
+    }
+    if (op == "*")
+    {
+        return Operation::multiplication;
+    }
+    if (op == R"(%)")
+    {
+        return Operation::modulo;
+    }
+    if (op == R"(/)")
+    {
+        return Operation::division;
+    }
+
+    return std::nullopt;
+}
+
+int evaluate(int a, Operation op, int b)
+{
+    switch (op)
+    {
+        case Operation::addition:
+        {
+            return a + b;
+        }
+        case Operation::subtraction:
+        {
+            return a - b;
+        }
+        case Operation::multiplication:
+        {
+            return a * b;
+        }
+        case Operation::division:
+        {
+            return a / b;
+        }
+        case Operation::modulo:
+        {
+            return a % b;
+        }
+
+        default:
+            throw std::invalid_argument("Unrecognised operation");
+    }
+}
+} // namespace expression
diff --git a/src/Utils.cpp b/src/Utils.cpp
index dd13113..b73e469 100644
--- a/src/Utils.cpp
+++ b/src/Utils.cpp
@@ -17,6 +17,7 @@
 
 #include "Utils.hpp"
 
+#include "Expression.hpp"
 #include "VariantVisitors.hpp"
 
 #include <boost/algorithm/string/classification.hpp>
@@ -297,7 +298,8 @@
         int number = std::visit(VariantToIntVisitor(), propValue);
 
         bool isOperator = true;
-        TemplateOperation next = TemplateOperation::addition;
+        std::optional<expression::Operation> next =
+            expression::Operation::addition;
 
         auto it = split.begin();
 
@@ -305,37 +307,18 @@
         {
             if (isOperator)
             {
-                if (*it == "+")
-                {
-                    next = TemplateOperation::addition;
-                }
-                else if (*it == "-")
-                {
-                    next = TemplateOperation::subtraction;
-                }
-                else if (*it == "*")
-                {
-                    next = TemplateOperation::multiplication;
-                }
-                else if (*it == R"(%)")
-                {
-                    next = TemplateOperation::modulo;
-                }
-                else if (*it == R"(/)")
-                {
-                    next = TemplateOperation::division;
-                }
-                else
+                next = expression::parseOperation(*it);
+                if (!next)
                 {
                     break;
                 }
             }
             else
             {
-                int constant = 0;
                 try
                 {
-                    constant = std::stoi(*it);
+                    int constant = std::stoi(*it);
+                    number = expression::evaluate(number, *next, constant);
                 }
                 catch (const std::invalid_argument&)
                 {
@@ -343,37 +326,6 @@
                               << "\n";
                     continue;
                 }
-                switch (next)
-                {
-                    case TemplateOperation::addition:
-                    {
-                        number += constant;
-                        break;
-                    }
-                    case TemplateOperation::subtraction:
-                    {
-                        number -= constant;
-                        break;
-                    }
-                    case TemplateOperation::multiplication:
-                    {
-                        number *= constant;
-                        break;
-                    }
-                    case TemplateOperation::division:
-                    {
-                        number /= constant;
-                        break;
-                    }
-                    case TemplateOperation::modulo:
-                    {
-                        number = number % constant;
-                        break;
-                    }
-
-                    default:
-                        break;
-                }
             }
             isOperator = !isOperator;
         }
diff --git a/src/meson.build b/src/meson.build
index d1112cc..939574e 100644
--- a/src/meson.build
+++ b/src/meson.build
@@ -4,6 +4,7 @@
 executable(
     'entity-manager',
     'EntityManager.cpp',
+    'Expression.cpp',
     'PerformScan.cpp',
     'PerformProbe.cpp',
     'Overlay.cpp',
@@ -27,6 +28,7 @@
     endif
     executable(
         'fru-device',
+        'Expression.cpp',
         'FruDevice.cpp',
         'Utils.cpp',
         'FruUtils.cpp',