1 files changed, 83 insertions, 0 deletions
diff --git a/src/buildtool/build_engine/expression/target_node.hpp b/src/buildtool/build_engine/expression/target_node.hpp
new file mode 100644
index 00000000..a2ab9c83
--- /dev/null
+++ b/src/buildtool/build_engine/expression/target_node.hpp
@@ -0,0 +1,83 @@
+#ifndef INCLUDED_SRC_BUILDTOOL_BUILDENGINE_EXPRESSION_TARGET_NODE_HPP
+#define INCLUDED_SRC_BUILDTOOL_BUILDENGINE_EXPRESSION_TARGET_NODE_HPP
+
+#include <type_traits>
+#include <variant>
+
+#include "src/buildtool/build_engine/expression/expression_ptr.hpp"
+#include "src/buildtool/build_engine/expression/target_result.hpp"
+
+class TargetNode {
+    using Value = ExpressionPtr;  // store result type
+
+  public:
+    struct Abstract {
+        std::string node_type;        // arbitrary string that maps to rule
+        ExpressionPtr string_fields;  // map to list of strings
+        ExpressionPtr target_fields;  // map to list of targets
+        [[nodiscard]] auto IsCacheable() const noexcept -> bool;
+    };
+
+    template <class NodeType>
+    requires(
+        std::is_same_v<NodeType, Value> or
+        std::is_same_v<NodeType, Abstract>) explicit TargetNode(NodeType node)
+        : data_{std::move(node)},
+          is_cacheable_{std::get<NodeType>(data_).IsCacheable()} {}
+
+    [[nodiscard]] auto IsCacheable() const noexcept -> bool {
+        return is_cacheable_;
+    }
+
+    [[nodiscard]] auto IsValue() const noexcept {
+        return std::holds_alternative<Value>(data_);
+    }
+
+    [[nodiscard]] auto IsAbstract() const noexcept {
+        return std::holds_alternative<Abstract>(data_);
+    }
+
+    [[nodiscard]] auto GetValue() const -> Value const& {
+        return std::get<Value>(data_);
+    }
+
+    [[nodiscard]] auto GetAbstract() const -> Abstract const& {
+        return std::get<Abstract>(data_);
+    }
+
+    [[nodiscard]] auto operator==(TargetNode const& other) const noexcept
+        -> bool {
+        if (data_.index() == other.data_.index()) {
+            try {
+                if (IsValue()) {
+                    return GetValue() == other.GetValue();
+                }
+                auto const& abs_l = GetAbstract();
+                auto const& abs_r = other.GetAbstract();
+                return abs_l.node_type == abs_r.node_type and
+                       abs_l.string_fields == abs_r.string_fields and
+                       abs_l.target_fields == abs_r.string_fields;
+            } catch (...) {
+                // should never happen
+            }
+        }
+        return false;
+    }
+
+    [[nodiscard]] auto ToString() const noexcept -> std::string {
+        try {
+            return ToJson().dump();
+        } catch (...) {
+            // should never happen
+        }
+        return {};
+    }
+
+    [[nodiscard]] auto ToJson() const -> nlohmann::json;
+
+  private:
+    std::variant<Value, Abstract> data_;
+    bool is_cacheable_;
+};
+
+#endif  // INCLUDED_SRC_BUILDTOOL_BUILDENGINE_EXPRESSION_TARGET_NODE_HPP