Closes #14

core/definition_key.h

@@ -0,0 +1,62 @@
+// SPDX-License-Identifier: MIT
+// Copyright (c) 2026 Dim Himro
+
+#ifndef DEFINITION_KEY_H
+#define DEFINITION_KEY_H
+
+#include <cstdint>
+#include <functional>
+#include <string>
+#include <utility>
+
+/**
+ * @brief Stable frame identifier: normalized CAN ID and frame type.
+ */
+struct FrameKey {
+    std::uint32_t canId = 0U;
+    bool isExtended = false;
+
+    FrameKey() = default;
+
+    FrameKey(std::uint32_t id, bool extended)
+        : canId(id), isExtended(extended) {
+    }
+
+    bool operator==(const FrameKey &other) const {
+        return (canId == other.canId) && (isExtended == other.isExtended);
+    }
+};
+
+/**
+ * @brief Hasher for frame key.
+ */
+struct FrameKeyHasher {
+    std::size_t operator()(const FrameKey &key) const {
+        const std::size_t a = static_cast<std::size_t>(key.canId);
+        const std::size_t b = key.isExtended ? 1U : 0U;
+        return (a * 1315423911U) ^ b;
+    }
+};
+
+/** Stable signal identifier within one logical DBC database. */
+struct SignalKey {
+    FrameKey frame;
+    std::string name;
+
+    SignalKey() = default;
+    SignalKey(FrameKey frameKey, std::string signalName)
+        : frame(frameKey), name(std::move(signalName)) {
+    }
+
+    bool operator==(const SignalKey &other) const {
+        return frame == other.frame && name == other.name;
+    }
+};
+
+struct SignalKeyHasher {
+    std::size_t operator()(const SignalKey &key) const {
+        return FrameKeyHasher()(key.frame) ^ (std::hash<std::string>()(key.name) << 1U);
+    }
+};
+
+#endif /* DEFINITION_KEY_H */