1 files changed, 78 insertions, 0 deletions
diff --git a/src/MultigroupCodec.cpp b/src/MultigroupCodec.cpp
new file mode 100644
index 0000000..81d305c
--- /dev/null
+++ b/src/MultigroupCodec.cpp
@@ -0,0 +1,78 @@
+#include "MultigroupCodec.h"
+
+#include "Merkle.h"
+
+namespace nt::MultigroupCodec
+{
+    // A relation with zero tuples reports an empty merkle_root externally.
+    // The merkle tree's payload type is fixed-width Hash32, so the codec
+    // maps "" ↔ the all-zero hash. The collision probability with a real
+    // SHA256 hitting all-zero (2^-256) is treated as unreachable.
+    static nt::Hash32 encode_payload(const std::string& hex)
+    {
+        if (hex.empty()) return nt::Hash32{};
+        return nt::hex_to_bin(hex);
+    }
+
+    static std::string decode_payload(const nt::Hash32& bin)
+    {
+        static const nt::Hash32 zero{};
+        if (bin == zero) return "";
+        return nt::bin_to_hex(bin);
+    }
+
+    std::string Build(IStorageBackend& store,
+                      const std::vector<RelationEntry>& relations)
+    {
+        std::string root;
+        for (const auto& [name, root_hex] : relations)
+            root = nt::Merkle<std::string>::Insert(store, root, name,
+                                                    encode_payload(root_hex));
+        return root;
+    }
+
+    std::vector<RelationEntry> List(IStorageBackend& store,
+                                     const std::string& root_hex)
+    {
+        std::vector<RelationEntry> out;
+        constexpr size_t kPageSize = 1024;
+        size_t offset = 0;
+        while (true)
+        {
+            auto page = nt::Merkle<std::string>::Page(store, root_hex,
+                                                      offset, kPageSize);
+            if (page.empty()) break;
+            for (auto& entry : page)
+                out.emplace_back(std::move(entry.key),
+                                  decode_payload(entry.payload));
+            if (page.size() < kPageSize) break;
+            offset += page.size();
+        }
+        return out;
+    }
+
+    std::string InsertOne(IStorageBackend& store,
+                          const std::string& root_hex,
+                          const std::string& relation_name,
+                          const std::string& relation_root_hex)
+    {
+        return nt::Merkle<std::string>::Insert(store, root_hex, relation_name,
+                                                encode_payload(relation_root_hex));
+    }
+
+    std::string RemoveOne(IStorageBackend& store,
+                          const std::string& root_hex,
+                          const std::string& relation_name)
+    {
+        return nt::Merkle<std::string>::Remove(store, root_hex, relation_name);
+    }
+
+    std::string Lookup(IStorageBackend& store,
+                       const std::string& root_hex,
+                       const std::string& relation_name)
+    {
+        auto found = nt::Merkle<std::string>::Get(store, root_hex, relation_name);
+        if (!found) return "";
+        return decode_payload(*found);
+    }
+}