sqlite backend with actual pagination

1 files changed, 55 insertions, 0 deletions

diff --git a/src/InMemoryBackend.cpp b/src/InMemoryBackend.cpp
new file mode 100644
index 0000000..4d637fe
--- /dev/null
+++ b/src/InMemoryBackend.cpp
@@ -0,0 +1,55 @@
+#include "InMemoryBackend.h"
+
+#include <picosha2.h>
+#include <numeric>
+
+namespace nt
+{
+    std::string InMemoryBackend::PathKey(const std::vector<std::string>& path)
+    {
+        return std::accumulate(
+            std::next(path.begin()), path.end(), path.front(),
+            [](std::string a, const std::string& b) { return std::move(a) + "/" + b; });
+    }
+
+    std::string InMemoryBackend::Put(std::vector<uint8_t> value)
+    {
+        const std::string hash = picosha2::hash256_hex_string(value.begin(), value.end());
+        kv_.emplace(hash, std::move(value));
+        return hash;
+    }
+
+    std::optional<std::vector<uint8_t>> InMemoryBackend::Get(const std::string& hash)
+    {
+        auto it = kv_.find(hash);
+        if (it == kv_.end())
+            return std::nullopt;
+        return it->second;
+    }
+
+    void InMemoryBackend::LinkTuple(const std::vector<std::string>& relation_path,
+                                    const std::string& tuple_hash)
+    {
+        auto& hashes = index_[PathKey(relation_path)];
+        for (const auto& h : hashes)
+            if (h == tuple_hash) return;
+        hashes.push_back(tuple_hash);
+    }
+
+    std::vector<std::string> InMemoryBackend::TupleHashes(
+        const std::vector<std::string>& relation_path,
+        std::size_t offset,
+        std::size_t limit)
+    {
+        auto it = index_.find(PathKey(relation_path));
+        if (it == index_.end() || offset >= it->second.size())
+            return {};
+
+        const auto& all = it->second;
+        auto begin = all.begin() + static_cast<ptrdiff_t>(offset);
+        auto end   = (offset + limit <= all.size())
+                     ? begin + static_cast<ptrdiff_t>(limit)
+                     : all.end();
+        return { begin, end };
+    }
+}