Add lua functions to get database content

2 files changed, 61 insertions, 0 deletions

diff --git a/src/database/database.cpp b/src/database/database.cpp
index 142735d8..0967eb95 100644
--- a/src/database/database.cpp
+++ b/src/database/database.cpp
@@ -857,4 +857,48 @@ auto IndexRecord::Expand(std::size_t page_size) const
   };
 }
 
+Iterator::Iterator(std::weak_ptr<Database> db, const IndexInfo& idx)
+    : db_(db), prev_pos_(), current_pos_() {
+  std::string prefix = EncodeIndexPrefix(
+      IndexKey::Header{.id = idx.id, .depth = 0, .components_hash = 0});
+  current_pos_ = Continuation{.prefix = {prefix.data(), prefix.size()},
+                              .start_key = {prefix.data(), prefix.size()},
+                              .forward = true,
+                              .was_prev_forward = true,
+                              .page_size = 1};
+}
+
+Iterator::Iterator(std::weak_ptr<Database> db, const Continuation& c)
+    : db_(db), prev_pos_(), current_pos_(c) {}
+
+auto Iterator::Prev() -> std::optional<IndexRecord> {
+  if (!prev_pos_) {
+    return {};
+  }
+  auto db = db_.lock();
+  if (!db) {
+    return {};
+  }
+  std::unique_ptr<Result<IndexRecord>> res{
+      db->GetPage<IndexRecord>(&*prev_pos_).get()};
+  prev_pos_ = res->prev_page();
+  current_pos_ = prev_pos_;
+  return *res->values()[0];
+}
+
+auto Iterator::Next() -> std::optional<IndexRecord> {
+  if (!current_pos_) {
+    return {};
+  }
+  auto db = db_.lock();
+  if (!db) {
+    return {};
+  }
+  std::unique_ptr<Result<IndexRecord>> res{
+      db->GetPage<IndexRecord>(&*current_pos_).get()};
+  prev_pos_ = current_pos_;
+  current_pos_ = res->next_page();
+  return *res->values()[0];
+}
+
 }  // namespace database
diff --git a/src/database/include/database.hpp b/src/database/include/database.hpp
index 544e4a62..972871db 100644
--- a/src/database/include/database.hpp
+++ b/src/database/include/database.hpp
@@ -183,4 +183,21 @@ auto Database::ParseRecord<std::pmr::string>(const leveldb::Slice& key,
                                              const leveldb::Slice& val)
     -> std::shared_ptr<std::pmr::string>;
 
+/*
+ * Utility for accessing a large set of database records, one record at a time.
+ */
+class Iterator {
+ public:
+  Iterator(std::weak_ptr<Database>, const IndexInfo&);
+  Iterator(std::weak_ptr<Database>, const Continuation&);
+
+  auto Prev() -> std::optional<IndexRecord>;
+  auto Next() -> std::optional<IndexRecord>;
+
+ private:
+  std::weak_ptr<Database> db_;
+  std::optional<Continuation> prev_pos_;
+  std::optional<Continuation> current_pos_;
+};
+
 }  // namespace database