add leveldb

1 files changed, 53 insertions, 0 deletions

diff --git a/src/database/include/table_reader.hpp b/src/database/include/table_reader.hpp
new file mode 100644
index 00000000..9f7cc4ee
--- /dev/null
+++ b/src/database/include/table_reader.hpp
@@ -0,0 +1,53 @@
+#pragma once
+
+#include <string>
+
+#include "result.hpp"
+#include "span.hpp"
+
+#include "table.hpp"
+
+namespace database {
+
+class TableReader {
+ public:
+  enum ReadError {
+    OUT_OF_RANGE,
+    IO_ERROR,
+    PARSE_ERROR,
+  };
+
+  auto ReadEntryAtIndex(Index_t index) -> cpp::result<DatabaseEntry, ReadError>;
+
+  template <typename T>
+  auto ReadColumnOffsetAtIndex(Column<T> col, Index_t index)
+      -> cpp::result<IndexOffset_t, ReadError>;
+
+  template <typename T>
+  auto ParseColumnAtIndex(Column<T> col, Index_t index)
+      -> cpp::result<T, ReadError> {
+    return ReadColumnOffsetAtIndex(col, index).map([&](IndexOffset_t offset) {
+      return ReadColumnAtOffset(col, offset);
+    });
+  }
+
+  template <typename T>
+  auto ParseColumnAtOffset(Column<T> col, IndexOffset_t offset)
+      -> cpp::result<T, ReadError> {
+    return ReadDataAtOffset(col.Filename(), offset)
+        .flat_map([&](cpp::span<std::byte> data) {
+          auto res = = col.ParseValue(data);
+          if (res) {
+            return *res;
+          } else {
+            return cpp::fail(PARSE_ERROR);
+          }
+        });
+  }
+
+ private:
+  auto ReadDataAtOffset(std::string filename, IndexOffset_t offset)
+      -> cpp::span<std::byte>;
+};
+
+}  // namespace database