feat: Extraction basics (#1733)

For #1596

src/etlng/ExtractorInterface.hpp

@@ -0,0 +1,54 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2024, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#pragma once
+
+#include "etlng/Models.hpp"
+
+#include <cstdint>
+#include <optional>
+
+namespace etlng {
+
+/**
+ * @brief An interface for the Extractor
+ */
+struct ExtractorInterface {
+    virtual ~ExtractorInterface() = default;
+
+    /**
+     * @brief Extract diff data for a particular ledger
+     *
+     * @param seq sequence of the ledger to extract
+     * @return Ledger data diff between sequence and parent if available
+     */
+    [[nodiscard]] virtual std::optional<model::LedgerData>
+    extractLedgerWithDiff(uint32_t seq) = 0;
+
+    /**
+     * @brief Extract data for a particular ledger
+     *
+     * @param seq sequence of the ledger to extract
+     * @return Ledger header and transaction+metadata blobs if available
+     */
+    [[nodiscard]] virtual std::optional<model::LedgerData>
+    extractLedgerOnly(uint32_t seq) = 0;
+};
+
+}  // namespace etlng