1 files changed, 60 insertions, 0 deletions
diff --git a/src/buildtool/file_system/git_cas.hpp b/src/buildtool/file_system/git_cas.hpp
new file mode 100644
index 00000000..d4341482
--- /dev/null
+++ b/src/buildtool/file_system/git_cas.hpp
@@ -0,0 +1,60 @@
+#ifndef INCLUDED_SRC_BUILDTOOL_FILE_SYSTEM_GIT_CAS_HPP
+#define INCLUDED_SRC_BUILDTOOL_FILE_SYSTEM_GIT_CAS_HPP
+
+#include <filesystem>
+#include <memory>
+#include <mutex>
+#include <optional>
+
+#include "src/buildtool/file_system/object_type.hpp"
+
+extern "C" {
+using git_odb = struct git_odb;
+}
+
+class GitCAS;
+using GitCASPtr = std::shared_ptr<GitCAS const>;
+
+/// \brief Git CAS that maintains its own libgit2 global state.
+class GitCAS {
+  public:
+    static auto Open(std::filesystem::path const& repo_path) noexcept
+        -> GitCASPtr;
+
+    GitCAS() noexcept;
+    ~GitCAS() noexcept;
+
+    // prohibit moves and copies
+    GitCAS(GitCAS const&) = delete;
+    GitCAS(GitCAS&& other) = delete;
+    auto operator=(GitCAS const&) = delete;
+    auto operator=(GitCAS&& other) = delete;
+
+    /// \brief Read object from CAS.
+    /// \param id         The object id.
+    /// \param is_hex_id  Specify whether `id` is hex string or raw.
+    [[nodiscard]] auto ReadObject(std::string const& id,
+                                  bool is_hex_id = false) const noexcept
+        -> std::optional<std::string>;
+
+    /// \brief Read object header from CAS.
+    /// \param id         The object id.
+    /// \param is_hex_id  Specify whether `id` is hex string or raw.
+    // Use with care. Quote from git2/odb.h:138:
+    //    Note that most backends do not support reading only the header of an
+    //    object, so the whole object will be read and then the header will be
+    //    returned.
+    [[nodiscard]] auto ReadHeader(std::string const& id,
+                                  bool is_hex_id = false) const noexcept
+        -> std::optional<std::pair<std::size_t, ObjectType>>;
+
+  private:
+    static inline std::mutex repo_mutex_{};
+    git_odb* odb_{nullptr};
+    bool initialized_{false};
+
+    [[nodiscard]] auto OpenODB(std::filesystem::path const& repo_path) noexcept
+        -> bool;
+};
+
+#endif  // INCLUDED_SRC_BUILDTOOL_FILE_SYSTEM_GIT_CAS_HPP