// Copyright 2022 Huawei Cloud Computing Technology Co., Ltd.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#ifndef INCLUDED_SRC_BUILDTOOL_FILE_SYSTEM_GIT_CAS_HPP
#define INCLUDED_SRC_BUILDTOOL_FILE_SYSTEM_GIT_CAS_HPP

#include <filesystem>
#include <memory>
#include <optional>
#include <shared_mutex>
#include <unordered_map>
#include <vector>

#include "src/buildtool/file_system/git_context.hpp"
#include "src/buildtool/file_system/git_utils.hpp"

class GitCAS;
using GitCASPtr = std::shared_ptr<GitCAS const>;

/// \brief Git CAS that maintains its Git context.
class GitCAS {
  public:
    static auto Open(std::filesystem::path const& repo_path) noexcept
        -> GitCASPtr;

    GitCAS() noexcept = default;
    ~GitCAS() noexcept = default;

    // 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:
    // IMPORTANT: the GitContext needs to be initialized before any git object!
    GitContext git_context_{};  // maintains a Git context while CAS is alive
    std::unique_ptr<git_odb, decltype(&odb_closer)> odb_{nullptr, odb_closer};
    // git folder path of repo
    std::filesystem::path git_path_{};

    // mutex to guard odb while setting up a "fake" repository; it needs to be
    // uniquely owned while wrapping the odb, but then git operations are free
    // to share it.
    mutable std::shared_mutex mutex_{};

    [[nodiscard]] auto OpenODB(std::filesystem::path const& repo_path) noexcept
        -> bool;

    friend class GitRepo;  // allow access to ODB
};

#endif  // INCLUDED_SRC_BUILDTOOL_FILE_SYSTEM_GIT_CAS_HPP