// Copyright 2023 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.

#include "src/buildtool/crypto/hash_function.hpp"

#include <cstddef>
#include <exception>
#include <fstream>
#include <limits>

#include "src/buildtool/logging/log_level.hpp"
#include "src/buildtool/logging/logger.hpp"

namespace {
[[nodiscard]] auto CreateGitTreeTag(std::size_t size) noexcept -> std::string {
    return std::string("tree ") + std::to_string(size) + '\0';
}
[[nodiscard]] auto CreateGitBlobTag(std::size_t size) noexcept -> std::string {
    return std::string("blob ") + std::to_string(size) + '\0';
}
}  // namespace

auto HashFunction::HashBlobData(std::string const& data) const noexcept
    -> Hasher::HashDigest {
    return HashTaggedLine(data, CreateGitBlobTag);
}

auto HashFunction::HashTreeData(std::string const& data) const noexcept
    -> Hasher::HashDigest {
    return HashTaggedLine(data, CreateGitTreeTag);
}

auto HashFunction::PlainHashData(std::string const& data) const noexcept
    -> Hasher::HashDigest {
    return HashTaggedLine(data, std::nullopt);
}

auto HashFunction::HashTaggedLine(std::string const& data,
                                  std::optional<TagCreator> tag_creator)
    const noexcept -> Hasher::HashDigest {
    auto hasher = MakeHasher();
    if (type_ == Type::GitSHA1 and tag_creator.has_value()) {
        hasher.Update(std::invoke(*tag_creator, data.size()));
    }
    hasher.Update(data);
    return std::move(hasher).Finalize();
}

auto HashFunction::HashBlobFile(std::filesystem::path const& path) const
    noexcept -> std::optional<std::pair<Hasher::HashDigest, std::uintmax_t>> {
    return HashTaggedFile(path, CreateGitBlobTag);
}

auto HashFunction::HashTreeFile(std::filesystem::path const& path) const
    noexcept -> std::optional<std::pair<Hasher::HashDigest, std::uintmax_t>> {
    return HashTaggedFile(path, CreateGitTreeTag);
}

auto HashFunction::HashTaggedFile(std::filesystem::path const& path,
                                  TagCreator const& tag_creator) const noexcept
    -> std::optional<std::pair<Hasher::HashDigest, std::uintmax_t>> {
    auto const size = std::filesystem::file_size(path);

    static constexpr std::size_t kChunkSize{4048};
    static_assert(kChunkSize < std::numeric_limits<std::streamsize>::max(),
                  "An overflow will occur while reading");

    auto hasher = MakeHasher();
    if (type_ == Type::GitSHA1) {
        hasher.Update(std::invoke(tag_creator, size));
    }

    try {
        auto chunk = std::string(kChunkSize, '\0');
        std::ifstream file_reader(path.string(), std::ios::binary);
        if (not file_reader.is_open()) {
            return std::nullopt;
        }

        while (file_reader.good()) {
            file_reader.read(chunk.data(),
                             static_cast<std::streamsize>(kChunkSize));

            auto const count = static_cast<std::size_t>(file_reader.gcount());
            hasher.Update(chunk.substr(0, count));
        }
        file_reader.close();
        return std::make_pair(std::move(hasher).Finalize(), size);
    } catch (std::exception const& e) {
        Logger::Log(LogLevel::Debug,
                    "Error while trying to hash {}: {}",
                    path.string(),
                    e.what());
    }
    return std::nullopt;
}
