#include "src/buildtool/file_system/git_cas.hpp"

#include <mutex>
#include <sstream>

#include "src/buildtool/file_system/file_system_manager.hpp"
#include "src/buildtool/logging/logger.hpp"
#include "src/utils/cpp/hex_string.hpp"

extern "C" {
#include <git2.h>
}

namespace {

constexpr auto kOIDRawSize{GIT_OID_RAWSZ};
constexpr auto kOIDHexSize{GIT_OID_HEXSZ};

[[nodiscard]] auto GitLastError() noexcept -> std::string {
    git_error const* err{nullptr};
    if ((err = git_error_last()) != nullptr and err->message != nullptr) {
        return fmt::format("error code {}: {}", err->klass, err->message);
    }
    return "<unknown error>";
}

[[nodiscard]] auto GitObjectID(std::string const& id,
                               bool is_hex_id = false) noexcept
    -> std::optional<git_oid> {
#ifndef BOOTSTRAP_BUILD_TOOL
    if (id.size() < (is_hex_id ? kOIDHexSize : kOIDRawSize)) {
        Logger::Log(LogLevel::Error,
                    "invalid git object id {}",
                    is_hex_id ? id : ToHexString(id));
        return std::nullopt;
    }
    git_oid oid{};
    if (is_hex_id and git_oid_fromstr(&oid, id.c_str()) == 0) {
        return oid;
    }
    if (not is_hex_id and
        git_oid_fromraw(
            &oid,
            reinterpret_cast<unsigned char const*>(id.data())  // NOLINT
            ) == 0) {
        return oid;
    }
    Logger::Log(LogLevel::Error,
                "parsing git object id {} failed with:\n{}",
                is_hex_id ? id : ToHexString(id),
                GitLastError());
#endif
    return std::nullopt;
}

[[nodiscard]] auto ToHexString(git_oid const& oid) noexcept
    -> std::optional<std::string> {
    std::string hex_id(GIT_OID_HEXSZ, '\0');
#ifndef BOOTSTRAP_BUILD_TOOL
    if (git_oid_fmt(hex_id.data(), &oid) != 0) {
        return std::nullopt;
    }
#endif
    return hex_id;
}

[[nodiscard]] auto ToRawString(git_oid const& oid) noexcept
    -> std::optional<std::string> {
    if (auto hex_id = ToHexString(oid)) {
        return FromHexString(*hex_id);
    }
    return std::nullopt;
}

[[nodiscard]] auto GitFileModeToObjectType(git_filemode_t const& mode) noexcept
    -> std::optional<ObjectType> {
    switch (mode) {
        case GIT_FILEMODE_BLOB:
            return ObjectType::File;
        case GIT_FILEMODE_BLOB_EXECUTABLE:
            return ObjectType::Executable;
        case GIT_FILEMODE_TREE:
            return ObjectType::Tree;
        default: {
            std::ostringstream str;
            str << std::oct << static_cast<int>(mode);
            Logger::Log(
                LogLevel::Error, "unsupported git filemode {}", str.str());
            return std::nullopt;
        }
    }
}

[[nodiscard]] auto GitTypeToObjectType(git_object_t const& type) noexcept
    -> std::optional<ObjectType> {
    switch (type) {
        case GIT_OBJECT_BLOB:
            return ObjectType::File;
        case GIT_OBJECT_TREE:
            return ObjectType::Tree;
        default:
            Logger::Log(LogLevel::Error,
                        "unsupported git object type {}",
                        git_object_type2string(type));
            return std::nullopt;
    }
}

[[maybe_unused]] [[nodiscard]] auto ValidateEntries(
    GitCAS::tree_entries_t const& entries) -> bool {
    return std::all_of(entries.begin(), entries.end(), [](auto entry) {
        auto const& [id, nodes] = entry;
        // for a given raw id, either all entries are trees or none of them
        return std::all_of(
                   nodes.begin(),
                   nodes.end(),
                   [](auto entry) { return IsTreeObject(entry.type); }) or
               std::none_of(nodes.begin(), nodes.end(), [](auto entry) {
                   return IsTreeObject(entry.type);
               });
    });
}

auto const repo_closer = [](gsl::owner<git_repository*> repo) {
    if (repo != nullptr) {
        git_repository_free(repo);
    }
};

auto const tree_closer = [](gsl::owner<git_tree*> tree) {
    if (tree != nullptr) {
        git_tree_free(tree);
    }
};

[[nodiscard]] auto flat_tree_walker(const char* /*root*/,
                                    const git_tree_entry* entry,
                                    void* payload) noexcept -> int {
    auto* entries =
        reinterpret_cast<GitCAS::tree_entries_t*>(payload);  // NOLINT

    std::string name = git_tree_entry_name(entry);
    auto const* oid = git_tree_entry_id(entry);
    if (auto raw_id = ToRawString(*oid)) {
        if (auto type =
                GitFileModeToObjectType(git_tree_entry_filemode(entry))) {
            (*entries)[*raw_id].emplace_back(std::move(name), *type);
            return 1;  // return >=0 on success, 1 == skip subtrees (flat)
        }
    }
    return -1;  // fail
}

}  // namespace

auto GitCAS::Open(std::filesystem::path const& repo_path) noexcept
    -> GitCASPtr {
#ifndef BOOTSTRAP_BUILD_TOOL
    try {
        auto cas = std::make_shared<GitCAS>();
        if (cas->OpenODB(repo_path)) {
            return std::static_pointer_cast<GitCAS const>(cas);
        }
    } catch (std::exception const& ex) {
        Logger::Log(LogLevel::Error,
                    "opening git object database failed with:\n{}",
                    ex.what());
    }
#endif
    return nullptr;
}

GitCAS::GitCAS() noexcept {
#ifndef BOOTSTRAP_BUILD_TOOL
    if (not(initialized_ = (git_libgit2_init() >= 0))) {
        Logger::Log(LogLevel::Error, "initializing libgit2 failed");
    }
#endif
}
GitCAS::~GitCAS() noexcept {
#ifndef BOOTSTRAP_BUILD_TOOL
    if (odb_ != nullptr) {
        git_odb_free(odb_);
        odb_ = nullptr;
    }
    if (initialized_) {
        git_libgit2_shutdown();
    }
#endif
}

auto GitCAS::ReadObject(std::string const& id, bool is_hex_id) const noexcept
    -> std::optional<std::string> {
#ifdef BOOTSTRAP_BUILD_TOOL
    return std::nullopt;
#else
    if (not initialized_) {
        return std::nullopt;
    }

    auto oid = GitObjectID(id, is_hex_id);
    if (not oid) {
        return std::nullopt;
    }

    git_odb_object* obj = nullptr;
    if (git_odb_read(&obj, odb_, &oid.value()) != 0) {
        Logger::Log(LogLevel::Error,
                    "reading git object {} from database failed with:\n{}",
                    is_hex_id ? id : ToHexString(id),
                    GitLastError());
        return std::nullopt;
    }

    std::string data(static_cast<char const*>(git_odb_object_data(obj)),
                     git_odb_object_size(obj));
    git_odb_object_free(obj);

    return data;
#endif
}

auto GitCAS::ReadTree(std::string const& id, bool is_hex_id) const noexcept
    -> std::optional<tree_entries_t> {
#ifdef BOOTSTRAP_BUILD_TOOL
    return std::nullopt;
#else
    // create object id
    auto oid = GitObjectID(id, is_hex_id);
    if (not oid) {
        return std::nullopt;
    }

    // create fake repository from ODB
    git_repository* repo_ptr{nullptr};
    if (git_repository_wrap_odb(&repo_ptr, odb_) != 0) {
        Logger::Log(LogLevel::Debug,
                    "failed to create fake Git repository from object db");
        return std::nullopt;
    }
    auto fake_repo = std::unique_ptr<git_repository, decltype(repo_closer)>{
        repo_ptr, repo_closer};

    // lookup tree
    git_tree* tree_ptr{nullptr};
    if (git_tree_lookup(&tree_ptr, fake_repo.get(), &(*oid)) != 0) {
        Logger::Log(LogLevel::Debug,
                    "failed to lookup Git tree {}",
                    is_hex_id ? std::string{id} : ToHexString(id));
        return std::nullopt;
    }
    auto tree =
        std::unique_ptr<git_tree, decltype(tree_closer)>{tree_ptr, tree_closer};

    // walk tree (flat) and create entries
    tree_entries_t entries{};
    entries.reserve(git_tree_entrycount(tree.get()));
    if (git_tree_walk(
            tree.get(), GIT_TREEWALK_PRE, flat_tree_walker, &entries) != 0) {
        Logger::Log(LogLevel::Debug,
                    "failed to walk Git tree {}",
                    is_hex_id ? std::string{id} : ToHexString(id));
        return std::nullopt;
    }

    gsl_EnsuresAudit(ValidateEntries(entries));

    return entries;
#endif
}

auto GitCAS::ReadHeader(std::string const& id, bool is_hex_id) const noexcept
    -> std::optional<std::pair<std::size_t, ObjectType>> {
#ifndef BOOTSTRAP_BUILD_TOOL
    if (not initialized_) {
        return std::nullopt;
    }

    auto oid = GitObjectID(id, is_hex_id);
    if (not oid) {
        return std::nullopt;
    }

    std::size_t size{};
    git_object_t type{};
    if (git_odb_read_header(&size, &type, odb_, &oid.value()) != 0) {
        Logger::Log(LogLevel::Error,
                    "reading git object header {} from database failed "
                    "with:\n{}",
                    is_hex_id ? id : ToHexString(id),
                    GitLastError());
        return std::nullopt;
    }

    if (auto obj_type = GitTypeToObjectType(type)) {
        return std::make_pair(size, *obj_type);
    }
#endif
    return std::nullopt;
}

auto GitCAS::OpenODB(std::filesystem::path const& repo_path) noexcept -> bool {
    static std::mutex repo_mutex{};
#ifdef BOOTSTRAP_BUILD_TOOL
    return false;
#else
    if (initialized_) {
        {  // lock as git_repository API has no thread-safety guarantees
            std::unique_lock lock{repo_mutex};
            git_repository* repo = nullptr;
            if (git_repository_open(&repo, repo_path.c_str()) != 0) {
                Logger::Log(LogLevel::Error,
                            "opening git repository {} failed with:\n{}",
                            repo_path.string(),
                            GitLastError());
                return false;
            }
            git_repository_odb(&odb_, repo);
            git_repository_free(repo);
        }
        if (odb_ == nullptr) {
            Logger::Log(LogLevel::Error,
                        "obtaining git object database {} failed with:\n{}",
                        repo_path.string(),
                        GitLastError());
            return false;
        }
    }
    return initialized_;
#endif
}