// Copyright Contributors to the DNF5 project.
// Copyright Contributors to the libdnf project.
// SPDX-License-Identifier: LGPL-2.1-or-later
//
// This file is part of libdnf: https://github.com/rpm-software-management/libdnf/
//
// Libdnf is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 2.1 of the License, or
// (at your option) any later version.
//
// Libdnf is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with libdnf.  If not, see <https://www.gnu.org/licenses/>.

#ifndef _GNU_SOURCE
// For renameat2()
#define _GNU_SOURCE 1
#endif

#include "libdnf5/logger/rotating_file_logger.hpp"

#include "libdnf5/utils/bgettext/bgettext-mark-domain.h"

#include <fcntl.h>
#include <fmt/format.h>
#include <stdio.h>
#include <string.h>
#ifdef HAVE_LIBACL
#include <sys/acl.h>
#include <sys/types.h>
#endif
#include <sys/file.h>
#include <sys/stat.h>
#include <unistd.h>

#include <mutex>

namespace libdnf5 {

const int LOG_FILE_OPEN_FLAGS = O_WRONLY | O_APPEND | O_CREAT | O_CLOEXEC;
const mode_t LOG_FILE_OPEN_MODE = S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH;

class RotatingFileLogger::Impl {
public:
    explicit Impl(const std::filesystem::path & base_file_path, std::size_t max_bytes, std::size_t backup_count);
    ~Impl();

    void write(const char * line) noexcept;

private:
    bool should_rotate(std::size_t msg_len) const noexcept;

    const std::filesystem::path base_file_path;
    const std::size_t max_bytes;
    const std::size_t backup_count;

    std::mutex stream_mutex;

    int log_file_fd{-1};
};


RotatingFileLogger::Impl::Impl(
    const std::filesystem::path & base_file_path, std::size_t max_bytes, std::size_t backup_count)
    : base_file_path{base_file_path},
      max_bytes{max_bytes},
      backup_count{backup_count},
      log_file_fd(::open(base_file_path.c_str(), LOG_FILE_OPEN_FLAGS, LOG_FILE_OPEN_MODE)) {
    if (log_file_fd == -1) {
        throw FileSystemError(errno, base_file_path, M_("Cannot open log file"));
    }
}


RotatingFileLogger::Impl::~Impl() {
    if (log_file_fd != -1) {
        ::close(log_file_fd);
    }
}

namespace {
// Copy file mode and POSIX access control list from a file descriptor to
// a file descriptor.
// @return true on success, false otherwise.
bool copy_mode(int from, int to) {
    bool success = true;
    // File mode
    struct stat stat;
    if (fstat(from, &stat))
        return false;
    if (fchmod(to, 07777 & stat.st_mode) != 0)
        success = false;
#ifdef HAVE_LIBACL
    // ACL
    auto acl = acl_get_fd(from);
    if (!acl) {
        // Handle file systems which do not support ACL gracefully
        if (errno != ENOTSUP)
            success = false;
        return success;
    }
    if (acl_set_fd(to, acl) != 0)
        success = false;
    acl_free((void *)acl);
#endif
    return success;
}
}  // namespace

void RotatingFileLogger::Impl::write(const char * line) noexcept {
    try {
        // required for thread safety
        std::lock_guard<std::mutex> guard(stream_mutex);

        auto line_len = strlen(line);
        while (true) {
            if (log_file_fd == -1) {
                // something is terribly wrong, cannot log
                return;
            }

            // acquire log file lock
            ::flock(log_file_fd, LOCK_EX);

            // verify that the log file has not been rotated by another process
            auto check_file_fd = ::open(base_file_path.c_str(), O_RDONLY | O_CLOEXEC);
            if (check_file_fd == -1) {
                // try to create log file in case it was removed by another process
                auto log_file_fd_tmp = ::open(base_file_path.c_str(), LOG_FILE_OPEN_FLAGS, LOG_FILE_OPEN_MODE);
                if (log_file_fd_tmp != -1) {
                    // log file created, update log_file_fd and retry
                    copy_mode(log_file_fd, log_file_fd_tmp);
                    ::close(log_file_fd);
                    log_file_fd = log_file_fd_tmp;
                    continue;
                }
                // cannot create the log file - this can mean that libdnf5 is
                // inside the rpm transaction which enters the chroot changing
                // path resolution. In such case just use log_file_fd without
                // checking rotation.
            } else {
                // check that log_file_fd and check_file_fd belong to the same inode
                struct stat log_fd_stat;
                struct stat check_fd_stat;
                if (::fstat(log_file_fd, &log_fd_stat) == -1 || fstat(check_file_fd, &check_fd_stat) == -1) {
                    // something went wrong, cannot stat log file.
                    // Close file descriptors and return
                    ::close(check_file_fd);
                    ::close(log_file_fd);
                    log_file_fd = -1;
                    return;
                }
                ::close(check_file_fd);
                if (log_fd_stat.st_ino != check_fd_stat.st_ino) {
                    // log file descriptor belongs to another file than base_file_path.
                    // Probably the log file was renamed manually and recreated by another process.

                    // Re-open log_file_fd and try again
                    ::close(log_file_fd);
                    log_file_fd = ::open(base_file_path.c_str(), LOG_FILE_OPEN_FLAGS, LOG_FILE_OPEN_MODE);
                    continue;
                }
                if (should_rotate(line_len)) {
                    // A log file rotation is needed and so far no one has done it.
                    try {
                        // Let's rotate the files but the last one
                        for (auto file_idx = backup_count; file_idx > 1; --file_idx) {
                            auto path_old = file_idx > 1 ? fmt::format("{}.{}", base_file_path.string(), file_idx - 1)
                                                         : base_file_path.string();
                            auto path_new = fmt::format("{}.{}", base_file_path.string(), file_idx);
                            ::rename(path_old.c_str(), path_new.c_str());
                        }

                        // Preperate a new log file, with rotated name, copied file
                        // mode, and held lock. Truncate the file in case
                        // a strayed file of the name existed before.
                        // The file will be atomically swapped with the
                        // current log file later.
                        auto new_name = fmt::format("{}.1", base_file_path.string());
                        int new_fd = ::open(new_name.c_str(), LOG_FILE_OPEN_FLAGS | O_TRUNC, LOG_FILE_OPEN_MODE);
                        if (new_fd != -1) {
                            copy_mode(log_file_fd, new_fd);
                            ::flock(new_fd, LOCK_EX);

                            // Rotate the last file by atomically swapping it with
                            // the prepared file.
                            if (!renameat2(
                                    AT_FDCWD,
                                    base_file_path.string().c_str(),
                                    AT_FDCWD,
                                    new_name.c_str(),
                                    RENAME_EXCHANGE)) {
                                ::close(log_file_fd);
                                log_file_fd = new_fd;
                            } else {
                                ::close(new_fd);
                            }
                        }
                    } catch (...) {
                    }

                    // and proceed with writing regardless the rotation
                    // succeded, or not.
                }
            }

            // write the log line
            std::size_t written = 0;
            ssize_t ret;
            do {
                ret = ::write(log_file_fd, line + written, line_len - written);
                if (ret <= 0) {
                    break;
                }
                written += static_cast<std::size_t>(ret);
            } while (written < line_len);

            // we are done, unlock the log_file_fd and return
            ::flock(log_file_fd, LOCK_UN);
            return;
        }
    } catch (...) {
    }
}


bool RotatingFileLogger::Impl::should_rotate(std::size_t msg_len) const noexcept {
    if (max_bytes == 0 || backup_count < 1) {
        return false;
    }
    auto len = ::lseek(log_file_fd, 0, SEEK_END);
    if (len < 0) {
        // error
        return false;
    }
    if (len == 0) {
        // file is empty, rotation makes no sense
        return false;
    }
    return static_cast<std::size_t>(len) + msg_len > max_bytes;
}


RotatingFileLogger::RotatingFileLogger(
    const std::filesystem::path & base_file_path, std::size_t max_bytes, std::size_t backup_count)
    : p_impl(new Impl(base_file_path, max_bytes, backup_count)) {}


RotatingFileLogger::~RotatingFileLogger() = default;


void RotatingFileLogger::write(const char * line) noexcept {
    p_impl->write(line);
}

}  // namespace libdnf5