//  MIT License
//
//  Copyright(c) 2017 Thomas Monkman
//
//  Permission is hereby granted, free of charge, to any person obtaining a copy
//  of this software and associated documentation files(the "Software"), to deal
//  in the Software without restriction, including without limitation the rights
//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
//  copies of the Software, and to permit persons to whom the Software is
//  furnished to do so, subject to the following conditions :
//
//  The above copyright notice and this permission notice shall be included in all
//  copies or substantial portions of the Software.
//
//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.IN NO EVENT SHALL THE
//  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
//  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
//  SOFTWARE.

#ifndef FILEWATCHER_H
#define FILEWATCHER_H

#ifdef _WIN32
#define WIN32_LEAN_AND_MEAN
#define stat _stat
#ifndef NOMINMAX
#define NOMINMAX
#endif
#include <windows.h>
#include <stdlib.h>
#include <stdio.h>
#include <tchar.h>
#include <Pathcch.h>
#include <shlwapi.h>
#endif // WIN32

#if __unix__
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/inotify.h>
#include <sys/stat.h>
#include <unistd.h>
#endif // __unix__

#include <algorithm>
#include <array>
#include <atomic>
#include <chrono>
#include <condition_variable>
#include <functional>
#include <future>
#include <iostream>
#include <map>
#include <mutex>
#include <regex>
#include <string>
#include <system_error>
#include <thread>
#include <type_traits>
#include <utility>
#include <vector>

namespace filewatch {
    enum class Event {
        added,
        removed,
        modified,
        renamed_old,
        renamed_new
    };

    /**
    * \class FileWatch
    *
    * \brief Watches a folder or file, and will notify of changes via function callback.
    *
    * \author Thomas Monkman
    *
    */
    template<class T>
    class FileWatch
    {
        typedef typename T::value_type C;
        typedef std::basic_string<C, std::char_traits<C>> UnderpinningString;
        typedef std::basic_regex<C, std::regex_traits<C>> UnderpinningRegex;

    public:

        FileWatch(T path, UnderpinningRegex pattern, std::function<void(const T& file, const Event event_type)> callback) :
            _path(path),
            _pattern(pattern),
            _callback(callback),
            _directory(get_directory(path))
        {
            init();
        }

        FileWatch(T path, std::function<void(const T& file, const Event event_type)> callback) :
            FileWatch<T>(path, UnderpinningRegex(_regex_all), callback) {}

        ~FileWatch() {
            destroy();
        }

        FileWatch(const FileWatch<T>& other) : FileWatch<T>(other._path, other._callback) {}

        FileWatch<T>& operator=(const FileWatch<T>& other)
        {
            if (this == &other) { return *this; }

            destroy();
            _path = other._path;
            _callback = other._callback;
            _directory = get_directory(other._path);
            init();
            return *this;
        }

        // Const memeber varibles don't let me implent moves nicely, if moves are really wanted std::unique_ptr should be used and move that.
        FileWatch<T>(FileWatch<T>&&) = delete;
        FileWatch<T>& operator=(FileWatch<T>&&) & = delete;

    private:
        static constexpr C _regex_all[] = { '.', '*', '\0' };
        static constexpr C _this_directory[] = { '.', '/', '\0' };

        struct PathParts
        {
            PathParts(T directory, T filename) : directory(directory), filename(filename) {}
            T directory;
            T filename;
        };
        const T _path;

        UnderpinningRegex _pattern;

        static constexpr std::size_t _buffer_size = { 1024 * 256 };

        // only used if watch a single file
        bool _watching_single_file = { false };
        T _filename;

        std::atomic<bool> _destory = { false };
        std::function<void(const T& file, const Event event_type)> _callback;

        std::thread _watch_thread;

        std::condition_variable _cv;
        std::mutex _callback_mutex;
        std::vector<std::pair<T, Event>> _callback_information;
        std::thread _callback_thread;

        std::promise<void> _running;

        std::chrono::time_point<std::chrono::system_clock> last_write_time_;
        unsigned long last_size_;

#ifdef _WIN32
        HANDLE _directory = { nullptr };
        HANDLE _close_event = { nullptr };

        const DWORD _listen_filters =
            FILE_NOTIFY_CHANGE_SECURITY |
            FILE_NOTIFY_CHANGE_CREATION |
            FILE_NOTIFY_CHANGE_LAST_ACCESS |
            FILE_NOTIFY_CHANGE_LAST_WRITE |
            FILE_NOTIFY_CHANGE_SIZE |
            FILE_NOTIFY_CHANGE_ATTRIBUTES |
            FILE_NOTIFY_CHANGE_DIR_NAME |
            FILE_NOTIFY_CHANGE_FILE_NAME;

        const std::map<DWORD, Event> _event_type_mapping = {
            { FILE_ACTION_ADDED, Event::added },
            { FILE_ACTION_REMOVED, Event::removed },
            { FILE_ACTION_MODIFIED, Event::modified },
            { FILE_ACTION_RENAMED_OLD_NAME, Event::renamed_old },
            { FILE_ACTION_RENAMED_NEW_NAME, Event::renamed_new }
        };

        // time epoch translation
        std::pair<ULARGE_INTEGER, std::chrono::time_point<std::chrono::system_clock>> base_;
#endif // WIN32

#if __unix__
        struct FolderInfo {
            int folder;
            int watch;
        };

        FolderInfo  _directory;

        const std::uint32_t _listen_filters = IN_MODIFY | IN_CREATE | IN_DELETE;

        const static std::size_t event_size = (sizeof(struct inotify_event));
#endif // __unix__

        void init()
        {
#ifdef _WIN32
            _close_event = CreateEvent(NULL, TRUE, FALSE, NULL);
            if (!_close_event) {
                throw std::system_error(GetLastError(), std::system_category());
            }
#endif // WIN32
            _callback_thread = std::move(std::thread([this]() {
                try {
                    callback_thread();
                } catch (...) {
                    try {
                        _running.set_exception(std::current_exception());
                    }
                    catch (...) {} // set_exception() may throw too
                }
            }));
            _watch_thread = std::move(std::thread([this]() {
                try {
                    monitor_directory();
                } catch (...) {
                    try {
                        _running.set_exception(std::current_exception());
                    }
                    catch (...) {} // set_exception() may throw too
                }
            }));

            std::future<void> future = _running.get_future();
            future.get(); //block until the monitor_directory is up and running
        }

        void destroy()
        {
            _destory = true;
            _running = std::promise<void>();
#ifdef _WIN32
            SetEvent(_close_event);
#elif __unix__
            inotify_rm_watch(_directory.folder, _directory.watch);
#endif // __unix__
            _cv.notify_all();
            _watch_thread.join();
            _callback_thread.join();
#ifdef _WIN32
            CloseHandle(_directory);
#elif __unix__
            close(_directory.folder);
#endif // __unix__
        }

        const PathParts split_directory_and_file(const T& path) const
        {
            const auto predict = [](C character) {
#ifdef _WIN32
                return character == C('\\') || character == C('/');
#elif __unix__
                return character == C('/');
#endif // __unix__
            };

            UnderpinningString path_string = path;
            const auto pivot = std::find_if(path_string.rbegin(), path_string.rend(), predict).base();
            //if the path is something like "test.txt" there will be no directory part, however we still need one, so insert './'
            const T directory = [&]() {
                const auto extracted_directory = UnderpinningString(path_string.begin(), pivot);
                return (extracted_directory.size() > 0) ? extracted_directory : UnderpinningString(_this_directory);
            }();
            const T filename = UnderpinningString(pivot, path_string.end());
            return PathParts(directory, filename);
        }

        bool pass_filter(const UnderpinningString& file_path)
        {
            if (_watching_single_file) {
                const UnderpinningString extracted_filename = { split_directory_and_file(file_path).filename };
                //if we are watching a single file, only that file should trigger action
                return extracted_filename == _filename;
            }
            return std::regex_match(file_path, _pattern);
        }

#ifdef _WIN32
        template<typename... Args> DWORD GetFileAttributesX(const char* lpFileName, Args... args) {
            return GetFileAttributesA(lpFileName, args...);
        }
        template<typename... Args> DWORD GetFileAttributesX(const wchar_t* lpFileName, Args... args) {
            return GetFileAttributesW(lpFileName, args...);
        }

        template<typename... Args> HANDLE CreateFileX(const char* lpFileName, Args... args) {
            return CreateFileA(lpFileName, args...);
        }
        template<typename... Args> HANDLE CreateFileX(const wchar_t* lpFileName, Args... args) {
            return CreateFileW(lpFileName, args...);
        }

        HANDLE get_directory(const T& path)
        {
            auto file_info = GetFileAttributesX(path.c_str());

            if (file_info == INVALID_FILE_ATTRIBUTES)
            {
                throw std::system_error(GetLastError(), std::system_category());
            }
            _watching_single_file = (file_info & FILE_ATTRIBUTE_DIRECTORY) == false;

            const T watch_path = [this, &path]() {
                if (_watching_single_file)
                {
                    const auto parsed_path = split_directory_and_file(path);
                    _filename = parsed_path.filename;
                    return parsed_path.directory;
                }
                else
                {
                    return path;
                }
            }();

            HANDLE directory = CreateFileX(
                watch_path.c_str(),           // pointer to the file name
                FILE_LIST_DIRECTORY,    // access (read/write) mode
                FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE, // share mode
                nullptr, // security descriptor
                OPEN_EXISTING,         // how to create
                FILE_FLAG_BACKUP_SEMANTICS | FILE_FLAG_OVERLAPPED, // file attributes
                HANDLE(0));                 // file with attributes to copy

            if (directory == INVALID_HANDLE_VALUE)
            {
                throw std::system_error(GetLastError(), std::system_category());
            }

            init_last_write_time();

            return directory;
        }

        void convert_wstring(const std::wstring& wstr, std::string& out)
        {
            int size_needed = WideCharToMultiByte(CP_UTF8, 0, &wstr[0], (int)wstr.size(), NULL, 0, NULL, NULL);
            out.resize(size_needed, '\0');
            WideCharToMultiByte(CP_UTF8, 0, &wstr[0], (int)wstr.size(), &out[0], size_needed, NULL, NULL);
        }

        void convert_wstring(const std::wstring& wstr, std::wstring& out)
        {
            out = wstr;
        }

        void monitor_directory()
        {
            std::vector<BYTE> buffer(_buffer_size);
            DWORD bytes_returned = 0;
            OVERLAPPED overlapped_buffer{ 0 };

            overlapped_buffer.hEvent = CreateEvent(NULL, TRUE, FALSE, NULL);
            if (!overlapped_buffer.hEvent) {
                std::cerr << "Error creating monitor event" << std::endl;
            }

            std::array<HANDLE, 2> handles{ overlapped_buffer.hEvent, _close_event };

            auto async_pending = false;
            _running.set_value();
            do {
                std::vector<std::pair<T, Event>> parsed_information;
                ReadDirectoryChangesW(
                    _directory,
                    buffer.data(), static_cast<DWORD>(buffer.size()),
                    TRUE,
                    _listen_filters,
                    &bytes_returned,
                    &overlapped_buffer, NULL);

                async_pending = true;

                switch (WaitForMultipleObjects(2, handles.data(), FALSE, INFINITE))
                {
                case WAIT_OBJECT_0:
                {
                    if (!GetOverlappedResult(_directory, &overlapped_buffer, &bytes_returned, TRUE)) {
                        throw std::system_error(GetLastError(), std::system_category());
                    }
                    async_pending = false;

                    // Get current time
                    _WIN32_FILE_ATTRIBUTE_DATA att;
                    GetFileAttributesExA(_path.c_str(), GetFileExInfoStandard, &att);

                    unsigned long current_size = att.nFileSizeLow;
                    auto current_time = base_.second
                        + std::chrono::duration<
                                typename std::chrono::time_point<std::chrono::system_clock>::rep,
                                std::ratio_multiply<std::hecto, typename std::chrono::nanoseconds::period>>(
                                    reinterpret_cast<ULARGE_INTEGER*>(&att.ftLastWriteTime)->QuadPart - base_.first.QuadPart);

                    if (bytes_returned == 0 || (current_time == last_write_time_) && current_size == last_size_ ) {
                        break;
                    }

                    FILE_NOTIFY_INFORMATION *file_information = reinterpret_cast<FILE_NOTIFY_INFORMATION*>(&buffer[0]);
                    do
                    {
                        std::wstring changed_file_w{ file_information->FileName, file_information->FileNameLength / sizeof(file_information->FileName[0]) };
                        UnderpinningString changed_file;
                        convert_wstring(changed_file_w, changed_file);
                        if (pass_filter(changed_file))
                        {
                            parsed_information.emplace_back(T{ changed_file }, _event_type_mapping.at(file_information->Action));
                        }

                        last_write_time_ = current_time;
                        last_size_ = current_size;

                        if (file_information->NextEntryOffset == 0) {
                            break;
                        }

                        file_information = reinterpret_cast<FILE_NOTIFY_INFORMATION*>(reinterpret_cast<BYTE*>(file_information) + file_information->NextEntryOffset);
                    } while (true);
                    break;
                }
                case WAIT_OBJECT_0 + 1:
                    // quit
                    break;
                case WAIT_FAILED:
                    break;
                }
                //dispatch callbacks
                {
                    std::lock_guard<std::mutex> lock(_callback_mutex);
                    _callback_information.insert(_callback_information.end(), parsed_information.begin(), parsed_information.end());
                }
                _cv.notify_all();
            } while (_destory == false);

            if (async_pending)
            {
                //clean up running async io
                CancelIo(_directory);
                GetOverlappedResult(_directory, &overlapped_buffer, &bytes_returned, TRUE);
            }
        }
#endif // WIN32

#if __unix__

        bool is_file(const T& path) const
        {
            struct stat statbuf = {};
            if (stat(path.c_str(), &statbuf) != 0)
            {
                throw std::system_error(errno, std::system_category());
            }
            return S_ISREG(statbuf.st_mode);
        }

        FolderInfo get_directory(const T& path)
        {
            const auto folder = inotify_init();
            if (folder < 0)
            {
                throw std::system_error(errno, std::system_category());
            }
            //const auto listen_filters = _listen_filters;

            _watching_single_file = is_file(path);

            const T watch_path = [this, &path]() {
                if (_watching_single_file)
                {
                    const auto parsed_path = split_directory_and_file(path);
                    _filename = parsed_path.filename;
                    return parsed_path.directory;
                }
                else
                {
                    return path;
                }
            }();

            const auto watch = inotify_add_watch(folder, watch_path.c_str(), IN_MODIFY | IN_CREATE | IN_DELETE );
            if (watch < 0)
            {
                throw std::system_error(errno, std::system_category());
            }

            init_last_write_time();

            return { folder, watch };
        }

        void monitor_directory()
        {
            std::vector<char> buffer(_buffer_size);

            _running.set_value();
            while (_destory == false)
            {
                const auto length = read(_directory.folder, static_cast<void*>(buffer.data()), buffer.size());

                struct stat result;
                stat(_path.c_str(), &result);

                using clock = std::chrono::system_clock;
                using duration = clock::duration;
                std::chrono::time_point<clock> current_time;
                current_time += std::chrono::duration_cast<duration>(std::chrono::seconds(result.st_mtim.tv_sec));
                current_time += std::chrono::duration_cast<duration>(std::chrono::nanoseconds(result.st_mtim.tv_nsec));

                unsigned long current_size = result.st_size;

                if (length > 0 && (current_time != last_write_time_ || current_size != last_size_))
                {
                    int i = 0;
                    last_write_time_ = current_time;
                    last_size_ = current_size;
                    std::vector<std::pair<T, Event>> parsed_information;
                    bool already_modified = false;
                    while (i < length)
                    {
                        struct inotify_event *event = reinterpret_cast<struct inotify_event *>(&buffer[i]); // NOLINT
                        if (event->len)
                        {
                            const UnderpinningString changed_file{ event->name };
                            if (pass_filter(changed_file))
                            {
                                if (event->mask & IN_CREATE)
                                {
                                    parsed_information.emplace_back(T{ changed_file }, Event::added);
                                }
                                else if (event->mask & IN_DELETE)
                                {
                                    parsed_information.emplace_back(T{ changed_file }, Event::removed);
                                }
                                else if (event->mask & IN_MODIFY && !already_modified)
                                {
                                    already_modified = true;
                                    parsed_information.emplace_back(T{ changed_file }, Event::modified);
                                }
                            }
                        }
                        i += event_size + event->len;
                    }
                    //dispatch callbacks
                    {
                        std::lock_guard<std::mutex> lock(_callback_mutex);
                        _callback_information.insert(_callback_information.end(), parsed_information.begin(), parsed_information.end());
                    }
                    _cv.notify_all();
                }
            }
        }
#endif // __unix__

        void callback_thread()
        {
            while (_destory == false) {
                std::unique_lock<std::mutex> lock(_callback_mutex);
                if (_callback_information.empty() && _destory == false) {
                    _cv.wait(lock, [this] { return _callback_information.size() > 0 || _destory; });
                }
                decltype(_callback_information) callback_information = {};
                std::swap(callback_information, _callback_information);
                lock.unlock();

                for (const auto& file : callback_information) {
                    if (_callback) {
                        try
                        {
                            _callback(file.first, file.second);
                        }
                        catch (const std::exception&)
                        {
                        }
                    }
                }
            }
        }

        void init_last_write_time()
        {
#ifdef _WIN32
            // Define epoch reference
            GetSystemTimeAsFileTime((LPFILETIME)&base_.first);
            base_.second = std::chrono::system_clock::now();

            // Initialize last_write_time_
            _WIN32_FILE_ATTRIBUTE_DATA att;
            GetFileAttributesExA(_path.c_str(), GetFileExInfoStandard, &att);

            last_write_time_ = base_.second
                + std::chrono::duration<
                        typename std::chrono::time_point<std::chrono::system_clock>::rep,
                        std::ratio_multiply<std::hecto, typename std::chrono::nanoseconds::period>>(
                            reinterpret_cast<ULARGE_INTEGER*>(&att.ftLastWriteTime)->QuadPart - base_.first.QuadPart);

            // Initialize filesize
            last_size_ = att.nFileSizeLow;
#else
            // Initialize last_write_time_
            struct stat result;
            stat(_path.c_str(), &result);

            using duration = std::chrono::system_clock::duration;
            last_write_time_ += std::chrono::duration_cast<duration>(std::chrono::seconds(result.st_mtim.tv_sec));
            last_write_time_ += std::chrono::duration_cast<duration>(std::chrono::nanoseconds(result.st_mtim.tv_nsec));

            // Initialize filesize
            last_size_ = result.st_size;
#endif
            
        }

    };

    template<class T> constexpr typename FileWatch<T>::C FileWatch<T>::_regex_all[];
    template<class T> constexpr typename FileWatch<T>::C FileWatch<T>::_this_directory[];
}
#endif
