#include <cstring>
#include <fcntl.h>
#include <signal.h>
#include <unistd.h>
#include <sys/wait.h>
#include <sys/epoll.h>
#include <system_error>

#include "log.h"
#include "misc.h"
#include "config.h"
#include "logcat_thread.h"
#include "logcat_entry.h"

#define EPOLL_MAX_EVENTS 10

static void mark_nonblock(int fd) {
    int flags = fcntl(fd, F_GETFL);
    if (flags < 0) {
        throw_system_error("fcntl(fd, F_GETFL)");
    }
    if (!(flags & O_NONBLOCK) && fcntl(fd, F_SETFL, flags | O_NONBLOCK) == -1) {
        throw_system_error("fcntl(fd, F_SETFL)");
    }
}

static inline void look_for_newlines(char buf[NEWLINE_BUF_SIZE], size_t* used, size_t previous_used,
        void(LogcatThread::*handle_line)(char*, size_t, bool), LogcatThread* logcat_thread, bool is_stdout) {
    size_t search_offset = previous_used;
    size_t real_offset = 0;

    while (*used > search_offset) {
        char* newline_ptr = static_cast<char*>(memchr(&buf[search_offset], '\n', (*used - search_offset) * sizeof(char)));
        if (!newline_ptr) {
            break;
        }

        size_t newline_length = (reinterpret_cast<size_t>(newline_ptr) - reinterpret_cast<size_t>(&buf[real_offset])) / sizeof(char);
        (logcat_thread->*handle_line)(&buf[real_offset], newline_length, is_stdout);

        real_offset += newline_length + 1;
        search_offset = real_offset;
    }

    if (real_offset) {
        if (*used > search_offset) {
            memcpy(buf, &buf[real_offset], (*used - real_offset) * sizeof(char));
            *used -= real_offset;
        } else {
            *used = 0;
        }
    }
}

static inline void handle_fd(int fd, char* buf, size_t* used,
        void(LogcatThread::*handle_line)(char*, size_t, bool), LogcatThread* logcat_thread, bool is_stdout) {
    while (true) {
        ssize_t read_size_u = read(fd, &buf[*used], (NEWLINE_BUF_SIZE - *used) * sizeof(char));
        if (read_size_u == 0) {
            return;
        } else if (read_size_u < 0 && (errno == EAGAIN || errno == EWOULDBLOCK)) {
            return;
        } else if (read_size_u < 0) {
            throw_system_error("read()");
        }
        size_t read_size = static_cast<size_t>(read_size_u) / sizeof(char);
        if (*used + read_size > NEWLINE_BUF_SIZE) {
            throw std::runtime_error("Received line longer than 512k");
        }
        size_t previous_used = *used;
        *used += read_size;

        look_for_newlines(buf, used, previous_used, handle_line, logcat_thread, is_stdout);
    }
}


LogcatThread::LogcatThread(const std::string* logcat_command) : _logcat_command(logcat_command) {
    int fds[2];
    struct epoll_event event = {.events = EPOLLIN | EPOLLET};

    if (pipe(fds)) {
        int errsv = errno;
        this->~LogcatThread();
        throw_system_error(errsv, "pipe() for stdout");
    }
    this->_stdout_read_fd = fds[0];
    this->_stdout_write_fd = fds[1];
    try {
        mark_nonblock(this->_stdout_read_fd);
    } catch (const std::exception& e) {
        this->~LogcatThread();
        throw;
    }

    if (pipe(fds)) {
        int errsv = errno;
        this->~LogcatThread();
        throw_system_error(errsv, "pipe() for stderr");
    }
    this->_stderr_read_fd = fds[0];
    this->_stderr_write_fd = fds[1];
    try {
        mark_nonblock(this->_stderr_read_fd);
    } catch (const std::exception& e) {
        this->~LogcatThread();
        throw;
    }

    this->_epoll_fd = epoll_create1(EPOLL_CLOEXEC);
    if (this->_epoll_fd == -1) {
        int errsv = errno;
        this->~LogcatThread();
        throw_system_error(errsv, "epoll_create1()");
    }
    event.data.fd = this->_stdout_read_fd;
    if (epoll_ctl(this->_epoll_fd, EPOLL_CTL_ADD, this->_stdout_read_fd, &event)) {
        int errsv = errno;
        this->~LogcatThread();
        throw_system_error(errsv, "epoll_ctl() for stdout");
    }
    event.data.fd = this->_stderr_read_fd;
    if (epoll_ctl(this->_epoll_fd, EPOLL_CTL_ADD, this->_stderr_read_fd, &event)) {
        int errsv = errno;
        this->~LogcatThread();
        throw_system_error(errsv, "epoll_ctl() for stderr");
    }

    this->_thread = std::thread(&LogcatThread::_run, this, this->_stop_source.get_token());
}

LogcatThread::~LogcatThread() {
    if (this->_epoll_fd != -1 && close(this->_epoll_fd)) {
        log(std::string("Failed to close epoll file descriptor: close(): ") + strerror(errno));
    }
    if (this->_stdout_read_fd != -1 && close(this->_stdout_read_fd)) {
        log(std::string("Failed to close stdout read pipe: close(): ") + strerror(errno));
    }
    if (this->_stdout_write_fd != -1 && close(this->_stdout_write_fd)) {
        log(std::string("Failed to close stdout write pipe: close(): ") + strerror(errno));
    }
    if (this->_stderr_read_fd != -1 && close(this->_stderr_read_fd)) {
        log(std::string("Failed to close stderr read pipe: close(): ") + strerror(errno));
    }
    if (this->_stderr_write_fd != -1 && close(this->_stderr_write_fd)) {
        log(std::string("Failed to close stderr write pipe: close(): ") + strerror(errno));
    }
}

void LogcatThread::request_stop() {
    this->_stop_source.request_stop();
}

void LogcatThread::join() {
    this->_thread.join();
}

void LogcatThread::_put_if_not_stopped(LogcatThreadItem item) {
    while (true) {
        if (this->atomic_ring_buffer.try_put_and_increment_write(item)) {
            break;
        }
        if (this->_stop_source.stop_requested()) {
            break;
        }
    }
}

void LogcatThread::_try_log(std::string message) {
    LogEntry log_entry = {time(nullptr), std::move(message)};
    print_log(log_entry);
    this->_put_if_not_stopped(std::move(log_entry));
}

void LogcatThread::_handle_line(char* buf, size_t length, bool is_stdout) {
    if (!is_stdout) {
        this->_try_log(std::string("Received from logcat stderr: ") + std::string(buf, length));
        return;
    }

    try {
        std::optional<LogcatEntry> logcat_entry = try_parse_logcat_entry(buf, length, this->_current_buffer);
        if (logcat_entry) {
            this->_put_if_not_stopped(std::move(*logcat_entry));
            return;
        }
    } catch (const std::exception& e) {
        this->_try_log(std::string("Failed to parse logcat entry: ") + e.what());
    }

    try {
        std::optional<Buffer> new_buffer = try_parse_buffer(buf, length);
        if (new_buffer) {
            this->_current_buffer = *new_buffer;
            return;
        }
    } catch (const std::exception& e) {
        this->_try_log(std::string("Failed to parse buffer line: ") + e.what());
    }

    this->_try_log(std::string("Cannot parse logcat stdout: ") + std::string(buf, length));
}

void LogcatThread::_run_epoll_round() {
    struct epoll_event events[EPOLL_MAX_EVENTS];

    int ready_fds = epoll_wait(this->_epoll_fd, events, EPOLL_MAX_EVENTS, 1000);
    if (ready_fds == -1) {
        int errsv = errno; // just in case if std::string overrides it
        this->_try_log(std::string("epoll_wait(): ") + strerror(errsv));
        return;
    }

    for (int i=0; i < ready_fds; i++) {
        const bool is_stdout = events[i].data.fd == this->_stdout_read_fd;
        char* buf = is_stdout ? this->_stdout_buf : this->_stderr_buf;
        size_t* used = is_stdout ? &this->_stdout_buf_used : &this->_stderr_buf_used;

        try {
            handle_fd(events[i].data.fd, buf, used, &LogcatThread::_handle_line, this, is_stdout);
        } catch (const std::exception& e) {
            this->_try_log(std::string("Failed to handle std") + (is_stdout ? "out: " : "err: ") + e.what());
        }
    }
}

void LogcatThread::_try_reap(bool has_request) {
    int wstatus;
    int res = waitpid(this->_logcat_pid, &wstatus, WNOHANG);
    if (res == -1) {
        try {
            throw_system_error("waitpid()");
        } catch (const std::exception& e) {
            this->_try_log(e.what());
        }
        return;
    } else if (res != this->_logcat_pid) {
        return;
    }

    this->_logcat_pid = -1;
    this->_logcat_process_kill_attempts = 0;
    // just in case if the process was terminated mid-write
    this->_stdout_buf_used = 0;
    this->_stderr_buf_used = 0;
    this->logcat_process_running.clear();

    if (WIFEXITED(wstatus)) {
        if (WEXITSTATUS(wstatus) && !has_request) {
            this->_try_log(std::string("Logcat exited with ") + std::to_string(WEXITSTATUS(wstatus)));
        }
    } else if (WIFSIGNALED(wstatus)) {
        if (!has_request) {
            this->_try_log(std::string("Logcat exited with -") + std::to_string(WTERMSIG(wstatus)));
        }
    } else {
        this->_try_log(std::string("Logcat disappeared (wstatus=") + std::to_string(wstatus) + ')');
    }
}

bool LogcatThread::_handle_stop_request() {
    if (this->_logcat_pid == -1) {
        return true;
    }

    int signal = this->_logcat_process_kill_attempts++ < 3 ? SIGTERM : SIGKILL;
    if (!kill(this->_logcat_pid, signal)) {
        return false;
    }
    try {
        throw_system_error("kill()");
    } catch (const std::exception& e) {
        this->_try_log(e.what());
    }
    return true;
}

bool LogcatThread::_handle_start_request() {
    if (this->_logcat_pid != -1) {
        this->_handle_stop_request();
        return false;
    }
    auto dup2_or_die = [](int oldfd, int newfd) {
        if (dup2(oldfd, newfd) == newfd) {
            return;
        }
        try {
            throw_system_error(std::string("dup2(") + std::to_string(oldfd) + ", " + std::to_string(newfd) + ')');
        } catch (const std::exception& e) {
            print_log({time(nullptr), e.what()});
        }
        exit(1);
    };
    auto close_or_warn = [](int fd) {
        if (!close(fd)) {
            return;
        }
        try {
            throw_system_error(std::string("close(") + std::to_string(fd) + ')');
        } catch (const std::exception& e) {
            print_log({time(nullptr), e.what()});
        }
    };

    std::string logcat_command = *this->_logcat_command;
    if (logcat_command.empty()) {
        logcat_command = default_logcat_command;
    }

    this->_logcat_pid = fork();
    if (this->_logcat_pid == -1) {
        try {
            throw_system_error("fork()");
        } catch (const std::exception& e) {
            this->_try_log(e.what());
        }
        return true;
    } else if (this->_logcat_pid == 0) {
        dup2_or_die(this->_stderr_write_fd, 2);
        dup2_or_die(this->_stdout_write_fd, 1);
        close_or_warn(this->_stdout_write_fd);
        close_or_warn(this->_stderr_write_fd);
        close_or_warn(this->_stdout_read_fd);
        close_or_warn(this->_stderr_read_fd);
        execlp("sh", "sh", "-c", logcat_command.c_str(), nullptr);
        try {
            throw_system_error("execlp()");
        } catch (const std::exception& e) {
            print_log({time(nullptr), e.what()});
        }
        exit(1);
    } else {
        this->logcat_process_running.test_and_set();
        return true;
    }
}

bool LogcatThread::_run_process_round(LogcatProcessRequest request) {
    bool task_done;
    switch (request) {
        case LogcatProcessRequest::None: task_done = false; break;
        case LogcatProcessRequest::Start: task_done = this->_handle_start_request(); break;
        case LogcatProcessRequest::Stop: task_done = this->_handle_stop_request(); break;
    };

    if (this->_logcat_pid != -1) {
        this->_try_reap(request != LogcatProcessRequest::None);
    }

    return task_done;
}

void LogcatThread::_run(std::stop_token stoken) {
    while (!stoken.stop_requested() || this->_logcat_pid != -1) {
#ifndef NDEBUG
        if (this->debug_log_request.test()) {
            this->_try_log("A log entry from the logcat thread :D");
            this->debug_log_request.clear();
        }
#endif

        this->_run_epoll_round();

        if (stoken.stop_requested() && this->_logcat_pid != -1) {
            this->_run_process_round(LogcatProcessRequest::Stop);
        } else if (this->_run_process_round(this->logcat_process_request.load())) {
            this->logcat_process_request.store(LogcatProcessRequest::None);
        }
    }
}