#include <iostream>
#include <vector>
#include <string>
#include <unordered_map>

#include <cstring>
#include <csignal>
#include <cstdio>

#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <unistd.h>

#include "dinit-client.h"
#include "service-constants.h"

// dinit-monitor: watch service states and report them via execution of a notification command

static constexpr uint16_t min_cp_version = 1;
static constexpr uint16_t max_cp_version = 1;

struct stringview {
    const char *str;
    size_t len;
};

class dinit_protocol_error {};

static std::vector<stringview> split_command(const char *cmd);
static bool load_service(int socknum, cpbuffer_t &rbuffer, const char *name, handle_t *handle,
        service_state_t *state);

// dummy handler, so we can wait for children
static void sigchld_handler(int) { }

int dinit_monitor_main(int argc, char **argv)
{
    bool show_help = argc < 2;
    std::string control_socket_str;
    const char *control_socket_path = nullptr;
    bool user_dinit = (getuid() != 0);  // communicate with user daemon

    const char *command_str = nullptr;
    std::vector<const char *> services;

    for (int i = 1; i < argc; i++) {
        if (argv[i][0] == '-') {
            if (strcmp(argv[i], "--help") == 0) {
                show_help = true;
                break;
            }
            else if (strcmp(argv[i], "--version") == 0) {
                std::cout << "Dinit version " << DINIT_VERSION << ".\n";
                return 0;
            }
            else if (strcmp(argv[i], "--system") == 0 || strcmp(argv[i], "-s") == 0) {
                user_dinit = false;
            }
            else if (strcmp(argv[i], "--user") == 0 || strcmp(argv[i], "-u") == 0) {
                user_dinit = true;
            }
            else if (strcmp(argv[i], "--socket-path") == 0 || strcmp(argv[i], "-p") == 0) {
                ++i;
                if (i == argc) {
                    std::cerr << "dinit-monitor: --socket-path/-p should be followed by socket path\n";
                    return 1;
                }
                control_socket_str = argv[i];
            }
            else if (strcmp(argv[i], "-c") == 0 || strcmp(argv[i], "--command")) {
                ++i;
                if (i == argc) {
                    std::cerr << "dinit-monitor: --command/-c should be followed by command\n";
                    return 1;
                }
                command_str = argv[i];
            }
        }
        else {
            services.emplace_back(argv[i]);
        }
    }

    if (show_help) {
        std::cout << "dinit-monitor:   monitor Dinit services\n"
                "\n"
                "Usage:\n"
                "    dinit-monitor [options] <service-names...>\n"
                "\n"
                "Options:\n"
                "  --help           : show this help\n"
                "  -s, --system     : monitor system daemon (default if run as root)\n"
                "  -u, --user       : monitor user daemon\n"
                "  --socket-path <path>, -p <path>\n"
                "                   : specify socket for communication with daemon\n"
                "  -c, --command    : specify command to execute on service status change\n"
                "                     (%n for service name, %s for status)\n";
        return 1;
    }

    if (services.empty()) {
        std::cerr << "dinit-monitor: specify at least one service name\n";
        return 1;
    }

    if (command_str == nullptr) {
        std::cerr << "dinit-monitor: command must specified\n";
        return 1;
    }

    std::vector<stringview> command_parts = split_command(command_str);
    if (command_parts.size() == 0) {
        std::cerr << "dinit-monitor: specified command is empty\n";
        return 1;
    }

    // Ignore SIGPIPE to avoid dying due to it, and set up a SIGCHLD handler (but mask it)
    sigset_t signal_mask;
    sigprocmask(SIG_SETMASK, nullptr, &signal_mask);
    sigaddset(&signal_mask, SIGCHLD);
    sigprocmask(SIG_SETMASK, &signal_mask, nullptr);
    signal(SIGPIPE, SIG_IGN);
    signal(SIGCHLD, sigchld_handler);

    // Locate control socket
    if (! control_socket_str.empty()) {
        control_socket_path = control_socket_str.c_str();
    }
    else {
        control_socket_path = get_default_socket_path(control_socket_str, user_dinit);
        if (control_socket_path == nullptr) {
            std::cerr << "dinit-monitor: cannot locate user home directory (set XDG_RUNTIME_DIR, "
                    "HOME, check /etc/passwd file, or specify socket path via -p)\n";
            return 1;
        }
    }

    try {
        int socknum = connect_to_daemon(control_socket_path);

        // Start by querying protocol version:
        cpbuffer_t rbuffer;
        check_protocol_version(min_cp_version, max_cp_version, rbuffer, socknum);

        // Load all services
        std::unordered_map<handle_t, const char *> service_map;

        for (const char *service_name : services) {

            handle_t hndl;
            service_state_t state;
            if (!load_service(socknum, rbuffer, service_name, &hndl, &state)) {
                std::cerr << "dinit-monitor: cannot load service: " << service_name << "\n";
                return 1;
            }

            service_map.emplace(hndl, service_name);
        }

        // Watch information packets; execute notification

        int r = rbuffer.fill_to(socknum, 2);
        while (r > 0) {
            if (rbuffer[0] >= 100) {
                int pktlen = (unsigned char) rbuffer[1];
                fill_buffer_to(rbuffer, socknum, pktlen);

                if (rbuffer[0] == DINIT_IP_SERVICEEVENT) {
                    handle_t ev_handle;
                    rbuffer.extract((char *) &ev_handle, 2, sizeof(ev_handle));
                    service_event_t event = static_cast<service_event_t>(rbuffer[2 + sizeof(ev_handle)]);

                    const char *service_name = service_map.at(ev_handle);
                    const char *event_str;

                    if (event == service_event_t::STARTED) {
                        event_str = "started";
                    }
                    else if (event == service_event_t::STOPPED) {
                        event_str = "stopped";
                    }
                    else if (event == service_event_t::FAILEDSTART) {
                        event_str = "failed";
                    }
                    else {
                        goto consume_packet;
                    }

                    std::vector<std::string> final_cmd_parts;
                    std::vector<const char *> final_cmd_parts_cstr;

                    for (stringview cmd_part : command_parts) {
                        std::string cmd_part_str;
                        cmd_part_str.reserve(cmd_part.len);

                        for (size_t i = 0; i < cmd_part.len; ++i) {
                            if (cmd_part.str[i] == '%') {
                                ++i;
                                if (i >= cmd_part.len) {
                                    cmd_part_str.append(1, '%');
                                    break;
                                }
                                if (cmd_part.str[i] == 'n') {
                                    cmd_part_str.append(service_name);
                                }
                                else if (cmd_part.str[i] == 's') {
                                    cmd_part_str.append(event_str);
                                }
                                else {
                                    // invalid specifier, just output as is
                                    cmd_part_str.append(1, '%');
                                    cmd_part_str.append(1, cmd_part_str[i]);
                                }
                            }
                            else if (cmd_part.str[i] == '"') {
                                // consume.
                            }
                            else {
                                cmd_part_str.append(1, cmd_part.str[i]);
                            }
                        }

                        final_cmd_parts.emplace_back(std::move(cmd_part_str));
                    }

                    for (const std::string &cmd_part : final_cmd_parts) {
                        final_cmd_parts_cstr.push_back(cmd_part.c_str());
                    }
                    final_cmd_parts_cstr.push_back(nullptr);

                    pid_t child_pid = fork();
                    if (child_pid == 0) {
                        // we are the child
                        char **argv = const_cast<char **>(final_cmd_parts_cstr.data());
                        execvp(argv[0], argv);
                        perror("dinit-monitor: exec");
                    }
                    else if (child_pid == -1) {
                        perror("dinit-monitor: fork");
                    }
                    else {
                        int wstatus;
                        if (wait(&wstatus) != -1) {
                            if (wstatus != 0) {
                                if (WIFEXITED(wstatus)) {
                                    std::cerr << "dinit-monitor: notification command terminated with exit status "
                                            << WEXITSTATUS(wstatus) << "\n";
                                }
                                if (WIFSIGNALED(wstatus)) {
                                    std::cerr << "dinit-monitor: notification command terminated due to signal "
                                            << WTERMSIG(wstatus) << "\n";
                                }
                            }
                        }

                        // Don't bother clearing any pending SIGCHLD. POSIX says that:
                        // - either SIGCHLD doesn't queue, in which case we're only leaving one pending signal
                        // - or, it does queue, but wait() removes it from the queue.
                    }
                }

                consume_packet:

                rbuffer.consume(pktlen);
                r = rbuffer.fill_to(socknum, 2);
            }
            else {
                // Not an information packet?
                std::cerr << "dinit-monitor: protocol error\n";
                return 1;
            }
        }

        if (r == -1) {
            perror("dinit-monitor: read");
        }
        else {
            std::cerr << "dinit-monitor: connection closed by server\n";
        }
        return 1;
    }
    catch (cp_old_client_exception &e) {
        std::cerr << "dinit-monitor: too old (server reports newer protocol version)\n";
    }
    catch (cp_old_server_exception &e) {
        std::cerr << "dinit-monitor: server too old or protocol error\n";
    }
    catch (cp_read_exception &e) {
        std::cerr << "dinit-monitor: control socket read failure or protocol error\n";
    }
    catch (cp_write_exception &e) {
        std::cerr << "dinit-monitor: control socket write error: " << std::strerror(e.errcode) << "\n";
    }
    catch (dinit_protocol_error &e) {
        std::cerr << "dinit-monitor: protocol error\n";
    }
    catch (general_error &ge) {
        std::cerr << "dinit-monitor";
        if (ge.get_action() != nullptr) {
            std::cerr << ": " << ge.get_action();
            std::string &arg = ge.get_arg();
            if (!arg.empty()) {
                std::cerr << " " << arg;
            }
        }
        if (ge.get_err() != 0) {
            std::cerr << ": " << strerror(ge.get_err());
        }
        std::cerr << '\n';
    }

    return 1;
}

int main(int argc, char **argv) {
    try {
        return dinit_monitor_main(argc, argv);
    }
    catch (std::bad_alloc &e) {
        std::cerr << "dinit-monitor: out of memory\n";
    }
    return 1;
}

static std::vector<stringview> split_command(const char *cmd)
{
    using std::locale;
    using std::isspace;
    const locale &classic_loc = locale::classic();
    std::vector<stringview> result;

    const char *c = cmd;

    do {
        while (*c != '\0' && isspace(*c, classic_loc)) ++c;
        if (*c == '\0') break;
        const char *str = c;

        while (*c != '\0' && !isspace(*c, classic_loc)) {
            if (*c == '"') {
                ++c; // skip begin quote
                while (*c != '\0' && *c != '"') ++c;
            }
            ++c;
        }

        size_t len = c - str;

        result.emplace_back(stringview {str, len});
    } while (*c != '\0');

    return result;
}

// Issue a "load service" command (DINIT_CP_LOADSERVICE), without waiting for
// a response. Returns 1 on failure (with error logged), 0 on success.
static int issue_load_service(int socknum, const char *service_name, bool find_only = false)
{
    // Build buffer;
    uint16_t sname_len = strlen(service_name);
    int bufsize = 3 + sname_len;

    std::unique_ptr<char[]> ubuf(new char[bufsize]);
    auto buf = ubuf.get();

    buf[0] = find_only ? DINIT_CP_FINDSERVICE : DINIT_CP_LOADSERVICE;
    memcpy(buf + 1, &sname_len, 2);
    memcpy(buf + 3, service_name, sname_len);

    write_all_x(socknum, buf, bufsize);

    return 0;
}

// Check that a "load service" reply was received, and that the requested service was found.
//   state_p may be null.
static int check_load_reply(int socknum, cpbuffer_t &rbuffer, handle_t *handle_p, service_state_t *state_p)
{
    using namespace std;

    if (rbuffer[0] == DINIT_RP_SERVICERECORD) {
        fill_buffer_to(rbuffer, socknum, 2 + sizeof(*handle_p));
        rbuffer.extract((char *) handle_p, 2, sizeof(*handle_p));
        if (state_p) *state_p = static_cast<service_state_t>(rbuffer[1]);
        //target_state = static_cast<service_state_t>(rbuffer[2 + sizeof(handle)]);
        rbuffer.consume(3 + sizeof(*handle_p));
        return 0;
    }
    else if (rbuffer[0] == DINIT_RP_NOSERVICE) {
        return 1;
    }
    else {
        throw dinit_protocol_error();
    }
}

// Load a service: issue load command, wait for reply. Return true on success, display error message
// and return false on failure.
//      socknum  - the socket fd to communicate via
//      rbuffer  - the buffer for communication
//      name     - the name of the service to load
//      handle   - where to store the handle of the loaded service
//      state    - where to store the state of the loaded service (may be null).
//      write_error - whether to write an error message if the service can't be loaded
static bool load_service(int socknum, cpbuffer_t &rbuffer, const char *name, handle_t *handle,
        service_state_t *state)
{
    // Load 'to' service:
    if (issue_load_service(socknum, name)) {
        return false;
    }

    wait_for_reply(rbuffer, socknum);

    if (check_load_reply(socknum, rbuffer, handle, state) != 0) {
        return false;
    }

    return true;
}