#include <arpa/inet.h>
#include <errno.h>
#include <getopt.h>
#include <netinet/in.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/select.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <sys/types.h>
#include <unistd.h>

#define max(a, b) ((a > b) ? a : b)

void exit_with_usage(int rc)
{
    fprintf(stderr, "Usage: nc [-l] [-v] [-h] [-N] [-s source] [-p source_port] [destination] [port]\n");
    exit(rc);
}

int main(int argc, char** argv)
{
    bool should_listen = false;
    bool verbose = false;
    char *source_addr = nullptr;
    int source_port = 0;
    bool should_close = false;

    int opt;
    while ((opt = getopt(argc, argv, "hlvs:p:N")) != -1) {
        switch (opt) {
        case 'h':
            exit_with_usage(0);
            break;
        case 'l':
            should_listen = true;
            break;
        case 'v':
            verbose = true;
            break;
        case 's':
            source_addr = strdup(optarg);
            break;
        case 'p':
            source_port = atoi(optarg);
            break;
        case 'N':
            should_close = true;
            break;
        }
    }

    int fd;

    if (should_listen) {
        int listen_fd = socket(AF_INET, SOCK_STREAM, 0);
        if (listen_fd < 0) {
            perror("socket");
            return 1;
        }

        struct sockaddr_in sa;
        memset(&sa, 0, sizeof sa);
        sa.sin_family = AF_INET;
        sa.sin_port = htons(source_port);
        sa.sin_addr.s_addr = htonl(INADDR_ANY);
        if (source_addr) {
            if (inet_pton(AF_INET, source_addr, &sa.sin_addr) < 0) {
                perror("inet_pton");
                return 1;
            }
        }

        if (bind(listen_fd, (struct sockaddr*)&sa, sizeof(sa)) == -1) {
            perror("bind");
            return 1;
        }

        if (listen(listen_fd, 1) == -1) {
            perror("listen");
            return 1;
        }

        char addr_str[100];

        struct sockaddr_in sin;
        socklen_t len;

        len = sizeof(sin);
        if (getsockname(listen_fd, (struct sockaddr*)&sin, &len) == -1) {
            perror("getsockname");
            return 1;
        }
        if (verbose)
            fprintf(stderr, "waiting for a connection on %s:%d\n", inet_ntop(sin.sin_family, &sin.sin_addr, addr_str, sizeof(addr_str) - 1), ntohs(sin.sin_port));

        len = sizeof(sin);
        fd = accept(listen_fd, (struct sockaddr*)&sin, &len);
        if (fd == -1) {
            perror("accept");
            return 1;
        }

        if (verbose)
            fprintf(stderr, "got connection from %s:%d\n", inet_ntop(sin.sin_family, &sin.sin_addr, addr_str, sizeof(addr_str) - 1), ntohs(sin.sin_port));

        if (close(listen_fd) == -1) {
            perror("close");
            return 1;
        };
    } else {
        if ((argc - optind) < 2) {
            exit_with_usage(-1);
        }

        const char* addr_arg = argv[optind];
        int port_arg = atoi(argv[optind + 1]);
        if (port_arg < 0) {
            perror("atoi");
            return 1;
        }

        fd = socket(AF_INET, SOCK_STREAM, 0);
        if (fd < 0) {
            perror("socket");
            return 1;
        }

        struct timeval timeout {
            3, 0
        };
        if (setsockopt(fd, SOL_SOCKET, SO_RCVTIMEO, &timeout, sizeof(timeout)) < 0) {
            perror("setsockopt");
            return 1;
        }
        if (setsockopt(fd, SOL_SOCKET, SO_SNDTIMEO, &timeout, sizeof(timeout)) < 0) {
            perror("setsockopt");
            return 1;
        }

        char addr_str[100];

        struct sockaddr_in dst_addr;
        memset(&dst_addr, 0, sizeof(dst_addr));

        dst_addr.sin_family = AF_INET;
        dst_addr.sin_port = htons(port_arg);
        if (inet_pton(AF_INET, addr_arg, &dst_addr.sin_addr) < 0) {
            perror("inet_pton");
            return 1;
        }

        if (verbose)
            fprintf(stderr, "connecting to %s:%d\n", inet_ntop(dst_addr.sin_family, &dst_addr.sin_addr, addr_str, sizeof(addr_str) - 1), ntohs(dst_addr.sin_port));
        if (connect(fd, (struct sockaddr*)&dst_addr, sizeof(dst_addr)) < 0) {
            perror("connect");
            return 1;
        }
        if (verbose)
            fprintf(stderr, "connected!\n");
    }

    bool stdin_closed = false;
    bool fd_closed = false;

    fd_set readfds, writefds, exceptfds;

    while (!stdin_closed || !fd_closed) {
        FD_ZERO(&readfds);
        FD_ZERO(&writefds);
        FD_ZERO(&exceptfds);

        int highest_fd = 0;

        if (!stdin_closed) {
            FD_SET(STDIN_FILENO, &readfds);
            FD_SET(STDIN_FILENO, &exceptfds);
            highest_fd = max(highest_fd, STDIN_FILENO);
        }
        if (!fd_closed) {
            FD_SET(fd, &readfds);
            FD_SET(fd, &exceptfds);
            highest_fd = max(highest_fd, fd);
        }

        int ready = select(highest_fd + 1, &readfds, &writefds, &exceptfds, NULL);
        if (ready == -1) {
            if (errno == EINTR)
                continue;

            perror("select");
            return 1;
        }

        if (!stdin_closed && FD_ISSET(STDIN_FILENO, &readfds)) {
            char buf[1024];
            int nread = read(STDIN_FILENO, buf, sizeof(buf));
            if (nread < 0) {
                perror("read(STDIN_FILENO)");
                return 1;
            }

            // stdin closed
            if (nread == 0) {
                stdin_closed = true;
                if (verbose)
                    fprintf(stderr, "stdin closed\n");
                if (should_close) {
                    close(fd);
                    fd_closed = true;
                }
            } else if (write(fd, buf, nread) < 0) {
                perror("write(fd)");
                return 1;
            }
        }

        if (!fd_closed && FD_ISSET(fd, &readfds)) {
            char buf[1024];
            int nread = read(fd, buf, sizeof(buf));
            if (nread < 0) {
                perror("read(fd)");
                return 1;
            }

            // remote end closed
            if (nread == 0) {
                close(STDIN_FILENO);
                stdin_closed = true;
                fd_closed = true;
                if (verbose)
                    fprintf(stderr, "remote closed\n");
            } else if (write(STDOUT_FILENO, buf, nread) < 0) {
                perror("write(STDOUT_FILENO)");
                return 1;
            }
        }
    }

    return 0;
}
