#include <time.h>
#include <stdio.h>
#include <signal.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <pthread.h>
#include <arpa/inet.h>
#include <sys/socket.h>

const uint16_t SERVER_PORT = 1092;
const uint16_t MAX_CLIENT_NUM = 20;
const uint16_t BUF_SIZE = 256;

int serv_sock;                                 // server socket
int clnt_socks[MAX_CLIENT_NUM];                // client sockets
struct sockaddr_in clnt_addrs[MAX_CLIENT_NUM]; // client addresses
struct buffer
{
    uint16_t ptr, len;
    char buf[BUF_SIZE];
} clnt_buf[MAX_CLIENT_NUM]; // client buffers

// get char from client socket
int sgetc(uint16_t clnt_id)
{
    struct buffer *b = &clnt_buf[clnt_id];

    if (b->ptr == b->len)
    {
        if (b->len == BUF_SIZE)
        {
            b->ptr = b->len = 0;
        }

        ssize_t n = read(clnt_socks[clnt_id], b->buf, BUF_SIZE - b->len);
        if (n == -1)
        {
            return -1;
        }
        if (n == 0)
        {
            return -2;
        }
    }

    return b->buf[b->ptr++];
}

void *conn(void *id)
{
    uint16_t clnt_id = *(uint16_t *)id;
    int clnt_sock = clnt_socks[clnt_id];

    for (;;)
    {
    }

    close(clnt_sock);
    printf("Client %hu disconnected.\n", clnt_id);
    clnt_socks[clnt_id] = -1;

    return NULL;
}

void stop_server(int sig)
{
    for (uint16_t i = 0; i < MAX_CLIENT_NUM; i++)
    {
        if (clnt_socks[i] != -1)
        {
            close(clnt_socks[i]);
            printf("Client %hu disconnected.\n", i);
            clnt_socks[i] = -1;
        }
    }

    close(serv_sock);
    puts("Stop listening.");

    exit(0);
}

int main()
{
    memset(clnt_socks, -1, sizeof(clnt_socks));

    serv_sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    if (serv_sock == -1)
    {
        puts("Create socket failed.");
        exit(1);
    }

    struct sockaddr_in serv_addr;
    memset(&serv_addr, 0, sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
    serv_addr.sin_port = htons(SERVER_PORT);
    if (bind(serv_sock, (const struct sockaddr *)&serv_addr, sizeof(serv_addr)) == -1)
    {
        puts("Bind socket failed.");
        exit(1);
    }

    if (listen(serv_sock, MAX_CLIENT_NUM) == -1)
    {
        puts("Listen socket failed.");
        exit(1);
    }
    puts("Start listening on port 1092...");

    signal(SIGINT, stop_server);

    for (;;)
    {
        struct sockaddr_in clnt_addr;
        socklen_t clnt_addr_size = sizeof(clnt_addr);
        int clnt_sock = accept(serv_sock, (struct sockaddr *)&clnt_addr, &clnt_addr_size);
        if (clnt_sock == -1)
        {
            puts("Create socket failed.");
            continue;
        }

        for (uint16_t i = 0; i < MAX_CLIENT_NUM; i++)
        {
            if (clnt_socks[i] == -1)
            {
                clnt_socks[i] = clnt_sock;
                clnt_addrs[i] = clnt_addr;

                pthread_t pid;
                if (pthread_create(&pid, NULL, conn, &i) != 0)
                {
                    puts("Create thread failed.");
                    clnt_socks[i] = -1;
                    break;
                }
                printf("Client %hu (%s:%hu) connected. pid = %lu.\n", i, inet_ntoa(clnt_addr.sin_addr), ntohs(clnt_addr.sin_port), pid);

                break;
            }
        }
    }

    return 0;
}