#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 int MAX_CLIENT_NUM = 20;
const int MESSAGE_LEN = 256;
const int HEADER_LEN = 4;

int serv_sock;
int clnt_socks[MAX_CLIENT_NUM];
struct sockaddr_in clnt_addrs[MAX_CLIENT_NUM];

struct message
{
    uint8_t opcode, status;
    uint16_t length;
    char data[MESSAGE_LEN - HEADER_LEN];
};

struct client
{
    uint16_t id, port;
    uint32_t addr;
};

void send_message(int clnt_sock, uint8_t opcode, uint8_t status, uint16_t length, char data[])
{
    struct message msg;
    msg.opcode = opcode;
    msg.status = status;
    msg.length = htons(length);
    memcpy(msg.data, data, length);
    write(clnt_sock, &msg, MESSAGE_LEN);
}

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

    char data[MESSAGE_LEN];
    sprintf(data, "Hello, client %hu.", clnt_id);
    send_message(clnt_sock, 0, 1, strlen(data), data);

    for (;;)
    {
        struct message msg;
        int expect = MESSAGE_LEN;
        for (char *p = (char *)&msg; expect > 0;)
        {
            int len = read(clnt_sock, p, expect);
            if (len <= 0)
            {
                break;
            }
            expect -= len;
            p += len;
        }
        if (expect > 0)
        {
            break;
        }
        printf("Receive message from client %hu. opcode = %hu.\n", clnt_id, msg.opcode);

        switch (msg.opcode)
        {
        case 1:
        {
            time_t now;
            time(&now);
            strcpy(data, ctime(&now));
            send_message(clnt_sock, 1, 1, strlen(data) - 1, data);

            break;
        }

        case 2:
        {
            gethostname(data, MESSAGE_LEN);
            send_message(clnt_sock, 2, 1, strlen(data), data);

            break;
        }

        case 3:
        {
            int cnt = 0;
            for (uint16_t i = 0; i < MAX_CLIENT_NUM; i++)
            {
                if (clnt_socks[i] != -1)
                {
                    ((struct client *)data)[cnt].id = htons(i);
                    ((struct client *)data)[cnt].addr = clnt_addrs[i].sin_addr.s_addr;
                    ((struct client *)data)[cnt].port = clnt_addrs[i].sin_port;
                    cnt++;
                }
            }
            send_message(clnt_sock, 3, 1, sizeof(struct client) * cnt, data);

            break;
        }

        case 4:
        {
            uint16_t id = ntohs(((uint16_t *)msg.data)[0]);
            if (clnt_socks[id] == -1)
            {
                send_message(clnt_sock, 4, 2, 0, NULL);
            }
            else
            {
                ((uint16_t *)msg.data)[0] = htons(clnt_id);
                send_message(clnt_sock, 4, 1, 0, NULL);
                send_message(clnt_socks[id], 0, 0, strlen(msg.data + 2) + 2, msg.data);
                printf("    Forward message to client %hu.\n", id);
            }

            break;
        }

        default:
        {
            sprintf(data, "Invalid operation.");
            send_message(clnt_sock, 0, 2, strlen(data), data);
        }
        }
    }

    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;
}