//
// Universal Internet Client
//
// Usage:
//          client [IP_address_of_server [port_of_server]]
//      where IP_address_of_server is either IP number of server
//      or a symbolic Internet name, default is "localhost";
//      port_of_server is a port number, default is 1234.
//

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <windows.h>
#include <winsock2.h>

static void usage();

// Receiving thread body function
static DWORD WINAPI receiveMessages(void* arg);

static HANDLE hReceivingThread = NULL;
static DWORD receivingThreadID = 0;

static CRITICAL_SECTION critSect;

static int s0 = (-1);   // Socket number
static char receiveBuffer[1024];
static char sendBuffer[1024];

int main(int argc, char *argv[]) {
    if (argc > 1 && *(argv[1]) == '-') {
        usage(); exit(1);
    }

    InitializeCriticalSection(&critSect);

    // Initialize Winsock DLL
    WORD wVersionRequested = MAKEWORD(2, 2);
    WSADATA wsaData;
    int err = WSAStartup(wVersionRequested, &wsaData);
    if (err != 0) {
        printf("WSAStartup failed with error: %d\n", err);
        exit(-1);
    }

    // Create a socket
    s0 = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    if (s0 < 0) {
        printf(
            "Could not create a socket: error=%d\n",
            WSAGetLastError()
        );
    }

    // Fill in the address of server
    struct sockaddr_in peeraddr;
    memset(&peeraddr, 0, sizeof(peeraddr));
    const char* peerHost = "localhost";
    if (argc > 1)
        peerHost = argv[1];

    // Resolve the server address (convert from symbolic name to IP number)
    struct hostent *host = gethostbyname(peerHost);
    if (host == NULL) {
        perror("Cannot define host address"); exit(1);
    }
    peeraddr.sin_family = AF_INET;
    short peerPort = 1234;
    if (argc >= 3)
        peerPort = (short) atoi(argv[2]);
    peeraddr.sin_port = htons(peerPort);

    // Print a resolved address of server (the first IP of the host)
    printf(
        "peer addr = %d.%d.%d.%d, port %d\n",
        (int) host->h_addr_list[0][0] & 0xff,
        (int) host->h_addr_list[0][1] & 0xff,
        (int) host->h_addr_list[0][2] & 0xff,
        (int) host->h_addr_list[0][3] & 0xff,
        (int) peerPort
    );

    // Write resolved IP address of a server to the address structure
    memmove(&(peeraddr.sin_addr.s_addr), host->h_addr_list[0], 4);

    // Connect to a remote server
    int res = connect(s0, (struct sockaddr*) &peeraddr, sizeof(peeraddr));
    if (res < 0) {
        printf(
            "Cannot connect: err=%d\n",
            WSAGetLastError()
        );
        exit(1);
    }
    printf("Connected!\n");
    fflush(stdout);

    // Create a receiving thread
    hReceivingThread = CreateThread(
        NULL,             // lpThreadAttributes
        0,                // dwStackSize - default
        &receiveMessages, // thread starting function
        NULL,             // parameter of thread starting function
        0,                // dwCreationFlags
        &receivingThreadID
    );
    if (hReceivingThread == NULL) {
        printf(
            "Cannot create receiving thread: error %d\n",
            (int) GetLastError()
        );
        exit(-1);
    }

    // Read messages from the keyboard and send
    // them to remote server
    while (true) {
        int s;
        EnterCriticalSection(&critSect);
        s = s0;
        LeaveCriticalSection(&critSect);
        if (s < 0)
            break;

        if (fgets(sendBuffer, 1022, stdin) == NULL)
            break;
        size_t len = strlen(sendBuffer);

        EnterCriticalSection(&critSect);
        s = s0;
        LeaveCriticalSection(&critSect);
        if (s < 0)
            break;

        if (
            strcmp(sendBuffer, ".\n") == 0 ||
            strcmp(sendBuffer, ".\r\n") == 0
        ) {
            // Close the connection
            EnterCriticalSection(&critSect);
            s0 = (-1);
            LeaveCriticalSection(&critSect);
            closesocket(s);
            break;
        }

        if (len > 0) {
            // Send data to server
            res = send(s, sendBuffer, len, 0);
            if (res < 0) {
                printf(
                    "Cannot send data: err=%d\n",
                    WSAGetLastError()
                );

                EnterCriticalSection(&critSect);
                s = s0;
                s0 = (-1);
                LeaveCriticalSection(&critSect);

                closesocket(s);
                break;
            }
        }
    } // end while

    // Socket is closed already!

    WaitForSingleObject(hReceivingThread, INFINITE);
    CloseHandle(hReceivingThread);

    WSACleanup();
    DeleteCriticalSection(&critSect);
    return 0;
}

static void usage() {
    printf(
        "A simple Internet client application.\n"
        "Usage:\n"
        "         client [IP_address_of_server [port_of_server]]\n"
        "     where IP_address_of_server is either IP number of server\n"
        "     or a symbolic Internet name, default is \"localhost\";\n"
        "     port_of_server is a port number, default is 1234.\n"
        "The client connects to a server which address is given in a\n"
        "command line, receives messages from a server, and sends messages\n"
        "that a user prints on keyboard.\n"
    );
}

static DWORD WINAPI receiveMessages(void* /* arg */) {
    // printf("Receiving thread is started.\n");
    // fflush(stdout);

    while (true) {
        int s;
        EnterCriticalSection(&critSect);
        s = s0;
        LeaveCriticalSection(&critSect);
        if (s < 0)
            break;

        int res = recv(s, receiveBuffer, 1022, 0);
        // printf("Received %d bytes.\n", res);
        // fflush(stdout);
        if (res <= 0) {

            /*...
            if (res < 0) {
                printf(
                    "Receive error: err=%d\n",
                    WSAGetLastError()
                );
                fflush(stdout);
            }
            ...*/

            EnterCriticalSection(&critSect);
            s0 = (-1);
            LeaveCriticalSection(&critSect);
            closesocket(s);
            break;
        }
        receiveBuffer[res] = 0;
        printf("%s", receiveBuffer);
        fflush(stdout);
    }

    return 0;
}