#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <Windows.h>

void errorExit(const char *txt);

int main(int argc, char* argv[]) {
    SECURITY_ATTRIBUTES sa;
    memset(&sa, 0, sizeof(sa));
    sa.nLength = sizeof(SECURITY_ATTRIBUTES); 
    sa.bInheritHandle = TRUE; 

    HANDLE hParentInput, hParentOutput;
    HANDLE hChildInput, hChildOutput;

    // Create a pipe for the child process's STDOUT. 
    if (!CreatePipe(
        &hParentInput, &hChildOutput, &sa, 0
    )) 
        errorExit("Child output pipe creation failed"); 
    // Ensure the hParentInput handle is not inherited.
    SetHandleInformation(
        hParentInput, HANDLE_FLAG_INHERIT, 0
    );

    // Create a pipe for the child process's STDIN. 
    if (!CreatePipe(
        &hChildInput, &hParentOutput, &sa, 0
    )) 
        errorExit("Child input pipe creation failed"); 
    // Ensure the hParentOutput handle is not inherited.
    SetHandleInformation(
        hParentOutput, HANDLE_FLAG_INHERIT, 0
    );

    // Create the child process
    PROCESS_INFORMATION pi;
    memset(&pi, 0, sizeof(pi));

    STARTUPINFO si;
    memset(&si, 0, sizeof(si));
    si.cb = sizeof(si);
    si.hStdError = hChildOutput;
    si.hStdOutput = hChildOutput;
    si.hStdInput = hChildInput;
    si.dwFlags |= STARTF_USESTDHANDLES;

    if (!CreateProcess(
        "rcalc.exe",    // Module name
        "rcalc.exe",    // Command line
        NULL,           // Process handle not inheritable
        NULL,           // Thread handle not inheritable
        TRUE,           // Inherit handles
        0, // CREATE_NEW_CONSOLE, // Creation flags
        NULL,           // Use parent's environment block
        NULL,           // Use parent's starting directory
        &si,            // Pointer to STARTUPINFO structure
        &pi             // Pointer to PROCESS_INFORMATION structure
    )) 
        errorExit("CreateProcess failed");

    // Close process and thread handles.
    CloseHandle(pi.hProcess);
    CloseHandle(pi.hThread);

    while (true) {
        char inputLine[256];
        char outputLine[64];

        if (fgets(inputLine, 254, stdin) <= 0)
            break;
        inputLine[255] = 0;  // for safety
        int len = (int) strlen(inputLine);
        if (
            inputLine[0] == '\n' ||
            inputLine[0] == 'q'
        )
            break;

        // Write to child
        DWORD written = 0;
        if (!WriteFile(
            hParentOutput, inputLine, len, 
            &written, NULL
        )) 
            break;

        // Receive from child
        DWORD numRead = 0;
        if (
            !ReadFile( 
                hParentInput, outputLine, 62, 
                &numRead, NULL
            ) ||
            numRead == 0
        ) 
            break;
        outputLine[numRead] = 0;
        outputLine[63] = 0;     // for safety
        printf("%s", outputLine);
    }
    if (!CloseHandle(hParentInput)) 
        errorExit("Closing input handle failed"); 
    if (!CloseHandle(hParentOutput)) 
        errorExit("Closing output handle failed"); 
    
    return 0;
}

void errorExit(const char *txt) {
   fprintf(
        stderr, "%s, error=%d\n", 
        txt, GetLastError()
    ); 
    ExitProcess(-1);
}