//! @file getcomputername.cpp
//! @author Aaron Katz <v-aakatz@microsoft.com>
//! @brief Implements GetComputerName Win32 API

#include <errno.h>
#include <langinfo.h>
#include <locale.h>
#include <unistd.h>
#include <string>
#include <unicode/unistr.h>
#include "getcomputername.h"

//! @brief GetComputerName retrieves the name of the host associated with
//! the current thread.
//!
//! GetComputerNameW is the Unicode variation. See [MSDN documentation].
//!
//! @param[out] lpBuffer
//! @parblock
//! A pointer to the buffer to receive the hosts's
//! name. If this buffer is not large enough to contain the
//! entire user hosts name, the function fails.
//!
//! WCHAR_T* is a Unicode [LPTSTR].
//! @endparblock
//!
//! @param[in, out] lpnSize
//! @parblock
//! On input, this variable specifies the size of the lpBuffer buffer,
//! in TCHARs. On output, the variable receives the number of TCHARs
//! copied to the buffer, including the terminating null character.
//!
//! TCHAR is a Unicode 16-bit [WCHAR].
//!
//! If lpBuffer is too small, the function fails and GetLastError
//! returns ERROR_INSUFFICIENT_BUFFER. This parameter receives the
//! required buffer size, including the terminating null character.
//! @endparblock
//!
//! @exception errno Passes these errors via errno to GetLastError:
//! - ERROR_INVALID_PARAMETER: parameter is not valid
//! - ERROR_BAD_ENVIRONMENT: locale is not UTF-8
//! - ERROR_TOO_MANY_OPEN_FILES: already have the maximum allowed number of open files
//! - ERROR_NO_ASSOCIATION: calling process has no controlling terminal
//! - ERROR_INSUFFICIENT_BUFFER: buffer not large enough to hold username string
//! - ERROR_NO_SUCH_USER: there was no corresponding entry in the utmp-file
//! - ERROR_OUTOFMEMORY: insufficient memory to allocate passwd structure
//! - ERROR_NO_ASSOCIATION: standard input didn't refer to a terminal
//! - ERROR_INVALID_FUNCTION: getlogin_r() returned an unrecognized error code
//!
//! @retval TRUE If the function succeeds, the return value is a nonzero
//! value, and the variable pointed to by lpnSize contains the number
//! of TCHARs copied to the buffer specified by lpBuffer, including
//! the terminating null character.
//!
//! @retval FALSE If the function fails, the return value is zero. To get
//! extended error information, call GetLastError.
//!
//! [MSDN documentation]: https://msdn.microsoft.com/en-us/library/windows/desktop/ms724295%28v=vs.85%29.aspx
//! [WCHAR]: https://msdn.microsoft.com/en-us/library/windows/desktop/aa383751(v=vs.85).aspx#WCHAR
//! [LPTSTR]: https://msdn.microsoft.com/en-us/library/windows/desktop/aa383751(v=vs.85).aspx#LPTSTR
BOOL GetComputerNameW(WCHAR_T* lpBuffer, LPDWORD lpnSize)
{
    errno = 0;
    
    // Check parameters
    if (!lpBuffer || !lpnSize) 
    {
        errno = ERROR_INVALID_PARAMETER;
        return FALSE;
    }
    
    // Select locale from environment
    setlocale(LC_ALL, "");
    // Check that locale is UTF-8
    if (nl_langinfo(CODESET) != std::string("UTF-8"))
    {
        errno = ERROR_BAD_ENVIRONMENT;
        return FALSE;
    }
    
    // Get computername from system in a thread-safe manner
    std::string computername(HOST_NAME_MAX, 0);
    int err = gethostname(&computername[0], computername.length());
    // Map errno to Win32 Error Codes
    if (err != 0) 
    {
        switch (errno) 
        {
            case EFAULT:
                errno = ERROR_INVALID_ADDRESS;
                break;
            case ENAMETOOLONG:
                errno = ERROR_BUFFER_OVERFLOW;
                break; 
            default:
                errno = ERROR_INVALID_FUNCTION;
        }
        return FALSE;
    }
    
    // Convert to UnicodeString
    auto computername16 = icu::UnicodeString::fromUTF8(computername.c_str());
    // Terminate string with null
    computername16.append('\0');
    
    // Size in WCHARs including null
    const DWORD size = computername16.length();
    
    //Check if parameters passed enough buffer space
    if (size > *lpnSize)
    {
        errno = ERROR_INSUFFICIENT_BUFFER;
        // Set lpnSize if buffer is too small to inform user
        // of necessary size
        *lpnSize= size;
        return FALSE;
    }
    
    // Extract string as UTF-16LE to buffer
    computername16.extract(0, size, reinterpret_cast<char*>(lpBuffer), "UTF-16LE");
    
    *lpnSize = size;
    return TRUE;
    
}