local ffi = require( "ffi" )
local def = [[
typedef enum _NvAPI_Status
{
    NVAPI_OK                                    =  0,      //!< Success. Request is completed.
    NVAPI_ERROR                                 = -1,      //!< Generic error
    NVAPI_LIBRARY_NOT_FOUND                     = -2,      //!< NVAPI support library cannot be loaded.
    NVAPI_NO_IMPLEMENTATION                     = -3,      //!< not implemented in current driver installation
    NVAPI_API_NOT_INITIALIZED                   = -4,      //!< NvAPI_Initialize has not been called (successfully)
    NVAPI_INVALID_ARGUMENT                      = -5,      //!< The argument/parameter value is not valid or NULL.
    NVAPI_NVIDIA_DEVICE_NOT_FOUND               = -6,      //!< No NVIDIA display driver, or NVIDIA GPU driving a display, was found.
    NVAPI_END_ENUMERATION                       = -7,      //!< No more items to enumerate
    NVAPI_INVALID_HANDLE                        = -8,      //!< Invalid handle
    NVAPI_INCOMPATIBLE_STRUCT_VERSION           = -9,      //!< An argument's structure version is not supported
    NVAPI_HANDLE_INVALIDATED                    = -10,     //!< The handle is no longer valid (likely due to GPU or display re-configuration)
    NVAPI_OPENGL_CONTEXT_NOT_CURRENT            = -11,     //!< No NVIDIA OpenGL context is current (but needs to be)
    NVAPI_INVALID_POINTER                       = -14,     //!< An invalid pointer, usually NULL, was passed as a parameter
    NVAPI_NO_GL_EXPERT                          = -12,     //!< OpenGL Expert is not supported by the current drivers
    NVAPI_INSTRUMENTATION_DISABLED              = -13,     //!< OpenGL Expert is supported, but driver instrumentation is currently disabled
    NVAPI_NO_GL_NSIGHT                          = -15,     //!< OpenGL does not support Nsight

    NVAPI_EXPECTED_LOGICAL_GPU_HANDLE           = -100,    //!< Expected a logical GPU handle for one or more parameters
    NVAPI_EXPECTED_PHYSICAL_GPU_HANDLE          = -101,    //!< Expected a physical GPU handle for one or more parameters
    NVAPI_EXPECTED_DISPLAY_HANDLE               = -102,    //!< Expected an NV display handle for one or more parameters
    NVAPI_INVALID_COMBINATION                   = -103,    //!< The combination of parameters is not valid. 
    NVAPI_NOT_SUPPORTED                         = -104,    //!< Requested feature is not supported in the selected GPU
    NVAPI_PORTID_NOT_FOUND                      = -105,    //!< No port ID was found for the I2C transaction
    NVAPI_EXPECTED_UNATTACHED_DISPLAY_HANDLE    = -106,    //!< Expected an unattached display handle as one of the input parameters.
    NVAPI_INVALID_PERF_LEVEL                    = -107,    //!< Invalid perf level 
    NVAPI_DEVICE_BUSY                           = -108,    //!< Device is busy; request not fulfilled
    NVAPI_NV_PERSIST_FILE_NOT_FOUND             = -109,    //!< NV persist file is not found
    NVAPI_PERSIST_DATA_NOT_FOUND                = -110,    //!< NV persist data is not found
    NVAPI_EXPECTED_TV_DISPLAY                   = -111,    //!< Expected a TV output display
    NVAPI_EXPECTED_TV_DISPLAY_ON_DCONNECTOR     = -112,    //!< Expected a TV output on the D Connector - HDTV_EIAJ4120.
    NVAPI_NO_ACTIVE_SLI_TOPOLOGY                = -113,    //!< SLI is not active on this device.
    NVAPI_SLI_RENDERING_MODE_NOTALLOWED         = -114,    //!< Setup of SLI rendering mode is not possible right now.
    NVAPI_EXPECTED_DIGITAL_FLAT_PANEL           = -115,    //!< Expected a digital flat panel.
    NVAPI_ARGUMENT_EXCEED_MAX_SIZE              = -116,    //!< Argument exceeds the expected size.
    NVAPI_DEVICE_SWITCHING_NOT_ALLOWED          = -117,    //!< Inhibit is ON due to one of the flags in NV_GPU_DISPLAY_CHANGE_INHIBIT or SLI active.
    NVAPI_TESTING_CLOCKS_NOT_SUPPORTED          = -118,    //!< Testing of clocks is not supported.
    NVAPI_UNKNOWN_UNDERSCAN_CONFIG              = -119,    //!< The specified underscan config is from an unknown source (e.g. INF)
    NVAPI_TIMEOUT_RECONFIGURING_GPU_TOPO        = -120,    //!< Timeout while reconfiguring GPUs
    NVAPI_DATA_NOT_FOUND                        = -121,    //!< Requested data was not found
    NVAPI_EXPECTED_ANALOG_DISPLAY               = -122,    //!< Expected an analog display
    NVAPI_NO_VIDLINK                            = -123,    //!< No SLI video bridge is present
    NVAPI_REQUIRES_REBOOT                       = -124,    //!< NVAPI requires a reboot for the settings to take effect
    NVAPI_INVALID_HYBRID_MODE                   = -125,    //!< The function is not supported with the current Hybrid mode.
    NVAPI_MIXED_TARGET_TYPES                    = -126,    //!< The target types are not all the same
    NVAPI_SYSWOW64_NOT_SUPPORTED                = -127,    //!< The function is not supported from 32-bit on a 64-bit system.
    NVAPI_IMPLICIT_SET_GPU_TOPOLOGY_CHANGE_NOT_ALLOWED = -128,    //!< There is no implicit GPU topology active. Use NVAPI_SetHybridMode to change topology.
    NVAPI_REQUEST_USER_TO_CLOSE_NON_MIGRATABLE_APPS = -129,      //!< Prompt the user to close all non-migratable applications.    
    NVAPI_OUT_OF_MEMORY                         = -130,    //!< Could not allocate sufficient memory to complete the call.
    NVAPI_WAS_STILL_DRAWING                     = -131,    //!< The previous operation that is transferring information to or from this surface is incomplete.
    NVAPI_FILE_NOT_FOUND                        = -132,    //!< The file was not found.
    NVAPI_TOO_MANY_UNIQUE_STATE_OBJECTS         = -133,    //!< There are too many unique instances of a particular type of state object.
    NVAPI_INVALID_CALL                          = -134,    //!< The method call is invalid. For example, a method's parameter may not be a valid pointer.
    NVAPI_D3D10_1_LIBRARY_NOT_FOUND             = -135,    //!< d3d10_1.dll cannot be loaded.
    NVAPI_FUNCTION_NOT_FOUND                    = -136,    //!< Couldn't find the function in the loaded DLL.
    NVAPI_INVALID_USER_PRIVILEGE                = -137,    //!< Current User is not Admin.
    NVAPI_EXPECTED_NON_PRIMARY_DISPLAY_HANDLE   = -138,    //!< The handle corresponds to GDIPrimary.
    NVAPI_EXPECTED_COMPUTE_GPU_HANDLE           = -139,    //!< Setting Physx GPU requires that the GPU is compute-capable.
    NVAPI_STEREO_NOT_INITIALIZED                = -140,    //!< The Stereo part of NVAPI failed to initialize completely. Check if the stereo driver is installed.
    NVAPI_STEREO_REGISTRY_ACCESS_FAILED         = -141,    //!< Access to stereo-related registry keys or values has failed.
    NVAPI_STEREO_REGISTRY_PROFILE_TYPE_NOT_SUPPORTED = -142, //!< The given registry profile type is not supported.
    NVAPI_STEREO_REGISTRY_VALUE_NOT_SUPPORTED   = -143,    //!< The given registry value is not supported.
    NVAPI_STEREO_NOT_ENABLED                    = -144,    //!< Stereo is not enabled and the function needed it to execute completely.
    NVAPI_STEREO_NOT_TURNED_ON                  = -145,    //!< Stereo is not turned on and the function needed it to execute completely.
    NVAPI_STEREO_INVALID_DEVICE_INTERFACE       = -146,    //!< Invalid device interface.
    NVAPI_STEREO_PARAMETER_OUT_OF_RANGE         = -147,    //!< Separation percentage or JPEG image capture quality is out of [0-100] range.
    NVAPI_STEREO_FRUSTUM_ADJUST_MODE_NOT_SUPPORTED = -148, //!< The given frustum adjust mode is not supported.
    NVAPI_TOPO_NOT_POSSIBLE                     = -149,    //!< The mosaic topology is not possible given the current state of the hardware.
    NVAPI_MODE_CHANGE_FAILED                    = -150,    //!< An attempt to do a display resolution mode change has failed.        
    NVAPI_D3D11_LIBRARY_NOT_FOUND               = -151,    //!< d3d11.dll/d3d11_beta.dll cannot be loaded.
    NVAPI_INVALID_ADDRESS                       = -152,    //!< Address is outside of valid range.
    NVAPI_STRING_TOO_SMALL                      = -153,    //!< The pre-allocated string is too small to hold the result.
    NVAPI_MATCHING_DEVICE_NOT_FOUND             = -154,    //!< The input does not match any of the available devices.
    NVAPI_DRIVER_RUNNING                        = -155,    //!< Driver is running.
    NVAPI_DRIVER_NOTRUNNING                     = -156,    //!< Driver is not running.
    NVAPI_ERROR_DRIVER_RELOAD_REQUIRED          = -157,    //!< A driver reload is required to apply these settings.
    NVAPI_SET_NOT_ALLOWED                       = -158,    //!< Intended setting is not allowed.
    NVAPI_ADVANCED_DISPLAY_TOPOLOGY_REQUIRED    = -159,    //!< Information can't be returned due to "advanced display topology".
    NVAPI_SETTING_NOT_FOUND                     = -160,    //!< Setting is not found.
    NVAPI_SETTING_SIZE_TOO_LARGE                = -161,    //!< Setting size is too large.
    NVAPI_TOO_MANY_SETTINGS_IN_PROFILE          = -162,    //!< There are too many settings for a profile. 
    NVAPI_PROFILE_NOT_FOUND                     = -163,    //!< Profile is not found.
    NVAPI_PROFILE_NAME_IN_USE                   = -164,    //!< Profile name is duplicated.
    NVAPI_PROFILE_NAME_EMPTY                    = -165,    //!< Profile name is empty.
    NVAPI_EXECUTABLE_NOT_FOUND                  = -166,    //!< Application not found in the Profile.
    NVAPI_EXECUTABLE_ALREADY_IN_USE             = -167,    //!< Application already exists in the other profile.
    NVAPI_DATATYPE_MISMATCH                     = -168,    //!< Data Type mismatch 
    NVAPI_PROFILE_REMOVED                       = -169,    //!< The profile passed as parameter has been removed and is no longer valid.
    NVAPI_UNREGISTERED_RESOURCE                 = -170,    //!< An unregistered resource was passed as a parameter. 
    NVAPI_ID_OUT_OF_RANGE                       = -171,    //!< The DisplayId corresponds to a display which is not within the normal outputId range.
    NVAPI_DISPLAYCONFIG_VALIDATION_FAILED       = -172,    //!< Display topology is not valid so the driver cannot do a mode set on this configuration.
    NVAPI_DPMST_CHANGED                         = -173,    //!< Display Port Multi-Stream topology has been changed.
    NVAPI_INSUFFICIENT_BUFFER                   = -174,    //!< Input buffer is insufficient to hold the contents.    
    NVAPI_ACCESS_DENIED                         = -175,    //!< No access to the caller.
    NVAPI_MOSAIC_NOT_ACTIVE                     = -176,    //!< The requested action cannot be performed without Mosaic being enabled.
    NVAPI_SHARE_RESOURCE_RELOCATED              = -177,    //!< The surface is relocated away from video memory.
    NVAPI_REQUEST_USER_TO_DISABLE_DWM           = -178,    //!< The user should disable DWM before calling NvAPI.
    NVAPI_D3D_DEVICE_LOST                       = -179,    //!< D3D device status is D3DERR_DEVICELOST or D3DERR_DEVICENOTRESET - the user has to reset the device.
    NVAPI_INVALID_CONFIGURATION                 = -180,    //!< The requested action cannot be performed in the current state.
    NVAPI_STEREO_HANDSHAKE_NOT_DONE             = -181,    //!< Call failed as stereo handshake not completed.
    NVAPI_EXECUTABLE_PATH_IS_AMBIGUOUS          = -182,    //!< The path provided was too short to determine the correct NVDRS_APPLICATION
    NVAPI_DEFAULT_STEREO_PROFILE_IS_NOT_DEFINED = -183,    //!< Default stereo profile is not currently defined
    NVAPI_DEFAULT_STEREO_PROFILE_DOES_NOT_EXIST = -184,    //!< Default stereo profile does not exist
    NVAPI_CLUSTER_ALREADY_EXISTS                = -185,    //!< A cluster is already defined with the given configuration.
    NVAPI_DPMST_DISPLAY_ID_EXPECTED             = -186,    //!< The input display id is not that of a multi stream enabled connector or a display device in a multi stream topology 
    NVAPI_INVALID_DISPLAY_ID                    = -187,    //!< The input display id is not valid or the monitor associated to it does not support the current operation
    NVAPI_STREAM_IS_OUT_OF_SYNC                 = -188,    //!< While playing secure audio stream, stream goes out of sync
    NVAPI_INCOMPATIBLE_AUDIO_DRIVER             = -189,    //!< Older audio driver version than required
    NVAPI_VALUE_ALREADY_SET                     = -190,    //!< Value already set, setting again not allowed.
    NVAPI_TIMEOUT                               = -191,    //!< Requested operation timed out 
} NvAPI_Status;

enum {
  NVAPI_GENERIC_STRING_MAX    = 4096,
  NVAPI_LONG_STRING_MAX       = 256,
  NVAPI_SHORT_STRING_MAX      = 64,
};

typedef char NvAPI_String[NVAPI_GENERIC_STRING_MAX];
typedef char NvAPI_LongString[NVAPI_LONG_STRING_MAX];
typedef char NvAPI_ShortString[NVAPI_SHORT_STRING_MAX];

extern void* nvapi_QueryInterface(uint32_t interface);

typedef struct NvAPI_Lib_ {
  int (*NvAPI_Initialize)();
  int (*NvAPI_SYS_GetDriverAndBranchVersion)(uint32_t* pDriverVersion, NvAPI_ShortString szBuildBranchString);
} NvAPI_Lib;
]]

ffi.cdef(def)
local lib = ffi.load("nvapi"..(ffi.abi("64bit") and "64" or ""))

-- codes taken from
-- http://t4629.codeinpro.us/q/51501e06e8432c042615189a
local ext = ffi.new("NvAPI_Lib")
ext.NvAPI_Initialize = lib.nvapi_QueryInterface(0x0150E828)
ext.NvAPI_SYS_GetDriverAndBranchVersion = lib.nvapi_QueryInterface(0x2926AAAD)

local init = ext.NvAPI_Initialize()
return init == lib.NVAPI_OK and ext or nil