/*
===========================================================================
Copyright (C) 1999-2005 Id Software, Inc.

This file is part of Quake III Arena source code.

Quake III Arena source code is free software; you can redistribute it
and/or modify it under the terms of the GNU General Public License as
published by the Free Software Foundation; either version 2 of the License,
or (at your option) any later version.

Quake III Arena source code is distributed in the hope that it will be
useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with Quake III Arena source code; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
===========================================================================
*/

#include "SDL.h"

#ifdef SMP
#include "SDL_thread.h"
#endif

#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>

#include "../renderer/tr_local.h"
#include "../client/client.h"
#include "../sys/sys_local.h"
#include "sdl_icon.h"

/* Just hack it for now. */
#ifdef MACOS_X
typedef CGLContextObj QGLContext;
#define GLimp_GetCurrentContext() CGLGetCurrentContext()
#define GLimp_SetCurrentContext(ctx) CGLSetCurrentContext(ctx)
#else
typedef void *QGLContext;
#define GLimp_GetCurrentContext() (NULL)
#define GLimp_SetCurrentContext(ctx)
#endif

static QGLContext opengl_context;

typedef enum
{
	RSERR_OK,

	RSERR_INVALID_FULLSCREEN,
	RSERR_INVALID_MODE,

	RSERR_UNKNOWN
} rserr_t;

static SDL_Surface *screen = NULL;

cvar_t *r_allowSoftwareGL; // Don't abort out if a hardware visual can't be obtained

PFNGLMULTITEXCOORD2FARBPROC qglMultiTexCoord2fARB;
PFNGLACTIVETEXTUREARBPROC qglActiveTextureARB;
PFNGLCLIENTACTIVETEXTUREARBPROC qglClientActiveTextureARB;

PFNGLLOCKARRAYSEXTPROC qglLockArraysEXT;
PFNGLUNLOCKARRAYSEXTPROC qglUnlockArraysEXT;

/*
===============
GLimp_Shutdown
===============
*/
void GLimp_Shutdown( void )
{
	IN_Shutdown();

	SDL_QuitSubSystem( SDL_INIT_VIDEO );
	screen = NULL;

	memset( &glConfig, 0, sizeof( glConfig ) );
	memset( &glState, 0, sizeof( glState ) );
}

/*
===============
GLimp_LogComment
===============
*/
void GLimp_LogComment( char *comment )
{
}

/*
===============
GLimp_SetMode
===============
*/
static int GLimp_SetMode( int mode, qboolean fullscreen )
{
	const char*   glstring;
	int sdlcolorbits;
	int colorbits, depthbits, stencilbits;
	int tcolorbits, tdepthbits, tstencilbits;
	int i = 0;
	SDL_Surface *vidscreen = NULL;

	ri.Printf( PRINT_ALL, "Initializing OpenGL display\n");

	ri.Printf (PRINT_ALL, "...setting mode %d:", mode );

	if ( !R_GetModeInfo( &glConfig.vidWidth, &glConfig.vidHeight, &glConfig.windowAspect, mode ) )
	{
		ri.Printf( PRINT_ALL, " invalid mode\n" );
		return RSERR_INVALID_MODE;
	}
	ri.Printf( PRINT_ALL, " %d %d\n", glConfig.vidWidth, glConfig.vidHeight);

	Uint32 flags = SDL_OPENGL;
	if (fullscreen)
	{
		flags |= SDL_FULLSCREEN;
		glConfig.isFullscreen = qtrue;
	}
	else
		glConfig.isFullscreen = qfalse;

	if (!r_colorbits->value)
		colorbits = 24;
	else
		colorbits = r_colorbits->value;

	if (!r_depthbits->value)
		depthbits = 24;
	else
		depthbits = r_depthbits->value;
	stencilbits = r_stencilbits->value;

	for (i = 0; i < 16; i++)
	{
		// 0 - default
		// 1 - minus colorbits
		// 2 - minus depthbits
		// 3 - minus stencil
		if ((i % 4) == 0 && i)
		{
			// one pass, reduce
			switch (i / 4)
			{
				case 2 :
					if (colorbits == 24)
						colorbits = 16;
					break;
				case 1 :
					if (depthbits == 24)
						depthbits = 16;
					else if (depthbits == 16)
						depthbits = 8;
				case 3 :
					if (stencilbits == 24)
						stencilbits = 16;
					else if (stencilbits == 16)
						stencilbits = 8;
			}
		}

		tcolorbits = colorbits;
		tdepthbits = depthbits;
		tstencilbits = stencilbits;

		if ((i % 4) == 3)
		{ // reduce colorbits
			if (tcolorbits == 24)
				tcolorbits = 16;
		}

		if ((i % 4) == 2)
		{ // reduce depthbits
			if (tdepthbits == 24)
				tdepthbits = 16;
			else if (tdepthbits == 16)
				tdepthbits = 8;
		}

		if ((i % 4) == 1)
		{ // reduce stencilbits
			if (tstencilbits == 24)
				tstencilbits = 16;
			else if (tstencilbits == 16)
				tstencilbits = 8;
			else
				tstencilbits = 0;
		}

		sdlcolorbits = 4;
		if (tcolorbits == 24)
			sdlcolorbits = 8;

		SDL_GL_SetAttribute( SDL_GL_RED_SIZE, sdlcolorbits );
		SDL_GL_SetAttribute( SDL_GL_GREEN_SIZE, sdlcolorbits );
		SDL_GL_SetAttribute( SDL_GL_BLUE_SIZE, sdlcolorbits );
		SDL_GL_SetAttribute( SDL_GL_DEPTH_SIZE, tdepthbits );
		SDL_GL_SetAttribute( SDL_GL_STENCIL_SIZE, tstencilbits );
		SDL_GL_SetAttribute( SDL_GL_DOUBLEBUFFER, 1 );

		// If not allowing software GL, demand accelerated
		if( !r_allowSoftwareGL->integer )
		{
			if( SDL_GL_SetAttribute( SDL_GL_ACCELERATED_VISUAL, 1 ) < 0 )
			{
				ri.Printf( PRINT_ALL, "Unable to guarantee accelerated "
						"visual with libSDL < 1.2.10\n" );
			}
		}

		if( SDL_GL_SetAttribute( SDL_GL_SWAP_CONTROL, r_swapInterval->integer ) < 0 )
			ri.Printf( PRINT_ALL, "r_swapInterval requires libSDL >= 1.2.10\n" );

#ifdef USE_ICON
		{
			SDL_Surface *icon = SDL_CreateRGBSurfaceFrom(
					(void *)CLIENT_WINDOW_ICON.pixel_data,
					CLIENT_WINDOW_ICON.width,
					CLIENT_WINDOW_ICON.height,
					CLIENT_WINDOW_ICON.bytes_per_pixel * 8,
					CLIENT_WINDOW_ICON.bytes_per_pixel * CLIENT_WINDOW_ICON.width,
#ifdef Q3_LITTLE_ENDIAN
					0x000000FF, 0x0000FF00, 0x00FF0000, 0xFF000000
#else
					0xFF000000, 0x00FF0000, 0x0000FF00, 0x000000FF
#endif
					);

			SDL_WM_SetIcon( icon, NULL );
			SDL_FreeSurface( icon );
		}
#endif

		SDL_WM_SetCaption(CLIENT_WINDOW_TITLE, CLIENT_WINDOW_MIN_TITLE);
		SDL_ShowCursor(0);

		if (!(vidscreen = SDL_SetVideoMode(glConfig.vidWidth, glConfig.vidHeight, colorbits, flags)))
		{
			ri.Printf( PRINT_DEVELOPER, "SDL_SetVideoMode failed: %s\n", SDL_GetError( ) );
			continue;
		}

		opengl_context = GLimp_GetCurrentContext();

		ri.Printf( PRINT_ALL, "Using %d/%d/%d Color bits, %d depth, %d stencil display.\n",
				sdlcolorbits, sdlcolorbits, sdlcolorbits, tdepthbits, tstencilbits);

		glConfig.colorBits = tcolorbits;
		glConfig.depthBits = tdepthbits;
		glConfig.stencilBits = tstencilbits;
		break;
	}

	if (!vidscreen)
	{
		ri.Printf( PRINT_ALL, "Couldn't get a visual\n" );
		return RSERR_INVALID_MODE;
	}

	screen = vidscreen;

	glstring = (char *) qglGetString (GL_RENDERER);
	ri.Printf( PRINT_ALL, "GL_RENDERER: %s\n", glstring );

	return RSERR_OK;
}

/*
===============
GLimp_StartDriverAndSetMode
===============
*/
static qboolean GLimp_StartDriverAndSetMode( int mode, qboolean fullscreen )
{
	rserr_t err;

	if (!SDL_WasInit(SDL_INIT_VIDEO))
	{
		ri.Printf( PRINT_ALL, "SDL_Init( SDL_INIT_VIDEO )... ");
		if (SDL_Init(SDL_INIT_VIDEO) == -1)
		{
			ri.Printf( PRINT_ALL, "FAILED (%s)\n", SDL_GetError());
			return qfalse;
		}
		ri.Printf( PRINT_ALL, "OK\n");
	}

	if (fullscreen && Cvar_VariableIntegerValue( "in_nograb" ) )
	{
		ri.Printf( PRINT_ALL, "Fullscreen not allowed with in_nograb 1\n");
		ri.Cvar_Set( "r_fullscreen", "0" );
		r_fullscreen->modified = qfalse;
		fullscreen = qfalse;
	}

	err = GLimp_SetMode( mode, fullscreen );

	switch ( err )
	{
		case RSERR_INVALID_FULLSCREEN:
			ri.Printf( PRINT_ALL, "...WARNING: fullscreen unavailable in this mode\n" );
			return qfalse;
		case RSERR_INVALID_MODE:
			ri.Printf( PRINT_ALL, "...WARNING: could not set the given mode (%d)\n", mode );
			return qfalse;
		default:
			break;
	}

	return qtrue;
}
/*
===============
GLimp_InitExtensions
===============
*/
static void GLimp_InitExtensions( void )
{
	if ( !r_allowExtensions->integer )
	{
		ri.Printf( PRINT_ALL, "* IGNORING OPENGL EXTENSIONS *\n" );
		return;
	}

	ri.Printf( PRINT_ALL, "Initializing OpenGL extensions\n" );

	// GL_S3_s3tc
	if ( Q_stristr( glConfig.extensions_string, "GL_S3_s3tc" ) )
	{
		if ( r_ext_compressed_textures->value )
		{
			glConfig.textureCompression = TC_S3TC;
			ri.Printf( PRINT_ALL, "...using GL_S3_s3tc\n" );
		}
		else
		{
			glConfig.textureCompression = TC_NONE;
			ri.Printf( PRINT_ALL, "...ignoring GL_S3_s3tc\n" );
		}
	}
	else
	{
		glConfig.textureCompression = TC_NONE;
		ri.Printf( PRINT_ALL, "...GL_S3_s3tc not found\n" );
	}

	// GL_EXT_texture_env_add
	glConfig.textureEnvAddAvailable = qfalse;
	if ( Q_stristr( glConfig.extensions_string, "EXT_texture_env_add" ) )
	{
		if ( r_ext_texture_env_add->integer )
		{
			glConfig.textureEnvAddAvailable = qtrue;
			ri.Printf( PRINT_ALL, "...using GL_EXT_texture_env_add\n" );
		}
		else
		{
			glConfig.textureEnvAddAvailable = qfalse;
			ri.Printf( PRINT_ALL, "...ignoring GL_EXT_texture_env_add\n" );
		}
	}
	else
	{
		ri.Printf( PRINT_ALL, "...GL_EXT_texture_env_add not found\n" );
	}

	// GL_ARB_multitexture
	qglMultiTexCoord2fARB = NULL;
	qglActiveTextureARB = NULL;
	qglClientActiveTextureARB = NULL;
	if ( Q_stristr( glConfig.extensions_string, "GL_ARB_multitexture" ) )
	{
		if ( r_ext_multitexture->value )
		{
			qglMultiTexCoord2fARB = ( PFNGLMULTITEXCOORD2FARBPROC ) SDL_GL_GetProcAddress( "glMultiTexCoord2fARB" );
			qglActiveTextureARB = ( PFNGLACTIVETEXTUREARBPROC ) SDL_GL_GetProcAddress( "glActiveTextureARB" );
			qglClientActiveTextureARB = ( PFNGLCLIENTACTIVETEXTUREARBPROC ) SDL_GL_GetProcAddress( "glClientActiveTextureARB" );

			if ( qglActiveTextureARB )
			{
				GLint glint = 0;
				qglGetIntegerv( GL_MAX_TEXTURE_UNITS_ARB, &glint );
				glConfig.maxActiveTextures = (int) glint;
				if ( glConfig.maxActiveTextures > 1 )
				{
					ri.Printf( PRINT_ALL, "...using GL_ARB_multitexture\n" );
				}
				else
				{
					qglMultiTexCoord2fARB = NULL;
					qglActiveTextureARB = NULL;
					qglClientActiveTextureARB = NULL;
					ri.Printf( PRINT_ALL, "...not using GL_ARB_multitexture, < 2 texture units\n" );
				}
			}
		}
		else
		{
			ri.Printf( PRINT_ALL, "...ignoring GL_ARB_multitexture\n" );
		}
	}
	else
	{
		ri.Printf( PRINT_ALL, "...GL_ARB_multitexture not found\n" );
	}

	// GL_EXT_compiled_vertex_array
	if ( Q_stristr( glConfig.extensions_string, "GL_EXT_compiled_vertex_array" ) )
	{
		if ( r_ext_compiled_vertex_array->value )
		{
			ri.Printf( PRINT_ALL, "...using GL_EXT_compiled_vertex_array\n" );
			qglLockArraysEXT = ( void ( APIENTRY * )( GLint, GLint ) ) SDL_GL_GetProcAddress( "glLockArraysEXT" );
			qglUnlockArraysEXT = ( void ( APIENTRY * )( void ) ) SDL_GL_GetProcAddress( "glUnlockArraysEXT" );
			if (!qglLockArraysEXT || !qglUnlockArraysEXT)
			{
				ri.Error (ERR_FATAL, "bad getprocaddress");
			}
		}
		else
		{
			ri.Printf( PRINT_ALL, "...ignoring GL_EXT_compiled_vertex_array\n" );
		}
	}
	else
	{
		ri.Printf( PRINT_ALL, "...GL_EXT_compiled_vertex_array not found\n" );
	}

	textureFilterAnisotropic = qfalse;
	if ( strstr( glConfig.extensions_string, "GL_EXT_texture_filter_anisotropic" ) )
	{
		if ( r_ext_texture_filter_anisotropic->integer ) {
			qglGetIntegerv( GL_MAX_TEXTURE_MAX_ANISOTROPY_EXT, (GLint *)&maxAnisotropy );
			if ( maxAnisotropy <= 0 ) {
				ri.Printf( PRINT_ALL, "...GL_EXT_texture_filter_anisotropic not properly supported!\n" );
				maxAnisotropy = 0;
			}
			else
			{
				ri.Printf( PRINT_ALL, "...using GL_EXT_texture_filter_anisotropic (max: %i)\n", maxAnisotropy );
				textureFilterAnisotropic = qtrue;
			}
		}
		else
		{
			ri.Printf( PRINT_ALL, "...ignoring GL_EXT_texture_filter_anisotropic\n" );
		}
	}
	else
	{
		ri.Printf( PRINT_ALL, "...GL_EXT_texture_filter_anisotropic not found\n" );
	}
}

#define R_MODE_FALLBACK 3 // 640 * 480

/*
===============
GLimp_Init

This routine is responsible for initializing the OS specific portions
of OpenGL
===============
*/
void GLimp_Init( void )
{
	qboolean success = qtrue;

	r_allowSoftwareGL = ri.Cvar_Get( "r_allowSoftwareGL", "0", CVAR_LATCH );

	// create the window and set up the context
	if( !GLimp_StartDriverAndSetMode( r_mode->integer, r_fullscreen->integer ) )
	{
		if( r_mode->integer != R_MODE_FALLBACK )
		{
			ri.Printf( PRINT_ALL, "Setting r_mode %d failed, falling back on r_mode %d",
					r_mode->integer, R_MODE_FALLBACK );
			if( !GLimp_StartDriverAndSetMode( R_MODE_FALLBACK, r_fullscreen->integer ) )
				success = qfalse;
		}
		else
			success = qfalse;
	}

	if( !success )
		ri.Error( ERR_FATAL, "GLimp_Init() - could not load OpenGL subsystem\n" );

	// This values force the UI to disable driver selection
	glConfig.driverType = GLDRV_ICD;
	glConfig.hardwareType = GLHW_GENERIC;
	glConfig.deviceSupportsGamma = !!( SDL_SetGamma( 1.0f, 1.0f, 1.0f ) >= 0 );

	// get our config strings
	Q_strncpyz( glConfig.vendor_string, (char *) qglGetString (GL_VENDOR), sizeof( glConfig.vendor_string ) );
	Q_strncpyz( glConfig.renderer_string, (char *) qglGetString (GL_RENDERER), sizeof( glConfig.renderer_string ) );
	if (*glConfig.renderer_string && glConfig.renderer_string[strlen(glConfig.renderer_string) - 1] == '\n')
		glConfig.renderer_string[strlen(glConfig.renderer_string) - 1] = 0;
	Q_strncpyz( glConfig.version_string, (char *) qglGetString (GL_VERSION), sizeof( glConfig.version_string ) );
	Q_strncpyz( glConfig.extensions_string, (char *) qglGetString (GL_EXTENSIONS), sizeof( glConfig.extensions_string ) );

	// initialize extensions
	GLimp_InitExtensions( );

	// This depends on SDL_INIT_VIDEO, hence having it here
	IN_Init( );

	return;
}


/*
===============
GLimp_EndFrame

Responsible for doing a swapbuffers
===============
*/
void GLimp_EndFrame( void )
{
	// don't flip if drawing to front buffer
	if ( Q_stricmp( r_drawBuffer->string, "GL_FRONT" ) != 0 )
	{
		SDL_GL_SwapBuffers();
	}

	if( r_fullscreen->modified )
	{
		qboolean    fullscreen;
		qboolean    sdlToggled = qfalse;
		SDL_Surface *s = SDL_GetVideoSurface( );

		if( s )
		{
			// Find out the current state
			if( s->flags & SDL_FULLSCREEN )
				fullscreen = qtrue;
			else
				fullscreen = qfalse;

			// Is the state we want different from the current state?
			if( !!r_fullscreen->integer != fullscreen )
				sdlToggled = SDL_WM_ToggleFullScreen( s );
			else
				sdlToggled = qtrue;
		}

		// SDL_WM_ToggleFullScreen didn't work, so do it the slow way
		if( !sdlToggled )
			Cbuf_AddText( "vid_restart" );

		r_fullscreen->modified = qfalse;
	}
}



#ifdef SMP
/*
===========================================================

SMP acceleration

===========================================================
*/

/*
 * I have no idea if this will even work...most platforms don't offer
 * thread-safe OpenGL libraries, and it looks like the original Linux
 * code counted on each thread claiming the GL context with glXMakeCurrent(),
 * which you can't currently do in SDL. We'll just have to hope for the best.
 */

static SDL_mutex *smpMutex = NULL;
static SDL_cond *renderCommandsEvent = NULL;
static SDL_cond *renderCompletedEvent = NULL;
static void (*glimpRenderThread)( void ) = NULL;
static SDL_Thread *renderThread = NULL;

/*
===============
GLimp_ShutdownRenderThread
===============
*/
static void GLimp_ShutdownRenderThread(void)
{
	if (smpMutex != NULL)
	{
		SDL_DestroyMutex(smpMutex);
		smpMutex = NULL;
	}

	if (renderCommandsEvent != NULL)
	{
		SDL_DestroyCond(renderCommandsEvent);
		renderCommandsEvent = NULL;
	}

	if (renderCompletedEvent != NULL)
	{
		SDL_DestroyCond(renderCompletedEvent);
		renderCompletedEvent = NULL;
	}

	glimpRenderThread = NULL;
}

/*
===============
GLimp_RenderThreadWrapper
===============
*/
static int GLimp_RenderThreadWrapper( void *arg )
{
	Com_Printf( "Render thread starting\n" );

	glimpRenderThread();

	GLimp_SetCurrentContext(NULL);

	Com_Printf( "Render thread terminating\n" );

	return 0;
}

/*
===============
GLimp_SpawnRenderThread
===============
*/
qboolean GLimp_SpawnRenderThread( void (*function)( void ) )
{
	static qboolean warned = qfalse;
	if (!warned)
	{
		Com_Printf("WARNING: You enable r_smp at your own risk!\n");
		warned = qtrue;
	}

#ifndef MACOS_X
	return qfalse;  /* better safe than sorry for now. */
#endif

	if (renderThread != NULL)  /* hopefully just a zombie at this point... */
	{
		Com_Printf("Already a render thread? Trying to clean it up...\n");
		SDL_WaitThread(renderThread, NULL);
		renderThread = NULL;
		GLimp_ShutdownRenderThread();
	}

	smpMutex = SDL_CreateMutex();
	if (smpMutex == NULL)
	{
		Com_Printf( "smpMutex creation failed: %s\n", SDL_GetError() );
		GLimp_ShutdownRenderThread();
		return qfalse;
	}

	renderCommandsEvent = SDL_CreateCond();
	if (renderCommandsEvent == NULL)
	{
		Com_Printf( "renderCommandsEvent creation failed: %s\n", SDL_GetError() );
		GLimp_ShutdownRenderThread();
		return qfalse;
	}

	renderCompletedEvent = SDL_CreateCond();
	if (renderCompletedEvent == NULL)
	{
		Com_Printf( "renderCompletedEvent creation failed: %s\n", SDL_GetError() );
		GLimp_ShutdownRenderThread();
		return qfalse;
	}

	glimpRenderThread = function;
	renderThread = SDL_CreateThread(GLimp_RenderThreadWrapper, NULL);
	if ( renderThread == NULL )
	{
		ri.Printf( PRINT_ALL, "SDL_CreateThread() returned %s", SDL_GetError() );
		GLimp_ShutdownRenderThread();
		return qfalse;
	}
	else
	{
		// tma 01/09/07: don't think this is necessary anyway?
		//
		// !!! FIXME: No detach API available in SDL!
		//ret = pthread_detach( renderThread );
		//if ( ret ) {
		//ri.Printf( PRINT_ALL, "pthread_detach returned %d: %s", ret, strerror( ret ) );
		//}
	}

	return qtrue;
}

static volatile void    *smpData = NULL;
static volatile qboolean smpDataReady;

/*
===============
GLimp_RendererSleep
===============
*/
void *GLimp_RendererSleep( void )
{
	void  *data = NULL;

	GLimp_SetCurrentContext(NULL);

	SDL_LockMutex(smpMutex);
	{
		smpData = NULL;
		smpDataReady = qfalse;

		// after this, the front end can exit GLimp_FrontEndSleep
		SDL_CondSignal(renderCompletedEvent);

		while ( !smpDataReady )
			SDL_CondWait(renderCommandsEvent, smpMutex);

		data = (void *)smpData;
	}
	SDL_UnlockMutex(smpMutex);

	GLimp_SetCurrentContext(opengl_context);

	return data;
}

/*
===============
GLimp_FrontEndSleep
===============
*/
void GLimp_FrontEndSleep( void )
{
	SDL_LockMutex(smpMutex);
	{
		while ( smpData )
			SDL_CondWait(renderCompletedEvent, smpMutex);
	}
	SDL_UnlockMutex(smpMutex);

	GLimp_SetCurrentContext(opengl_context);
}

/*
===============
GLimp_WakeRenderer
===============
*/
void GLimp_WakeRenderer( void *data )
{
	GLimp_SetCurrentContext(NULL);

	SDL_LockMutex(smpMutex);
	{
		assert( smpData == NULL );
		smpData = data;
		smpDataReady = qtrue;

		// after this, the renderer can continue through GLimp_RendererSleep
		SDL_CondSignal(renderCommandsEvent);
	}
	SDL_UnlockMutex(smpMutex);
}

#else

// No SMP - stubs
void GLimp_RenderThreadWrapper( void *arg )
{
}

qboolean GLimp_SpawnRenderThread( void (*function)( void ) )
{
	ri.Printf( PRINT_WARNING, "ERROR: SMP support was disabled at compile time\n");
	return qfalse;
}

void *GLimp_RendererSleep( void )
{
	return NULL;
}

void GLimp_FrontEndSleep( void )
{
}

void GLimp_WakeRenderer( void *data )
{
}

#endif