/* 

  * tclLink.c --

  *

  *	This file implements linked variables (a C variable that is

  *	tied to a Tcl variable).  The idea of linked variables was

  *	first suggested by Andreas Stolcke and this implementation is

  *	based heavily on a prototype implementation provided by

  *	him.

  *

  * Copyright (c) 1993 The Regents of the University of California.

  * Copyright (c) 1994-1997 Sun Microsystems, Inc.

  * Portions Copyright (c) 2007-2008 Nokia Corporation and/or its subsidiaries. All rights reserved.  

  *

  * See the file "license.terms" for information on usage and redistribution

  * of this file, and for a DISCLAIMER OF ALL WARRANTIES.

  *

  * RCS: @(#) $Id: tclLink.c,v 1.8.2.2 2007/05/10 18:23:58 dgp Exp $

  */

 #include "tclInt.h"

 /*

  * For each linked variable there is a data structure of the following

  * type, which describes the link and is the clientData for the trace

  * set on the Tcl variable.

  */

 typedef struct Link {

     Tcl_Interp *interp;		/* Interpreter containing Tcl variable. */

     Tcl_Obj *varName;		/* Name of variable (must be global).  This

 				 * is needed during trace callbacks, since

 				 * the actual variable may be aliased at

 				 * that time via upvar. */

     char *addr;			/* Location of C variable. */

     int type;			/* Type of link (TCL_LINK_INT, etc.). */

     union {

 	int i;

 	double d;

 	Tcl_WideInt w;

     } lastValue;		/* Last known value of C variable;  used to

 				 * avoid string conversions. */

     int flags;			/* Miscellaneous one-bit values;  see below

 				 * for definitions. */

 } Link;

 /*

  * Definitions for flag bits:

  * LINK_READ_ONLY -		1 means errors should be generated if Tcl

  *				script attempts to write variable.

  * LINK_BEING_UPDATED -		1 means that a call to Tcl_UpdateLinkedVar

  *				is in progress for this variable, so

  *				trace callbacks on the variable should

  *				be ignored.

  */

 #define LINK_READ_ONLY		1

 #define LINK_BEING_UPDATED	2

 /*

  * Forward references to procedures defined later in this file:

  */

 static char *		LinkTraceProc _ANSI_ARGS_((ClientData clientData,

 			    Tcl_Interp *interp, CONST char *name1, 

                             CONST char *name2, int flags));

 static Tcl_Obj *	ObjValue _ANSI_ARGS_((Link *linkPtr));

 /*

  *----------------------------------------------------------------------

  *

  * Tcl_LinkVar --

  *

  *	Link a C variable to a Tcl variable so that changes to either

  *	one causes the other to change.

  *

  * Results:

  *	The return value is TCL_OK if everything went well or TCL_ERROR

  *	if an error occurred (the interp's result is also set after

  *	errors).

  *

  * Side effects:

  *	The value at *addr is linked to the Tcl variable "varName",

  *	using "type" to convert between string values for Tcl and

  *	binary values for *addr.

  *

  *----------------------------------------------------------------------

  */

 EXPORT_C int

 Tcl_LinkVar(interp, varName, addr, type)

     Tcl_Interp *interp;		/* Interpreter in which varName exists. */

     CONST char *varName;	/* Name of a global variable in interp. */

     char *addr;			/* Address of a C variable to be linked

 				 * to varName. */

     int type;			/* Type of C variable: TCL_LINK_INT, etc. 

 				 * Also may have TCL_LINK_READ_ONLY

 				 * OR'ed in. */

 {

     Tcl_Obj *objPtr, *resPtr;

     Link *linkPtr;

     int code;

     linkPtr = (Link *) ckalloc(sizeof(Link));

     linkPtr->interp = interp;

     linkPtr->varName = Tcl_NewStringObj(varName, -1);

     Tcl_IncrRefCount(linkPtr->varName);

     linkPtr->addr = addr;

     linkPtr->type = type & ~TCL_LINK_READ_ONLY;

     if (type & TCL_LINK_READ_ONLY) {

 	linkPtr->flags = LINK_READ_ONLY;

     } else {

 	linkPtr->flags = 0;

     }

     objPtr = ObjValue(linkPtr);

     Tcl_IncrRefCount(objPtr);

     resPtr = Tcl_ObjSetVar2(interp, linkPtr->varName, NULL, objPtr,

 	    TCL_GLOBAL_ONLY|TCL_LEAVE_ERR_MSG);

     Tcl_DecrRefCount(objPtr);

     if (resPtr == NULL) {

 	Tcl_DecrRefCount(linkPtr->varName);

 	ckfree((char *) linkPtr);

 	return TCL_ERROR;

     }

     code = Tcl_TraceVar(interp, varName, TCL_GLOBAL_ONLY|TCL_TRACE_READS

 	    |TCL_TRACE_WRITES|TCL_TRACE_UNSETS, LinkTraceProc,

 	    (ClientData) linkPtr);

     if (code != TCL_OK) {

 	Tcl_DecrRefCount(linkPtr->varName);

 	ckfree((char *) linkPtr);

     }

     return code;

 }

 /*

  *----------------------------------------------------------------------

  *

  * Tcl_UnlinkVar --

  *

  *	Destroy the link between a Tcl variable and a C variable.

  *

  * Results:

  *	None.

  *

  * Side effects:

  *	If "varName" was previously linked to a C variable, the link

  *	is broken to make the variable independent.  If there was no

  *	previous link for "varName" then nothing happens.

  *

  *----------------------------------------------------------------------

  */

 EXPORT_C void

 Tcl_UnlinkVar(interp, varName)

     Tcl_Interp *interp;		/* Interpreter containing variable to unlink. */

     CONST char *varName;	/* Global variable in interp to unlink. */

 {

     Link *linkPtr;

     linkPtr = (Link *) Tcl_VarTraceInfo(interp, varName, TCL_GLOBAL_ONLY,

 	    LinkTraceProc, (ClientData) NULL);

     if (linkPtr == NULL) {

 	return;

     }

     Tcl_UntraceVar(interp, varName,

 	    TCL_GLOBAL_ONLY|TCL_TRACE_READS|TCL_TRACE_WRITES|TCL_TRACE_UNSETS,

 	    LinkTraceProc, (ClientData) linkPtr);

     Tcl_DecrRefCount(linkPtr->varName);

     ckfree((char *) linkPtr);

 }

 /*

  *----------------------------------------------------------------------

  *

  * Tcl_UpdateLinkedVar --

  *

  *	This procedure is invoked after a linked variable has been

  *	changed by C code.  It updates the Tcl variable so that

  *	traces on the variable will trigger.

  *

  * Results:

  *	None.

  *

  * Side effects:

  *	The Tcl variable "varName" is updated from its C value,

  *	causing traces on the variable to trigger.

  *

  *----------------------------------------------------------------------

  */

 EXPORT_C void

 Tcl_UpdateLinkedVar(interp, varName)

     Tcl_Interp *interp;		/* Interpreter containing variable. */

     CONST char *varName;	/* Name of global variable that is linked. */

 {

     Link *linkPtr;

     int savedFlag;

     Tcl_Obj *objPtr;

     linkPtr = (Link *) Tcl_VarTraceInfo(interp, varName, TCL_GLOBAL_ONLY,

 	    LinkTraceProc, (ClientData) NULL);

     if (linkPtr == NULL) {

 	return;

     }

     savedFlag = linkPtr->flags & LINK_BEING_UPDATED;

     linkPtr->flags |= LINK_BEING_UPDATED;

     objPtr = ObjValue(linkPtr);

     Tcl_IncrRefCount(objPtr);

     Tcl_ObjSetVar2(interp, linkPtr->varName, NULL, objPtr, TCL_GLOBAL_ONLY);

     Tcl_DecrRefCount(objPtr);

     linkPtr->flags = (linkPtr->flags & ~LINK_BEING_UPDATED) | savedFlag;

 }

 /*

  *----------------------------------------------------------------------

  *

  * LinkTraceProc --

  *

  *	This procedure is invoked when a linked Tcl variable is read,

  *	written, or unset from Tcl.  It's responsible for keeping the

  *	C variable in sync with the Tcl variable.

  *

  * Results:

  *	If all goes well, NULL is returned; otherwise an error message

  *	is returned.

  *

  * Side effects:

  *	The C variable may be updated to make it consistent with the

  *	Tcl variable, or the Tcl variable may be overwritten to reject

  *	a modification.

  *

  *----------------------------------------------------------------------

  */

 static char *

 LinkTraceProc(clientData, interp, name1, name2, flags)

     ClientData clientData;	/* Contains information about the link. */

     Tcl_Interp *interp;		/* Interpreter containing Tcl variable. */

     CONST char *name1;		/* First part of variable name. */

     CONST char *name2;		/* Second part of variable name. */

     int flags;			/* Miscellaneous additional information. */

 {

     Link *linkPtr = (Link *) clientData;

     int changed, valueLength;

     CONST char *value;

     char **pp, *result;

     Tcl_Obj *objPtr, *valueObj, *tmpPtr;

     /*

      * If the variable is being unset, then just re-create it (with a

      * trace) unless the whole interpreter is going away.

      */

     if (flags & TCL_TRACE_UNSETS) {

 	if (Tcl_InterpDeleted(interp)) {

 	    Tcl_DecrRefCount(linkPtr->varName);

 	    ckfree((char *) linkPtr);

 	} else if (flags & TCL_TRACE_DESTROYED) {

 	    tmpPtr = ObjValue(linkPtr);

 	    Tcl_IncrRefCount(tmpPtr);

 	    Tcl_ObjSetVar2(interp, linkPtr->varName, NULL, tmpPtr,

 		    TCL_GLOBAL_ONLY);

 	    Tcl_DecrRefCount(tmpPtr);

 	    Tcl_TraceVar(interp, Tcl_GetString(linkPtr->varName),

 		    TCL_GLOBAL_ONLY|TCL_TRACE_READS|TCL_TRACE_WRITES

 		    |TCL_TRACE_UNSETS, LinkTraceProc, (ClientData) linkPtr);

 	}

 	return NULL;

     }

     /*

      * If we were invoked because of a call to Tcl_UpdateLinkedVar, then

      * don't do anything at all.  In particular, we don't want to get

      * upset that the variable is being modified, even if it is

      * supposed to be read-only.

      */

     if (linkPtr->flags & LINK_BEING_UPDATED) {

 	return NULL;

     }

     /*

      * For read accesses, update the Tcl variable if the C variable

      * has changed since the last time we updated the Tcl variable.

      */

     if (flags & TCL_TRACE_READS) {

 	switch (linkPtr->type) {

 	case TCL_LINK_INT:

 	case TCL_LINK_BOOLEAN:

 	    changed = *(int *)(linkPtr->addr) != linkPtr->lastValue.i;

 	    break;

 	case TCL_LINK_DOUBLE:

 	    changed = *(double *)(linkPtr->addr) != linkPtr->lastValue.d;

 	    break;

 	case TCL_LINK_WIDE_INT:

 	    changed = *(Tcl_WideInt *)(linkPtr->addr) != linkPtr->lastValue.w;

 	    break;

 	case TCL_LINK_STRING:

 	    changed = 1;

 	    break;

 	default:

 	    return "internal error: bad linked variable type";

 	}

 	if (changed) {

 	    tmpPtr = ObjValue(linkPtr);

 	    Tcl_IncrRefCount(tmpPtr);

 	    Tcl_ObjSetVar2(interp, linkPtr->varName, NULL, tmpPtr,

 		    TCL_GLOBAL_ONLY);

 	    Tcl_DecrRefCount(tmpPtr);

 	}

 	return NULL;

     }

     /*

      * For writes, first make sure that the variable is writable.  Then

      * convert the Tcl value to C if possible.  If the variable isn't

      * writable or can't be converted, then restore the varaible's old

      * value and return an error.  Another tricky thing: we have to save

      * and restore the interpreter's result, since the variable access

      * could occur when the result has been partially set.

      */

     if (linkPtr->flags & LINK_READ_ONLY) {

 	tmpPtr = ObjValue(linkPtr);

 	Tcl_IncrRefCount(tmpPtr);

 	Tcl_ObjSetVar2(interp, linkPtr->varName, NULL, tmpPtr,

 		TCL_GLOBAL_ONLY);

 	Tcl_DecrRefCount(tmpPtr);

 	return "linked variable is read-only";

     }

     valueObj = Tcl_ObjGetVar2(interp, linkPtr->varName,NULL, TCL_GLOBAL_ONLY);

     if (valueObj == NULL) {

 	/*

 	 * This shouldn't ever happen.

 	 */

 	return "internal error: linked variable couldn't be read";

     }

     objPtr = Tcl_GetObjResult(interp);

     Tcl_IncrRefCount(objPtr);

     Tcl_ResetResult(interp);

     result = NULL;

     switch (linkPtr->type) {

     case TCL_LINK_INT:

 	if (Tcl_GetIntFromObj(interp, valueObj, &linkPtr->lastValue.i)

 		!= TCL_OK) {

 	    Tcl_SetObjResult(interp, objPtr);

 	    tmpPtr = ObjValue(linkPtr);

 	    Tcl_IncrRefCount(tmpPtr);

 	    Tcl_ObjSetVar2(interp, linkPtr->varName, NULL, tmpPtr,

 		    TCL_GLOBAL_ONLY);

 	    Tcl_DecrRefCount(tmpPtr);

 	    result = "variable must have integer value";

 	    goto end;

 	}

 	*(int *)(linkPtr->addr) = linkPtr->lastValue.i;

 	break;

     case TCL_LINK_WIDE_INT:

 	if (Tcl_GetWideIntFromObj(interp, valueObj, &linkPtr->lastValue.w)

 		!= TCL_OK) {

 	    Tcl_SetObjResult(interp, objPtr);

 	    tmpPtr = ObjValue(linkPtr);

 	    Tcl_IncrRefCount(tmpPtr);

 	    Tcl_ObjSetVar2(interp, linkPtr->varName, NULL, tmpPtr,

 		    TCL_GLOBAL_ONLY);

 	    Tcl_DecrRefCount(tmpPtr);

 	    result = "variable must have integer value";

 	    goto end;

 	}

 	*(Tcl_WideInt *)(linkPtr->addr) = linkPtr->lastValue.w;

 	break;

     case TCL_LINK_DOUBLE:

 	if (Tcl_GetDoubleFromObj(interp, valueObj, &linkPtr->lastValue.d)

 		!= TCL_OK) {

 	    Tcl_SetObjResult(interp, objPtr);

 	    tmpPtr = ObjValue(linkPtr);

 	    Tcl_IncrRefCount(tmpPtr);

 	    Tcl_ObjSetVar2(interp, linkPtr->varName, NULL, tmpPtr,

 		    TCL_GLOBAL_ONLY);

 	    Tcl_DecrRefCount(tmpPtr);

 	    result = "variable must have real value";

 	    goto end;

 	}

 	*(double *)(linkPtr->addr) = linkPtr->lastValue.d;

 	break;

     case TCL_LINK_BOOLEAN:

 	if (Tcl_GetBooleanFromObj(interp, valueObj, &linkPtr->lastValue.i)

 	    != TCL_OK) {

 	    Tcl_SetObjResult(interp, objPtr);

 	    tmpPtr = ObjValue(linkPtr);

 	    Tcl_IncrRefCount(tmpPtr);

 	    Tcl_ObjSetVar2(interp, linkPtr->varName, NULL, tmpPtr,

 		    TCL_GLOBAL_ONLY);

 	    Tcl_DecrRefCount(tmpPtr);

 	    result = "variable must have boolean value";

 	    goto end;

 	}

 	*(int *)(linkPtr->addr) = linkPtr->lastValue.i;

 	break;

     case TCL_LINK_STRING:

 	value = Tcl_GetStringFromObj(valueObj, &valueLength);

 	valueLength++;

 	pp = (char **)(linkPtr->addr);

 	if (*pp != NULL) {

 	    ckfree(*pp);

 	}

 	*pp = (char *) ckalloc((unsigned) valueLength);

 	memcpy(*pp, value, (unsigned) valueLength);

 	break;

     default:

 	return "internal error: bad linked variable type";

     }

     end:

     Tcl_DecrRefCount(objPtr);

     return result;

 }

 /*

  *----------------------------------------------------------------------

  *

  * ObjValue --

  *

  *	Converts the value of a C variable to a Tcl_Obj* for use in a

  *	Tcl variable to which it is linked.

  *

  * Results:

  *	The return value is a pointer to a Tcl_Obj that represents

  *	the value of the C variable given by linkPtr.

  *

  * Side effects:

  *	None.

  *

  *----------------------------------------------------------------------

  */

 static Tcl_Obj *

 ObjValue(linkPtr)

     Link *linkPtr;		/* Structure describing linked variable. */

 {

     char *p;

     switch (linkPtr->type) {

     case TCL_LINK_INT:

 	linkPtr->lastValue.i = *(int *)(linkPtr->addr);

 	return Tcl_NewIntObj(linkPtr->lastValue.i);

     case TCL_LINK_WIDE_INT:

 	linkPtr->lastValue.w = *(Tcl_WideInt *)(linkPtr->addr);

 	return Tcl_NewWideIntObj(linkPtr->lastValue.w);

     case TCL_LINK_DOUBLE:

 	linkPtr->lastValue.d = *(double *)(linkPtr->addr);

 	return Tcl_NewDoubleObj(linkPtr->lastValue.d);

     case TCL_LINK_BOOLEAN:

 	linkPtr->lastValue.i = *(int *)(linkPtr->addr);

 	return Tcl_NewBooleanObj(linkPtr->lastValue.i != 0);

     case TCL_LINK_STRING:

 	p = *(char **)(linkPtr->addr);

 	if (p == NULL) {

 	    return Tcl_NewStringObj("NULL", 4);

 	}

 	return Tcl_NewStringObj(p, -1);

     /*

      * This code only gets executed if the link type is unknown

      * (shouldn't ever happen).

      */

     default:

 	return Tcl_NewStringObj("??", 2);

     }

 }