/*
 * tclResolve.c --
 *
 *      Contains hooks for customized command/variable name resolution
 *      schemes.  These hooks allow extensions like [incr Tcl] to add
 *      their own name resolution rules to the Tcl language.  Rules can
 *      be applied to a particular namespace, to the interpreter as a
 *      whole, or both.
 *
 * Copyright (c) 1998 Lucent Technologies, Inc.
 *
 * See the file "license.terms" for information on usage and redistribution
 * of this file, and for a DISCLAIMER OF ALL WARRANTIES.
 */

#include "tclInt.h"

/*
 * Declarations for procedures local to this file:
 */

static void		BumpCmdRefEpochs _ANSI_ARGS_((Namespace *nsPtr));


/*
 *----------------------------------------------------------------------
 *
 * Tcl_AddInterpResolvers --
 *
 *	Adds a set of command/variable resolution procedures to an
 *	interpreter.  These procedures are consulted when commands
 *	are resolved in Tcl_FindCommand, and when variables are
 *	resolved in TclLookupVar and LookupCompiledLocal.  Each
 *	namespace may also have its own set of resolution procedures
 *	which take precedence over those for the interpreter.
 *
 *	When a name is resolved, it is handled as follows.  First,
 *	the name is passed to the resolution procedures for the
 *	namespace.  If not resolved, the name is passed to each of
 *	the resolution procedures added to the interpreter.  Finally,
 *	if still not resolved, the name is handled using the default
 *	Tcl rules for name resolution.
 *
 * Results:
 *	Returns pointers to the current name resolution procedures
 *	in the cmdProcPtr, varProcPtr and compiledVarProcPtr
 *	arguments.
 *
 * Side effects:
 *	If a compiledVarProc is specified, this procedure bumps the
 *	compileEpoch for the interpreter, forcing all code to be
 *	recompiled.  If a cmdProc is specified, this procedure bumps
 *	the cmdRefEpoch in all namespaces, forcing commands to be
 *	resolved again using the new rules.
 *
 *----------------------------------------------------------------------
 */

void
Tcl_AddInterpResolvers(interp, name, cmdProc, varProc, compiledVarProc)

    Tcl_Interp *interp;			/* Interpreter whose name resolution
					 * rules are being modified. */
    CONST char *name;			/* Name of this resolution scheme. */
    Tcl_ResolveCmdProc *cmdProc;	/* New procedure for command
					 * resolution */
    Tcl_ResolveVarProc *varProc;	/* Procedure for variable resolution
					 * at runtime */
    Tcl_ResolveCompiledVarProc *compiledVarProc;
					/* Procedure for variable resolution
					 * at compile time. */
{
    Interp *iPtr = (Interp*)interp;
    ResolverScheme *resPtr;

    /*
     *  Since we're adding a new name resolution scheme, we must force
     *  all code to be recompiled to use the new scheme.  If there
     *  are new compiled variable resolution rules, bump the compiler
     *  epoch to invalidate compiled code.  If there are new command
     *  resolution rules, bump the cmdRefEpoch in all namespaces.
     */
    if (compiledVarProc) {
        iPtr->compileEpoch++;
    }
    if (cmdProc) {
        BumpCmdRefEpochs(iPtr->globalNsPtr);
    }

    /*
     *  Look for an existing scheme with the given name.  If found,
     *  then replace its rules.
     */
    for (resPtr = iPtr->resolverPtr; resPtr != NULL; resPtr = resPtr->nextPtr) {
        if (*name == *resPtr->name && strcmp(name, resPtr->name) == 0) {
            resPtr->cmdResProc = cmdProc;
            resPtr->varResProc = varProc;
            resPtr->compiledVarResProc = compiledVarProc;
            return;
        }
    }

    /*
     *  Otherwise, this is a new scheme.  Add it to the FRONT
     *  of the linked list, so that it overrides existing schemes.
     */
    resPtr = (ResolverScheme *) ckalloc(sizeof(ResolverScheme));
    resPtr->name = (char*)ckalloc((unsigned)(strlen(name)+1));
    strcpy(resPtr->name, name);
    resPtr->cmdResProc = cmdProc;
    resPtr->varResProc = varProc;
    resPtr->compiledVarResProc = compiledVarProc;
    resPtr->nextPtr = iPtr->resolverPtr;
    iPtr->resolverPtr = resPtr;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_GetInterpResolvers --
 *
 *	Looks for a set of command/variable resolution procedures with
 *	the given name in an interpreter.  These procedures are
 *	registered by calling Tcl_AddInterpResolvers.
 *
 * Results:
 *	If the name is recognized, this procedure returns non-zero,
 *	along with pointers to the name resolution procedures in
 *	the Tcl_ResolverInfo structure.  If the name is not recognized,
 *	this procedure returns zero.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

int
Tcl_GetInterpResolvers(interp, name, resInfoPtr)

    Tcl_Interp *interp;			/* Interpreter whose name resolution
					 * rules are being queried. */
    CONST char *name;                   /* Look for a scheme with this name. */
    Tcl_ResolverInfo *resInfoPtr;	/* Returns pointers to the procedures,
					 * if found */
{
    Interp *iPtr = (Interp*)interp;
    ResolverScheme *resPtr;

    /*
     *  Look for an existing scheme with the given name.  If found,
     *  then return pointers to its procedures.
     */
    for (resPtr = iPtr->resolverPtr; resPtr != NULL; resPtr = resPtr->nextPtr) {
        if (*name == *resPtr->name && strcmp(name, resPtr->name) == 0) {
	    resInfoPtr->cmdResProc = resPtr->cmdResProc;
	    resInfoPtr->varResProc = resPtr->varResProc;
	    resInfoPtr->compiledVarResProc = resPtr->compiledVarResProc;
            return 1;
        }
    }

    return 0;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_RemoveInterpResolvers --
 *
 *	Removes a set of command/variable resolution procedures
 *	previously added by Tcl_AddInterpResolvers.  The next time
 *	a command/variable name is resolved, these procedures
 *	won't be consulted.
 *
 * Results:
 *	Returns non-zero if the name was recognized and the
 *	resolution scheme was deleted.  Returns zero otherwise.
 *
 * Side effects:
 *	If a scheme with a compiledVarProc was deleted, this procedure
 *	bumps the compileEpoch for the interpreter, forcing all code
 *	to be recompiled.  If a scheme with a cmdProc was deleted,
 *	this procedure bumps the cmdRefEpoch in all namespaces,
 *	forcing commands to be resolved again using the new rules.
 *
 *----------------------------------------------------------------------
 */

int
Tcl_RemoveInterpResolvers(interp, name)

    Tcl_Interp *interp;			/* Interpreter whose name resolution
					 * rules are being modified. */
    CONST char *name;                   /* Name of the scheme to be removed. */
{
    Interp *iPtr = (Interp*)interp;
    ResolverScheme **prevPtrPtr, *resPtr;

    /*
     *  Look for an existing scheme with the given name.
     */
    prevPtrPtr = &iPtr->resolverPtr;
    for (resPtr = iPtr->resolverPtr; resPtr != NULL; resPtr = resPtr->nextPtr) {
        if (*name == *resPtr->name && strcmp(name, resPtr->name) == 0) {
            break;
        }
        prevPtrPtr = &resPtr->nextPtr;
    }

    /*
     *  If we found the scheme, delete it.
     */
    if (resPtr) {
        /*
         *  If we're deleting a scheme with compiled variable resolution
         *  rules, bump the compiler epoch to invalidate compiled code.
         *  If we're deleting a scheme with command resolution rules,
         *  bump the cmdRefEpoch in all namespaces.
         */
        if (resPtr->compiledVarResProc) {
            iPtr->compileEpoch++;
        }
        if (resPtr->cmdResProc) {
            BumpCmdRefEpochs(iPtr->globalNsPtr);
        }

        *prevPtrPtr = resPtr->nextPtr;
        ckfree(resPtr->name);
        ckfree((char *) resPtr);

        return 1;
    }
    return 0;
}

/*
 *----------------------------------------------------------------------
 *
 * BumpCmdRefEpochs --
 *
 *	This procedure is used to bump the cmdRefEpoch counters in
 *	the specified namespace and all of its child namespaces.
 *	It is used whenever name resolution schemes are added/removed
 *	from an interpreter, to invalidate all command references.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	Bumps the cmdRefEpoch in the specified namespace and its
 *	children, recursively.
 *
 *----------------------------------------------------------------------
 */

static void
BumpCmdRefEpochs(nsPtr)
    Namespace *nsPtr;			/* Namespace being modified. */
{
    Tcl_HashEntry *entry;
    Tcl_HashSearch search;
    Namespace *childNsPtr;

    nsPtr->cmdRefEpoch++;

    for (entry = Tcl_FirstHashEntry(&nsPtr->childTable, &search);
	    entry != NULL;
	    entry = Tcl_NextHashEntry(&search)) {

        childNsPtr = (Namespace *) Tcl_GetHashValue(entry);
        BumpCmdRefEpochs(childNsPtr);
    }
}


/*
 *----------------------------------------------------------------------
 *
 * Tcl_SetNamespaceResolvers --
 *
 *	Sets the command/variable resolution procedures for a namespace,
 *	thereby changing the way that command/variable names are
 *	interpreted.  This allows extension writers to support different
 *	name resolution schemes, such as those for object-oriented
 *	packages.
 *
 *	Command resolution is handled by a procedure of the following
 *	type:
 *
 *	  typedef int (Tcl_ResolveCmdProc) _ANSI_ARGS_((
 *		Tcl_Interp* interp, CONST char* name, Tcl_Namespace *context,
 *              int flags, Tcl_Command *rPtr));
 *          
 *	Whenever a command is executed or Tcl_FindCommand is invoked
 *	within the namespace, this procedure is called to resolve the
 *	command name.  If this procedure is able to resolve the name,
 *	it should return the status code TCL_OK, along with the
 *	corresponding Tcl_Command in the rPtr argument.  Otherwise,
 *	the procedure can return TCL_CONTINUE, and the command will
 *	be treated under the usual name resolution rules.  Or, it can
 *	return TCL_ERROR, and the command will be considered invalid.
 *
 *	Variable resolution is handled by two procedures.  The first
 *	is called whenever a variable needs to be resolved at compile
 *	time:
 *
 *        typedef int (Tcl_ResolveCompiledVarProc) _ANSI_ARGS_((
 *	        Tcl_Interp* interp, CONST char* name, Tcl_Namespace *context,
 *	        Tcl_ResolvedVarInfo *rPtr));
 *
 *      If this procedure is able to resolve the name, it should return
 *      the status code TCL_OK, along with variable resolution info in
 *      the rPtr argument; this info will be used to set up compiled
 *	locals in the call frame at runtime.  The procedure may also
 *	return TCL_CONTINUE, and the variable will be treated under
 *	the usual name resolution rules.  Or, it can return TCL_ERROR,
 *	and the variable will be considered invalid.
 *
 *	Another procedure is used whenever a variable needs to be
 *	resolved at runtime but it is not recognized as a compiled local.
 *	(For example, the variable may be requested via
 *	Tcl_FindNamespaceVar.) This procedure has the following type:
 *
 *	  typedef int (Tcl_ResolveVarProc) _ANSI_ARGS_((
 *	        Tcl_Interp* interp, CONST char* name, Tcl_Namespace *context,
 *	        int flags, Tcl_Var *rPtr));
 *
 *	This procedure is quite similar to the compile-time version.
 *	It returns the same status codes, but if variable resolution
 *	succeeds, this procedure returns a Tcl_Var directly via the
 *	rPtr argument.
 *
 * Results:
 *	Nothing.
 *
 * Side effects:
 *	Bumps the command epoch counter for the namespace, invalidating
 *	all command references in that namespace.  Also bumps the
 *	resolver epoch counter for the namespace, forcing all code
 *	in the namespace to be recompiled.
 *
 *----------------------------------------------------------------------
 */

void
Tcl_SetNamespaceResolvers(namespacePtr, cmdProc, varProc, compiledVarProc)
    Tcl_Namespace *namespacePtr;	/* Namespace whose resolution rules
					 * are being modified. */
    Tcl_ResolveCmdProc *cmdProc;	/* Procedure for command resolution */
    Tcl_ResolveVarProc *varProc;	/* Procedure for variable resolution
					 * at runtime */
    Tcl_ResolveCompiledVarProc *compiledVarProc;
					/* Procedure for variable resolution
					 * at compile time. */
{
    Namespace *nsPtr = (Namespace*)namespacePtr;

    /*
     *  Plug in the new command resolver, and bump the epoch counters
     *  so that all code will have to be recompiled and all commands
     *  will have to be resolved again using the new policy.
     */
    nsPtr->cmdResProc = cmdProc;
    nsPtr->varResProc = varProc;
    nsPtr->compiledVarResProc = compiledVarProc;

    nsPtr->cmdRefEpoch++;
    nsPtr->resolverEpoch++;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_GetNamespaceResolvers --
 *
 *	Returns the current command/variable resolution procedures
 *	for a namespace.  By default, these procedures are NULL.
 *	New procedures can be installed by calling
 *	Tcl_SetNamespaceResolvers, to provide new name resolution
 *	rules.
 *
 * Results:
 *	Returns non-zero if any name resolution procedures have been
 *	assigned to this namespace; also returns pointers to the
 *	procedures in the Tcl_ResolverInfo structure.  Returns zero
 *	otherwise.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

int
Tcl_GetNamespaceResolvers(namespacePtr, resInfoPtr)

    Tcl_Namespace *namespacePtr;	/* Namespace whose resolution rules
					 * are being modified. */
    Tcl_ResolverInfo *resInfoPtr;	/* Returns: pointers for all
					 * name resolution procedures
					 * assigned to this namespace. */
{
    Namespace *nsPtr = (Namespace*)namespacePtr;

    resInfoPtr->cmdResProc = nsPtr->cmdResProc;
    resInfoPtr->varResProc = nsPtr->varResProc;
    resInfoPtr->compiledVarResProc = nsPtr->compiledVarResProc;

    if (nsPtr->cmdResProc != NULL ||
        nsPtr->varResProc != NULL ||
        nsPtr->compiledVarResProc != NULL) {
	return 1;
    }
    return 0;
}
