#include <string.h>

 #include <stdlib.h>

 #include <assert.h>

 #include "sm_trie.h"

 /**

  * Double Array Trie algorithm, based on:

  * An Efficient Implementation of Trie Structures, by

  *  Jun-ichi Aoe and Katsushi Maromoto, and Takashi Sato

  * from Sofiware - Practice and Experience, Vol. 22(9), 695-721 (September 1992)

  *

  *  A Trie is a simple data structure which stores strings as DFAs, with each 

  * transition state being a string entry.  For example, observe the following strings:

  *

  * BAILOPAN, BAT, BACON, BACK

  *  These transition as the follow production rules:

  *  B -> ...                  B

  *       A -> ...             BA

  *            I -> ...        BAI

  *                 LOPAN      BAILOPAN

  *            T -> ...        BAT

  *            C ->            BAC

  *                 O -> ...   BACO

  *                      N     BACON

  *                 K          BACK

  *

  *  The standard implementation for this - using lists - gives a slow linear lookup, somewhere between

  * O(N+M) or O(log n).  A faster implementation is proposed in the paper above, which is based on compacting

  * the transition states into two arrays.  In the paper's implementation, two arrays are used, and thus it is

  * called the "Double Array" algorithm.  However, the CHECK array's size is maintained the same as BASE, 

  * so they can be combined into one structure.  The array seems complex at first, but is very simple: it is a

  * tree structure flattened out into a single vector.  I am calling this implementation the Flat Array Trie.

  *

  *  BASE[] is an array where each member is a node in the Trie.  The node can either be UNUSED (empty), an ARC

  * (containing an offset to the next set of ARCs), or a TERMINATOR (contains the rest of a string).

  * Each node has an index which must be interpeted based on the node type.  If the node is a TERMINATOR, then the

  * index is an index into a string table, to find the rest of the string.  

  *  If the node is an ARC, the index is another index into BASE.  For each possible token that can follow the

  * current token, the value of those tokens can be added to the index given in the ARC.  Thus, given a current

  * position and the next desired token, the current arc will jump to another arc which can contain either:

  *   1) An invalid production (collision, no entry exists)

  *   2) An empty production (no entry exists)

  *   3) Another arc label (the string ends here or continues into more productions)

  *   4) A TERMINATOR (the string ends here and contains an unused set of productions)

  * 

  *  So, given current offset N (starting at N=1), jumping to token C means the next offset will be:

  *      offs = BASE[n] + C

  *  Thus, the next node will be at:

  *      BASE[BASE[n] + C]

  * 

  *  This allows each ARC to specify the base offset for any of its ARC children, like a tree.  Each node specifies

  * its parent ARC -- so if an invalid offset is specified, the parent will not match, and thus no such derived 

  * string exists.

  *

  *  This means that arrays can be laid out "sparsely," maximizing their usage.  Note that N need not be related to

  * the range of tokens (1-256).  I.e., a base index does not have to be at 1, 256, 512, et cetera.  This is because

  * insertion comes with a small deal of complexity.  To insert a new set of tokens T, the algorithm finds a new 

  * BASE index N such that BASE[N+T[i]] is unused for each T[i].  Thus, indirection is not necessarily linear; 

  * traversing a chain of ARC nodes can _and will_ jump around BASE.

  *

  *  Of course, given this level of flexibility in the array organization, there are collisions.  This is largely 

  * where insertions become slow, as the old chain must be relocated before the new one is used.  Relocation means 

  * finding one or more new base indexes, and this means traversing BASE until an acceptable index is found, such 

  * that each offset is unused (see description in previous paragraph).

  *

  *  However, it is not insertion time we are concerned about.  The "trie" name comes from reTRIEval.  We are only

  * concerned with lookup and deletion.  Both lookup and deletion are O(k), where k is relative to the length of the 

  * input string.  Note that it is best case O(1) and worst case O(k).  Deleting the entire trie is always O(1).

  */

 /**

  * Optimization ideas for the future:

  * 1) Store a reference count for each arc, with the count of sub-children.

  *    This could let us break out of "children searches" for case 4 easily.

  * 2) Use a 'free list' so we can easily search the trie for free points.

  *    This would drastically speed up x_check*

  */

 enum NodeType

 {

 	Node_Unused = 0,		/* Node is not being used (sparse) */

 	Node_Arc,				/* Node is part of an arc and does not terminate */

 	Node_Term,				/* Node is a terminator */

 };

 struct TrieNode

 {

 	/**

 	 * For Node_Arc, this index stores the 'base' offset to the next arc chain.

 	 *   I.e. to jump from this arc to character C, it will be at base[idx+C].

 	 * For Node_Term, this is an index into the string table.

 	 */

 	unsigned int idx;

 	/**

 	 * This contains the prior arc that we must have come from.

 	 * For example, if arc 63 has a base jump of index 12, and we want to see if

 	 * there is a valid character C, the parent of 12+C must be 63.

 	 */

 	unsigned int parent;

 	void *value;			/* Value associated with this node */

 	NodeType mode;			/* Current usage type of the node */

 	bool valset;			/* Whether or not a value is set */

 };

 struct Trie

 {

 	TrieNode *base;			/* Base array for the sparse tables */

 	char *stringtab;		/* String table pointer */

 	unsigned int baseSize;	/* Size of the base array, in members */

 	unsigned int stSize;	/* Size of the string table, in bytes */

 	unsigned int tail;		/* Current unused offset into the string table */

 };

 inline unsigned char charval(char c)

 {

 	return (unsigned char)c;

 }

 bool sm_trie_grow(Trie *trie)

 {

 	/* The current # of nodes in the tree is trie->baseSize + 1 */

 	unsigned int curSize = trie->baseSize;

 	unsigned int newSize = curSize * 2;

 	//:TODO: Make functions calling this return failure if this fails 

 	trie->base = (TrieNode *)realloc(trie->base, (newSize + 1) * sizeof(TrieNode));

 	if (!trie->base)

 	{

 		return false;

 	}

 	memset(&trie->base[curSize+1], 0, (newSize - curSize) * sizeof(TrieNode));

 	trie->baseSize = newSize;

 	return true;

 }

 unsigned int x_check(Trie *trie, char c, unsigned int start=1)

 {

 	TrieNode *base = trie->base;

 	unsigned char _c = charval(c);

 	unsigned int to_check = trie->baseSize - _c;

 	for (unsigned int i=start; i<=to_check; i++)

 	{

 		if (base[i+_c].mode == Node_Unused)

 		{

 			return i;

 		}

 	}

 	sm_trie_grow(trie);

 	return x_check(trie, c, to_check+1);

 }

 unsigned int x_check2(Trie *trie, char c1, char c2, unsigned int start=1)

 {

 	TrieNode *base = trie->base;

 	unsigned char _c1 = charval(c1);

 	unsigned char _c2 = charval(c2);

 	unsigned int to_check = trie->baseSize - (_c1 > _c2 ? _c1 : _c2);

 	for (unsigned int i=start; i<=to_check; i++)

 	{

 		if (base[i+_c1].mode == Node_Unused

 			&& base[i+_c2].mode == Node_Unused)

 		{

 			return i;

 		}

 	}

 	sm_trie_grow(trie);

 	return x_check2(trie, c1, c2, to_check+1);

 }

 unsigned int x_check_multi(Trie *trie, 

 							unsigned int offsets[], 

 							unsigned int count,

 							unsigned int start=1)

 {

 	TrieNode *base = trie->base;

 	TrieNode *cur;

 	unsigned int to_check = trie->baseSize;

 	unsigned int highest = 0;

 	for (unsigned int i=0; i<count; i++)

 	{

 		if (offsets[i] > highest)

 		{

 			highest = offsets[i];

 		}

 	}

 	to_check -= highest;

 	for (unsigned int i=start; i<=to_check; i++)

 	{

 		bool okay = true;

 		for (unsigned int j=0; j<count; j++)

 		{

 			cur = &base[i+offsets[j]];

 			if (cur->mode != Node_Unused)

 			{

 				okay = false;

 				break;

 			}

 		}

 		if (okay)

 		{

 			return i;

 		}

 	}

 	sm_trie_grow(trie);

 	return x_check_multi(trie, offsets, count, to_check+1);

 }

 unsigned int x_addstring(Trie *trie, const char *ptr)

 {

 	size_t len = strlen(ptr) + 1;

 	if (trie->tail + len >= trie->stSize)

 	{		

 		while (trie->tail + len >= trie->stSize)

 		{

 			trie->stSize *= 2;

 		}

 		trie->stringtab = (char *)realloc(trie->stringtab, trie->stSize);

 	}

 	unsigned int tail = trie->tail;

 	strcpy(&trie->stringtab[tail], ptr);

 	trie->tail += len;

 	return tail;

 }

 Trie *sm_trie_create()

 {

 	Trie *t = new Trie;

 	t->base = (TrieNode *)malloc(sizeof(TrieNode) * (256 + 1));

 	t->stringtab = (char *)malloc(sizeof(char) * 256);

 	t->baseSize = 256;

 	t->stSize = 256;

 	t->tail = 0;

 	memset(t->base, 0, sizeof(TrieNode) * (256 + 1));

 	memset(t->stringtab, 0, sizeof(char) * 256);

 	/* Sentinel root node */

 	t->base[1].idx = 1;

 	t->base[1].mode = Node_Arc;

 	t->base[1].parent = 1;

 	return t;

 }

 void sm_trie_destroy(Trie *trie)

 {

 	free(trie->base);

 	free(trie->stringtab);

 	delete trie;

 }

 bool sm_trie_delete(Trie *trie, const char *key)

 {

 	unsigned int lastidx = 1;		/* the last node index */

 	unsigned int curidx;			/* current node index */

 	const char *keyptr = key;		/* input stream at current token */

 	TrieNode *node = NULL;			/* current node being processed */

 	TrieNode *base = trie->base;

 	if (!*key)

 	{

 		return false;

 	}

 	/* Start traversing at the root node */

 	do

 	{

 		/* Find where the next character is, then advance */

 		curidx = base[lastidx].idx;

 		node = &base[curidx];

 		curidx += charval(*keyptr);

 		node = &base[curidx];

 		keyptr++;

 		/* Check if this slot is supposed to be empty or is a collision */

 		if ((curidx > trie->baseSize) || node->mode == Node_Unused || node->parent != lastidx)

 		{

 			return false;

 		} else if (node->mode == Node_Term) {

 			char *term = &trie->stringtab[node->idx];

 			if (strcmp(keyptr, term) == 0)

 			{

 				break;

 			}

 		}

 		lastidx = curidx;

 	} while (*keyptr != '\0');

 	assert(node != NULL);

 	if (!node->valset)

 	{

 		return false;

 	}

 	node->valset = false;

 	node->value = NULL;

 	return true;

 }

 bool sm_trie_retrieve(Trie *trie, const char *key, void **value)

 {

 	unsigned int lastidx = 1;		/* the last node index */

 	unsigned int curidx;			/* current node index */

 	const char *keyptr = key;		/* input stream at current token */

 	TrieNode *node = NULL;			/* current node being processed */

 	TrieNode *base = trie->base;

 	if (!*key)

 	{

 		return false;

 	}

 	/* Start traversing at the root node */

 	do

 	{

 		/* Find where the next character is, then advance */

 		curidx = base[lastidx].idx;

 		node = &base[curidx];

 		curidx += charval(*keyptr);

 		node = &base[curidx];

 		keyptr++;

 		/* Check if this slot is supposed to be empty or is a collision */

 		if ((curidx > trie->baseSize) || node->mode == Node_Unused || node->parent != lastidx)

 		{

 			return false;

 		} else if (node->mode == Node_Term) {

 			char *term = &trie->stringtab[node->idx];

 			if (strcmp(keyptr, term) == 0)

 			{

 				break;

 			}

 		}

 		lastidx = curidx;

 	} while (*keyptr != '\0');

 	assert(node != NULL);

 	if (!node->valset)

 	{

 		return false;

 	}

 	if (value)

 	{

 		*value = node->value;

 	}

 	return true;

 }

 bool sm_trie_insert(Trie *trie, const char *key, void *value)

 {

 	unsigned int lastidx = 1;		/* the last node index */

 	unsigned int curidx;			/* current node index */

 	const char *keyptr = key;		/* input stream at current token */

 	TrieNode *node = NULL;			/* current node being processed */

 	TrieNode *basenode = NULL;		/* current base node being processed */

 	unsigned int q;					/* temporary var for x_check results */

 	TrieNode *base = trie->base;

 	unsigned int curoffs;			/* current offset */

 	/* Do not handle empty strings for simplicity */

 	if (!*key)

 	{

 		return false;

 	}

 	/* Start traversing at the root node (1) */

 	do

 	{

 		/* Find where the next character is, then advance */

 		curidx = base[lastidx].idx;

 		basenode = &base[curidx];

 		curoffs = charval(*keyptr);

 		curidx += curoffs;

 		node = &base[curidx];

 		keyptr++;

 		/* Check if this slot is supposed to be empty.  If so, we need to handle CASES 1/2:

 		 * Insertion without collisions

 		 */

 		if ( (curidx > trie->baseSize) || (node->mode == Node_Unused) )

 		{

 			if (curidx > trie->baseSize)

 			{

 				if (!sm_trie_grow(trie))

 				{

 					return false;

 				}

 				node = &trie->base[curidx];

 			}

 			node->parent = lastidx;

 			if (*keyptr == '\0')

 			{

 				node->mode = Node_Arc;

 			} else {

 				node->idx = x_addstring(trie, keyptr);

 				node->mode = Node_Term;

 			}

 			node->valset = true;

 			node->value = value;

 			return true;

 		} else if (node->parent != lastidx) {

 			/* Collision! We have to split up the tree here.  CASE 4:

 			 * Insertion when a new word is inserted with a collision.

 			 * NOTE: This is the hardest case to handle.  All below examples are based on:

 			 * BACHELOR, BADGE, inserting BABY.

 			 * The problematic production here is A -> B, where B is already being used.

 			 *

 			 * This process has to rotate one half of the 'A' arc.  We generate two lists:

 			 *  Outgoing Arcs - Anything leaving this 'A'

 			 *  Incoming Arcs - Anything going to this 'A'

 			 * Whichever list is smaller will be moved.  Note that this works because the intersection

 			 * affects both arc chains, and moving one will make the slot available to either.

 			 */

 			TrieNode *cur;

 			/* Find every node arcing from the last node.

 			 * I.e. for BACHELOR, BADGE, BABY,

 			 * The arcs leaving A will be C and D, but our current node is B -> *.

 			 * Thus, we use the last index (A) to find the base for arcs leaving A.

 			 */

 			unsigned int outgoing_base = base[lastidx].idx;

 			unsigned int outgoing_list[256];

 			unsigned int outgoing_count = 0;	/* count the current index here */

 			cur = &base[outgoing_base] + 1;

 			unsigned int outgoing_limit = 255;

 			if (outgoing_base + outgoing_limit > trie->baseSize)

 			{

 				outgoing_limit = trie->baseSize - outgoing_base;

 			}

 			for (unsigned int i=1; i<=outgoing_limit; i++,cur++)

 			{

 				if (cur->mode == Node_Unused || cur->parent != lastidx)

 				{

 					continue;

 				}

 				outgoing_list[outgoing_count++] = i;

 			}

 			outgoing_list[outgoing_count++] = curidx - outgoing_base;

 			/* Now we need to find all the arcs leaving our parent...

 			 * Note: the inconsistency is the base of our parent.  

 			 */

 			assert(base[node->parent].mode == Node_Arc);

 			unsigned int incoming_list[256];

 			unsigned int incoming_base = base[node->parent].idx;

 			unsigned int incoming_count = 0;

 			unsigned int incoming_limit = 255;

 			cur = &base[incoming_base] + 1;

 			if (incoming_base + incoming_limit > trie->baseSize)

 			{

 				incoming_limit = trie->baseSize - incoming_base;

 			}

 			assert(incoming_limit > 0 && incoming_limit <= 255);

 			for (unsigned int i=1; i<=255; i++,cur++)

 			{

 				if (cur->mode == Node_Arc || cur->mode == Node_Term)

 				{

 					if (cur->parent == node->parent)

 					{

 						incoming_list[incoming_count++] = i;

 					}

 				}

 			}

 			if (incoming_count < outgoing_count + 1)

 			{

 				unsigned int q = x_check_multi(trie, incoming_list, incoming_count);

 				base = trie->base;

 				node = &base[curidx];

 				/* If we're incoming, we need to modify our parent */

 				base[node->parent].idx = q;

 				/* For each node in the "to move" list,

 				 * Relocate the node's info to the new position.

 				 */

 				unsigned int idx, newidx, oldidx;

 				for (unsigned int i=0; i<incoming_count; i++)

 				{

 					idx = incoming_list[i];

 					newidx = q + idx;

 					oldidx = incoming_base + idx;

 					if (oldidx == lastidx)

 					{

 						/* Important! Make sure we're not invalidating our sacred lastidx */

 						lastidx = newidx;

 					}

 					base[newidx] = base[oldidx];

 					assert(base[base[newidx].parent].mode == Node_Arc);

 					memset(&base[oldidx], 0, sizeof(TrieNode));

 					/* If we are not a terminator, we have children we must take care of */

 					if (base[newidx].mode == Node_Arc)

 					{

 						TrieNode *check_base = &base[base[newidx].idx] + 1;

 						for (unsigned int j=1; j<=255; j++, check_base++)

 						{

 							if (check_base->parent == oldidx)

 							{

 								check_base->parent = newidx;

 							}

 						}

 					}

 				}

 			} else {

 				unsigned int q = x_check_multi(trie, outgoing_list, outgoing_count);

 				base = trie->base;

 				node = &base[curidx];

 				/* If we're outgoing, we need to modify our own base */

 				base[lastidx].idx = q;

 				/* Take the last index (curidx) out of the list.  Technically we are not moving this,

 				 * since it's already being used by something else.  

 				 */

 				outgoing_count--;

 				/* For each node in the "to move" list,

 				 * Relocate the node's info to the new position.

 				 */

 				unsigned int idx, newidx, oldidx;

 				for (unsigned int i=0; i<outgoing_count; i++)

 				{

 					idx = outgoing_list[i];

 					newidx = q + idx;

 					oldidx = outgoing_base + idx;

 					if (oldidx == lastidx)

 					{

 						/* Important! Make sure we're not invalidating our sacred lastidx */

 						lastidx = newidx;

 					}

 					base[newidx] = base[oldidx];

 					assert(base[base[newidx].parent].mode == Node_Arc);

 					memset(&base[oldidx], 0, sizeof(TrieNode));

 					/* If we are not a terminator, we have children we must take care of */

 					if (base[newidx].mode == Node_Arc)

 					{

 						TrieNode *check_base = &base[base[newidx].idx] + 1;

 						for (unsigned int j=1; j<=255; j++, check_base++)

 						{

 							if (check_base->parent == oldidx)

 							{

 								check_base->parent = newidx;

 							}

 						}

 					}

 				}

 				/* Take the invisible node and use it as our new node */

 				node = &base[q + outgoing_list[outgoing_count]];

 			}

 			/* We're finally done! */

 			node->parent = lastidx;

 			if (*keyptr == '\0')

 			{

 				node->mode = Node_Arc;

 			} else {

 				node->idx = x_addstring(trie, keyptr);

 				node->mode = Node_Term;

 			}

 			node->valset = true;

 			node->value = value;

 			return true;

 		} else {

 			/* See what's in the next node - special case if terminator! */

 			if (node->mode == Node_Term)

 			{

 				/* If we're a terminator, we need to handle CASE 3:

 				 * Insertion when a terminating collision occurs

 				 */

 				char *term = &trie->stringtab[node->idx];

 				/* Do an initial browsing to make sure they're not the same string */

 				if (strcmp(keyptr, term) == 0)

 				{

 					if (!node->valset)

 					{

 						node->valset = true;

 						node->value = value;

 						return true;

 					}

 					/* Same string.  We can't insert. */

 					return false;

 				}

 				/* For each matching character pair, we need to disband the terminator.

 				 * This splits the similar prefix into a single arc path.

 				 * First, save the old values so we can move them to a new node.

 				 * Next, for each loop:

 				 *  Take the current (invalid) node, and point it to the next arc base.

 				 *  Set the current node to the node at the next arc.

 				 */

 				void *oldvalue = node->value;

 				bool oldvalset = node->valset;

 				if (*term == *keyptr)

 				{

 				while (*term == *keyptr)

 				{

 					/* Find the next free slot in the check array.

 					 * This is the "vector base" essentially

 					 */

 					q = x_check(trie, *term);

 						base = trie->base;

 						node = &base[curidx];

 					/* Point the node to the next new base */

 					node->idx = q;

 					node->mode = Node_Arc;

 					node->valset = false;

 					/* Advance the input stream and local variables */

 					lastidx = curidx;

 					curidx = q + charval(*term);

 					node = &base[curidx];

 					/* Make sure the new current node has its parent set. */

 					node->parent = lastidx;

 					node->mode = Node_Arc;	/* Just in case we run x_check again */

 					*term = '\0';	/* Unmark the string table here */

 					term++;

 					keyptr++;

 					}

 				} else {

 					node->valset = false;

 				}

 				/* We're done inserting new pairs.  If one of them is exhausted,

 				 * we take special shortcuts.

 				 */

 				if (*term == '\0')				//EX: BADGERHOUSE added over B -> ADGER.  

 				{

 					/* First backpatch the current node - it ends the newly split terminator.

 					 * In the example, this would mean the node is the production from R -> ?

 					 * This node ends the old BADGER, so we set it here.

 					 */

 					node->valset = oldvalset;

 					node->value = oldvalue;

 					/* The terminator was split up, but pieces of keyptr remain.

 					 * We need to generate a new production, in this example, R -> H,

 					 * with H being a terminator to OUSE.  Thus we get:

 					 * B,A,D,G,E,R*,H*->OUSE (* = value set).

 					 * NOTE: parent was last set at the end of the while loop.

 					 */

 					/* Get the new base and apply re-basing */

 					q = x_check(trie, *keyptr);

 					base = trie->base;

 					node = &base[curidx];

 					node->idx = q;

 					node->mode = Node_Arc;

 					lastidx = curidx;

 					/* Finish the final node */

 					curidx = q + charval(*keyptr);

 					node = &trie->base[curidx];

 					keyptr++;

 					/* Optimize - don't add to string table if there's nothing more to eat */

 					if (*keyptr == '\0')

 					{

 						node->mode = Node_Arc;

 					} else {

 						node->idx = x_addstring(trie, keyptr);

 						node->mode = Node_Term;

 					}

 					node->parent = lastidx;

 					node->valset = true;

 					node->value = value;

 				} else if (*keyptr == '\0') {	//EX: BADGER added over B -> ADGERHOUSE

 					/* First backpatch the current node - it ends newly split input string.

 					 * This is the exact opposite of the above procedure.

 					 */

 					node->valset = true;

 					node->value = value;

 					/* Get the new base and apply re-basing */

 					q = x_check(trie, *term);

 					base = trie->base;

 					node = &base[curidx];

 					node->idx = q;

 					node->mode = Node_Arc;

 					lastidx = curidx;

 					/* Finish the final node */

 					curidx = q + charval(*term);

 					node = &trie->base[curidx];

 					term++;

 					/* Optimize - don't add to string table if there's nothing more to eat */

 					if (*term == '\0')

 					{

 						node->mode = Node_Arc;

 					} else {

 						node->idx = (term - trie->stringtab); /* Already in the string table! */

 						node->mode = Node_Term;

 					}

 					node->parent = lastidx;

 					node->valset = oldvalset;

 					node->value = oldvalue;

 				} else {

 					/* Finally, we have to create two new nodes instead of just one. */

 					node->mode = Node_Arc;

 					/* Get the new base and apply re-basing */

 					q = x_check2(trie, *keyptr, *term);

 					base = trie->base;

 					node = &base[curidx];

 					node->idx = q;

 					lastidx = curidx;

 					/* Re-create the old terminated node */

 					curidx = q + charval(*term);

 					node = &trie->base[curidx];

 					term++;

 					node->valset = oldvalset;

 					node->value = oldvalue;

 					node->parent = lastidx;

 					if (*term == '\0')

 					{

 						node->mode = Node_Arc;

 					} else {

 						node->mode = Node_Term;

 						node->idx = (term - trie->stringtab); /* Already in the string table! */

 					}

 					/* Create the new keyed input node */

 					curidx = q + charval(*keyptr);

 					node = &trie->base[curidx];

 					keyptr++;

 					node->valset = true;

 					node->value = value;

 					node->parent = lastidx;

 					if (*keyptr == '\0')

 					{

 						node->mode = Node_Arc;

 					} else {

 						node->mode = Node_Term;

 						node->idx = x_addstring(trie, keyptr);

 					}

 				}

 				/* Phew! */

 				return true;

 			} else {

 				assert(node->mode == Node_Arc);

 			}

 		}

 		lastidx = curidx;

 	} while (*keyptr != '\0');

 	assert(node);

 	/* If we've exhausted the string and we have a valid reached node,

 	 * the production rule already existed.  Make sure it's valid to set first.

 	 */

 	/* We have to be an Arc.  If the last result was anything else, we would have returned a new 

 	 * production earlier.

 	 */

 	assert(node->mode == Node_Arc);

 	/* Furthermore, if this is the last arc label in an arc, we should have a value set. */

 	if (node->idx == 0)

 	{

 		assert(node->valset == true);

 	}

 	if (!node->valset)

 	{

 		/* Insert is only possible if we have no production */

 		node->valset = true;

 		node->value = value;

 		return true;

 	}

 	return false;

 }