/**

 * vim: set ts=4 :

 * ================================================================

 * SourceMod

 * Copyright (C) 2004-2007 AlliedModders LLC.  All rights reserved.

 * ================================================================

 *

 * This program is free software; you can redistribute it and/or 

 * modify it under the terms of the GNU General Public License, 

 * version 3.0, as published by the Free Software Foundation.

 * 

 * This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.

 *

 * As a special exception, AlliedModders LLC gives you permission to 

 * link the code of this program (as well as its derivative works) to 

 * "Half-Life 2," the "Source Engine," the "SourcePawn JIT," and any 

 * Game MODs that run on software by the Valve Corporation.  You must 

 * obey the GNU General Public License in all respects for all other 

 * code used. Additionally, AlliedModders LLC grants this exception 

 * to all derivative works. AlliedModders LLC defines further 

 * exceptions, found in LICENSE.txt (as of this writing, version 

 * JULY-31-2007), or <http://www.sourcemod.net/license.php>.

 *

 * Version: $Id$

 */

#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 Software - 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 interpreted 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;

	sm_trie_clear(t);

	return t;

}

void sm_trie_clear(Trie *trie)

{

	trie->tail = 0;

	memset(trie->base, 0, sizeof(TrieNode) * (trie->baseSize + 1));

	memset(trie->stringtab, 0, sizeof(char) * trie->stSize);

	/* Sentinel root node */

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

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

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

}

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

{

	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<=incoming_limit; 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++)