/*
 *	aegis - project change supervisor
 *	Copyright (C) 1991, 1993, 1994 Peter Miller.
 *	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 as published by
 *	the Free Software Foundation; either version 2 of the License, or
 *	(at your option) any later version.
 *
 *	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, write to the Free Software
 *	Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111, USA.
 *
 * MANIFEST: functions to make fuzzy comparisons between strings
 *
 * This code is based on the heart of a file comparison program
 * written by David I. Bell, and used by kind permission.
 * This notice must be retained in all copies and derivatives.
 * Contact the author of aegis for a copy of the file comparison program.
 *
 * This code is based on the algorithm in:
 *	An O(ND) Difference Algorithm and Its Variations
 *	Eugene W. Myers
 *	(TR 85-6, April 10, 1985)
 *	Department of Computer Science
 *	The University of Arizona
 *	Tuscon, Arizona 85721
 *
 * Also see:
 *	A File Comparison Program
 *	Webb Miller and Eugene W. Myers
 *	Software Practice and Experience
 *	(Volume 15, No. 11, November 1985)
 */

#include <ac/string.h>

#include <error.h>
#include <fstrcmp.h>
#include <mem.h>
#include <trace.h>


typedef struct snake_t snake_t;
struct snake_t
{
	long	line1;
	long	line2;
	long	count;
	snake_t	*next;
};

static	long	tablesize;		/* needed table size */
static	long	tablesize_max;		/* allocated table size */
static	long	*V1;		/* the row containing the last d */
static	long	*V1_table;
static	long	*V2;		/* another row */
static	long	*V2_table;
static	snake_t	*nextsnake;	/* next allocable snake structure */
static	snake_t	*snake_table;	/* allocable snake structures */

typedef struct file file;
struct file
{
	char	*f_lines;
	long	f_linecount;
};

typedef struct fc_t fc_t;
struct fc_t
{
	file	fileA;
	file	fileB;
	long	maxlines;
	long	minlines;
	long	inserts;
	long	deletes;
	long	matches;
};

static fc_t fc;


/*
 * Routine to find the middle snake of an optimial D-path spanning
 * lines A to A+N in file A to lines B to B+N in file B.  Returns the
 * length D of the D-path as a return value, and the upper left and
 * lower right relative coordinates of a snake midway through the D-path.
 */

static long midsnake _((int depth, long A, long N, long B, long M, long *ulx,
	long *uly, long *lrx, long *lry));

static long
midsnake(depth, A, N, B, M, ulx, uly, lrx, lry)
	int		depth;
	long		A;
	long		N;
	long		B;
	long		M;
	long		*ulx;
	long		*uly;
	long		*lrx;
	long		*lry;
{
	long		x;
	long		y;
	long		k;
	long		oldx;
	char		*lp1;
	char		*lp2;
	long		DELTA;
	long		odd;
	long		MAXD;
	long		changes;
	long		D;

	trace(("midsnake(depth = %d, A = %ld, N = %ld, B = %ld, M = %ld)\n{\n"
		/*}*/, depth, A, N, B, M));
	trace(("searching: %ld,%ld to %ld,%ld\n", A, B, A + N, B + M));

	DELTA = N - M;
	odd = DELTA & 1;
	MAXD = (M + N + 1) / 2;
	V1[1] = 0;
	V2[-1] = 0;
	changes = -odd - 2;

	/*
	 * This is the main loop for searching for the snake.
	 * D is the distance off the diagonals, and is the number
	 * of changes needed to get from the upper left to the
	 * lower right corner of the region.
	 */
	for (D = 0; D <= MAXD; D++)
	{
		changes += 2;

		/*
		 * Examine all diagonals within current distance.
		 * First search from upper left to lower right,
		 * and then search from lower right to upper left.
		 */
		for (k = -D; k <= D; k += 2)
		{
			/*
			 * Find the end of the furthest forward D-path
			 * in diagonal k.
			 */
			if (k == -D || (k != D && (V1[k-1] < V1[k+1])))
				x = V1[k+1];
			else
				x = V1[k-1] + 1;
			y = x - k;
			lp1 = &fc.fileA.f_lines[A+x];
			lp2 = &fc.fileB.f_lines[B+y];
			oldx = x;
			while (x < N && y < M && *lp1 == *lp2)
			{
				x++;
				y++;
				lp1++;
				lp2++;
			}
			V1[k] = x;

			/*
			 * See if path overlaps furthest reverse D-path.
			 * If so, then we have found the snake.
			 */
			if (odd && (k >= (DELTA - (D-1))) && (k <= (DELTA + (D-1))))
			{
				if ((x + V2[k-DELTA]) >= N)
				{
					*ulx = oldx;
					*uly = oldx - k;
					*lrx = x;
					*lry = y;
					trace(("midsnake: %ld,%ld to %ld,%ld (odd)\n", *ulx, *uly, *lrx, *lry));
					trace(("return %ld;\n", changes));
					trace((/*{*/"}\n"));
					return changes;
				}
			}
		}

		for (k = -D; k <= D; k += 2)
		{
			/*
			 * Find the end of the furthest reaching reverse
			 * path in diagonal k+DELTA.
			 */
			if (k == D || (k != -D && (V2[k+1] < V2[k-1])))
				x = V2[k-1];
			else
				x = V2[k+1] + 1;
			y = x + k;
			lp1 = &fc.fileA.f_lines[A+N-x-1];
			lp2 = &fc.fileB.f_lines[B+M-y-1];
			oldx = x;
			while (x < N && y < M && *lp1 == *lp2)
			{
				x++;
				y++;
				lp1--;
				lp2--;
			}
			V2[k] = x;

			/*
			 * See if path overlaps furthest forward D-path.
			 * If so, then we have found the snake.
			 */
			if (!odd && (k <= D-DELTA) && (k >= -D-DELTA))
			{
				if ((x + V1[k+DELTA]) >= N)
				{
					*ulx = N - x;
					*uly = M - y;
					*lrx = N - oldx;
					*lry = *lrx + *uly - *ulx;
					trace(("midsnake: %ld,%ld to %ld,%ld (even)\n", *ulx, *uly, *lrx, *lry));
					trace(("return %ld;\n", changes));
					trace((/*{*/"}\n"));
					return changes;
				}
			}
		}
	}

	/*
	 * Middle snake procedure failed!
	 */
	assert(0);
	return 0;
}


/*
 * Recursive routine to find a minimal D-path through the edit graph
 * of the two input files.  Arguments are the beginning line numbers in
 * the files, and the number of lines to examine.  This is basically a
 * divide-and-conquer routine which finds the middle snake of an optimal
 * D-path, then calls itself to find the remainder of the path before the
 * snake and after the snake.
 */

static void findsnake _((int depth, long A, long N, long B, long M));

static void
findsnake(depth, A, N, B, M)
	int		depth;
	long		A;
	long		N;
	long		B;
	long		M;
{
	snake_t		*sp;
	long		ulx;
	long		uly;
	long		lrx;
	long		lry;
	long		D;
	long		count;

	trace(("findsnake(depth = %d, A = %ld, N = %ld, B = %ld, M = %ld)\n{\n"
		/*}*/, depth, A, N, B, M));

	/*
	 * If more than one change needed, then call ourself for each part.
	 */
	D = midsnake(depth, A, N, B, M, &ulx, &uly, &lrx, &lry);

	if (D > 1)
	{
		if (ulx > 0 && uly > 0)
			findsnake(depth + 1, A, ulx, B, uly);
		count = lrx - ulx;
		sp = nextsnake++;
		sp->line1 = A + ulx;
		sp->line2 = B + uly;
		sp->count = count;
		N -= lrx;
		M -= lry;
		if (N > 0 && M > 0)
			findsnake(depth + 1, A + lrx, N, B + lry, M);
		trace((/*{*/"}\n"));
		return;
	}

	/*
	 * Only 0 or 1 change needed, so we can compute the result directly.
	 * First compute the snake coming from the upper left corner if any.
	 */
	if (N > M)
		count = uly;
	else
		count = ulx;
	sp = nextsnake++;
	sp->line1 = A;
	sp->line2 = B;
	sp->count = count;

	/*
	 * Finally compute the snake coming from the lower right corner if any.
	 */
	count = lrx - ulx;
	sp = nextsnake++;
	sp->line1 = A + ulx;
	sp->line2 = B + uly;
	sp->count = count;
	trace((/*{*/"}\n"));
}


double
fstrcmp(s1, s2)
	char		*s1;
	char		*s2;
{
	double		result;
	snake_t		*sp;	/* current snake element */
	long		line1;	/* current line in file A */
	long		line2;	/* current line in file B */

	trace(("fstrcmp(s1 = %08lX, s2 = %08lX)\n{\n"/*}*/, s1, s2));
	trace(("s1 = \"%s\";\n", s1));
	trace(("s2 = \"%s\";\n", s2));
	fc.fileA.f_lines = s1;
	fc.fileA.f_linecount = strlen(s1);
	fc.fileB.f_lines = s2;
	fc.fileB.f_linecount = strlen(s2);

	/*
	 * Check for trivial case of two empty strings.
	 * This also avoids a division by zero at the end of is function.
	 */
	if (!fc.fileA.f_linecount && !fc.fileB.f_linecount)
	{
		trace(("return 1;\n"));
		trace((/*{*/"}\n"));
		return 1;
	}

	if (fc.fileA.f_linecount < fc.fileB.f_linecount)
	{
		fc.minlines = fc.fileA.f_linecount;
		fc.maxlines = fc.fileB.f_linecount;
	}
	else
	{
		fc.minlines = fc.fileB.f_linecount;
		fc.maxlines = fc.fileA.f_linecount;
	}

	tablesize = fc.maxlines * 2 + 1;
	if (tablesize > tablesize_max)
	{
		tablesize_max = tablesize;
		V1_table =
			mem_change_size
			(
				V1_table,
				sizeof(long) * tablesize_max
			);
		V2_table =
			mem_change_size
			(
				V2_table,
				sizeof(long) * tablesize_max
			);
		snake_table =
			mem_change_size
			(
				snake_table,
				sizeof(snake_t) * tablesize_max
			);
	}

	V1 = V1_table + fc.maxlines;
	V2 = V2_table + fc.maxlines;
	nextsnake = snake_table;
	if (fc.fileA.f_linecount > 0 && fc.fileB.f_linecount > 0)
	{
		findsnake
		(
			0,
			0L,
			fc.fileA.f_linecount,
			0L,
			fc.fileB.f_linecount
		);
	}

	/*
	 * End the list with the lower right endpoint
	 */
	sp = nextsnake++;
	sp->line1 = fc.fileA.f_linecount;
	sp->line2 = fc.fileB.f_linecount;
	sp->count = 0;

	/*
	 * print out the snake list
	 */
#ifdef DEBUG
	for (sp = snake_table; sp < nextsnake; sp++)
	{
		trace
		((
			"%d: line1 = %ld; line2 = %ld; count = %ld;\n",
			sp - snake_table,
			sp->line1,
			sp->line2,
			sp->count
		));
	}
#endif

	/*
	 * Scan the snake list and calculate the number of inserted,
	 * deleted, and matching lines.
	 */
	line1 = 0;
	line2 = 0;
	fc.deletes = 0;
	fc.inserts = 0;
	fc.matches = 0;
	for (sp = snake_table; sp < nextsnake; sp++)
	{
		fc.deletes += (sp->line1 - line1);
		fc.inserts += (sp->line2 - line2);
		fc.matches += sp->count;
		line1 = sp->line1 + sp->count;
		line2 = sp->line2 + sp->count;
	}

	/*
	 * the result is 0 if the strings are entirely unalike,
	 * and 1 if the strings are identical, and somewhere in between
	 * if the are in any way similar.
	 */
	result =
		(
			1
		-
			(double)(fc.inserts + fc.deletes)
		/
			(fc.fileA.f_linecount + fc.fileB.f_linecount)
		);
	trace(("return %.6f;\n", result));
	trace((/*{*/"}\n"));
	return result;
}