/* $Id: rank1.c,v 1.14 2003/03/26 16:57:24 adam Exp $
   Copyright (C) 1995,1996,1997,1998,1999,2000,2001,2002,2003
   Index Data Aps

This file is part of the Zebra server.

Zebra 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, or (at your option) any later
version.

Zebra 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 Zebra; see the file LICENSE.zebra.  If not, write to the
Free Software Foundation, 59 Temple Place - Suite 330, Boston, MA
02111-1307, USA.
*/



#include <stdio.h>
#include <assert.h>
#ifdef WIN32
#include <io.h>
#else
#include <unistd.h>
#endif

#define DEBUG_RANK 0

#include "index.h"

struct rank_class_info {
    int dummy;
};

struct rank_term_info {
    int local_occur;
    int global_occur;
    int global_inv;
    int rank_flag;
    int rank_weight;
};

struct rank_set_info {
    int last_pos;
    int no_entries;
    int no_rank_entries;
    struct rank_term_info *entries;
};

static int log2_int (unsigned g)
{
    int n = 0;
    while ((g = g>>1))
	n++;
    return n;
}

/*
 * create: Creates/Initialises this rank handler. This routine is 
 *  called exactly once. The routine returns the class_handle.
 */
static void *create (ZebraHandle zh)
{
    struct rank_class_info *ci = (struct rank_class_info *)
	xmalloc (sizeof(*ci));

    yaz_log (LOG_DEBUG, "rank-1 create");
    return ci;
}

/*
 * destroy: Destroys this rank handler. This routine is called
 *  when the handler is no longer needed - i.e. when the server
 *  dies. The class_handle was previously returned by create.
 */
static void destroy (struct zebra_register *reg, void *class_handle)
{
    struct rank_class_info *ci = (struct rank_class_info *) class_handle;

    yaz_log (LOG_DEBUG, "rank-1 destroy");
    xfree (ci);
}


/*
 * begin: Prepares beginning of "real" ranking. Called once for
 *  each result set. The returned handle is a "set handle" and
 *  will be used in each of the handlers below.
 */
static void *begin (struct zebra_register *reg, void *class_handle, RSET rset)
{
    struct rank_set_info *si = (struct rank_set_info *) xmalloc (sizeof(*si));
    int i;

#if DEBUG_RANK
    yaz_log (LOG_LOG, "rank-1 begin");
#endif
    si->no_entries = rset->no_rset_terms;
    si->no_rank_entries = 0;
    si->entries = (struct rank_term_info *)
	xmalloc (sizeof(*si->entries)*si->no_entries);
    for (i = 0; i < si->no_entries; i++)
    {
	int g = rset->rset_terms[i]->nn;
#if DEBUG_RANK
        yaz_log(LOG_LOG, "i=%d flags=%s", i, rset->rset_terms[i]->flags);
#endif
	if (!strncmp (rset->rset_terms[i]->flags, "rank,", 5))
	{
            const char *cp = strstr(rset->rset_terms[i]->flags+4, ",w=");
	    si->entries[i].rank_flag = 1;
            if (cp)
                si->entries[i].rank_weight = atoi (cp+3);
            else
                si->entries[i].rank_weight = 34;
#if DEBUG_RANK
            yaz_log (LOG_LOG, " i=%d weight=%d", i,
                     si->entries[i].rank_weight);
#endif
	    (si->no_rank_entries)++;
	}
	else
	    si->entries[i].rank_flag = 0;
	si->entries[i].local_occur = 0;
	si->entries[i].global_occur = g;
	si->entries[i].global_inv = 32 - log2_int (g);
	yaz_log (LOG_DEBUG, " global_inv = %d g = %d", 32 - log2_int (g), g);
    }
    return si;
}

/*
 * end: Terminates ranking process. Called after a result set
 *  has been ranked.
 */
static void end (struct zebra_register *reg, void *set_handle)
{
    struct rank_set_info *si = (struct rank_set_info *) set_handle;
    yaz_log (LOG_DEBUG, "rank-1 end");
    xfree (si->entries);
    xfree (si);
}

/*
 * add: Called for each word occurence in a result set. This routine
 *  should be as fast as possible. This routine should "incrementally"
 *  update the score.
 */
static void add (void *set_handle, int seqno, int term_index)
{
    struct rank_set_info *si = (struct rank_set_info *) set_handle;
#if DEBUG_RANK
    yaz_log (LOG_LOG, "rank-1 add seqno=%d term_index=%d", seqno, term_index);
#endif
    si->last_pos = seqno;
    si->entries[term_index].local_occur++;
}

/*
 * calc: Called for each document in a result. This handler should 
 *  produce a score based on previous call(s) to the add handler. The
 *  score should be between 0 and 1000. If score cannot be obtained
 *  -1 should be returned.
 */
static int calc (void *set_handle, int sysno)
{
    int i, lo, divisor, score = 0;
    struct rank_set_info *si = (struct rank_set_info *) set_handle;

    if (!si->no_rank_entries)
	return -1;

#if DEBUG_RANK
    yaz_log(LOG_LOG, "calc");
#endif
    for (i = 0; i < si->no_entries; i++)
    {
#if DEBUG_RANK
        yaz_log(LOG_LOG, "i=%d rank_flag=%d lo=%d",
                i, si->entries[i].rank_flag, si->entries[i].local_occur);
#endif
	if (si->entries[i].rank_flag && (lo = si->entries[i].local_occur))
	    score += (8+log2_int (lo)) * si->entries[i].global_inv *
                si->entries[i].rank_weight;
    }
    divisor = si->no_rank_entries * (8+log2_int (si->last_pos/si->no_entries));
    score = score / divisor;
#if DEBUG_RANK
    yaz_log (LOG_LOG, "sysno=%d score=%d", sysno, score);
#endif
    if (score > 1000)
	score = 1000;
    for (i = 0; i < si->no_entries; i++)
	si->entries[i].local_occur = 0;
    return score;
}

/*
 * Pseudo-meta code with sequence of calls as they occur in a
 * server. Handlers are prefixed by --:
 *
 *     server init
 *     -- create
 *     foreach search
 *        rank result set
 *        -- begin
 *        foreach record
 *           foreach word
 *              -- add
 *           -- calc
 *        -- end
 *     -- destroy
 *     server close
 */

static struct rank_control rank_control = {
    "rank-1",
    create,
    destroy,
    begin,
    end,
    calc,
    add,
};
 
struct rank_control *rank1_class = &rank_control;