/* -*- Mode: C; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
/*
 * libthai - Thai Language Support Library
 * Copyright (C) 2001  Theppitak Karoonboonyanan <thep@linux.thai.net>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */

/*
 * thinp.c - Thai string input sequence filtering
 * Created: 2001-08-04
 * Author:  Theppitak Karoonboonyanan <thep@linux.thai.net>
 */

#include <string.h>
#include <thai/thinp.h>
#include <thai/thctype.h>
#include <thai/tis.h>
#include <thai/wtt.h>


/**
 * @brief  Check for acceptance of input sequence
 *
 * @param  c1 : previous character
 * @param  c2 : the newly input character
 * @param  s  : strictness level
 *
 * @return  non-zero if accepted, 0 otherwise
 *
 * Checks if, according to WTT 2.0 strictness level @a s, @a c2 is allowed 
 * after @a c1.
 */
int
th_isaccept (thchar_t c1, thchar_t c2, thstrict_t s)
{
    switch (s) {
    case ISC_PASSTHROUGH:
        return 1;

    case ISC_BASICCHECK:
        return TACio_op (c1, c2) != RJ;

    case ISC_STRICT:
        {
            WTTOp op = TACio_op (c1, c2);
            return op != RJ && op != SR;
        }

    default:
        return 0;
    }
}

static const struct correction_t {
    thchar_t c1, c2, to[3];
} corrections[] = {
    { TIS_RU, TIS_SARA_AA, { TIS_RU, TIS_LAKKHANGYAO, 0 } },
    { TIS_LU, TIS_SARA_AA, { TIS_LU, TIS_LAKKHANGYAO, 0 } },
    { TIS_NIKHAHIT, TIS_SARA_AA, { TIS_SARA_AM, 0, 0 } },
    { 0, 0, { 0, 0, 0 } }
};

static int
correct_ (thchar_t c_1, thchar_t c, thchar_t conv[3])
{
    const struct correction_t *p;
    for (p = corrections; p->c1; ++p) {
        if (c_1 == (thchar_t) p->c1 && c == (thchar_t) p->c2) {
            strcpy ((char *) conv, (const char *) p->to);
            return 1;
        }
    }
    return 0;
}

/**
 * @brief  Check and try to correct input sequence
 *
 * @param  context : previous cell
 * @param  c       : the newly input character
 * @param  conv    : the storage for resulting correction info
 *
 * @returns  0 if the input is to be rejected
 *           non-zero otherwise.
 *
 * Given the previous cell as @a context, edit the input buffer using
 * the given input @a c, maintaining WTT canonical order, and do some
 * convenient correction in @a conv.
 */
int
th_validate (struct thcell_t context, thchar_t c, struct thinpconv_t *conv)
{
    thchar_t prev_c = context.top ?
                          context.top :
                          (context.hilo ? context.hilo : context.base);
    int ret;

    /* SARA_AM, if present, is always the last char of the cell */
    if (context.hilo == TIS_SARA_AM) {
        prev_c = TIS_SARA_AM;
    }

    /* try predefined corrections */
    ret = correct_ (prev_c, c, conv->conv);
    if (ret) {
        conv->offset = -1;
        return 1;
    }

    /* normal cases, using Strict level */
    if (th_isaccept (prev_c, c, ISC_STRICT)) {
        conv->conv[0] = c; conv->conv[1] = 0;
        conv->offset = 0;
        return 1;
    }

    /* try correction by conversion */
    switch (th_chlevel(c)) {
    case 3:
    case 2:
        if (context.hilo && th_isaccept (context.hilo, c, ISC_STRICT)) {
            /* hilo OK, replace top only */
            conv->offset = 0;
            conv->conv[0] = c; conv->conv[1] = 0;
            if (context.top) {
                --conv->offset;
            }
            return 1;
        }
        /* hilo not OK with c (hilo == SARA_AM falls here), or no hilo */
        if (th_isaccept (context.base, c, ISC_STRICT)
            && (context.hilo != TIS_SARA_AM
                || th_isaccept (c, TIS_SARA_AM, ISC_STRICT)))
        {
            /* replace from hilo on, using new top */
            int i = 0;
            conv->offset = 0;
            conv->conv[i++] = c;
            if (context.hilo) {
                --conv->offset;
                if (context.hilo == TIS_SARA_AM) {
                    conv->conv[i++] = TIS_SARA_AM;
                }
            }
            if (context.top) {
                --conv->offset;
            }
            conv->conv[i] = 0;
            return 1;
        }
        if (th_chlevel(c) == 2)
            break;
        /* fall through for level 3 */
    case -1:
    case 1:
        if (th_isaccept (context.base, c, ISC_STRICT)) {
            /* replace from hilo on; use new hilo + old top if OK */
            int i = 0;
            conv->offset = 0;
            conv->conv[i++] = c;
            if (context.hilo) {
                --conv->offset;
            }
            if (context.top) {
                --conv->offset;
                if (th_isaccept (c, context.top, ISC_STRICT)) {
                    conv->conv[i++] = context.top;
                }
            }
            conv->conv[i] = 0;
            return 1;
        }
        break;
    }

    return 0;
}

/*
vi:ts=4:ai:expandtab
*/