/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */

/*
 * Copyright (c) 1995, by Sun Microsystems, Inc.
 * All rights reserved.
 */

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include "cns11643_big5.h"      /* CNS 11643 to Big-5 mapping table */

#define MSB     0x80    /* most significant bit */
#define MBYTE   0x8e    /* multi-byte (4 byte character) */
#define PMASK   0xa0    /* plane number mask */
#define ONEBYTE 0xff    /* right most byte */
#define MSB_OFF 0x7f    /* mask off MBS */

#define NON_ID_CHAR '_' /* non-identified character */

typedef struct _icv_state {
        char    keepc[4];       /* maximum # byte of CNS11643 code */
        short   cstate;         /* state machine id */
        int     _errno;         /* internal errno */
} _iconv_st;

enum _CSTATE    { C0, C1, C2, C3 };


static int get_plane_no_by_char(const char);
static int cns_to_big5(int, char[], char*, size_t);
static int binsearch(unsigned long, table_t[], int);


/*
 * Open; called from iconv_open()
 */
void *
_icv_open()
{
        _iconv_st *st;

        if ((st = (_iconv_st *)malloc(sizeof(_iconv_st))) == NULL) {
                errno = ENOMEM;
                return ((void *) -1);
        }

        st->cstate = C0;
        st->_errno = 0;

#ifdef DEBUG
    fprintf(stderr, "==========     iconv(): CNS11643 --> Big-5     ==========\n");
#endif

        return ((void *) st);
}


/*
 * Close; called from iconv_close()
 */
void
_icv_close(_iconv_st *st)
{
        if (!st)
                errno = EBADF;
        else
                free(st);
}


/*
 * Actual conversion; called from iconv()
 */
/*=======================================================
 *
 *   State Machine for interpreting CNS 11643 code
 *
 *=======================================================
 *
 *                          plane 2 - 16
 *                1st C         2nd C       3rd C
 *    +------> C0 -----> C1 -----------> C2 -----> C3
 *    |  ascii |  plane 1 |                   4th C |
 *    ^        v  2nd C   v                         v
 *    +----<---+-----<----+-------<---------<-------+
 *
 *=======================================================*/
size_t
_icv_iconv(_iconv_st *st, char **inbuf, size_t *inbytesleft,
                                char **outbuf, size_t *outbytesleft)
{
        int             plane_no = -1, n;

        if (st == NULL) {
                errno = EBADF;
                return ((size_t) -1);
        }

        if (inbuf == NULL || *inbuf == NULL) { /* Reset request. */
                st->cstate = C0;
                st->_errno = 0;
                return ((size_t) 0);
        }

#ifdef DEBUG
    fprintf(stderr, "=== (Re-entry)   iconv(): CNS 11643 --> Big-5 ===\n");
#endif
        st->_errno = 0;         /* reset internal errno */
        errno = 0;              /* reset external errno */

        /* a state machine for interpreting CNS 11643 code */
        while (*inbytesleft > 0 && *outbytesleft > 0) {
                switch (st->cstate) {
                case C0:                /* assuming ASCII in the beginning */
                        if (**inbuf & MSB) {
                                st->keepc[0] = (**inbuf);
                                st->cstate = C1;
                        } else {        /* real ASCII */
                                **outbuf = **inbuf;
                                (*outbuf)++;
                                (*outbytesleft)--;
                        }
                        break;
                case C1:                /* Chinese characters: 2nd byte */
                        if ((st->keepc[0] & ONEBYTE) == MBYTE) { /* 4-byte (0x8e) */
                                plane_no = get_plane_no_by_char(**inbuf);
                                if (plane_no == -1) {   /* illegal plane */
                                        st->_errno = errno = EILSEQ;
                                } else {        /* 4-byte Chinese character */
                                        st->keepc[1] = (**inbuf);
                                        st->cstate = C2;
                                }
                        } else {        /* 2-byte Chinese character - plane #1 */
                                if (**inbuf & MSB) {    /* plane #1 */
                                        st->keepc[1] = (**inbuf);
                                        st->keepc[2] = st->keepc[3] = '\0';
                                        n = cns_to_big5(1, st->keepc, *outbuf,
                                                        *outbytesleft);
                                        if (n > 0) {
                                                (*outbuf) += n;
                                                (*outbytesleft) -= n;

                                                st->cstate = C0;
                                        } else {        /* don't reset state */
                                                st->_errno = errno = E2BIG;
                                        }
                                } else {        /* input char doesn't belong
                                                 * to the input code set
                                                 */
                                        st->_errno = errno = EILSEQ;
                                }
                        }
                        break;
                case C2:        /* plane #2 - #16 (4 bytes): get 3nd byte */
                        if (**inbuf & MSB) {    /* 3rd byte */
                                st->keepc[2] = (**inbuf);
                                st->cstate = C3;
                        } else {
                                st->_errno = errno = EILSEQ;
                        }
                        break;
                case C3:        /* plane #2 - #16 (4 bytes): get 4th byte */
                        if (**inbuf & MSB) {    /* 4th byte */
                                st->keepc[3] = (**inbuf);
                                n = cns_to_big5(plane_no, st->keepc, *outbuf,
                                                *outbytesleft );
                                if (n > 0) {
                                        (*outbuf) += n;
                                        (*outbytesleft) -= n;

                                        st->cstate = C0;        /* reset state */
                                } else {        /* don't reset state */
                                        st->_errno = errno = E2BIG;
                                }
                        } else {
                                st->_errno = errno = EILSEQ;
                        }
                        break;
                default:                        /* should never come here */
                        st->_errno = errno = EILSEQ;
                        st->cstate = C0;        /* reset state */
                        break;
                }

                if (st->_errno) {
#ifdef DEBUG
    fprintf(stderr, "!!!!!\tst->_errno = %d\tst->cstate = %d\n",
                st->_errno, st->cstate);
#endif
                        break;
                }

                (*inbuf)++;
                (*inbytesleft)--;
        }

        if (errno) return ((size_t) -1);

        if (*inbytesleft == 0 && st->cstate != C0) {
                errno = EINVAL;
                return ((size_t) -1);
        }

        if (*inbytesleft > 0 && *outbytesleft == 0) {
                errno = E2BIG;
                return((size_t)-1);
        }
        return (*inbytesleft);
}


/*
 * Get plane number by char; i.e. 0xa2 returns 2, 0xae returns 14, etc.
 * Returns -1 on error conditions
 */
static int get_plane_no_by_char(const char inbuf)
{
        int ret;
        unsigned char uc = (unsigned char) inbuf;

        ret = uc - PMASK;
        switch (ret) {
        case 1:         /* 0x8EA1 */
        case 2:         /* 0x8EA2 */
        case 3:         /* 0x8EA3 */
        case 4:         /* 0x8EA4 */
        case 5:         /* 0x8EA5 */
        case 6:         /* 0x8EA6 */
        case 7:         /* 0x8EA7 */
        case 12:        /* 0x8EAC */
        case 14:        /* 0x8EAE */
        case 15:        /* 0x8EAF */
        case 16:        /* 0x8EB0 */
                return (ret);
        default:
                return (-1);
        }
}


/*
 * CNS 11643 code --> Big-5
 * Return: > 0 - converted with enough space in output buffer
 *         = 0 - no space in outbuf
 */
static int cns_to_big5(int plane_no, char keepc[], char *buf, size_t buflen)
{
        char            cns_str[3];
        unsigned long   cns_val;        /* MSB mask off CNS 11643 value */
        int             unidx;          /* binary search index */
        unsigned long   big5_val, val;  /* Big-5 code */

#ifdef DEBUG
    fprintf(stderr, "%s %d ", keepc, plane_no);
#endif
        if (buflen < 2) {
                errno = E2BIG;
                return(0);
        }

        if (plane_no == 1) {
                cns_str[0] = keepc[0] & MSB_OFF;
                cns_str[1] = keepc[1] & MSB_OFF;
        } else {
                cns_str[0] = keepc[2] & MSB_OFF;
                cns_str[1] = keepc[3] & MSB_OFF;
        }
        cns_val = (cns_str[0] << 8) + cns_str[1];
#ifdef DEBUG
    fprintf(stderr, "%x\t", cns_val);
#endif

        switch (plane_no) {
        case 1:
                unidx = binsearch(cns_val, cns_big5_tab1, MAX_CNS1_NUM);
                if (unidx >= 0)
                        big5_val = cns_big5_tab1[unidx].value;
                break;
        case 2:
                unidx = binsearch(cns_val, cns_big5_tab2, MAX_CNS2_NUM);
                if (unidx >= 0)
                        big5_val = cns_big5_tab2[unidx].value;
                break;
        case 3:
                unidx = binsearch(cns_val, cns_big5_tab3, MAX_CNS3_NUM);
                if (unidx >= 0)
                        big5_val = cns_big5_tab3[unidx].value;
                break;
        default:
                unidx = -1;     /* no mapping from CNS to Big-5 */
                break;
        }

#ifdef DEBUG
    fprintf(stderr, "unidx = %d, value = %x\t", unidx, big5_val);
#endif

        if (unidx < 0) {        /* no match from CNS to Big-5 */
                *buf = *(buf+1) = NON_ID_CHAR;
        } else {
                val = big5_val & 0xffff;
                *buf = (char) ((val & 0xff00) >> 8);
                *(buf+1) = (char) (val & 0xff);
        }

#ifdef DEBUG
    fprintf(stderr, "\t->%x %x<-\n", *buf, *(buf+1));
#endif

        return(2);
}


/* binsearch: find x in v[0] <= v[1] <= ... <= v[n-1] */
static int binsearch(unsigned long x, table_t v[], int n)
{
        int low, high, mid;

        low = 0;
        high = n - 1;
        while (low <= high) {
                mid = (low + high) / 2;
                if (x < v[mid].key)
                        high = mid - 1;
                else if (x > v[mid].key)
                        low = mid + 1;
                else    /* found match */
                        return mid;
        }
        return (-1);    /* no match */
}