/*
 * 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>

#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 MSB */

#define SI      0x0f    /* shift in */
#define SO      0x0e    /* shift out */
#define ESC     0x1b    /* escape */

/* static const char plane_char[] = "0GH23456789:;<=>?"; */
static const char plane_char[] = "0GHIJKLMNOPQRSTUV";

#define GET_PLANEC(i)   (plane_char[i])

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

typedef struct _icv_state {
        char    keepc[4];       /* maximum # byte of CNS11643 code */
        short   cstate;         /* state machine id (CNS) */
        short   istate;         /* state machine id (ISO) */
        short   plane_no;       /* plane no */
        short   SOset;          /* So is set */
        short   SS2set;         /* SS2 is set */
        char    SS3char;        /* SS3 char. */
        int     _errno;         /* internal errno */
} _iconv_st;

enum _CSTATE    { C0, C1, C2, C3, C4 };
enum _ISTATE    { IN, OUT };
enum _truefalse { False, True };


static int get_plane_no_by_char(const char);

/*
 * 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->istate = IN;
        st->_errno = 0;
        st->plane_no = -1;
        st->SOset = False;
        st->SS2set = False;
        st->SS3char = '0';

#ifdef DEBUG
    fprintf(stderr, "==========     iconv(): CNS11643 --> ISO 2022-CN     ==========\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
 *
 *=======================================================
 *
 *               (ESC,SO)   plane 2 - 16
 *                1st C         2nd C       3rd C
 *    +------> C0 -----> C1 -----------> C2 -----> C3
 *    |  ascii |  plane 1 |                   4th C |
 *    ^        |  2nd C   v                         v
 *    |        |         C4 <------<--------<-------+
 *    |        v          | (SI)
 *    +----<---+-----<----v
 *
 *=======================================================*/
#define LEFT_CHECK(i)           if (*outbytesleft < i) {\
                                    st->_errno = errno = E2BIG;\
                                    return((size_t)-1);\
                                } else\
                                    (*outbytesleft) -= i
#define BUF_INPUT(c1, c2, c3, c4)\
                                *(*outbuf)++ = c1;\
                                *(*outbuf)++ = c2;\
                                *(*outbuf)++ = c3;\
                                *(*outbuf)++ = c4
size_t
_icv_iconv(_iconv_st *st, char **inbuf, size_t *inbytesleft,
                                char **outbuf, size_t *outbytesleft)
{
        if (st == NULL) {
            errno = EBADF;
            return ((size_t) -1);
        }

        if (inbuf == NULL || *inbuf == NULL) { /* Reset request. */
            if (st->istate == OUT) {
                if (outbytesleft && *outbytesleft >= 1 && outbuf && *outbuf) {
                    **outbuf = SI;
                    (*outbuf)++;
                    (*outbytesleft)--;
                } else {
                    errno = E2BIG;
                    return((size_t) -1);
                }
            }
            st->cstate = C0;
            st->istate = IN;
            st->_errno = 0;
            st->plane_no = -1;
            st->SOset = False;
            st->SS2set = False;
            st->SS3char = '0';
            return ((size_t) 0);
        }

#ifdef DEBUG
    fprintf(stderr, "=== (Re-entry)     iconv(): CNS11643 --> ISO 2022-CN     ===\n");
    fprintf(stderr, "st->cstate=%d\tst->istate=%d\tst->_errno=%d\tplane_no=%d\n",
        st->cstate, st->istate, st->_errno, st->plane_no);
#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 */
                    if (st->istate == OUT) {
                        st->istate = IN;
                        *(*outbuf)++ = SI;
                        (*outbytesleft)--;
                        if (*outbytesleft <= 0) {
                            errno = E2BIG;
                            return ((size_t) -1);
                        }
                    }
                    *(*outbuf)++ = **inbuf;
                    (*outbytesleft)--;
                    if (**inbuf == '\n') {
                        st->SOset = False;
                        st->SS2set = False;
                        st->SS3char = '0';
                    }
                }
                break;
            case C1:            /* Chinese characters: 2nd byte */
                if ((st->keepc[0] & ONEBYTE) == MBYTE) { /* 4-byte (0x8e) */
                    st->plane_no = get_plane_no_by_char(**inbuf);
                    if (st->plane_no == -1) {   /* illegal plane */
                        st->cstate = C0;
                        st->istate = IN;
                        st->_errno = errno = EILSEQ;
                    } else {    /* 4-byte Chinese character */
                        st->cstate = C2;
                        st->keepc[1] = (**inbuf);
                    }
                } else {        /* 2-byte Chinese character - plane #1 */
                    if (**inbuf & MSB) {        /* plane #1 */
                        st->cstate = C4;
                        st->keepc[1] = (**inbuf);
                        st->plane_no = 1;
                        continue;       /* should not advance *inbuf */
                    } else {    /* input char doesn't belong
                                     * to the input code set */
                        st->cstate = C0;
                        st->istate = IN;
                        st->_errno = errno = EINVAL;
                    }
                }
                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 = EINVAL;
                    st->cstate = C0;
                }
                break;
            case C3:    /* plane #2 - #16 (4 bytes): get 4th byte */
                if (**inbuf & MSB) {    /* 4th byte */
                    st->cstate = C4;
                    st->keepc[3] = (**inbuf);
                    continue;       /* should not advance *inbuf */
                } else {
                    st->_errno = errno = EINVAL;
                    st->cstate = C0;
                }
                break;
            case C4:    /* Convert code from CNS 11643 to ISO 2022-CN */
                if (st->plane_no == 1) {
                    if (st->istate == IN) {
                        if (st->SOset == False) {
                            LEFT_CHECK(4);
                            BUF_INPUT(ESC, '$', ')', 'G');
                            st->SOset = True;
                        }
                        LEFT_CHECK(1);
                        *(*outbuf)++ = SO;
                        st->istate = OUT;
                    }
                    LEFT_CHECK(2);
                    *(*outbuf)++ = st->keepc[0] & MSB_OFF;
                    *(*outbuf)++ = st->keepc[1] & MSB_OFF;

                } else if (st->plane_no == 2) {
                    if (st->SS2set == False) {
                        LEFT_CHECK(4);
                        BUF_INPUT(ESC, '$', '*', 'H');
                        st->SS2set = True;
                    }
                    LEFT_CHECK(4);
                    BUF_INPUT(ESC, 0x4E, st->keepc[2] & MSB_OFF, st->keepc[3] & MSB_OFF);
                } else {
                    if (st->SS3char != GET_PLANEC(st->plane_no)) {
                        LEFT_CHECK(4);
                        st->SS3char = GET_PLANEC(st->plane_no);
                        BUF_INPUT(ESC, '$', '+', st->SS3char);
                    }
                    LEFT_CHECK(4);
                    BUF_INPUT(ESC, 0x4F, st->keepc[2] & MSB_OFF, st->keepc[3] & MSB_OFF);
                }
                st->cstate = C0;
                break;
            default:                    /* should never come here */
                st->_errno = errno = EILSEQ;
                st->cstate = C0;        /* reset state */
                break;
            }

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

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