/*   Some conversion functions for handling UTF-8
 *
 *   copyright Marcoen Hirschberg (2004,2005)
 *
 *   I got all the info from:
 *   http://www.cl.cam.ac.uk/~mgk25/unicode.html#utf-8
 *   and
 *   http://en.wikipedia.org/wiki/Unicode
 */

#include <stdio.h>
#include "file.h"
#include "debug.h"
#include "rbunicode.h"

#ifndef O_BINARY
#define O_BINARY 0
#endif

#define NUM_TABLES 5
#define NUM_CODEPAGES 13

static int default_codepage = 0;
static unsigned short codepage_table[MAX_CP_TABLE_SIZE];
static int loaded_cp_table = 0;


static const unsigned char utf8comp[6] = 
{
    0x00, 0xC0, 0xE0, 0xF0, 0xF8, 0xFC
};

static const char *filename[NUM_TABLES] =
{
    CODEPAGE_DIR"/iso.cp",
    CODEPAGE_DIR"/932.cp",  /* SJIS    */
    CODEPAGE_DIR"/936.cp",  /* GB2312  */
    CODEPAGE_DIR"/949.cp",  /* KSX1001 */
    CODEPAGE_DIR"/950.cp"   /* BIG5    */
};

static const char cp_2_table[NUM_CODEPAGES] =
{
    0, 1, 1, 1, 1, 1, 1, 1, 2, 3, 4, 5
};

/* Load codepage file into memory */
int load_cp_table(int cp)
{
    int i=0;
    int table = cp_2_table[cp];
    int file, tablesize;
    unsigned char tmp[2];

    if (cp == 0 || table == loaded_cp_table)
        return 1;

    file = open(filename[table-1], O_RDONLY|O_BINARY);

    if (file < 0) {
        DEBUGF("Can't open codepage file: %s.cp\n", filename[table-1]);
        return 0;
    }

    tablesize = lseek(file, 0, SEEK_END) / 2;
    lseek(file, 0, SEEK_SET);

    if (tablesize > MAX_CP_TABLE_SIZE) {
        DEBUGF("Invalid codepage file: %s.cp\n", filename[table-1]);
        close(file);
        return 0;
    }

    while (i < tablesize) {
        if (!read(file, tmp, 2)) {
            DEBUGF("Can't read from codepage file: %s.cp\n", 
                    filename[table-1]);
            loaded_cp_table = 0;
            return 0;
        }
        codepage_table[i++] = (tmp[1] << 8) | tmp[0];
    }

    loaded_cp_table = table;
    close(file);
    return 1;
}

/* Encode a UCS value as UTF-8 and return a pointer after this UTF-8 char. */
unsigned char* utf8encode(unsigned long ucs, unsigned char *utf8)
{
    int tail = 0;

    if (ucs > 0x7F)
        while (ucs >> (5*tail + 6))
            tail++;

    *utf8++ = (ucs >> (6*tail)) | utf8comp[tail];
    while (tail--)
        *utf8++ = ((ucs >> (6*tail)) & (MASK ^ 0xFF)) | COMP;

    return utf8;
}

/* Recode an iso encoded string to UTF-8 */
unsigned char* iso_decode(const unsigned char *iso, unsigned char *utf8,
                          int cp, int count)
{
    unsigned short ucs, tmp;

    if (cp == -1) /* use default codepage */
       cp = default_codepage;

    if (!load_cp_table(cp)) cp = 0;

    while (count--) {
        if (*iso < 128)
            *utf8++ = *iso++;

        else {

            /* cp tells us which codepage to convert from */
            switch (cp) {
                case 0x01: /* Greek (ISO-8859-7) */
                case 0x02: /* Hebrew (ISO-8859-8) */
                case 0x03: /* Russian (CP1251) */
                case 0x04: /* Thai (ISO-8859-11) */
                case 0x05: /* Arabic (ISO-8859-6) */
                case 0x06: /* Turkish (ISO-8859-9) */
                case 0x07: /* Latin Extended (ISO-8859-2) */
                    tmp = ((cp-1)*128) + (*iso++ - 128);
                    ucs = codepage_table[tmp];
                    break;

                case 0x08: /* Japanese (SJIS) */
                    if (*iso > 0xA0 && *iso < 0xE0) {
                        tmp = *iso | 0xA100;
                        ucs = codepage_table[tmp];
                        break;
                    }

                case 0x09: /* Simplified Chinese (GB2312) */
                case 0x0A: /* Korean (KSX1001) */
                case 0x0B: /* Traditional Chinese (BIG5) */
                    if (count < 1 || !iso[1]) {
                        ucs = *iso++;
                        break;
                    }

                    /* we assume all cjk strings are written
                       in big endian order */
                    tmp = *iso++ << 8;
                    tmp |= *iso++;
                    tmp -= 0x8000;
                    ucs = codepage_table[tmp];
                    count--;
                    break;

                case 0x0C: /* UTF-8, do nothing */
                default:
                    ucs = *iso++;
                    break;
            }

            if (ucs == 0) /* unknown char, assume invalid encoding */
                ucs = 0xffff;
            utf8 = utf8encode(ucs, utf8);
        }
    }
    return utf8;
}

/* Recode a UTF-16 string with little-endian byte ordering to UTF-8 */
unsigned char* utf16LEdecode(const unsigned char *utf16, unsigned char *utf8,
        unsigned int count)
{
    unsigned long ucs;

    while (count != 0) {
        /* Check for a surrogate pair */
        if (utf16[1] >= 0xD8 && utf16[1] < 0xE0) {
            ucs = 0x10000 + ((utf16[0] << 10) | ((utf16[1] - 0xD8) << 18)
                    | utf16[2] | ((utf16[3] - 0xDC) << 8));
            utf16 += 4;
            count -= 2;
        } else {
            ucs = (utf16[0] | (utf16[1] << 8));
            utf16 += 2;
            count -= 1;
        }
        utf8 = utf8encode(ucs, utf8);
    }
    return utf8;
}

/* Recode a UTF-16 string with big-endian byte ordering to UTF-8 */
unsigned char* utf16BEdecode(const unsigned char *utf16, unsigned char *utf8,
        unsigned int count)
{
    unsigned long ucs;

    while (count != 0) {
        if (*utf16 >= 0xD8 && *utf16 < 0xE0) { /* Check for a surrogate pair */
            ucs = 0x10000 + (((utf16[0] - 0xD8) << 18) | (utf16[1] << 10)
                    | ((utf16[2] - 0xDC) << 8) | utf16[3]);
            utf16 += 4;
            count -= 2;
        } else {
            ucs = (utf16[0] << 8) | utf16[1];
            utf16 += 2;
            count -= 1;
        }
        utf8 = utf8encode(ucs, utf8);
    }
    return utf8;
}

/* Recode any UTF-16 string to UTF-8 */
unsigned char* utf16decode(const unsigned char *utf16, unsigned char *utf8,
        unsigned int count)
{
    unsigned long ucs;

    ucs = *(utf16++) << 8;
    ucs |= *(utf16++);

    if (ucs == 0xFEFF) /* Check for BOM */
        return utf16BEdecode(utf16, utf8, count-1);
    else if (ucs == 0xFFFE)
        return utf16LEdecode(utf16, utf8, count-1);
    else { /* ADDME: Should default be LE or BE? */
        utf16 -= 2;
        return utf16BEdecode(utf16, utf8, count);
    }
}

/* Return the number of UTF-8 chars in a string */
unsigned long utf8length(const unsigned char *utf8)
{
    unsigned long l = 0;

    while (*utf8 != 0)
        if ((*utf8++ & MASK) != COMP)
            l++;

    return l;
}

/* Decode 1 UTF-8 char and return a pointer to the next char. */
const unsigned char* utf8decode(const unsigned char *utf8, unsigned short *ucs)
{
    unsigned char c = *utf8++;
    unsigned long code;
    int tail = 0;

    if ((c <= 0x7f) || (c >= 0xc2)) {
        /* Start of new character. */
        if (c < 0x80) {        /* U-00000000 - U-0000007F, 1 byte */
            code = c;
        } else if (c < 0xe0) { /* U-00000080 - U-000007FF, 2 bytes */
            tail = 1;
            code = c & 0x1f;
        } else if (c < 0xf0) { /* U-00000800 - U-0000FFFF, 3 bytes */
            tail = 2;
            code = c & 0x0f;
        } else if (c < 0xf5) { /* U-00010000 - U-001FFFFF, 4 bytes */
            tail = 3;
            code = c & 0x07;
        } else {
            /* Invalid size. */
            code = 0xffff;
        }

        while (tail-- && ((c = *utf8++) != 0)) {
            if ((c & 0xc0) == 0x80) {
                /* Valid continuation character. */
                code = (code << 6) | (c & 0x3f);

            } else {
                /* Invalid continuation char */
                code = 0xffff;
                utf8--;
                break;
            }
        }
    } else {
        /* Invalid UTF-8 char */
        code = 0xffff;
    }
    /* currently we don't support chars above U-FFFF */
    *ucs = (code < 0x10000) ? code : 0xffff;
    return utf8;
}

void set_codepage(int cp)
{
    default_codepage = cp;
    return;
}

/* seek to a given char in a utf8 string and
   return its start position in the string */
int utf8seek(const unsigned char* utf8, int offset)
{
    int pos = 0;

    while (offset--) {
        pos++;
        while ((utf8[pos] & MASK) == COMP)
            pos++;
    }
    return pos;
}