#include "unicode.h"

/*
 * Sample implementation from Unicode home page.
 * http://www.stonehand.com/unicode/standard/fss-utf.html
 */
struct utf8_table {
	int     cmask;
	int     cval;
	int     shift;
	long    lmask;
	long    lval;
};

static struct utf8_table utf8_table[] =
{
    {0x80,  0x00,   0*6,    0x7F,           0,         /* 1 byte sequence */},
    {0xE0,  0xC0,   1*6,    0x7FF,          0x80,      /* 2 byte sequence */},
    {0xF0,  0xE0,   2*6,    0xFFFF,         0x800,     /* 3 byte sequence */},
    {0xF8,  0xF0,   3*6,    0x1FFFFF,       0x10000,   /* 4 byte sequence */},
    {0xFC,  0xF8,   4*6,    0x3FFFFFF,      0x200000,  /* 5 byte sequence */},
    {0xFE,  0xFC,   5*6,    0x7FFFFFFF,     0x4000000, /* 6 byte sequence */},
    {0,						       /* end of table    */}
};

int
utf8_mbtowc(wchar_t *p, const char *s, int n)
{
	wchar_t l;
	int c0, c, nc;
	struct utf8_table *t;

	nc = 0;
	c0 = *s;
	l = c0;
	for (t = utf8_table; t->cmask; t++) {
		nc++;
		if ((c0 & t->cmask) == t->cval) {
			l &= t->lmask;
			if (l < t->lval)
				return -nc;
			*p = l;
			return nc;
		}
		if (n <= nc)
			return 0;
		s++;
		c = (*s ^ 0x80) & 0xFF;
		if (c & 0xC0)
			return -nc;
		l = (l << 6) | c;
	}
	return -nc;
}

int
utf8_mbstowcs(wchar_t *pwcs, const char *s, int n)
{
	wchar_t *op;
	const char *ip;
	int size;

	op = pwcs;
	ip = s;
	while (*ip && n > 0) {
		if (*ip & 0x80) {
			size = utf8_mbtowc(op, ip, n);
			if (size == -1) {
				/* Ignore character and move on */
				ip++;
				n--;
			} else {
				op += size;
				ip += size;
				n -= size;
			}
		} else {
			*op++ = *ip++;
		}
	}
	return (op - pwcs);
}

int
utf8_wctomb(char *s, wchar_t wc, int maxlen)
{
	long l;
	int c, nc;
	struct utf8_table *t;

	if (s == 0)
		return 0;

	l = wc;
	nc = 0;
	for (t = utf8_table; t->cmask && maxlen; t++, maxlen--) {
		nc++;
		if (l <= t->lmask) {
			c = t->shift;
			*s = t->cval | (l >> c);
			while (c > 0) {
				c -= 6;
				s++;
				*s = 0x80 | ((l >> c) & 0x3F);
			}
			return nc;
		}
	}
	return -1;
}

int
utf8_wcstombs(char *s, const wchar_t *pwcs, int maxlen)
{
	const wchar_t *ip;
	char *op;
	int size;

	op = s;
	ip = pwcs;
	while (*ip && maxlen > 0) {
		if (*ip > 0x7f) {
			size = utf8_wctomb(op, *ip, maxlen);
			if (size == -1) {
				/* Ignore character and move on */
				maxlen--;
			} else {
				op += size;
				maxlen -= size;
			}
		} else {
			*op++ = (char) *ip;
		}
		ip++;
	}
	return (op - s);
}