#include <unistd.h>

#include <unistd.h>
#include "lt_types.h"

// Return number of bytes in the UTF-8 sequence which begins with a given byte.
int wchar_len(byte b) {
if ((b & 0xE0) == 0xC0) return 2;
if ((b & 0xF0) == 0xE0) return 3;
if ((b & 0xF8) == 0xF0) return 4;
return 1;
}

void store_wchar(byte** p, wchar ch) {
if (ch < 0x80) {
*(*p)++ = (char) ch;
} else if (ch < 0x800) {
*(*p)++ = (byte) (0xC0 | ((ch >> 6) & 0x1F));
*(*p)++ = (byte) (0x80 | (ch & 0x3F));
} else if (ch < 0x10000) {
*(*p)++ = (byte) (0xE0 | ((ch >> 12) & 0x0F));
*(*p)++ = (byte) (0x80 | ((ch >> 6) & 0x3F));
*(*p)++ = (byte) (0x80 | (ch & 0x3F));
} else {
*(*p)++ = (byte) (0xF0 | ((ch >> 18) & 0x07));
*(*p)++ = (byte) (0x80 | ((ch >> 12) & 0x3F));
*(*p)++ = (byte) (0x80 | ((ch >> 6) & 0x3F));
*(*p)++ = (byte) (0x80 | (ch & 0x3F));
}
}

wchar load_wchar(const byte** p) {
wchar ch;
switch (wchar_len(**p)) {
default:
ch = *(*p)++ & 0xFF;
break;
case 2:
ch = (*(*p)++ & 0x1F) << 6;
ch |= *(*p)++ & 0x3F;
break;
case 3:
ch = (*(*p)++ & 0x0F) << 12;
ch |= (*(*p)++ & 0x3F) << 6;
ch |= (*(*p)++ & 0x3F);
break;
case 4:
ch = (*(*p)++ & 0x07) << 18;
ch |= (*(*p)++ & 0x3F) << 12;
ch |= (*(*p)++ & 0x3F) << 6;
ch |= (*(*p)++ & 0x3F);
break;
}
return ch;
}

wchar read_wchar(int fd) {
byte cbuf[UNICODE_MAX_BYTES];
int n = read(fd, &cbuf[0], 1);
if (n <= 0)
return 0;
int len = wchar_len(cbuf[0]);
int i;
for (i = 1; i < len; ++i) {
int n = read(fd, &cbuf[i], 1);
if (n != 1) return 0;
}
const byte* cp = cbuf;
wchar ch = load_wchar(&cp);
// assert(cp-cbuf == len);
return ch;
}