/*
 * Copyright (c) 2009 Petri Lehtinen <petri@digip.org>
 *
 * Jansson is free software; you can redistribute it and/or modify
 * it under the terms of the MIT license. See LICENSE for details.
 */

#include "config.h"

int
utf8_encode (int codepoint, char *buffer, int *size)
{
	if (codepoint < 0)
		return -1;
	else if (codepoint < 0x80) {
		buffer[0] = (char)codepoint;
		*size = 1;
	}
	else if (codepoint < 0x800) {
		buffer[0] = 0xC0 + ((codepoint & 0x7C0) >> 6);
		buffer[1] = 0x80 + ((codepoint & 0x03F));
		*size = 2;
	}
	else if (codepoint < 0x10000) {
		buffer[0] = 0xE0 + ((codepoint & 0xF000) >> 12);
		buffer[1] = 0x80 + ((codepoint & 0x0FC0) >> 6);
		buffer[2] = 0x80 + ((codepoint & 0x003F));
		*size = 3;
	}
	else if (codepoint <= 0x10FFFF) {
		buffer[0] = 0xF0 + ((codepoint & 0x1C0000) >> 18);
		buffer[1] = 0x80 + ((codepoint & 0x03F000) >> 12);
		buffer[2] = 0x80 + ((codepoint & 0x000FC0) >> 6);
		buffer[3] = 0x80 + ((codepoint & 0x00003F));
		*size = 4;
	}
	else
		return -1;

	return 0;
}

int
utf8_check_first (char byte)
{
	unsigned char                   u = (unsigned char)byte;

	if (u < 0x80)
		return 1;

	if (0x80 <= u && u <= 0xBF) {
		/* second, third or fourth byte of a multi-byte
		   sequence, i.e. a "continuation byte" */
		return 0;
	}
	else if (u == 0xC0 || u == 0xC1) {
		/* overlong encoding of an ASCII byte */
		return 0;
	}
	else if (0xC2 <= u && u <= 0xDF) {
		/* 2-byte sequence */
		return 2;
	}

	else if (0xE0 <= u && u <= 0xEF) {
		/* 3-byte sequence */
		return 3;
	}
	else if (0xF0 <= u && u <= 0xF4) {
		/* 4-byte sequence */
		return 4;
	}
	else {						/* u >= 0xF5 */
		/* Restricted (start of 4-, 5- or 6-byte sequence) or invalid
		   UTF-8 */
		return 0;
	}
}

int
utf8_check_full (const char *buffer, int size)
{
	int                             i, value = 0;
	unsigned char                   u = (unsigned char)buffer[0];

	if (size == 2) {
		value = u & 0x1F;
	}
	else if (size == 3) {
		value = u & 0xF;
	}
	else if (size == 4) {
		value = u & 0x7;
	}
	else
		return 0;

	for (i = 1; i < size; i++) {
		u = (unsigned char)buffer[i];

		if (u < 0x80 || u > 0xBF) {
			/* not a continuation byte */
			return 0;
		}

		value = (value << 6) + (u & 0x3F);
	}

	if (value > 0x10FFFF) {
		/* not in Unicode range */
		return 0;
	}

	else if (0xD800 <= value && value <= 0xDFFF) {
		/* invalid code point (UTF-16 surrogate halves) */
		return 0;
	}

	else if ((size == 2 && value < 0x80) || (size == 3 && value < 0x800) || (size == 4 && value < 0x10000)) {
		/* overlong encoding */
		return 0;
	}

	return 1;
}

int
utf8_check_string (const char *string, int length)
{
	int                             i;

	if (length == -1)
		length = strlen (string);

	for (i = 0; i < length; i++) {
		int                             count = utf8_check_first (string[i]);
		if (count == 0)
			return 0;
		else if (count > 1) {
			if (i + count > length)
				return 0;

			if (!utf8_check_full (&string[i], count))
				return 0;

			i += count - 1;
		}
	}

	return 1;
}
