import std.utf;

/*
   Slice UTF-8 string like it do string[from..to] for ASCII;
   Use negative index to access string from end
 */
string slice(in string a, int from, int to)
{
	int getIndexOfSymbol(in string a, int pos)
	{
		int res;

		if (pos < 0) { pos += std.utf.count(a); }

		for (; pos > 0; pos--)
		{
			res += a.stride(res);
		}
		return res;
	}

	return a[getIndexOfSymbol(a, from)..getIndexOfSymbol(a, to)];
}

unittest
{
	string ascii = "Hello";
	assert(slice(ascii, 2, 3) == ascii[2..3]);
	assert(slice(ascii, 2, -1) == ascii[2..$]);
	assert(slice(ascii, 2, -2) == ascii[2..$-1]);
	assert(slice(ascii, 0, 3) == ascii[0..3]);
	assert(slice(ascii, -2, -1) == ascii[$-1..$]);

	assert(slice("Привет", 2, 3) == "ив");
	assert(slice("Привет", 2, -1) == "ивет");
	assert(slice("Привет", 0, 3) == "Прив");
	assert(slice("Привет", -2, -1) == "ет");
}