use bytes;

// Returns the index of the first occurance of 'needle' in the 'haystack', or
// void if not present. The index returned is the rune-wise index, not the
// byte-wise index.
export fn index(haystack: str, needle: (str | rune)) (size | void) = {
	return match (needle) {
		r: rune => index_rune(haystack, r),
		s: str => abort(), // TODO
	};
};

fn index_rune(s: str, r: rune) (size | void) = {
	let iter = iter(s);
	for (let i = 0z; true; i += 1) match (next(&iter)) {
		n: rune => if (r == n) return i,
		void => break,
	};
};

@test fn index() void = {
	assert(index("hello world", 'w') as size == 6);
	assert(index("こんにちは", 'ち') as size == 3);
	assert(index("こんにちは", 'q') is void);
};