// strings — operations over the immutable str type ({ *u8, len }).

use os;

export fn len(s: str) i32 = {
	return s.len;
};

export fn isempty(s: str) bool = {
	return s.len == 0;
};

export fn equal(a: str, b: str) bool = {
	if (a.len != b.len) { return false; };
	let i: i32 = 0;
	for (i < a.len) {
		if (a[i] != b[i]) { return false; };
		i += 1;
	};
	return true;
};

export fn hasprefix(s: str, p: str) bool = {
	if (p.len > s.len) { return false; };
	let i: i32 = 0;
	for (i < p.len) {
		if (s[i] != p[i]) { return false; };
		i += 1;
	};
	return true;
};

export fn hassuffix(s: str, suf: str) bool = {
	if (suf.len > s.len) { return false; };
	let off: i32 = s.len - suf.len;
	let i: i32 = 0;
	for (i < suf.len) {
		if (s[off + i] != suf[i]) { return false; };
		i += 1;
	};
	return true;
};

// indexbyte — first index of `c` in `s`, or -1 if absent. Plan 9-
// style sentinel return; callers that prefer a fallible shape can
// wrap this in their own (i32 | str). No allocation.
export fn indexbyte(s: str, c: u8) i32 = {
	let i: i32 = 0;
	for (i < s.len) {
		if (s[i] == c) { return i; };
		i += 1;
	};
	return -1;
};

// index — first index of `sub` in `s`, or -1. Naive scan; fine for
// short patterns and small strings, which dominate config and CLI
// parsing. Empty `sub` matches at 0.
export fn index(s: str, sub: str) i32 = {
	if (sub.len == 0) { return 0; };
	if (sub.len > s.len) { return -1; };
	let last: i32 = s.len - sub.len;
	let i: i32 = 0;
	for (i <= last) {
		let j: i32 = 0;
		let ok: bool = true;
		for (j < sub.len) {
			if (s[i + j] != sub[j]) { ok = false; j = sub.len; }
			else { j += 1; };
		};
		if (ok) { return i; };
		i += 1;
	};
	return -1;
};

export fn contains(s: str, sub: str) bool = {
	return index(s, sub) >= 0;
};

// concat — joins two strings into a fresh str. Caller owns the
// returned str's storage; release via `os.free(r.ptr, r.len)`. Mirrors
// Hare's strings::concat shape.
export fn concat(a: str, b: str) str = {
	let total: i32 = a.len + b.len;
	let buf: *u8 = os.alloc(total: u64): *u8;
	let i: i32 = 0;
	for (i < a.len) { buf[i] = a[i]; i += 1; };
	let j: i32 = 0;
	for (j < b.len) { buf[a.len + j] = b[j]; j += 1; };
	let r: str;
	r.ptr = buf;
	r.len = total;
	return r;
};