// strings — operations over the immutable str type ({ *u8, len }).
// Mirrors Hare's strings::; `len` and `is-empty` aren't functions
// (callers use `s.len` and `s.len == 0` directly).

use os;

// compare — bytewise three-way comparison: negative if a<b, 0 if equal,
// positive if a>b. Matches Hare's strings::compare. ASCII-order, not
// locale-aware. Callers that just need equality use `compare(a, b) == 0`.
export fn compare(a: str, b: str) i32 = {
	let n: i32 = a.len;
	if (b.len < n) { n = b.len; };
	let i: i32 = 0;
	for (i < n) {
		if (a[i] != b[i]) { return (a[i]: i32) - (b[i]: i32); };
		i += 1;
	};
	return a.len - b.len;
};

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;
};

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

// rbyteindex — last index of byte `c` in `s`, or -1 if absent. Mirrors
// Hare's strings::rbyteindex.
export fn rbyteindex(s: str, c: u8) i32 = {
	let i: i32 = s.len - 1;
	for (i >= 0) {
		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;
};