// strconv — number↔string conversions. Decimal i64 to/from a fixed
// buffer. Two error idioms ship side by side:
//   - Plan 9 style (atoi64): tuple `(value, ok)`. Pre-dates the
//     tagged-union work; kept for callers that already use it.
//   - Hare style (stoi64/stou64): `(value | str)`. The error
//     variant carries a short, allocation-free message describing
//     why the parse failed. Prefer this for new code.

// u64tos — write `v` in decimal into `buf` and return the byte count.
// Hare name; the buffer-in shape is the sanctioned Plan 9 subset of
// Hare's `u64tos(u, base) const str`. Unsigned-only so callers don't
// have to think about wraparound when printing a u64 with the high
// bit set.
export fn u64tos(buf: []u8, v: u64) i32 = {
	let tmp: [32]u8;
	let i: i32 = 0;
	let n: u64 = v;
	for (n > 0u64) {
		tmp[i] = ((n % 10u64) + 48u64): u8;
		n = n / 10u64;
		i += 1;
	};
	if (i == 0) {
		tmp[0] = 48u8;
		i = 1;
	};
	let out: i32 = 0;
	for (i > 0) {
		i -= 1;
		buf[out] = tmp[i];
		out += 1;
	};
	return out;
};

export fn i64tos(buf: []u8, v: i64) i32 = {
	let neg: bool = false;
	let n: i64 = v;
	if (n < 0) {
		neg = true;
		n = -n;
	};
	let tmp: [32]u8;
	let i: i32 = 0;
	for (n > 0) {
		tmp[i] = ((n % 10) + 48): u8;
		n = n / 10;
		i += 1;
	};
	if (i == 0) {
		tmp[0] = 48u8;
		i = 1;
	};
	let out: i32 = 0;
	if (neg) {
		buf[out] = 45u8;	// '-'
		out += 1;
	};
	for (i > 0) {
		i -= 1;
		buf[out] = tmp[i];
		out += 1;
	};
	return out;
};

export fn atoi64(s: str) (i64, bool) = {
	let v: i64 = 0;
	let i: i32 = 0;
	let neg: bool = false;
	if (s.len > 0) {
		if (s[0] == 45u8) { neg = true; i = 1; };
	};
	if (i >= s.len) { return 0, false; };
	for (i < s.len) {
		let c: u8 = s[i];
		if (c < 48u8) { return 0, false; };
		if (c > 57u8) { return 0, false; };
		v = v * 10 + ((c: i64) - 48);
		i += 1;
	};
	if (neg) { v = -v; };
	return v, true;
};

// stoi64 — Hare-style fallible signed decimal parser. The value
// variant is i64; the error variant is a short str (subset of Hare's
// (invalid | overflow) tagged-union). No locale, no whitespace, no
// underscores: a leading '-' is the only non-digit accepted, and only
// at position 0.
export fn stoi64(s: str) (i64 | str) = {
	if (s.len == 0) { return "parse: empty"; };
	let i: i32 = 0;
	let neg: bool = false;
	if (s[0] == 45u8) { neg = true; i = 1; };
	if (i >= s.len) { return "parse: lone sign"; };
	let v: i64 = 0;
	for (i < s.len) {
		let c: u8 = s[i];
		if (c < 48u8) { return "parse: invalid digit"; };
		if (c > 57u8) { return "parse: invalid digit"; };
		v = v * 10 + ((c: i64) - 48);
		i += 1;
	};
	if (neg) { v = -v; };
	return v;
};

// stou64 — fallible unsigned decimal parser. No leading sign. Mirrors
// Hare's strconv::stou64.
export fn stou64(s: str) (u64 | str) = {
	if (s.len == 0) { return "parse: empty"; };
	let v: u64 = 0u64;
	let i: i32 = 0;
	for (i < s.len) {
		let c: u8 = s[i];
		if (c < 48u8) { return "parse: invalid digit"; };
		if (c > 57u8) { return "parse: invalid digit"; };
		v = v * 10u64 + ((c: u64) - 48u64);
		i += 1;
	};
	return v;
};