// Copyright 2026 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package sgutil

import (
	"strconv"
	"strings"
)

// isDigit returns true if the byte is an ASCII digit.
func isDigit(b byte) bool {
	return b >= '0' && b <= '9'
}

// CompareNatural performs a "natural sort" comparison of two strings.
// It compares non-digit sections lexicographically and digit sections
// numerically.  In the case of string-unequal "equal" strings like
// "a01b" and "a1b", strings.Compare breaks the tie.
//
// It returns:
//
//	-1 if s1 < s2
//	 0 if s1 == s2
//	+1 if s1 > s2
func CompareNatural(s1, s2 string) int {
	i, j := 0, 0
	len1, len2 := len(s1), len(s2)

	for i < len1 && j < len2 {
		// Find a non-digit segment or a number segment in both strings.
		if isDigit(s1[i]) && isDigit(s2[j]) {
			// Number segment comparison.
			numStart1 := i
			for i < len1 && isDigit(s1[i]) {
				i++
			}
			num1, _ := strconv.Atoi(s1[numStart1:i])

			numStart2 := j
			for j < len2 && isDigit(s2[j]) {
				j++
			}
			num2, _ := strconv.Atoi(s2[numStart2:j])

			if num1 < num2 {
				return -1
			}
			if num1 > num2 {
				return 1
			}
			// "1" < "01".  Don't expect it in simdgen, but just in case.
			if ln1, ln2 := i-numStart1, j-numStart2; ln1 != ln2 {
				return ln1 - ln2
			}
			// If numbers are equal, continue to the next segment.
		} else {
			// Non-digit comparison.
			if s1[i] < s2[j] {
				return -1
			}
			if s1[i] > s2[j] {
				return 1
			}
			i++
			j++
		}
	}

	// deal with a01b vs a1b; there needs to be an order.
	return strings.Compare(s1, s2)
}