// Copyright 2025 The Gitea Authors. All rights reserved.
// SPDX-License-Identifier: MIT

package zoekt

import "unicode/utf8"

// Bitmap used by func special to check whether a character needs to be escaped.
var specialBytes [16]byte

// special reports whether byte b needs to be escaped by QuoteMeta.
func special(b byte) bool {
	return b < utf8.RuneSelf && specialBytes[b%16]&(1<<(b/16)) != 0
}

func init() {
	for _, b := range []byte(`-:\.+*?()|[]{}^$`) {
		specialBytes[b%16] |= 1 << (b / 16)
	}
}

func QuoteMeta(s string) string {
	// A byte loop is correct because all metacharacters are ASCII.
	var i int
	for i = 0; i < len(s); i++ {
		if special(s[i]) {
			break
		}
	}
	// No meta characters found, so return original string.
	if i >= len(s) {
		return s
	}

	b := make([]byte, 3*len(s)-2*i)
	copy(b, s[:i])
	j := i
	for ; i < len(s); i++ {
		if special(s[i]) {
			b[j] = '\\'
			j++
			b[j] = '\\'
			j++
		}
		b[j] = s[i]
		j++
	}
	return string(b[:j])
}