package chunk

import (
	"strings"
	"unicode/utf8"
)

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

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

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

// FindSetMatches returns list of values that can be equality matched on.
// copied from Prometheus querier.go, removed check for Prometheus wrapper.
func FindSetMatches(pattern string) []string {
	escaped := false
	sets := []*strings.Builder{{}}
	for i := 0; i < len(pattern); i++ {
		if escaped {
			switch {
			case isRegexMetaCharacter(pattern[i]):
				sets[len(sets)-1].WriteByte(pattern[i])
			case pattern[i] == '\\':
				sets[len(sets)-1].WriteByte('\\')
			default:
				return nil
			}
			escaped = false
		} else {
			switch {
			case isRegexMetaCharacter(pattern[i]):
				if pattern[i] == '|' {
					sets = append(sets, &strings.Builder{})
				} else {
					return nil
				}
			case pattern[i] == '\\':
				escaped = true
			default:
				sets[len(sets)-1].WriteByte(pattern[i])
			}
		}
	}
	matches := make([]string, 0, len(sets))
	for _, s := range sets {
		if s.Len() > 0 {
			matches = append(matches, s.String())
		}
	}
	return matches
}