package check

import (
	"unicode"
	"unicode/utf8"
)

// letterAt reports whether offset i holds a letter or a digit. Cyrillic takes
// two bytes in UTF-8, so a single byte is not enough to decide.
func letterAt(text string, i int) bool {
	if i >= len(text) {
		return false
	}
	r, _ := utf8.DecodeRuneInString(text[i:])
	return unicode.IsLetter(r) || unicode.IsDigit(r)
}

// letterBefore reports whether a letter or a digit stands before offset i.
func letterBefore(text string, i int) bool {
	if i <= 0 {
		return false
	}
	r, _ := utf8.DecodeLastRuneInString(text[:i])
	return unicode.IsLetter(r) || unicode.IsDigit(r)
}

func digitAt(text string, i int) bool {
	if i >= len(text) {
		return false
	}
	r, _ := utf8.DecodeRuneInString(text[i:])
	return unicode.IsDigit(r)
}

func digitBefore(text string, i int) bool {
	if i <= 0 {
		return false
	}
	r, _ := utf8.DecodeLastRuneInString(text[:i])
	return unicode.IsDigit(r)
}