lancet/strutil/string_internal.go

package strutil

import (
	"unicode"
)

func splitIntoStrings(s string, upperCase bool) []string {
	var runes [][]rune
	lastCharType := 0
	charType := 0

	// split into fields based on type of unicode character
	for _, r := range s {
		switch true {
		case isLower(r):
			charType = 1
		case isUpper(r):
			charType = 2
		case isDigit(r):
			charType = 3
		default:
			charType = 4
		}

		if charType == lastCharType {
			runes[len(runes)-1] = append(runes[len(runes)-1], r)
		} else {
			runes = append(runes, []rune{r})
		}
		lastCharType = charType
	}

	for i := 0; i < len(runes)-1; i++ {
		if isUpper(runes[i][0]) && isLower(runes[i+1][0]) {
			length := len(runes[i]) - 1
			temp := runes[i][length]
			runes[i+1] = append([]rune{temp}, runes[i+1]...)
			runes[i] = runes[i][:length]
		}
	}

	// filter all none letters and none digit
	var result []string
	for _, rs := range runes {
		if len(rs) > 0 && (unicode.IsLetter(rs[0]) || isDigit(rs[0])) {
			if upperCase {
				result = append(result, string(toUpperAll(rs)))
			} else {
				result = append(result, string(toLowerAll(rs)))
			}
		}
	}

	return result
}

// isDigit checks if a character is digit ('0' to '9')
func isDigit(r rune) bool {
	return r >= '0' && r <= '9'
}

// isLower checks if a character is lower case ('a' to 'z')
func isLower(r rune) bool {
	return r >= 'a' && r <= 'z'
}

// isUpper checks if a character is upper case ('A' to 'Z')
func isUpper(r rune) bool {
	return r >= 'A' && r <= 'Z'
}

// toLower converts a character  'A' to 'Z' to its lower case
func toLower(r rune) rune {
	if r >= 'A' && r <= 'Z' {
		return r + 32
	}
	return r
}

// toLowerAll converts a character  'A' to 'Z' to its lower case
func toLowerAll(rs []rune) []rune {
	for i := range rs {
		rs[i] = toLower(rs[i])
	}
	return rs
}

// toUpper converts a character  'a' to 'z' to its upper case
func toUpper(r rune) rune {
	if r >= 'a' && r <= 'z' {
		return r - 32
	}
	return r
}

// toUpperAll converts a character  'a' to 'z' to its upper case
func toUpperAll(rs []rune) []rune {
	for i := range rs {
		rs[i] = toUpper(rs[i])
	}
	return rs
}

// padWithPosition pads string
func padAtPosition(str string, length int, padStr string, position int) string {
	if len(str) >= length {
		return str
	}

	if padStr == "" {
		padStr = " "
	}

	length = length - len(str)
	startPadLen := 0
	if position == 0 {
		startPadLen = length / 2
	} else if position == 1 {
		startPadLen = length
	}
	endPadLen := length - startPadLen

	charLen := len(padStr)
	leftPad := ""
	cur := 0
	for cur < startPadLen {
		leftPad += string(padStr[cur%charLen])
		cur++
	}

	cur = 0
	rightPad := ""
	for cur < endPadLen {
		rightPad += string(padStr[cur%charLen])
		cur++
	}

	return leftPad + str + rightPad
}

// isLetter checks r is a letter but not CJK character.
func isLetter(r rune) bool {
	if !unicode.IsLetter(r) {
		return false
	}

	switch {
	// cjk char: /[\u3040-\u30ff\u3400-\u4dbf\u4e00-\u9fff\uf900-\ufaff\uff66-\uff9f]/

	// hiragana and katakana (Japanese only)
	case r >= '\u3034' && r < '\u30ff':
		return false

	// CJK unified ideographs extension A (Chinese, Japanese, and Korean)
	case r >= '\u3400' && r < '\u4dbf':
		return false

	// CJK unified ideographs (Chinese, Japanese, and Korean)
	case r >= '\u4e00' && r < '\u9fff':
		return false

	// CJK compatibility ideographs (Chinese, Japanese, and Korean)
	case r >= '\uf900' && r < '\ufaff':
		return false

	// half-width katakana (Japanese only)
	case r >= '\uff66' && r < '\uff9f':
		return false
	}

	return true
}