padding space between en and zh words

padding_space.go

package main

import (
	"bufio"
	"fmt"
	"os"
	"unicode"
	"unicode/utf8"
)

var (
	zh_en_mapping = map[rune]rune{
		'：': ':',
	}
	mdchars = []rune{'`', '*', '-', '_', '>', '(', ')', '[', ']', '"', '\'', ':', ';',
		'@', '!', '/', '.', '=', '&', '\\', '+', '{', '}', '~', '\\', '\'', '"', ',', '?'}
)

func is_md_char(r rune) bool {
	for _, v := range mdchars {
		if v == r {
			return true
		}
	}
	return false
}

func special(r rune) bool {
	return unicode.IsSpace(r) || unicode.IsPunct(r) || is_md_char(r)
}

func padding(text string) {
	b := []byte(text)

	var (
		last_r    rune
		last_size int
	)

	for len(b) > 0 {

		r, size := utf8.DecodeRune(b)

		skip := size

		if last_size == 1 && size > 1 {
			// songtianyi：$ --> songtianyi:$
			if v, ok := zh_en_mapping[r]; ok {
				// replace
				r = v
				size = 1
			}
		}

		if ((last_size-size) == 2 || (last_size-size) == -2) &&
			!special(last_r) &&
			!special(r) {
			// space padding
			fmt.Printf("%c", ' ')
		}

		// print original stuff
		fmt.Printf("%c", r)

		last_r = r
		last_size = size
		b = b[skip:]
	}
}

func main() {
	scanner := bufio.NewScanner(os.Stdin)
	for scanner.Scan() {
		padding(scanner.Text())
		fmt.Printf("\n")
	}
	if err := scanner.Err(); err != nil {
		fmt.Fprintln(os.Stderr, "reading standard input:", err)
	}

}