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path: root/go/phone-number/phone_number.go
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package phonenumber

import (
	"fmt"
	"unicode"
)

func Number(s string) (string, error) {
	r := []rune{}
	for _, v := range s {
		if unicode.IsNumber(v) {
			r = append(r, v)
		}
	}
	switch {
	case len(r) == 11 && r[0] == '1':
		return string(r)[1:], nil
	case len(r) == 10:
		return string(r), nil
	}
	return "", fmt.Errorf("bad number")
}

func AreaCode(s string) (string, error) {
	num, err := Number(s)
	if err != nil {
		return "", err
	}
	return num[:3], nil
}

func Format(s string) (string, error) {
	num, err := Number(s)
	if err != nil {
		return "", err
	}
	return fmt.Sprintf("(%v) %v-%v", num[:3], num[3:6], num[6:]), nil
}