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margin.go
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margin.go
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package main
import (
"fmt"
"regexp"
"strconv"
"strings"
)
var (
digitOnly = regexp.MustCompile(`^\d+$`)
colonSeparatedDigits = regexp.MustCompile(`^(\d+):(\d+)$`)
)
type Margin struct {
left int
right int
}
func NewMargin(format string) (*Margin, error) {
m := &Margin{}
switch {
case format == "":
m.left, m.right = 1, 1
case digitOnly.MatchString(format):
n, err := strconv.Atoi(format)
if err != nil {
return nil, err
}
m.left, m.right = n, n
case colonSeparatedDigits.MatchString(format):
a := colonSeparatedDigits.FindAllStringSubmatch(format, -1)[0]
l, err := strconv.Atoi(a[1])
if err != nil {
return nil, err
}
r, err := strconv.Atoi(a[2])
if err != nil {
return nil, err
}
m.left, m.right = l, r
default:
return nil, fmt.Errorf("margin: invalid format: %s", format)
}
return m, nil
}
func NewMarginWithNumber(left, right int) *Margin {
return &Margin{
left: left,
right: right,
}
}
func (m *Margin) Join(a []string) string {
switch len(a) {
case 0:
return ""
case 1:
return a[0]
}
l, r := m.left, m.right
if l < 0 {
l = 0
}
if r < 0 {
r = 0
}
buflen := (l + r) * (len(a) / 2)
if len(a)%2 == 0 {
buflen -= r
}
for i := 0; i < len(a); i++ {
buflen += len(a[i])
}
lm, rm := strings.Repeat(" ", l), strings.Repeat(" ", r)
b := make([]byte, buflen)
bp := copy(b, a[0])
for i := 2; i <= len(a); i += 2 {
bp += copy(b[bp:], lm)
bp += copy(b[bp:], a[i-1])
if i != len(a) {
bp += copy(b[bp:], rm)
bp += copy(b[bp:], a[i])
}
}
return string(b)
}