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package text
import (
"bytes"
"math"
)
var (
nl = []byte{'\n'}
sp = []byte{' '}
)
const defaultPenalty = 1e5
// Wrap wraps s into a paragraph of lines of length lim, with minimal
// raggedness.
func Wrap(s string, lim int) string {
return string(WrapBytes([]byte(s), lim))
}
// WrapBytes wraps b into a paragraph of lines of length lim, with minimal
// raggedness.
func WrapBytes(b []byte, lim int) []byte {
words := bytes.Split(bytes.Replace(bytes.TrimSpace(b), nl, sp, -1), sp)
var lines [][]byte
for _, line := range WrapWords(words, 1, lim, defaultPenalty) {
lines = append(lines, bytes.Join(line, sp))
}
return bytes.Join(lines, nl)
}
// WrapWords is the low-level line-breaking algorithm, useful if you need more
// control over the details of the text wrapping process. For most uses, either
// Wrap or WrapBytes will be sufficient and more convenient.
//
// WrapWords splits a list of words into lines with minimal "raggedness",
// treating each byte as one unit, accounting for spc units between adjacent
// words on each line, and attempting to limit lines to lim units. Raggedness
// is the total error over all lines, where error is the square of the
// difference of the length of the line and lim. Too-long lines (which only
// happen when a single word is longer than lim units) have pen penalty units
// added to the error.
func WrapWords(words [][]byte, spc, lim, pen int) [][][]byte {
n := len(words)
length := make([][]int, n)
for i := 0; i < n; i++ {
length[i] = make([]int, n)
length[i][i] = len(words[i])
for j := i + 1; j < n; j++ {
length[i][j] = length[i][j-1] + spc + len(words[j])
}
}
nbrk := make([]int, n)
cost := make([]int, n)
for i := range cost {
cost[i] = math.MaxInt32
}
for i := n - 1; i >= 0; i-- {
if length[i][n-1] <= lim {
cost[i] = 0
nbrk[i] = n
} else {
for j := i + 1; j < n; j++ {
d := lim - length[i][j-1]
c := d*d + cost[j]
if length[i][j-1] > lim {
c += pen // too-long lines get a worse penalty
}
if c < cost[i] {
cost[i] = c
nbrk[i] = j
}
}
}
}
var lines [][][]byte
i := 0
for i < n {
lines = append(lines, words[i:nbrk[i]])
i = nbrk[i]
}
return lines
}
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