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