gopkg.in/tools/godep.v56@v56.0.0-20160226230103-b32db8cfcaad/Godeps/_workspace/src/github.com/kr/text/wrap.go (about)

     1  package text
     2  
     3  import (
     4  	"bytes"
     5  	"math"
     6  )
     7  
     8  var (
     9  	nl = []byte{'\n'}
    10  	sp = []byte{' '}
    11  )
    12  
    13  const defaultPenalty = 1e5
    14  
    15  // Wrap wraps s into a paragraph of lines of length lim, with minimal
    16  // raggedness.
    17  func Wrap(s string, lim int) string {
    18  	return string(WrapBytes([]byte(s), lim))
    19  }
    20  
    21  // WrapBytes wraps b into a paragraph of lines of length lim, with minimal
    22  // raggedness.
    23  func WrapBytes(b []byte, lim int) []byte {
    24  	words := bytes.Split(bytes.Replace(bytes.TrimSpace(b), nl, sp, -1), sp)
    25  	var lines [][]byte
    26  	for _, line := range WrapWords(words, 1, lim, defaultPenalty) {
    27  		lines = append(lines, bytes.Join(line, sp))
    28  	}
    29  	return bytes.Join(lines, nl)
    30  }
    31  
    32  // WrapWords is the low-level line-breaking algorithm, useful if you need more
    33  // control over the details of the text wrapping process. For most uses, either
    34  // Wrap or WrapBytes will be sufficient and more convenient.
    35  //
    36  // WrapWords splits a list of words into lines with minimal "raggedness",
    37  // treating each byte as one unit, accounting for spc units between adjacent
    38  // words on each line, and attempting to limit lines to lim units. Raggedness
    39  // is the total error over all lines, where error is the square of the
    40  // difference of the length of the line and lim. Too-long lines (which only
    41  // happen when a single word is longer than lim units) have pen penalty units
    42  // added to the error.
    43  func WrapWords(words [][]byte, spc, lim, pen int) [][][]byte {
    44  	n := len(words)
    45  
    46  	length := make([][]int, n)
    47  	for i := 0; i < n; i++ {
    48  		length[i] = make([]int, n)
    49  		length[i][i] = len(words[i])
    50  		for j := i + 1; j < n; j++ {
    51  			length[i][j] = length[i][j-1] + spc + len(words[j])
    52  		}
    53  	}
    54  
    55  	nbrk := make([]int, n)
    56  	cost := make([]int, n)
    57  	for i := range cost {
    58  		cost[i] = math.MaxInt32
    59  	}
    60  	for i := n - 1; i >= 0; i-- {
    61  		if length[i][n-1] <= lim {
    62  			cost[i] = 0
    63  			nbrk[i] = n
    64  		} else {
    65  			for j := i + 1; j < n; j++ {
    66  				d := lim - length[i][j-1]
    67  				c := d*d + cost[j]
    68  				if length[i][j-1] > lim {
    69  					c += pen // too-long lines get a worse penalty
    70  				}
    71  				if c < cost[i] {
    72  					cost[i] = c
    73  					nbrk[i] = j
    74  				}
    75  			}
    76  		}
    77  	}
    78  
    79  	var lines [][][]byte
    80  	i := 0
    81  	for i < n {
    82  		lines = append(lines, words[i:nbrk[i]])
    83  		i = nbrk[i]
    84  	}
    85  	return lines
    86  }