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// Copyright 2013 Canonical Ltd. This software is licensed under the
// GNU Lesser General Public License version 3 (see the file COPYING).
package dedent
import (
"regexp"
"strings"
)
const emptyString = ""
var reLine = regexp.MustCompile(`(?m-s)^.*$`)
// Split the given text into lines.
func splitLines(text string) []string {
return reLine.FindAllString(text, -1)
}
// Match leading whitespace or tabs. \p{Zs} is a Unicode character class:
// http://en.wikipedia.org/wiki/Mapping_of_Unicode_characters#General_Category
var reLeadingWhitespace = regexp.MustCompile(`^[\p{Zs}\t]+`)
// Find the longest leading margin common between the given lines.
func calculateMargin(lines []string) string {
var margin string
var first bool = true
for _, line := range lines {
indent := reLeadingWhitespace.FindString(line)
switch {
case len(indent) == len(line):
// The line is either empty or whitespace and will be ignored for
// the purposes of calculating the margin.
case first:
// This is the first line with an indent, so start from here.
margin = indent
first = false
case strings.HasPrefix(indent, margin):
// This line's indent is longer or equal to the margin. The
// current margin remains unalterered.
case strings.HasPrefix(margin, indent):
// This line's indent is compatible with the margin but shorter
// (strictly it could be equal, however that condition is handled
// earlier in this switch). The current indent becomes the margin.
margin = indent
default:
// There is no common margin so stop scanning.
return emptyString
}
}
return margin
}
// Remove a prefix from each line, if present.
func trimPrefix(lines []string, prefix string) {
trim := len(prefix)
for i, line := range lines {
if strings.HasPrefix(line, prefix) {
lines[i] = line[trim:]
}
}
}
func Dedent(text string) string {
lines := splitLines(text)
trimPrefix(lines, calculateMargin(lines))
return strings.Join(lines, "\n")
}
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