lines.go

package strings

import (
	"strings"
	"unicode"
)

// TrimShiftLines will trim each line in s (separated by newlines) as follows:
//
// If the line is only whitespace, it will become an empty line.
//
// Whitespace at the end of each line will be removed.
//
// Each line that has content will be examined for whitespace in front of the content, and the smallest
// length of white space found in all the lines will then be removed from the front of every line, provided.
// that whitespace is found at the front of every line.
// Note that tabs will not be converted to spaces. The whitespace characters must match.
// The effect will be to shift all the lines to the left so that the line closest to the left
// will now be flush with the left, and all other lines will be shifted left the same amount.
func TrimShiftLines(s string) string {
	lines := strings.Split(s, "\n")
	var prefix string
	var noMatch bool
	// Pass one, making obvious fixes
	for i, line := range lines {
		if IsWhitespace(line) {
			lines[i] = ""
			continue
		}
		line = TrimRightSpace(line)
		lines[i] = line

		// Find first non-whitespace rune
		start := 0
		var r rune
		for start, r = range line {
			if !unicode.IsSpace(r) {
				break
			}
		}
		if !noMatch {
			if prefix == "" {
				prefix = line[:start]
			} else if len(prefix) <= start {
				if prefix != line[:len(prefix)] {
					noMatch = true
				}
			} else {
				if prefix[:start] != line[:start] {
					noMatch = true
				} else {
					// new prefix
					prefix = line[:start]
				}
			}
		}
	}

	if !noMatch {
		// Strip prefix from all lines
		for i, line := range lines {
			lines[i] = strings.TrimPrefix(line, prefix)
		}
	}

	return strings.Join(lines, "\n")
}