Refactor: move wrapMessageToWidth to utils/lines.go

to make it more generally usable by clients other than ConfirmationHelper, which
we will do later in this branch. Rename it to WrapViewLinesToWidth while we're
at it.

Add tests; in particular, add a sanity check that we wrap lines the same way as
gocui does. The tests that are added here are the same ones as in gocui for its
lineWrap function, but we'll extend them a bit in later commits in this branch.

pkg/utils/lines.go

@@ -3,6 +3,8 @@ package utils
 import (
 	"bytes"
 	"strings"
+
+	"github.com/mattn/go-runewidth"
 )
 
 // SplitLines takes a multiline string and splits it on newlines
@@ -100,3 +102,56 @@ func ScanLinesAndTruncateWhenLongerThanBuffer(maxBufferSize int) func(data []byt
 		return 0, nil, nil
 	}
 }
+
+// Wrap lines to a given width.
+// If wrap is false, the text is returned as is.
+// This code needs to behave the same as `gocui.lineWrap` does.
+func WrapViewLinesToWidth(wrap bool, text string, width int) []string {
+	lines := strings.Split(text, "\n")
+	if !wrap {
+		return lines
+	}
+
+	wrappedLines := make([]string, 0, len(lines))
+
+	for _, line := range lines {
+		n := 0
+		offset := 0
+		lastWhitespaceIndex := -1
+		for i, currChr := range line {
+			rw := runewidth.RuneWidth(currChr)
+			n += rw
+
+			if n > width {
+				if currChr == ' ' {
+					wrappedLines = append(wrappedLines, line[offset:i])
+					offset = i + 1
+					n = 0
+				} else if currChr == '-' {
+					wrappedLines = append(wrappedLines, line[offset:i])
+					offset = i
+					n = rw
+				} else if lastWhitespaceIndex != -1 {
+					if line[lastWhitespaceIndex] == '-' {
+						wrappedLines = append(wrappedLines, line[offset:lastWhitespaceIndex+1])
+					} else {
+						wrappedLines = append(wrappedLines, line[offset:lastWhitespaceIndex])
+					}
+					offset = lastWhitespaceIndex + 1
+					n = runewidth.StringWidth(line[offset : i+1])
+				} else {
+					wrappedLines = append(wrappedLines, line[offset:i])
+					offset = i
+					n = rw
+				}
+				lastWhitespaceIndex = -1
+			} else if currChr == ' ' || currChr == '-' {
+				lastWhitespaceIndex = i
+			}
+		}
+
+		wrappedLines = append(wrappedLines, line[offset:])
+	}
+
+	return wrappedLines
+}