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truncate.go
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package text
import (
runewidth "github.com/mattn/go-runewidth"
"github.com/rivo/uniseg"
)
const (
ellipsisWidth = 3
minWidthForEllipsis = 5
)
// DisplayWidth calculates what the rendered width of a string may be
func DisplayWidth(s string) int {
g := uniseg.NewGraphemes(s)
w := 0
for g.Next() {
w += graphemeWidth(g)
}
return w
}
// Truncate shortens a string to fit the maximum display width
func Truncate(maxWidth int, s string) string {
w := DisplayWidth(s)
if w <= maxWidth {
return s
}
useEllipsis := false
if maxWidth >= minWidthForEllipsis {
useEllipsis = true
maxWidth -= ellipsisWidth
}
g := uniseg.NewGraphemes(s)
r := ""
rWidth := 0
for {
g.Next()
gWidth := graphemeWidth(g)
if rWidth+gWidth <= maxWidth {
r += g.Str()
rWidth += gWidth
continue
} else {
break
}
}
if useEllipsis {
r += "..."
}
if rWidth < maxWidth {
r += " "
}
return r
}
// graphemeWidth calculates what the rendered width of a grapheme may be
func graphemeWidth(g *uniseg.Graphemes) int {
// If grapheme spans one rune use that rune width
// If grapheme spans multiple runes use the first non-zero rune width
w := 0
for _, r := range g.Runes() {
w = runewidth.RuneWidth(r)
if w > 0 {
break
}
}
return w
}