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clipperhouse wants to merge 1 commit into from
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New IgnoreANSI option and implementation #17

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213 changes: 189 additions & 24 deletions width.go
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Original file line number Diff line number Diff line change
Expand Up @@ -12,12 +12,20 @@ import (
// characters are treated as width 1. When EastAsianWidth is true, ambiguous
// East Asian characters are treated as width 2.
type Options struct {
// EastAsianWidth specifies how ambiguous East Asian characters are treated.
// true means width 2, false (default) means width 1.
EastAsianWidth bool
// IgnoreANSI specifies whether ANSI escape codes should be ignored.
// true means ignore, false (default) means treat codes as any other text.
IgnoreANSI bool
}

// DefaultOptions is the default options for the display width
// calculation, which is EastAsianWidth: false.
var DefaultOptions = Options{EastAsianWidth: false}
var DefaultOptions = Options{
EastAsianWidth: false,
IgnoreANSI: false,
}

// String calculates the display width of a string,
// by iterating over grapheme clusters in the string
Expand All @@ -33,6 +41,13 @@ func (options Options) String(s string) int {
pos := 0

for pos < len(s) {
if options.IgnoreANSI {
if n := ansiSequenceLength(s[pos:]); n > 0 {
pos += n
continue
}
}

// Try ASCII optimization
asciiLen := printableASCIILength(s[pos:])
if asciiLen > 0 {
Expand All @@ -54,6 +69,10 @@ func (options Options) String(s string) int {
if pos < len(s) && s[pos] >= 0x20 && s[pos] <= 0x7E {
break
}
// If next byte is ESC and we ignore ANSI, break so we skip the sequence at top of loop
if options.IgnoreANSI && pos < len(s) && s[pos] == esc {
break
}
}

// Defensive, should not happen: if no progress was made,
Expand Down Expand Up @@ -81,6 +100,13 @@ func (options Options) Bytes(s []byte) int {
pos := 0

for pos < len(s) {
if options.IgnoreANSI {
if n := ansiSequenceLength(s[pos:]); n > 0 {
pos += n
continue
}
}

// Try ASCII optimization
asciiLen := printableASCIILength(s[pos:])
if asciiLen > 0 {
Expand All @@ -102,6 +128,10 @@ func (options Options) Bytes(s []byte) int {
if pos < len(s) && s[pos] >= 0x20 && s[pos] <= 0x7E {
break
}
// If next byte is ESC and we ignore ANSI, break so we skip the sequence at top of loop
if options.IgnoreANSI && pos < len(s) && s[pos] == esc {
break
}
}

// Defensive, should not happen: if no progress was made,
Expand Down Expand Up @@ -158,20 +188,57 @@ const _Default property = 0
// equal to maxWidth.
func (options Options) TruncateString(s string, maxWidth int, tail string) string {
maxWidthWithoutTail := maxWidth - options.String(tail)
width := 0
pos := 0
var lastFitPos int

for pos < len(s) {
if options.IgnoreANSI {
if n := ansiSequenceLength(s[pos:]); n > 0 {
pos += n
continue
}
}

asciiLen := printableASCIILength(s[pos:])
if asciiLen > 0 {
for i := 0; i < asciiLen; i++ {
if width+1 <= maxWidthWithoutTail {
lastFitPos = pos + i + 1
}
width++
if width > maxWidth {
return s[:lastFitPos] + tail
}
}
pos += asciiLen
continue
}

var pos, total int
g := graphemes.FromString(s)
for g.Next() {
gw := graphemeWidth(g.Value(), options)
if total+gw <= maxWidthWithoutTail {
pos = g.End()
g := graphemes.FromString(s[pos:])
start := pos
for g.Next() {
v := g.Value()
gw := graphemeWidth(v, options)
if width+gw <= maxWidthWithoutTail && gw > 0 {
lastFitPos = pos + len(v)
}
width += gw
pos += len(v)
if width > maxWidth {
return s[:lastFitPos] + tail
}
if pos < len(s) && s[pos] >= 0x20 && s[pos] <= 0x7E {
break
}
if options.IgnoreANSI && pos < len(s) && s[pos] == esc {
break
}
}
total += gw
if total > maxWidth {
return s[:pos] + tail
if pos == start {
pos++
}
}
// No truncation
return s
}

Expand All @@ -191,23 +258,63 @@ func TruncateString(s string, maxWidth int, tail string) string {
// equal to maxWidth.
func (options Options) TruncateBytes(s []byte, maxWidth int, tail []byte) []byte {
maxWidthWithoutTail := maxWidth - options.Bytes(tail)
width := 0
pos := 0
var lastFitPos int

for pos < len(s) {
if options.IgnoreANSI {
if n := ansiSequenceLength(s[pos:]); n > 0 {
pos += n
continue
}
}

var pos, total int
g := graphemes.FromBytes(s)
for g.Next() {
gw := graphemeWidth(g.Value(), options)
if total+gw <= maxWidthWithoutTail {
pos = g.End()
asciiLen := printableASCIILength(s[pos:])
if asciiLen > 0 {
for i := 0; i < asciiLen; i++ {
if width+1 <= maxWidthWithoutTail {
lastFitPos = pos + i + 1
}
width++
if width > maxWidth {
result := make([]byte, 0, lastFitPos+len(tail))
result = append(result, s[:lastFitPos]...)
result = append(result, tail...)
return result
}
}
pos += asciiLen
continue
}

g := graphemes.FromBytes(s[pos:])
start := pos
for g.Next() {
v := g.Value()
gw := graphemeWidth(v, options)
if width+gw <= maxWidthWithoutTail && gw > 0 {
lastFitPos = pos + len(v)
}
width += gw
pos += len(v)
if width > maxWidth {
result := make([]byte, 0, lastFitPos+len(tail))
result = append(result, s[:lastFitPos]...)
result = append(result, tail...)
return result
}
if pos < len(s) && s[pos] >= 0x20 && s[pos] <= 0x7E {
break
}
if options.IgnoreANSI && pos < len(s) && s[pos] == esc {
break
}
}
total += gw
if total > maxWidth {
result := make([]byte, 0, pos+len(tail))
result = append(result, s[:pos]...)
result = append(result, tail...)
return result
if pos == start {
pos++
}
}
// No truncation
return s
}

Expand Down Expand Up @@ -263,6 +370,64 @@ func asciiWidth(b byte) int {
return 1
}

const esc = 0x1B

// ansiSequenceLength returns the number of bytes of an ANSI escape sequence
// at the start of s, or 0 if s does not start with a complete sequence.
// It does not interpret the sequence; it only returns the length to skip.
// Covers CSI (e.g. SGR color codes), OSC (e.g. hyperlinks), and 2-character
// escape sequences per ECMA-48 / ISO 6429.
func ansiSequenceLength[T ~string | ~[]byte](s T) int {
if len(s) < 2 || s[0] != esc {
return 0
}
switch s[1] {
case '[':
// CSI: ESC [ P...P I...I F (final byte 0x40-0x7E)
i := 2
for i < len(s) {
b := s[i]
if b >= 0x40 && b <= 0x7E {
return i + 1
}
if (b >= 0x30 && b <= 0x3F) || (b >= 0x20 && b <= 0x2F) {
i++
continue
}
return 0
}
return 0
case ']':
// OSC: ESC ] ... BEL (0x07) or ST (ESC \)
i := 2
for i < len(s) {
if s[i] == 0x07 {
return i + 1
}
if s[i] == esc && i+1 < len(s) && s[i+1] == '\\' {
return i + 2
}
i++
}
return 0
case 'P', 'X', '^', '_':
// DCS, SOS, PM, APC: ... ST (ESC \)
i := 2
for i < len(s) {
if s[i] == esc && i+1 < len(s) && s[i+1] == '\\' {
return i + 2
}
i++
}
return 0
default:
if s[1] >= 0x40 && s[1] <= 0x5F {
return 2
}
return 0
}
}

// printableASCIILength returns the length of consecutive printable ASCII bytes
// starting at the beginning of s.
func printableASCIILength[T string | []byte](s T) int {
Expand Down
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