Initial QSfera import
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Курнат Андрей
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package displaywidth
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import (
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"strings"
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"unicode/utf8"
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"github.com/clipperhouse/uax29/v2/graphemes"
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)
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// Options allows you to specify the treatment of ambiguous East Asian
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// characters and ANSI escape sequences.
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type Options struct {
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// EastAsianWidth specifies whether to treat ambiguous East Asian characters
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// as width 1 or 2. When false (default), ambiguous East Asian characters
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// are treated as width 1. When true, they are width 2.
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EastAsianWidth bool
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// ControlSequences specifies whether to ignore ECMA-48 escape sequences
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// when calculating the display width. When false (default), ANSI escape
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// sequences are treated as just a series of characters. When true, they are
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// treated as a single zero-width unit.
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//
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// Note that this option is about *sequences*. Individual control characters
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// are already treated as zero-width. With this option, ANSI sequences such as
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// "\x1b[31m" and "\x1b[0m" do not count towards the width of a string.
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ControlSequences bool
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}
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// DefaultOptions is the default options for the display width
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// calculation, which is EastAsianWidth false and ControlSequences false.
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var DefaultOptions = Options{EastAsianWidth: false, ControlSequences: false}
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// String calculates the display width of a string,
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// by iterating over grapheme clusters in the string
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// and summing their widths.
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func String(s string) int {
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return DefaultOptions.String(s)
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}
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// String calculates the display width of a string, for the given options, by
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// iterating over grapheme clusters in the string and summing their widths.
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func (options Options) String(s string) int {
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width := 0
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pos := 0
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for pos < len(s) {
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// Try ASCII optimization
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asciiLen := printableASCIILength(s[pos:])
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if asciiLen > 0 {
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width += asciiLen
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pos += asciiLen
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continue
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}
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// Not ASCII, use grapheme parsing
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g := graphemes.FromString(s[pos:])
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g.AnsiEscapeSequences = options.ControlSequences
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start := pos
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for g.Next() {
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v := g.Value()
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width += graphemeWidth(v, options)
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pos += len(v)
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// Quick check: if remaining might have printable ASCII, break to outer loop
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if pos < len(s) && s[pos] >= 0x20 && s[pos] <= 0x7E {
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break
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}
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}
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// Defensive, should not happen: if no progress was made,
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// skip a byte to prevent infinite loop. Only applies if
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// the grapheme parser misbehaves.
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if pos == start {
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pos++
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}
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}
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return width
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}
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// Bytes calculates the display width of a []byte,
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// by iterating over grapheme clusters in the byte slice
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// and summing their widths.
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func Bytes(s []byte) int {
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return DefaultOptions.Bytes(s)
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}
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// Bytes calculates the display width of a []byte, for the given options, by
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// iterating over grapheme clusters in the slice and summing their widths.
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func (options Options) Bytes(s []byte) int {
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width := 0
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pos := 0
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for pos < len(s) {
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// Try ASCII optimization
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asciiLen := printableASCIILength(s[pos:])
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if asciiLen > 0 {
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width += asciiLen
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pos += asciiLen
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continue
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}
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// Not ASCII, use grapheme parsing
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g := graphemes.FromBytes(s[pos:])
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g.AnsiEscapeSequences = options.ControlSequences
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start := pos
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for g.Next() {
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v := g.Value()
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width += graphemeWidth(v, options)
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pos += len(v)
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// Quick check: if remaining might have printable ASCII, break to outer loop
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if pos < len(s) && s[pos] >= 0x20 && s[pos] <= 0x7E {
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break
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}
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}
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// Defensive, should not happen: if no progress was made,
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// skip a byte to prevent infinite loop. Only applies if
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// the grapheme parser misbehaves.
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if pos == start {
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pos++
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}
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}
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return width
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}
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// Rune calculates the display width of a rune. You
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// should almost certainly use [String] or [Bytes] for
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// most purposes.
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//
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// The smallest unit of display width is a grapheme
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// cluster, not a rune. Iterating over runes to measure
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// width is incorrect in many cases.
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func Rune(r rune) int {
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return DefaultOptions.Rune(r)
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}
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// Rune calculates the display width of a rune, for the given options.
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//
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// You should almost certainly use [String] or [Bytes] for most purposes.
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//
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// The smallest unit of display width is a grapheme cluster, not a rune.
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// Iterating over runes to measure width is incorrect in many cases.
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func (options Options) Rune(r rune) int {
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if r < utf8.RuneSelf {
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return asciiWidth(byte(r))
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}
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// Surrogates (U+D800-U+DFFF) are invalid UTF-8.
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if r >= 0xD800 && r <= 0xDFFF {
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return 0
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}
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var buf [4]byte
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n := utf8.EncodeRune(buf[:], r)
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// Skip the grapheme iterator
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return graphemeWidth(buf[:n], options)
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}
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const _Default property = 0
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// TruncateString truncates a string to the given maxWidth, and appends the
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// given tail if the string is truncated.
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//
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// It ensures the visible width, including the width of the tail, is less than or
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// equal to maxWidth.
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//
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// When [Options.ControlSequences] is true, ANSI escape sequences that appear
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// after the truncation point are preserved in the output. This ensures that
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// escape sequences such as SGR resets are not lost, preventing color bleed
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// in terminal output.
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func (options Options) TruncateString(s string, maxWidth int, tail string) string {
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maxWidthWithoutTail := maxWidth - options.String(tail)
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var pos, total int
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g := graphemes.FromString(s)
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g.AnsiEscapeSequences = options.ControlSequences
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for g.Next() {
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gw := graphemeWidth(g.Value(), options)
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if total+gw <= maxWidthWithoutTail {
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pos = g.End()
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}
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total += gw
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if total > maxWidth {
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if options.ControlSequences {
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// Build result with trailing ANSI escape sequences preserved
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var b strings.Builder
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b.Grow(len(s) + len(tail)) // at most original + tail
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b.WriteString(s[:pos])
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b.WriteString(tail)
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rem := graphemes.FromString(s[pos:])
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rem.AnsiEscapeSequences = true
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for rem.Next() {
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v := rem.Value()
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if len(v) > 0 && v[0] == 0x1B {
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b.WriteString(v)
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}
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}
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return b.String()
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}
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return s[:pos] + tail
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}
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}
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// No truncation
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return s
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}
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// TruncateString truncates a string to the given maxWidth, and appends the
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// given tail if the string is truncated.
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//
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// It ensures the total width, including the width of the tail, is less than or
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// equal to maxWidth.
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func TruncateString(s string, maxWidth int, tail string) string {
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return DefaultOptions.TruncateString(s, maxWidth, tail)
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}
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// TruncateBytes truncates a []byte to the given maxWidth, and appends the
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// given tail if the []byte is truncated.
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//
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// It ensures the visible width, including the width of the tail, is less than or
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// equal to maxWidth.
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//
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// When [Options.ControlSequences] is true, ANSI escape sequences that appear
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// after the truncation point are preserved in the output. This ensures that
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// escape sequences such as SGR resets are not lost, preventing color bleed
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// in terminal output.
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func (options Options) TruncateBytes(s []byte, maxWidth int, tail []byte) []byte {
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maxWidthWithoutTail := maxWidth - options.Bytes(tail)
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var pos, total int
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g := graphemes.FromBytes(s)
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g.AnsiEscapeSequences = options.ControlSequences
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for g.Next() {
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gw := graphemeWidth(g.Value(), options)
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if total+gw <= maxWidthWithoutTail {
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pos = g.End()
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}
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total += gw
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if total > maxWidth {
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if options.ControlSequences {
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// Build result with trailing ANSI escape sequences preserved
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result := make([]byte, 0, len(s)+len(tail)) // at most original + tail
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result = append(result, s[:pos]...)
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result = append(result, tail...)
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rem := graphemes.FromBytes(s[pos:])
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rem.AnsiEscapeSequences = true
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for rem.Next() {
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v := rem.Value()
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if len(v) > 0 && v[0] == 0x1B {
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result = append(result, v...)
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}
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}
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return result
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}
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result := make([]byte, 0, pos+len(tail))
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result = append(result, s[:pos]...)
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result = append(result, tail...)
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return result
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}
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}
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// No truncation
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return s
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}
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// TruncateBytes truncates a []byte to the given maxWidth, and appends the
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// given tail if the []byte is truncated.
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//
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// It ensures the total width, including the width of the tail, is less than or
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// equal to maxWidth.
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func TruncateBytes(s []byte, maxWidth int, tail []byte) []byte {
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return DefaultOptions.TruncateBytes(s, maxWidth, tail)
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}
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// graphemeWidth returns the display width of a grapheme cluster.
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// The passed string must be a single grapheme cluster.
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func graphemeWidth[T ~string | []byte](s T, options Options) int {
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// Optimization: no need to look up properties
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switch len(s) {
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case 0:
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return 0
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case 1:
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return asciiWidth(s[0])
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}
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// Multi-byte grapheme clusters led by a C0 control (0x00-0x1F)
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if s[0] <= 0x1F {
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return 0
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}
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p, sz := lookup(s)
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prop := property(p)
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// Variation Selector 16 (VS16) requests emoji presentation
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if prop != _Wide && sz > 0 && len(s) >= sz+3 {
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vs := s[sz : sz+3]
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if isVS16(vs) {
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prop = _Wide
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}
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// VS15 (0x8E) requests text presentation but does not affect width,
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// in my reading of Unicode TR51. Falls through to return the base
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// character's property.
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}
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if options.EastAsianWidth && prop == _East_Asian_Ambiguous {
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prop = _Wide
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}
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if prop > upperBound {
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prop = _Default
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}
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return propertyWidths[prop]
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}
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func asciiWidth(b byte) int {
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if b <= 0x1F || b == 0x7F {
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return 0
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}
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return 1
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}
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// printableASCIILength returns the length of consecutive printable ASCII bytes
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// starting at the beginning of s.
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func printableASCIILength[T string | []byte](s T) int {
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i := 0
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for ; i < len(s); i++ {
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b := s[i]
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// Printable ASCII is 0x20-0x7E (space through tilde)
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if b < 0x20 || b > 0x7E {
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break
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}
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}
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// If the next byte is non-ASCII (>= 0x80), back off by 1. The grapheme
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// parser may group the last ASCII byte with subsequent non-ASCII bytes,
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// such as combining marks.
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if i > 0 && i < len(s) && s[i] >= 0x80 {
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i--
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}
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return i
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}
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// isVS16 checks if the slice matches VS16 (U+FE0F) UTF-8 encoding
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// (EF B8 8F). It assumes len(s) >= 3.
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func isVS16[T ~string | []byte](s T) bool {
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return s[0] == 0xEF && s[1] == 0xB8 && s[2] == 0x8F
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}
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// propertyWidths is a jump table of sorts, instead of a switch
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var propertyWidths = [4]int{
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_Default: 1,
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_Zero_Width: 0,
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_Wide: 2,
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_East_Asian_Ambiguous: 1,
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}
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const upperBound = property(len(propertyWidths) - 1)
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