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331 lines
9.7 KiB
Go
331 lines
9.7 KiB
Go
package uniseg
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import "unicode/utf8"
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// Graphemes implements an iterator over Unicode grapheme clusters, or
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// user-perceived characters. While iterating, it also provides information
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// about word boundaries, sentence boundaries, line breaks, and monospace
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// character widths.
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//
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// After constructing the class via [NewGraphemes] for a given string "str",
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// [Graphemes.Next] is called for every grapheme cluster in a loop until it
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// returns false. Inside the loop, information about the grapheme cluster as
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// well as boundary information and character width is available via the various
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// methods (see examples below).
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//
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// This class basically wraps the [StepString] parser and provides a convenient
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// interface to it. If you are only interested in some parts of this package's
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// functionality, using the specialized functions starting with "First" is
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// almost always faster.
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type Graphemes struct {
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// The original string.
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original string
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// The remaining string to be parsed.
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remaining string
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// The current grapheme cluster.
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cluster string
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// The byte offset of the current grapheme cluster relative to the original
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// string.
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offset int
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// The current boundary information of the [Step] parser.
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boundaries int
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// The current state of the [Step] parser.
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state int
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}
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// NewGraphemes returns a new grapheme cluster iterator.
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func NewGraphemes(str string) *Graphemes {
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return &Graphemes{
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original: str,
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remaining: str,
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state: -1,
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}
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}
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// Next advances the iterator by one grapheme cluster and returns false if no
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// clusters are left. This function must be called before the first cluster is
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// accessed.
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func (g *Graphemes) Next() bool {
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if len(g.remaining) == 0 {
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// We're already past the end.
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g.state = -2
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g.cluster = ""
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return false
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}
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g.offset += len(g.cluster)
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g.cluster, g.remaining, g.boundaries, g.state = StepString(g.remaining, g.state)
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return true
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}
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// Runes returns a slice of runes (code points) which corresponds to the current
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// grapheme cluster. If the iterator is already past the end or [Graphemes.Next]
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// has not yet been called, nil is returned.
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func (g *Graphemes) Runes() []rune {
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if g.state < 0 {
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return nil
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}
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return []rune(g.cluster)
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}
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// Str returns a substring of the original string which corresponds to the
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// current grapheme cluster. If the iterator is already past the end or
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// [Graphemes.Next] has not yet been called, an empty string is returned.
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func (g *Graphemes) Str() string {
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return g.cluster
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}
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// Bytes returns a byte slice which corresponds to the current grapheme cluster.
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// If the iterator is already past the end or [Graphemes.Next] has not yet been
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// called, nil is returned.
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func (g *Graphemes) Bytes() []byte {
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if g.state < 0 {
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return nil
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}
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return []byte(g.cluster)
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}
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// Positions returns the interval of the current grapheme cluster as byte
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// positions into the original string. The first returned value "from" indexes
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// the first byte and the second returned value "to" indexes the first byte that
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// is not included anymore, i.e. str[from:to] is the current grapheme cluster of
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// the original string "str". If [Graphemes.Next] has not yet been called, both
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// values are 0. If the iterator is already past the end, both values are 1.
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func (g *Graphemes) Positions() (int, int) {
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if g.state == -1 {
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return 0, 0
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} else if g.state == -2 {
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return 1, 1
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}
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return g.offset, g.offset + len(g.cluster)
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}
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// IsWordBoundary returns true if a word ends after the current grapheme
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// cluster.
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func (g *Graphemes) IsWordBoundary() bool {
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if g.state < 0 {
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return true
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}
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return g.boundaries&MaskWord != 0
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}
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// IsSentenceBoundary returns true if a sentence ends after the current
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// grapheme cluster.
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func (g *Graphemes) IsSentenceBoundary() bool {
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if g.state < 0 {
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return true
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}
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return g.boundaries&MaskSentence != 0
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}
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// LineBreak returns whether the line can be broken after the current grapheme
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// cluster. A value of [LineDontBreak] means the line may not be broken, a value
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// of [LineMustBreak] means the line must be broken, and a value of
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// [LineCanBreak] means the line may or may not be broken.
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func (g *Graphemes) LineBreak() int {
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if g.state == -1 {
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return LineDontBreak
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}
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if g.state == -2 {
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return LineMustBreak
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}
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return g.boundaries & MaskLine
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}
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// Width returns the monospace width of the current grapheme cluster.
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func (g *Graphemes) Width() int {
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if g.state < 0 {
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return 0
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}
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return g.boundaries >> ShiftWidth
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}
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// Reset puts the iterator into its initial state such that the next call to
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// [Graphemes.Next] sets it to the first grapheme cluster again.
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func (g *Graphemes) Reset() {
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g.state = -1
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g.offset = 0
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g.cluster = ""
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g.remaining = g.original
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}
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// GraphemeClusterCount returns the number of user-perceived characters
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// (grapheme clusters) for the given string.
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func GraphemeClusterCount(s string) (n int) {
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state := -1
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for len(s) > 0 {
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_, s, _, state = FirstGraphemeClusterInString(s, state)
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n++
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}
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return
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}
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// ReverseString reverses the given string while observing grapheme cluster
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// boundaries.
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func ReverseString(s string) string {
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str := []byte(s)
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reversed := make([]byte, len(str))
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state := -1
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index := len(str)
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for len(str) > 0 {
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var cluster []byte
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cluster, str, _, state = FirstGraphemeCluster(str, state)
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index -= len(cluster)
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copy(reversed[index:], cluster)
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if index <= len(str)/2 {
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break
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}
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}
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return string(reversed)
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}
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// The number of bits the grapheme property must be shifted to make place for
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// grapheme states.
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const shiftGraphemePropState = 4
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// FirstGraphemeCluster returns the first grapheme cluster found in the given
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// byte slice according to the rules of [Unicode Standard Annex #29, Grapheme
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// Cluster Boundaries]. This function can be called continuously to extract all
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// grapheme clusters from a byte slice, as illustrated in the example below.
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//
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// If you don't know the current state, for example when calling the function
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// for the first time, you must pass -1. For consecutive calls, pass the state
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// and rest slice returned by the previous call.
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//
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// The "rest" slice is the sub-slice of the original byte slice "b" starting
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// after the last byte of the identified grapheme cluster. If the length of the
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// "rest" slice is 0, the entire byte slice "b" has been processed. The
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// "cluster" byte slice is the sub-slice of the input slice containing the
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// identified grapheme cluster.
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//
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// The returned width is the width of the grapheme cluster for most monospace
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// fonts where a value of 1 represents one character cell.
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//
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// Given an empty byte slice "b", the function returns nil values.
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//
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// While slightly less convenient than using the Graphemes class, this function
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// has much better performance and makes no allocations. It lends itself well to
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// large byte slices.
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//
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// [Unicode Standard Annex #29, Grapheme Cluster Boundaries]: http://unicode.org/reports/tr29/#Grapheme_Cluster_Boundaries
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func FirstGraphemeCluster(b []byte, state int) (cluster, rest []byte, width, newState int) {
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// An empty byte slice returns nothing.
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if len(b) == 0 {
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return
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}
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// Extract the first rune.
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r, length := utf8.DecodeRune(b)
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if len(b) <= length { // If we're already past the end, there is nothing else to parse.
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var prop int
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if state < 0 {
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prop = propertyGraphemes(r)
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} else {
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prop = state >> shiftGraphemePropState
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}
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return b, nil, runeWidth(r, prop), grAny | (prop << shiftGraphemePropState)
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}
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// If we don't know the state, determine it now.
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var firstProp int
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if state < 0 {
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state, firstProp, _ = transitionGraphemeState(state, r)
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} else {
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firstProp = state >> shiftGraphemePropState
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}
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width += runeWidth(r, firstProp)
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// Transition until we find a boundary.
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for {
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var (
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prop int
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boundary bool
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)
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r, l := utf8.DecodeRune(b[length:])
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state, prop, boundary = transitionGraphemeState(state&maskGraphemeState, r)
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if boundary {
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return b[:length], b[length:], width, state | (prop << shiftGraphemePropState)
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}
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if firstProp == prExtendedPictographic {
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if r == vs15 {
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width = 1
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} else if r == vs16 {
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width = 2
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}
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} else if firstProp != prRegionalIndicator && firstProp != prL {
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width += runeWidth(r, prop)
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}
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length += l
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if len(b) <= length {
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return b, nil, width, grAny | (prop << shiftGraphemePropState)
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}
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}
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}
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// FirstGraphemeClusterInString is like [FirstGraphemeCluster] but its input and
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// outputs are strings.
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func FirstGraphemeClusterInString(str string, state int) (cluster, rest string, width, newState int) {
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// An empty string returns nothing.
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if len(str) == 0 {
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return
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}
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// Extract the first rune.
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r, length := utf8.DecodeRuneInString(str)
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if len(str) <= length { // If we're already past the end, there is nothing else to parse.
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var prop int
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if state < 0 {
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prop = propertyGraphemes(r)
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} else {
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prop = state >> shiftGraphemePropState
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}
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return str, "", runeWidth(r, prop), grAny | (prop << shiftGraphemePropState)
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}
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// If we don't know the state, determine it now.
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var firstProp int
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if state < 0 {
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state, firstProp, _ = transitionGraphemeState(state, r)
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} else {
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firstProp = state >> shiftGraphemePropState
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}
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width += runeWidth(r, firstProp)
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// Transition until we find a boundary.
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for {
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var (
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prop int
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boundary bool
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)
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r, l := utf8.DecodeRuneInString(str[length:])
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state, prop, boundary = transitionGraphemeState(state&maskGraphemeState, r)
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if boundary {
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return str[:length], str[length:], width, state | (prop << shiftGraphemePropState)
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}
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if firstProp == prExtendedPictographic {
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if r == vs15 {
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width = 1
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} else if r == vs16 {
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width = 2
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}
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} else if firstProp != prRegionalIndicator && firstProp != prL {
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width += runeWidth(r, prop)
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}
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length += l
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if len(str) <= length {
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return str, "", width, grAny | (prop << shiftGraphemePropState)
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}
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}
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}
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