subsonic-tui/vendor/github.com/rivo/uniseg/grapheme.go
Sagi Dayan 26e526f07e
initial commit
Signed-off-by: Sagi Dayan <sagidayan@gmail.com>
2024-02-20 19:10:14 +02:00

332 lines
9.7 KiB
Go

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