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package uniseg
import "unicode/utf8"
// The states of the grapheme cluster parser.
const (
grAny = iota
grCR
grControlLF
grL
grLVV
grLVTT
grPrepend
grExtendedPictographic
grExtendedPictographicZWJ
grRIOdd
grRIEven
)
// The grapheme cluster parser's breaking instructions.
const (
grNoBoundary = iota
grBoundary
)
// The grapheme cluster parser's state transitions. Maps (state, property) to
// (new state, breaking instruction, rule number). The breaking instruction
// always refers to the boundary between the last and next code point.
//
// This map is queried as follows:
//
// 1. Find specific state + specific property. Stop if found.
// 2. Find specific state + any property.
// 3. Find any state + specific property.
// 4. If only (2) or (3) (but not both) was found, stop.
// 5. If both (2) and (3) were found, use state and breaking instruction from
// the transition with the lower rule number, prefer (3) if rule numbers
// are equal. Stop.
// 6. Assume grAny and grBoundary.
var grTransitions = map[[2]int][3]int{
// GB5
{grAny, prCR}: {grCR, grBoundary, 50},
{grAny, prLF}: {grControlLF, grBoundary, 50},
{grAny, prControl}: {grControlLF, grBoundary, 50},
// GB4
{grCR, prAny}: {grAny, grBoundary, 40},
{grControlLF, prAny}: {grAny, grBoundary, 40},
// GB3.
{grCR, prLF}: {grAny, grNoBoundary, 30},
// GB6.
{grAny, prL}: {grL, grBoundary, 9990},
{grL, prL}: {grL, grNoBoundary, 60},
{grL, prV}: {grLVV, grNoBoundary, 60},
{grL, prLV}: {grLVV, grNoBoundary, 60},
{grL, prLVT}: {grLVTT, grNoBoundary, 60},
// GB7.
{grAny, prLV}: {grLVV, grBoundary, 9990},
{grAny, prV}: {grLVV, grBoundary, 9990},
{grLVV, prV}: {grLVV, grNoBoundary, 70},
{grLVV, prT}: {grLVTT, grNoBoundary, 70},
// GB8.
{grAny, prLVT}: {grLVTT, grBoundary, 9990},
{grAny, prT}: {grLVTT, grBoundary, 9990},
{grLVTT, prT}: {grLVTT, grNoBoundary, 80},
// GB9.
{grAny, prExtend}: {grAny, grNoBoundary, 90},
{grAny, prZWJ}: {grAny, grNoBoundary, 90},
// GB9a.
{grAny, prSpacingMark}: {grAny, grNoBoundary, 91},
// GB9b.
{grAny, prPreprend}: {grPrepend, grBoundary, 9990},
{grPrepend, prAny}: {grAny, grNoBoundary, 92},
// GB11.
{grAny, prExtendedPictographic}: {grExtendedPictographic, grBoundary, 9990},
{grExtendedPictographic, prExtend}: {grExtendedPictographic, grNoBoundary, 110},
{grExtendedPictographic, prZWJ}: {grExtendedPictographicZWJ, grNoBoundary, 110},
{grExtendedPictographicZWJ, prExtendedPictographic}: {grExtendedPictographic, grNoBoundary, 110},
// GB12 / GB13.
{grAny, prRegionalIndicator}: {grRIOdd, grBoundary, 9990},
{grRIOdd, prRegionalIndicator}: {grRIEven, grNoBoundary, 120},
{grRIEven, prRegionalIndicator}: {grRIOdd, grBoundary, 120},
}
// Graphemes implements an iterator over Unicode extended grapheme clusters,
// specified in the Unicode Standard Annex #29. Grapheme clusters correspond to
// "user-perceived characters". These characters often consist of multiple
// code points (e.g. the "woman kissing woman" emoji consists of 8 code points:
// woman + ZWJ + heavy black heart (2 code points) + ZWJ + kiss mark + ZWJ +
// woman) and the rules described in Annex #29 must be applied to group those
// code points into clusters perceived by the user as one character.
type Graphemes struct {
// The code points over which this class iterates.
codePoints []rune
// The (byte-based) indices of the code points into the original string plus
// len(original string). Thus, len(indices) = len(codePoints) + 1.
indices []int
// The current grapheme cluster to be returned. These are indices into
// codePoints/indices. If start == end, we either haven't started iterating
// yet (0) or the iteration has already completed (1).
start, end int
// The index of the next code point to be parsed.
pos int
// The current state of the code point parser.
state int
}
// NewGraphemes returns a new grapheme cluster iterator.
func NewGraphemes(s string) *Graphemes {
l := utf8.RuneCountInString(s)
codePoints := make([]rune, l)
indices := make([]int, l+1)
i := 0
for pos, r := range s {
codePoints[i] = r
indices[i] = pos
i++
}
indices[l] = len(s)
g := &Graphemes{
codePoints: codePoints,
indices: indices,
}
g.Next() // Parse ahead.
return g
}
// 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 {
g.start = g.end
// The state transition gives us a boundary instruction BEFORE the next code
// point so we always need to stay ahead by one code point.
// Parse the next code point.
for g.pos <= len(g.codePoints) {
// GB2.
if g.pos == len(g.codePoints) {
g.end = g.pos
g.pos++
break
}
// Determine the property of the next character.
nextProperty := property(g.codePoints[g.pos])
g.pos++
// Find the applicable transition.
var boundary bool
transition, ok := grTransitions[[2]int{g.state, nextProperty}]
if ok {
// We have a specific transition. We'll use it.
g.state = transition[0]
boundary = transition[1] == grBoundary
} else {
// No specific transition found. Try the less specific ones.
transAnyProp, okAnyProp := grTransitions[[2]int{g.state, prAny}]
transAnyState, okAnyState := grTransitions[[2]int{grAny, nextProperty}]
if okAnyProp && okAnyState {
// Both apply. We'll use a mix (see comments for grTransitions).
g.state = transAnyState[0]
boundary = transAnyState[1] == grBoundary
if transAnyProp[2] < transAnyState[2] {
g.state = transAnyProp[0]
boundary = transAnyProp[1] == grBoundary
}
} else if okAnyProp {
// We only have a specific state.
g.state = transAnyProp[0]
boundary = transAnyProp[1] == grBoundary
// This branch will probably never be reached because okAnyState will
// always be true given the current transition map. But we keep it here
// for future modifications to the transition map where this may not be
// true anymore.
} else if okAnyState {
// We only have a specific property.
g.state = transAnyState[0]
boundary = transAnyState[1] == grBoundary
} else {
// No known transition. GB999: Any x Any.
g.state = grAny
boundary = true
}
}
// If we found a cluster boundary, let's stop here. The current cluster will
// be the one that just ended.
if g.pos-1 == 0 /* GB1 */ || boundary {
g.end = g.pos - 1
break
}
}
return g.start != g.end
}
// Runes returns a slice of runes (code points) which corresponds to the current
// grapheme cluster. If the iterator is already past the end or Next() has not
// yet been called, nil is returned.
func (g *Graphemes) Runes() []rune {
if g.start == g.end {
return nil
}
return g.codePoints[g.start:g.end]
}
// Str returns a substring of the original string which corresponds to the
// current grapheme cluster. If the iterator is already past the end or Next()
// has not yet been called, an empty string is returned.
func (g *Graphemes) Str() string {
if g.start == g.end {
return ""
}
return string(g.codePoints[g.start:g.end])
}
// Bytes returns a byte slice which corresponds to the current grapheme cluster.
// If the iterator is already past the end or Next() has not yet been called,
// nil is returned.
func (g *Graphemes) Bytes() []byte {
if g.start == g.end {
return nil
}
return []byte(string(g.codePoints[g.start:g.end]))
}
// 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 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) {
return g.indices[g.start], g.indices[g.end]
}
// Reset puts the iterator into its initial state such that the next call to
// Next() sets it to the first grapheme cluster again.
func (g *Graphemes) Reset() {
g.start, g.end, g.pos, g.state = 0, 0, 0, grAny
g.Next() // Parse ahead again.
}
// GraphemeClusterCount returns the number of user-perceived characters
// (grapheme clusters) for the given string. To calculate this number, it
// iterates through the string using the Graphemes iterator.
func GraphemeClusterCount(s string) (n int) {
g := NewGraphemes(s)
for g.Next() {
n++
}
return
}
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