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