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neutral.go
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neutral.go
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package bidih
import (
"github.com/bobyang007/helper/unicodeh/bidih/internal/bidi"
"sort"
)
const maxBracketStack = 63
// = B, S, WS, ON, FSI, LRI, RLI or PDI
func isNeutralOrIsolate(class bidi.Class) bool {
return class == bidi.ParagraphSeparator || class == bidi.SegmentSeparator || class == bidi.WhiteSpace || class == bidi.OtherNeutral || class == bidi.FirstStrongIsolate || class == bidi.LeftToRightIsolate || class == bidi.RightToLeftIsolate || class == bidi.PopDirectionalIsolate
}
// = NI or BN
func isPossibleNeutralOrIsolate(class bidi.Class) bool {
return isNeutralOrIsolate(class) || class == bidi.BoundaryNeutral
}
// = L, R, AL, EN or AN
func isN0Strong(class bidi.Class) bool {
return isStrong(class) || class == bidi.EuropeanNumber || class == bidi.ArabicNumber
}
func n0Direction(class bidi.Class) bidi.Class {
if class == bidi.ArabicLetter || class == bidi.EuropeanNumber || class == bidi.ArabicNumber {
class = bidi.RightToLeft
}
return class
}
type bracketPairElement struct {
start sequenceState
end sequenceState
}
func n0IsExpectedCloseBracket(expectedRune, gotRune rune) bool {
// TODO assumption about canonical equivalent brackets
return expectedRune == gotRune || (expectedRune == 0x232a && gotRune == 0x3009) || (expectedRune == 0x3009 && gotRune == 0x232a) // Special case for conical equivalent brackets.
}
func n0ComputeBracketPairs(sequence runSequence, runes []rune) (bracketPairs []bracketPairElement) {
type bracketStackElement struct {
start sequenceState
pair rune
}
bracketStack := make([]bracketStackElement, 0, maxBracketStack)
for sequence.start(); !sequence.isEnd(); sequence.next() {
bracketPairShift := bidi.GetBracketPairShift(runes[sequence.runeI])
switch {
case bracketPairShift > 0:
if len(bracketStack) < maxBracketStack {
bracketStack = append(bracketStack, bracketStackElement{sequence.saveState(), runes[sequence.runeI] + bracketPairShift})
} else {
return
}
case bracketPairShift < 0:
for stackI := len(bracketStack) - 1; stackI >= 0; stackI-- {
if n0IsExpectedCloseBracket(bracketStack[stackI].pair, runes[sequence.runeI]) {
bracketPairs = append(bracketPairs, bracketPairElement{bracketStack[stackI].start, sequence.saveState()})
bracketStack = bracketStack[:stackI]
break
}
}
}
}
sort.Slice(bracketPairs, func(i, j int) bool { return bracketPairs[i].start.runeI < bracketPairs[j].start.runeI })
return
}
// Inspects enclosed runes for strong (as N0 defines) direction.
// (sequence.runeI; end)
func n0InspectEnclosed(sequence runSequence, end int, embeddingDirection bidi.Class, directions []bidi.Class) (strongFound bool, toEmbeddingDirection bool) {
for sequence.next(); !sequence.isEnd() && sequence.runeI < end; sequence.next() {
if isN0Strong(directions[sequence.runeI]) {
strongFound = true
}
if n0Direction(directions[sequence.runeI]) == embeddingDirection {
return true, true
}
}
return
}
// Returns previous strong (as N0 defines) direction.
// [sos; sequence.runeI)
func n0InspectPrevious(sequence runSequence, directions []bidi.Class) (previousStrongDirection bidi.Class) {
for sequence.prev(); !sequence.isStart() && !isN0Strong(directions[sequence.runeI]); sequence.prev() {
}
if sequence.isStart() {
return sequence.sos
}
return n0Direction(directions[sequence.runeI])
}
func n0Decide(sequence runSequence, end int, embeddingDirection bidi.Class, directions []bidi.Class) (replace bool, replaceWith bidi.Class) {
strongFound, toEmbeddingDirection := n0InspectEnclosed(sequence, end, embeddingDirection, directions)
if toEmbeddingDirection {
return true, embeddingDirection
}
if !strongFound {
return false, 0
}
return true, n0InspectPrevious(sequence, directions)
}
func n0FollowingNSM(sequence runSequence, classes []bidi.Class, directions []bidi.Class, replaceWith bidi.Class) {
for sequence.next(); !sequence.isEnd() && classes[sequence.runeI] == bidi.NonSpacingMark; sequence.next() {
directions[sequence.runeI] = replaceWith
}
}
// rule N0
func n0(sequence runSequence, runes []rune, classes []bidi.Class, levels []EmbeddingLevel, directions []bidi.Class) {
bracketPairs := n0ComputeBracketPairs(sequence, runes)
embeddingDirection := levels[sequence.ranges[0].from].direction()
for _, bracketPair := range bracketPairs {
sequence.loadState(bracketPair.start)
replace, replaceWith := n0Decide(sequence, bracketPair.end.runeI, embeddingDirection, directions)
if replace {
directions[bracketPair.start.runeI] = replaceWith
directions[bracketPair.end.runeI] = replaceWith
sequence.loadState(bracketPair.start)
n0FollowingNSM(sequence, classes, directions, replaceWith)
sequence.loadState(bracketPair.end)
n0FollowingNSM(sequence, classes, directions, replaceWith)
}
}
}
func n1GetSequence(sequence *runSequence, directions []bidi.Class) bool {
if directions[sequence.runeI] == bidi.BoundaryNeutral {
for sequence.next(); !sequence.isEnd() && directions[sequence.runeI] == bidi.BoundaryNeutral; sequence.next() {
}
if sequence.isEnd() || !isNeutralOrIsolate(directions[sequence.runeI]) {
return false
}
}
for sequence.next(); !sequence.isEnd() && isPossibleNeutralOrIsolate(directions[sequence.runeI]); sequence.next() {
}
return true
}
// rule N1 & N2
func n12(sequence runSequence, levels []EmbeddingLevel, directions []bidi.Class) {
previousDirection := sequence.sos
sequence.start()
for !sequence.isEnd() {
if isPossibleNeutralOrIsolate(directions[sequence.runeI]) {
// Compute sequence
start := sequence.runeI
if !n1GetSequence(&sequence, directions) {
continue // TODO prevDir
}
// Compute nextDirection
var nextDirection bidi.Class
if sequence.isEnd() {
nextDirection = sequence.eos
} else {
nextDirection = directions[sequence.runeI]
}
// Replace sequence with surrounded strong direction, or with embedding direction
if isN0Strong(previousDirection) && isN0Strong(nextDirection) && (previousDirection == bidi.LeftToRight) == (nextDirection == bidi.LeftToRight) {
var newDirection bidi.Class
if previousDirection == bidi.LeftToRight {
newDirection = bidi.LeftToRight
} else {
newDirection = bidi.RightToLeft
}
state := sequence.saveState()
for sequence.prev(); sequence.runeI >= start && !sequence.isStart(); sequence.prev() {
directions[sequence.runeI] = newDirection
}
sequence.loadState(state)
} else {
state := sequence.saveState()
for sequence.prev(); sequence.runeI >= start && !sequence.isStart(); sequence.prev() {
directions[sequence.runeI] = levels[sequence.runeI].direction()
}
sequence.loadState(state)
}
} else {
sequence.next()
}
previousDirection = directions[sequence.runeI-1]
}
}