// DirectionString reports the direction of the given label as defined by RFC
// 5893. The Bidi Rule does not have to be applied to labels of the category
// LeftToRight.
func DirectionString(s string) bidi.Direction {
for i := 0; i < len(s); {
e, sz := bidi.LookupString(s[i:])
if sz == 0 {
i++
}
c := e.Class()
if c == bidi.R || c == bidi.AL || c == bidi.AN {
return bidi.RightToLeft
}
i += sz
}
return bidi.LeftToRight
}
func (t *Transformer) advanceString(s string) (n int, ok bool) {
var e bidi.Properties
var sz int
for n < len(s) {
if s[n] < utf8.RuneSelf {
e, sz = asciiTable[s[n]], 1
} else {
e, sz = bidi.LookupString(s[n:])
if sz <= 1 {
if sz == 1 {
return n, false // invalid UTF-8
}
return n, true // incomplete UTF-8 encoding
}
}
// TODO: using CompactClass results in noticeable speedup.
// See unicode/bidi/prop.go:Properties.CompactClass.
c := uint16(1 << e.Class())
t.seen |= c
if t.seen&exclusiveRTL == exclusiveRTL {
t.state = ruleInvalid
return n, false
}
switch tr := transitions[t.state]; {
case tr[0].mask&c != 0:
t.state = tr[0].next
case tr[1].mask&c != 0:
t.state = tr[1].next
default:
t.state = ruleInvalid
if t.isRTL() {
return n, false
}
}
n += sz
}
return n, true
}